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Old 02-23-2008, 04:25 AM   #1
AEAJR
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Cool Everything You Wanted To Know About Electric Powered Flight

Note that even though this was originally posted in 2008, this gets regular review and updates to keep the chapters current and relevant and I add new chapters from time to time.



EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
An E-Book by Ed Anderson
Updated August 2013


PREFACE

A number of people have suggested I write a book on the topic of electric flight. I would, but I find the electric field is changing too fast. Paper based books go out of date too quickly. Instead I am going to create a thread that is my version of an e-book on the subject of electric powered flight. This e-format allows me to provide updates and to answer questions, things I can't do in paper form.

Whether you are a new flyer, a wet fuel pilot, or a glider pilot who wants to add an electric motor to your glider, I hope you find value here. Of course, I will fail to live up to the title as you can't know everything, but I will try to hit the essentials. I am also going to provide an index for your convenience.

The principals of weigt, lift, drag, stall and all the other things we know about flying apply the same regardless of what motor or engine the plane may have. The power systems may differ, and each has its unique benefits and quirks, but the principles of flight remain the same.

For new pilots who have no background, just relax, breath deeply and read. I have tried to put it all in one place for you. Don't expect to know it all in one reading. After you take your early flights, come back and read again as you will now have some real life experience to compare to what is contained here.

If you are starting with an RTF electric airplane, you really don't need to know all this stuff. However be sure to look at the articles on RTFs and the Six Keys to Success for New Pilots. I think you will find them helpful.

For wet fuel pilots coming into electric, the first problem is terms and their meanings. The first two articles are specifically focused on this need.

I want to change your question from "What is the electric equivalent of a .40 glow engine?” to "What electric power system would be right for a 40 size glow plane?" The first question is VERY hard to answer, the second is not. I am going to ask you to put aside what you know of wet fuel systems and look at electric power with a fresh mind.

Electric motor systems are both simpler and more complex than wet fuel systems. It is just a matter of looking at them in terms that make sense for electric power and not trying to make them fit the wet fuel framework.

What about batteries? How do I choose between NiCd, NiMh, Lipo, and others? We will cover that.

Battery chargers are a mystery too, yet they are an integral part of electric flight. We will cover those.

What about tools to tell what is going on in your electric power system? Yes, we will cover that also.

I will be adding new chapters and topics and will reorganize the articles as makes sense. For example I added an article on the ESC and placed it before the articles on the BEC and LVC, were it made the most sense. So visit again and check the table of contests as you might see a new topic that interests you and it might not be the last post.

If you post a question or a comment, you will be "subscribed" and will receive notification when I post new articles. And don't hesitate to suggest topics that need to be covered.

I invite others who have experience in this area to add their knowledge and become co-authors of this e-book. If you have an area of expertise, share it with us. If you come across a good discussion or a reference source somewhere, post a link to it and tell us why you found it helpful.

Take notes of the date

You will find my articles and posts rich in links to other resources. Be sure to take a look. Note the
date they were posted and whether I have posted a revision or not. Some information changes fast
and some remains valid for years. However when a specific product is mentioned note the last edit
on that article. That product may no longer be available. Don't hesitate to post a question, reference
the article and ask about current models that would replace it.


If you have a question, by all means ask as others will have the same question.

I hope you find this helpful. I hope you will contribute your knowledge as well.

TABLE OF CONTENTS

Post# ..... Topic

1 ............Preface
2 ............Amps vs Volts vs C
3 ............Sizing Power Systems
4.............Props vs. Amps
5 ............What is an Electronic Speed Control
6 ............The LVC, Low Voltage Cut-off
7 ............Who Needs a Wattmeter?
8 ............Why Use a Gearbox?
9 ............Extended Flight Times and Balance
10 ...........Battery Basics
11 ...........Lithium Batteries, Chargers and Balancers
12 ...........Six Keys to Success for New Pilots
13 ...........Things to Check on an RTF
14 ...........Now its Your Turn!
23 ...........The Role of the BEC in your ESC
24 ...........The Mythical Best First Plane
33 ...........What You Need to Know About Receivers
43 ...........WHAT DO THE KV RATINGS ON MOTORS MEAN?
51 ...........A DOWNLOADABLE EDITED VERSION OF THIS E-BOOK (editing by Ken Meyers)
....................the .pdf was current as of 2009 and does not contain updates or new chapters
71 ...........Estimating Battery Run Time
147 .........How to Select Your First Radio
148 .........What Goes on Which Stick?
150 .........Basic Servo Set-up Process


As the book progresses, I have expanded the range of the discussion beyond strictly electric topics but I have tried to stay within those topics that I feel are relevant to electric flyers. For example the electric "parkflyer" class of planes has a large number of rudder/elevator/throttle planes. As pilots move from 2 or 3 channels to 4 channel planes sometimes people get confused as to were the rudder should reside on the radio. The article at post 148 addresses this question.

Post 43 addresses a question that comes up over and over related to kV. and 147 talks to the subject of picking your first radio. Note that this is slanted to electric and glider pilots more so than to glow or gas pilots.

Looking back, I would have organized the chapters/articles in a different order, but I am not going to trash the thread to do it, so I hope you will not find it too confusing as it appears here.

This book also appears on RCUniverse at:
http://www.rcuniverse.com/forum/elec...ic-flight.html. The chapters are the same but their numbers and sequence may be different as the discussion has progressed differently over there.

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www.lisf.org
Eastern Soaring League
www.flyesl.org
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Old 02-23-2008, 04:25 AM   #2
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AMPS vs. VOLTS vs. C
By Ed Anderson
aeajr on the forums

This brief discussion is intended to clear up a few terms and concepts
around electricity as it applies to electric airplanes.

Think of electricity like water. Volts = pressure Amps = flow

Volts is like pounds per square inch, psi. Says nothing about how much
water is flowing, just how hard it is being pushed. You can have 100 psi
with zero water flow.

Amps is flow, like gallons per hour. You can have flow at low pressure and
you can have flow at high pressure.

Amp hours is how much flow can be sustained for how long. It is used as a
way of measuring how much electricity is in the battery. Like how many
gallons of gas in your tank. It is a capacity number. Says nothing about
flow or pressure, it is about capacity.

Amps and mili amps? We are just moving the decimal point around.

1 amp (short for ampere) = 1000 miliamps (mili means 1/1000 amps)

Examples

So a 7 cell NIMH or NICD pack provides 8.4V (pressure).

The motor will draw electricity from the pack at a certain flow rate, or
amps.

If you have a have a 650 mili amp hour pack, it can deliver a flow of .650
amps (650 miliamps) for one hour. If you draw it out faster, it
doesn't last as long. So your motor might pull 6.5 amps for 1/10 of an
hour, or about 6 minutes.

A 1300 mah pack has double the capacity of the 650 mah pack, so it should
last "about" twice as long.


What is C in relation to batteries?

C ratings are simply a way of talking about charge and discharge rates for
batteries.

1C, = 1 time the rated mah capacity of the battery. So if you charge your
650 mah pack at 1C, you charge it a 650 miliamps, or .650 amps.

1C on a 1100 pack would be 1.1 amps.

2 C on your 1100 pack would be 2.2 amps

Motor batteries, especially lithium batteries, are often rated in Discharge C and charge C.

So a 1100 mah pack (1.1 amp hour) might be rated for 10C discharge, so you
can pull 11 amps ( flow ) without damaging the battery.

Then it might be rated at 2C charge rate (flow), so you charge it at 2.2
amps (2200 mah)

How did I do? Things clearing up? Terms starting to make sense?

If you have a 500 mah pack - any kind - and it is rated at 16C that means it
can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 8C that means it
can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 12C that means
it can deliver 12 amps

If you have a 1500 mah pack (1.5 amp hour) - any kind - and it is rate at 8C
that means it can deliver 12 amps (1.5 X 12 = 8)

If you have a 1500 mah pack - any kind - and it is rated at 20 C that means
it can deliver 30 amps.

If you have a 3000 mah pack - any kind - and it is rated at 10 C that means
it can deliver 30 amps.

So, if you need 12 amps you can use a pack with a higher C rating or a pack
with a higher mah rating to get to needed amp delivery level.

One last point. Motor batteries vs. receiver batteries

Some batteries can sustain high discharge rates. Other batteries can not.

Those used as transmitter/receiver packs typically are made for lower flow/amp
rates while those made for motor packs can sustain higher rates.

Having a 600 mah pack does not tell you if it is a motor pack that can put
out 6 amps, or if it is a transmitter/receiver pack that would be damaged if
you tried to pull power at 6 amps. It is enough to say that they are
different.

Clearly a motor pack could be used for a transmitter/receiver job, but a
transmitter/receiver pack should not generally be used as a motor pack.

I suggest you size your battery packs so they run somewhat below their
maximum C rating. You will stress them less and they will last longer. For
example, if your motor needs a pack that can deliver 10 amps, getting a 1000
mah pack that is rated for 10C ( 10 amps ) will meet the spec, but it is
running at its limit. A 15 C rated 1000 mah pack would be better, or
perhaps a 1300 mah 10 C pack. In either of these cases, the pack will be
less stressed and should handle the load much better over the long term.

That's it for the first chapter. Hopefully some of the terms of electric flight
will start to make sense. If you are still confused, go back and read again.
Or, take a look at the links, they may help too.



Other Resources

Basics - article is more than 5 years old but still useful.
http://www.modelaircraft.org/mag/FTGU/Part8/index.html

Lithium Batteries - again a few years old, but it marks a breakthrough in electric flight
http://www.rchobbies.org/lithium_battery_breakthrough.htm

Lithium Balancers and Balancing Chargers
http://www.rcgroups.com/forums/showthread.php?t=599287

New Electric Flyer FAQs
http://www.ezonemag.com/pages/faq/a105.shtml

A series of posts on electric power system basics
http://www.wattflyer.com/forums/showthread.php?t=1933
http://www.rcgroups.com/forums/showthread.php?t=417868

MotoCalc
MotoCalc will tell you everything you need to know: Amps, Volts, Watts, RPM,
Thrust, Rate of Climb, and much more! It is a popular tool for predicting
the proper motor, prop, battery pack for electric planes.
http://www.motocalc.com/

e-CALC - A free power system sizing tool
http://www.ecalc.ch/



Electric Motors Described
http://adamone.rchomepage.com/guide5.htm

< Message edited by aeajr -- 2/19/2008 9:44:08 AM >

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Old 02-23-2008, 04:27 AM   #3
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SIZING POWER SYSTEMS FOR ELECTRIC AIRPLANES
by Ed Anderson
aeajr on the forums
Revised 12/1/2012

This may get a little technical but I will try to keep it as simple as I
can. I will draw parallels to cars and bicycles in many places as most
people can relate to these and know at least a little about how they work.
I will use round numbers where I can and will use some high level examples.
If you are an engineer you will see that I am taking some liberties here for
the sake of simplicity. I will go through the parts of the power system,
then, toward the end, I will show you how we tie these all together to come
up with a complete power system.


POWER = WATTS

I will be using the terms Volts, Amps and Watts throughout this discussion.
Let me define them.

Volts = the pressure at which the electric energy is being delivered - like
pounds per square inch or PSI in a fuel system or water from a garden hose.
Volts is about pressure, it says nothing about flow. You will see volts
abbreviated as V.

Amps = the quantity or flow of electricity being delivered, like gallons per
minute in a fuel system or that same garden hose. Amps is about flow, it
says nothing about pressure. You will see amps abbreviated as A.

Watts = V X A. This is a measure of the energy or power being delivered.
This is how we measure the ability of that electricity to do work, in our
case the work of turning a propeller to move our airplane through the air.
Watts is about both pressure and flow. This serves the same purpose as
the horsepower rating of your car's engine. In fact 746 watts = 1
horsepower. So if you had an electric car, the strength of its motor could
be reported in either watts or horsepower. You will see watts abbreviated as
W.

If you want more depth on this, visit this thread.
http://www.wattflyer.com/forums/showthread.php?t=1933


MOTOR EFFICIENCY - Brushed vs. Brushless

Whether brushed or brushless, the motor's job is to convert electricity into
mechanical motion to turn the propeller to move air. Efficiency is how we
measure how much of the power, the watts, that our battery delivers to the
motor is actually turned into useful work and how much is wasted as heat.
A higher efficiency motor delivers more energy to the prop, and wastes
less.

A typical brushed motor, say a speed 400, is only about 40-50% efficient.
Only about half the watts delivered to the motor actually end up as useful
work turning the propeller. The rest is wasted. Motors that have a "speed"
designation, like speed 400, are brushed motors. There are other names for
brushed motors but the "speed" term is a common one. They are inexpensive
and they work. For example, you can buy a speed 400 motor and electronic
speed control, ESC, for $20. A comparable brushless motor/ESC combination
would likely be 1.5 to 3 times that much, but prices have been coming down fast.

Brushless motors tend to be more efficient. They typically deliver 70-90%
of that input power to the propeller, Thus you get better performance per
watt with brushless motors. Seen a different way, if you use a brushless
motor, then, for the same flying performance you will use less energy which
means your battery will last longer. Or you can use a smaller size and
weight brushless motor/battery combo to get comparable performance
because the motor turns more of the watts from the battery into useful work
of turning the propeller.

As with many decisions we make, this is a cost benefit decision. Am I
willing to pay more to get more? That is up to you.


THE BATTERY IS MORE THAN JUST THE FUEL TANK

Think of the battery as the fuel tank plus the fuel pump and a supercharger
all rolled into one. It feeds/pushes energy to the motor. So you have to
look at the battery and the motor as one unit when you are sizing power
systems for electric planes. In many cases we start with the battery when
we size our systems because the motor can't deliver the power to the prop if
the battery can't deliver the power to the motor.

The higher the voltage rating of the battery, the higher the pressure, like
a supercharger on a car engine. More pressure delivers more air/fuel
mixture to the engine which allows the engine to produce more power to turn
the wheels of the car.

Higher voltage pushes more electricity into the motor to produce more power,
IF AND ONLY IF, the battery has the ability to deliver more electricity.
Again using the car analogy, if you put a big motor in a car and put a tiny
fuel line and a weak fuel pump, the motor will never develop full power. In
fact the motor might starve and stall once you got past idle. Such is the
same with batteries. We need voltage, we need capacity, but we also need to
know how many amps the battery is capable of delivering at peak.

If we compare an 8 cell AAA battery pack to an 8 cell C battery pack we get
9.6 V for both packs. However the AAA pack may only be able to deliver 6
amps. After that the cells will heat up and either be damaged or the
voltage will start to drop fast. The C pack, also 9.6 V, might be able to
deliver 60 amps without damage. So we have to size not only by voltage, but
by the ability to deliver amps to the motor. Again, think of the fuel line
and the fuel pump as your image of what I am trying to explain. If the
motor needs 12 ounces of fuel per minute to run but the fuel line can only
deliver 8, the engine will starve and die.

Using our electric motors, a given motor may want to draw 10 amps
( the quantity of electricity flowing ) at 8.4 volts ( the pressure at which
the electricity is being delivered) to spin a certain propeller. We would
say that the battery is delivering, or that the motor is drawing 84 watts,
i.e.: 8.4V x 10A. If you bump up the voltage to 9.6 volts, the motor will
try to spin faster which will turn the prop faster. In order to do this the
motor will draw and the battery must deliver more amps into the motor, more
energy to the motor, which will produce more power to the propeller but it
will also produce more heat in the motor. In this example, if we move from
an 8.4V battery pack to a 9.6V battery pack the motor may now take 14 amps.
But can this particular electric motor handle 14 amps? Can the electronic
speed control handle 14 amps?

If you bump up the pressure too much, you can break something.
Putting a big supercharger on an engine that is not designed for it will
break parts of the engine. Too much voltage can over power your electric
motor and damage it. So there is a balance that has to be struck.
Different motors can take different amounts of power, watts, volts X amps,
without damage. For example, a speed 400 motor might be fine taking 10 amps
at 9.6 volts or 96 watts. However bump it up to 12 volts, while spinning
the same prop, and it might draw 18 amps which could burn it out.

Our goal is a balanced power system. If you match the right battery with
the right motor, you get good performance without damage to the motor. In
many cases airplane designers will design planes around a specific
motor/battery combination so that they match the size and weight of the
plane to the power system for good performance.

REVOLUTIONS PER VOLT - kV

An important fact about electric motors is that they tend to want to spin
at a certain speed for every volt that we apply to them. We won't go into a
lot of depth here, but it is important to understand that if you apply 5
volts to a motor, it will try and spin at a given speed. If you apply 10
volts it will try to turn twice as fast. This fact is noted on the specs of
your motor in the form of the kV rating. Basically a kV rating of 1000
means that the motor will spin at 1000 RPMs for every volt applied.

If you apply 10 volts, it will try to spin at 10,000 rpms. It will try to
achieve this RPM level regardless of the load we put on it. It will draw
more and more amps from the battery trying to hit this number.

By boosting the voltage on a motor, and getting it to spin faster we can get
it to produce more power, but we must be careful not to over work the motor.
Even if it is 80% efficient, 20% of the power that goes into it turns into
heat. Too much heat can melt insulation, cause shafts to expand in bearings
and all sorts of bad things can happen. So, as we change the voltage we
apply to our airplane motors we sometimes
change the propeller too.


PROPELLERS

Propellers are sized by diameter and pitch.

The diameter of the propeller determines the volume of air the propeller
will move, producing thrust, or pushing force. Roughly speaking the
diameter of the propeller will have the biggest impact on the size and
weight of the plane that we can fly. Larger, heavier planes will typically
fly better with larger diameter propellers.

Pitch refers to the angle of the propeller blade and refers to the distance
the propeller would move forward if there were no slippage in the air. So a
7 inch pitch propeller would move forward 7 inches per rotation, if there
were no slippage in the air. If we combine pitch with the rotational speed
of the propeller we can calculate the pitch "speed" of the propeller. So,
at 10000 revolutions per minute, that prop would move forward
70,000 inches per minute. If we do the math, that comes out to a little
over 66 miles per hour.

By changing the diameter and the pitch of the propeller we can have a
similar effect to changing the gears in your car or a bicycle. It will be
harder for your motor to turn a 9X7 propeller than an 8X7 propeller. And
it would be harder to turn a 9X7 propeller than a 9X6 propeller. The
larger or steeper pitched propellers will require more energy, more watts,
more horsepower, to turn them. Therefore we need to balance the diameter
and pitch with the power or wattage of the motor/battery system.
Fortunately we don't actually have to do this ourselves as motor
manufacturers will often publish suggested
propellers to use with a given motor/battery combination. We can use these
as our starting point. If we want we can try different propellers that are
near these specifications and use a wattmeter to measure the results. More
on wattmeters later.


GEARBOXES

While unusual on glow or gas planes, gearboxes are common on electric
planes. Their primary function is similar to the transmission on a car. The
greater the gear ratio, the higher the numerical value, the slower the
propeller will turn but the larger the propeller we can turn. So you can
use a gearbox to help provide more thrust so you can fly larger planes with
a given motor. However you will be turning the propeller slower so the
plane will not go as fast with the same propeller.

With direct drive, that is when the propeller is directly attached to the
motor shaft, we are running in high gear ( no gear reduction). Like pulling
your car away from the light in high gear. Assuming the motor doesn't stall,
acceleration will be slow, but over time you will hit a high top end!
Typically direct drive propellers on a given motor will have a smaller
diameter.

With the geared motor, it would be like pulling away from the green light in
first gear - tons of low end power and lots of acceleration, but your top
speed is reduced.

So, by matching up the right gear ratios made up of the propeller and,
optionally, a gearbox we can adjust the kind of performance we can get out
of a given battery/motor combination. How this is done is beyond the scope
of this article.


NOW WE CAN START TO MATCH UP THE PIECES!

The simplest approach I have seen to figuring power systems in electrics is
input watts per pound of "all up" airplane weight. The following guidelines
were developed before brushless motors were common but it seems to hold
pretty well so we will use it regardless of what kind of motor is being
used. You may see variations on these numbers but the concept is the same.

50 watts per pound = Casual/scale flying

75 watts per pound = Sport flying and sport aerobatics

100 watts per pound = aggressive aerobatics and perhaps mild 3D

150+ watts per pound = all out performance.

Remember that Watts = Volts X Amps. This is a power measurement.
In case you were wondering, 746 watts equals 1 horsepower.


AN EXAMPLE!

This should be fun. Let's see where these formulas take us! We will use a
24 ounce, 1.5 pound plane as our example. If we want basic flight you will
need 50 watts per pound or about 75 watts input to your motor for this 1.5
pound plane. That is, 50 watts per pound X 1.5 pounds = 75 watts needed
for basic flying performance. If you want a little more spirited plane, we
could use 75 watts X 1.5 pounds which is about 112.5 watts.

Lets use 100 watts as the total target, just to be simple, shall we? I am
going to use a lot of round numbers here. I hope you can follow.

The Battery:

If we use an 8 cell NiMh battery pack at 9.6 V it will have to deliver 10.4
amps to hit our 100 watts input target ( 100 watts/9.6 V = 10.41amps) If
my battery pack cells are NiMh cells that are rated at 10C then I need an 8
cell pack rated at 1100 mah to be able to deliver 11 amps. Sounds about
right.

Now I select a motor that can handle 100 watts or about 10.4 amps at 9.6
Volts. From experience we know this could be a speed 400, a speed 480 or
some kind of a brushless motor.

We now need a propeller that will cause the motor to draw about 100 watts. I
don't know off the top of my head what that would be. I would go to some mfg
chart as a starting point. GWS has good charts!
http://www.gwsus.com/english/product...tem/edp400.htm

I see that if I use a direct drive speed 400 with a 5X4.3 prop at 9.6V then
the motor will draw about 12.4 amps or about 119 watts. This would be a
good candidate motor/prop for the plane using a 9.6V pack that can put out
12.4 or more amps. This would be a set-up for a fast plane as that motor
will spin that small prop very fast.

However maybe I don't want such a fast plane but one with a really good
climb and lots of low end pull to help out a new pilot who is in training or
to do more low speed aerobatics

I can also use a speed 400 with a 2.38 gearbox and run it at 9.6V spinning a
9X7 prop and run at about 12.8 amps for 120 watts.
http://www.gwsus.com/english/product...em/eps400c.htm

The larger prop will give this plane a strong climb, but since the prop
speed has been reduced by 2.38 times, it won't be as fast. Spinning a
bigger prop gives me more thrust. Also note went from a pitch of 4.3 on the
direct drive set-up to a pitch of 7 with the gearbox. This is because the
prop is turning 2.38 times slower now so we increase the pitch to somewhat
balance that.

Back to battery packs and motors

So if I shop for a 9.6V pack to be able to handle about 15-20 amps, I should
do just fine and not over stress the batteries. In NiMh that would probably
be a 2/3 or 4/5 A pack of about 1500 -1600 mah capacity.

We view the battery and motor as a linked unit with a target power profile,
in this case about 100 watts. We use the prop and gearbox, if any, to
adjust the manner in which we want to deliver that power to the air to
pull/push the plane.

If this is a pusher, I may not have clearance to spin that big prop so we
may have to go for the smaller but faster prop combo.

If this is a puller, then we can choose our prop with more flexibility but
we may have to limit it by ground clearance or some other criteria.


See, that was easy, right? ( well sorta but ....)


But we are not done! Oh no!

I could try to do it with a 2 cell lithium pack rated 7.4V. To get 100 watts
I now need a pack that can deliver 13.5 amps and a motor/prop combination
that will draw that much. So if I have 10 C rated lithiums, then the pack
better be at least 1350 mah. Probably use a 1500 mah pack to be safe.

Well, when I look at the chart for the geared speed 400 I see that,
regardless of prop, at 7.4V I am not going to have enough voltage (
pressure) to draw 13 amps based on the propellers they tried. So the
2 cell lithium won't meet my performance goal of 100 watts+ per
pound using this gear box.

If I go back to the charts and look at a different gear boxes. I can't hit
my power goals using 7.4V. Maybe we go back to direct drive.
http://www.gwsus.com/english/product...tem/edp400.htm

We see that the best I can get this speed 400 to do is a total of 70 watts
at 7.2V ( close enough ) so I can't hit my power goals using a speed 400 at
this voltage. but 70 watts would be about 48 watts per pound so I could have
a flyable plane, but not an aerobatic plane using this two cell pack.


REALITY CHECK!

Now, in fact that is NOT how I would do this. I would decide on the watt
target, go to the chart, find a combo that meets my goals, then select a
battery that will meet the demand and see if my weight comes up at the
target I set. A little tuning and I come up with a workable combo.

I often use the MaxxProd combos for reference. If you read the details on
each package they have wonderful information. And, the fact is that I
generally go with brushless motors these days. Costs are reasonable and
their higher efficiency gives me more performance and longer flight times.
http://www.maxxprod.com/mpi/mpi-264.html

Following the example above, the combo 10 on that page would be an excellent
fit for my 1.5 pound plane for sport flying. The Combo 049 might be a good
fit for a slow flyer. Either way the package has all I need.

If I wanted the plane to have all out performance, the 15A or 19A package
would be my pick. Note that these would need either higher voltage or
higher amperage battery packs. The flyers/PDF for the packages make
recommendations.

For those who like to be even more analytical about it, there are packages
like MotoCalc that will allow me to play with all sorts of combinations and
make suggestions on what I should use. There is a link for MotoCalc below.


SUMMARY

So, in these few paragraphs you have taken in a basic knowledge of how
electric power systems are sized, the factors that are considered an how to
predict the outcome. Simple, right?

Of course there is a lot more to know and time and experience will teach
you plenty, but with this basic understanding you are better prepared to
begin playing with the power systems you put in your planes.

Here are some additional resources that may be helpful.

Good luck e-pilot!

Clear Skies and Safe Flying!
Ed Anderson


RESOURCES

EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC FLIGHT
an e-book by Ed Anderson
http://www.wattflyer.com/forums/showthread.php?t=31071
http://www.rcuniverse.com/forum/m_7100376/tm.htm


Battery Packs
http://www.cheapbatterypacks.com

Maxx Products has a pretty good tip sheet on coming up
with a glow to electric power comparison. You can find it here:
http://www.maxxprod.com/mpi/tips3.html

This reader says Keith Shaw originated the watts per pound rule
http://www.rcgroups.com/forums/showp...0&postcount=39

MotoCalc - Fee
A commercial tool that will tell you everything you need to know: Amps,
Volts, Watts, RPM, Thrust, Rate of Climb, and much more! It is a popular
tool for predicting the proper motor, prop, battery pack for electric
planes. There is a fee but if you are going to do a lot of this kind of
work, it may be a good investment.
http://www.motocalc.com/

Electricalc - Fee
Like Motcalc, this is a commercial tool that is very extensive. Well worth
the money for anyone who is doing a lot of power system design.
http://www.slkelectronics.com/ecalc/index.htm
or
http://www.hobby-lobby.com/ecalc.htm...QueryId=447678

e-CALC - A free power system sizing tool
http://www.ecalc.ch/


Webocalc - Free
A free calculator that can help you get close to the proper design. You put
in certain parameters and it will give you the proper prop combo for that
motor set-up. It does not list by brands and it is not as full featured as
the
programs that charge a fee, but hey, it's free. This is the one I use most
of the time.
http://flbeagle.rchomepage.com/softw.../webocalc.html


What's Inside an Electronic Speed control?
http://www.youtube.com/watch?v=22CpR...ure=digest_sat

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www.flyesl.org
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Old 02-23-2008, 04:28 AM   #4
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PROP vs. AMPS

Your electric motor draws a certain amount of energy to do its job, which is to turn the propeller. With no prop attached it draws very little energy. If you put a big prop on the motor it draws a lot of energy.

This is similar to pulling a boat trailer behind your car. The car might get 20 mpg normally, but put a boat on a trailer behind the car and mileage will drop off to perhaps 15 mpg because the motor is using more energy just to maintain the same speed and travel the same distance. However as long as the boat and trailer are not too heavy, no real damage occurs, you just use more gas.

If you put too big a trailer behind your car, something will break. The motor may fail, the transmission may fail or something else. That is because you are asking the drive train to produce more work, use more energy then it was built to handle. Fuel mileage goes way down and then something breaks. You have over stressed things.

Back to your plane.

Your electric motor needs to "draw" a certain amount of energy in order to turn a given propeller at a given speed. Let's use a speed 400 motor as an example and let's say you have a 6X5 prop on it. That means the propeller is 6" across and has a pitch of 5" per revolution. Pitch indicates how far the prop would move forward through the air if there was no slippage. As either of these numbers go up, the motor is asked to do more work.

Now let's apply some numbers. These are made up numbers for illustration only. Don't assume that these are accurate for your motor in your plane turning your prop.

Let's say that, to turn that 6X5 prop your speed 400 motor draws 6 amps of electricity using a battery that delivers 10 volts, just to make the math simple. That would be 60 watts of energy that the motor consumes to turn that prop. (6 amps X 10 Volts)

If we go to a larger prop, say 7 inches and keep the pitch the same 5 inches, the draw might go up to 8 amps at 10 volts or 80 watts.

Likewise if we went to a 7X6 prop, the draw would go up again, say to 9 amps or 90 watts.

In each case we are increasing the amount of work the motor has to do to turn the prop. The harder it works the more electricity it draws. This is also placing an increasing amount of stress on the motor causing it to generate heat and placing more pressure on the bearings. If we push it too far, the motor will be unable to turn the prop fast enough to be useful in flying the plane and/or it will fail from stress, just like the car example above with the trailer that is too big.

What we try to do is to get the best balance of propeller and amp draw so that the motor operates efficiently without being over stressed.

Likewise if you have that same speed 400 motor and keep the prop at 6X5 but increase the electric pressure, volts, to 12 volts it will try to spin the motor faster causing it to draw more amps into the motor. This would be like putting a supercharger on your car's motor which forces more fuel/air mix into the car's engine. It will produce more power so it can do more work. However if we exceed the amount of power it was designed to handle, it will fail. It might not fail right away, but over a very short time it will start to degrade, perform badly and perhaps suddenly fail all together.

If we push the voltage up too high or the amp draw too high, we will over stress the motor and damage it.

The goal is get a good balance of propeller and power draw.


OTHER RESOURCES

A comparison of Glow vs. Electric power
http://www.maxxprod.com/mpi/tips3.html

Electric Motors Described
http://adamone.rchomepage.com/guide5.htm

MotoCalc
MotoCalc will tell you everything you need to know: Amps, Volts, Watts, RPM, Thrust, Rate of Climb, and much more! It is a popular tool for predicting the proper motor, prop, battery pack for electric planes.
http://www.motocalc.com/

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www.lisf.org
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www.flyesl.org
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Understanding the Electronic Speed Control
By Ed Anderson

When we look at model airplanes that have electric motors as opposed to liquid fuels, the things we notice first are the quiet electric motor and the battery. However there is a component that sits between them called the electronic speed control that is really the master control point for all power in the plane. We are going to look at its make-up and how it does its job.

On the surface we can see that the electronic speed control, the ESC, takes over the function of the throttle servo that would operate the carburetor in a glow or gas powerd plane. Just as the throttle servo controls the speed of these wet fuel motors, the ESC controls the speed of the electric motor. But there is more to it than that.

The first thing that we want to recognize is that there are two different kinds of ESCs that are specific to the type of motor they control. There are brushed motors, such as the speed series or the Mabuchi motors, and then there are the brushless motors. Each type of motor needs a different electronic speed control.


Understanding the Wires

When you look at an electronic speed control, you notice that you have three sets of wires. Typically two sets of thick wires and one set that looks like a servo wire.

Two of the thick wires, typically black and red, connect to the battery. The ESC will usually be marked to tell you which are the battery wires. They would connect to the battery as red to red and black to black.

A second set of wires, typically thinner than the battery connection wires, has a plug on the end that looks like a servo plug. This will be connected to the receiver and will serve two purposes as it sends power to the receiver and gets signals from the receiver.

If we look at the wires on this plug they usually run from a dark or black wire on one side to a light or white wire on the other side. I am going to use black, red and white for this discussion. Yours may be dark brown, orange, yellow or something similar.

The black and red wires feed power to the receiver which in turn distributes power out to the servos and other accessories that are plugged into the receiver. Note that the red wire is in the center. This is the power wire. Since it is in the center you can insert the plug into the receiver either way and nothing bad will happen. You won’t get any response from the servos if you put it in wrong, but you won’t damage anything. Note that, on some older systems, particularly Airtronics radio systems, the red wire was on the end. If you plugged it in the wrong way it could damage the receiver and possibly the servos. However the center red design has been fairly universal for many years.

The third wire, the white wire is the signal wire that sends commands from the receiver to the ESC to tell it how to control the motor. As you move the throttle control on your transmitter, the receiver gets the command and passes it up the white wire to the ESC so it knows how much speed you want from the motor.

There is a third set of wires that go to the motor. The ESC is usually marked to show which wires are the motor wires. If this is a brushed motor ESC then there will be two wires, typically red and black.

On a brushed motor ESC, if we connect red to red on the motor, and black to black, the motor will turn in the expected direction. If we reverse them the motor will spin in the opposite direction.

On a brushless ESC, you match color to color as well. However if the colors don’t match then you need to observe the direction of the motor. If it is spinning in the wrong direction, reversing any two wires will correct this.

Note that on some older brushless motors there were additional wires that attached to a sensor in the motor. However, unless you have an old motor and ESC combination you won’t see that on any of the current designs.

Some ESCs have an integrated switch. In most cases this will allow or prevent the motor from running and pass or block power to the receiver. However it typically does not stop the flow of current from the battery to the ESC. In fact, even if there is no switch there is always current flowing to the ESC which will drain the battery.

It is for this reason that you should never leave your battery connected when you store your plane. This small current drain will take your battery to zero charge over time. If you are using NiCd or NiMh, the damage may be minor. If you are using Lithium batteries, you lithium battery pack will likely be ruined. So, don’t leave your battery connected unless you are preparing to fly.


Connectors

The connector/plug that goes to the receiver is standardized. It is the same wire scheme and plug type as is used for the servos. Today all makers, except Futaba, use the universal plug.

On the Futaba J plug you have the same wiring scheme but there is an extra tab on the plug that insures the connector is inserted properly into the receiver. If you have a receiver that accepts this slotted plug it will also accept universal plugs. However if you have a receiver that expects the universal plug, then you will need to trim off this tab with a hobby knife or you can sand it off. Once trimmed, the plug will work fine.

Battery and motor connectors are not as simple.

There is an emerging standard for motor/ESC connection on brushless motors. The connectors are round and are called bullet connectors. Most brushless motor/ESC makers seem to be using these now, so on brushless motors this connector standard seems to be established. However, for brushed motor connections there is no standard.

On the motor side we have the option of not using a connector as we can solder the motor and ESC wires together. This works fine if you don’t plan to remove the motor or the ESC and it gives the best connection. However if you do have to remove one of them for service, you will need the soldering iron in order to take the connection apart.

On the battery side we always use a connector so that we can remove the battery for charging and storage. When flying electric planes it is common to have several battery packs so the connector allows us to remove one pack and insert a fresh one while the first is charging.

Whatever batter or motor connector you use, make sure that is has a current, amp, rating that is larger than what the motor is likely to pull. The reason the wires for these links are thicker is that the battery has to deliver high current to the motor as opposed to the relatively small current that goes to the receiver. If the connector can’t handle the flow, it will heat up and potentially be damaged. Likewise, if the connector can’t handle the current the motor will never develop full power. Too light a connector can also cause a serious voltage drop.

This lack of standards leads to situations where you buy a motor that has one connector, your battery has a different connector and your ESC has a third type. Or, as seems to becoming more common, none of them have connectors and you have to add your own.

My suggestion is to standardize connectors. Once standardized, any motor or battery connection that doesn’t have your standard connector gets a connector replacement. It takes time and soldering but with one standard, all of your batteries will work in any plane for which they are appropriate and you can move motors and ESC around as you desire.

This will also simplify your battery to charger connections. One or two adapters for your charger will handle all of your batteries. Just make sure the connector you use can handle the current.

I have three standards. For brushlesss motors, I use the bullet connectors. For brushed motors and batteries in very small light planes where the current will typically be under 5 amps, I use the red BEC connectors. These are sometimes called GWS connectors as they are common on GWS motors, batteries and ESC. They are small and light and are well suited for small light planes.

For my high current applications I use the Deans Ultra connectors. They can handle up very high currents, are easy to solder and can be easily removed and reused. However there are many other high current connector that are equally as good. As long as it can handle the current flow, it will be fine.


Sizing an ESC

Electronic Speed Controls are sized according to how many amps they can control and the voltage that they can handle. So you may see an ESC marked as 20 amps and 7-10 NiXXcells or 2-3 cell Lipo. That says it can handle a 20 amp flow using a battery pack that ranges between 7.4V and 12 volts. If you use it with a motor/battery system that is outside this range it will likely fail. When it fails it may simply not run the motor or it may also cut power to the receiver, which will lead to a crash.

You size your ESC according to the motor and the battery you are using. I won’t go into how we determine what the motor and battery will need. That is covered in another article. It is enough to say that, if your motor is going to draw 20 amps you will need an ESC that is rated for at least 20 amps. There is no problem having an ESC that is rated for more amps than you need, but and ESC that is rated below the expected current load will likely lead to a failed ESC.

The same goes for the voltage. Use your ESC outside the voltage it is designed for and you can expect it to fail.

Your ESC will likely have an integrated battery elimination circuit, a BEC. This is the part that delivers the power to the receiver. Always check the specs for the BEC. While the ESC might be able to handle 14.4 volts, the instructions may say that for uses above 11.1V you may have to disable the BEC. There is a complete article on the BEC, so I won’t go into it here. Let’s just say you need to check this.

I recommend that you always have at least a 20% margin between the amp requirements of your motor and the rating of your ESC. This way you will know you will not be overloading the ESC. A bigger margin is also fine.


How the ESC controls the Motor

Motors are rated by Kv, which means the number of revelations the motor will turn when you apply 1 volt of electricity. So a 1200 Kv motor will spin at 12,000 rpm if you apply 10 volts.

From this you might imply that the ESC changes the voltage to the motor in order to change the speed of the motor, but that is not the case. If you look at the specifications for your ESC you will probably see a frequency number. This might range from 2 KHz to 12 KHz or higher. This is related to how fast the ESC can pulse power to the motor. You see your ESC is not a variable resistor that adjusts the voltage to the motor, it is a fast switch that pulses power to the motor.

You can think of this as a duty cycle control. How long will the ESC leave the power on till it turns it off? Then, how long will it be off before it turns it back on? There is no need for you to know this cycle time, only that on every on cycle your motor is getting the full voltage of your battery.

I take the time to explain this because people mistakenly believe that if they run their motor at partial throttle they are sending reduced voltage to the motor. If the motor is not supposed to get more than 7.4 volts and you put in an 11.1V battery, running the motor at throttle does not reduce the voltage to the motor. It is getting 11.1V hits every time the ESC switches on. On a brushed motor that is receiving too much voltage, this will typically produce arcing which will burn up the brushes on the motor. In addition to this arcing on brushed motors, this higher electric pressure may push too much current that will overheat the motor.

If you have had a motor “burn up” even thought you usually ran it at a partial throttle setting, this may be the reason. Understanding how the ESC controls your motor will help you diagnose problems.

Note also that, since the ESC is switching power on and off it is also producing electromagnetic pulses, or radio waves. The electronics in the ESC will typically be designed to reduce or shield some of this radio wave noise, but it can’t block it all. This is why we recommend keeping the ESC and the receiver as far apart as possible as this ESC noise can interfere with the receiver. If you are getting “glitching” or odd pulses to your servos, these may be coming from ESC noise bothering the receiver. Try moving things around.


Other Components in the ESC

I am going to address these in later articles, but there are typically two other components that are integrated into your ESC. We already mentioned the BEC. The other is the LVC, the low voltage cutoff. These are not directly involved in controlling the speed of your motor, but as you will see in the articles that are focused on these that they are very valuable parts of your ESC that you will want to understand.


Summary

The electronics speed control is the power system controller for your airplane. Its various components distribute power to the receiver and control the speed of the motor. Understanding how it works will give you the ability to properly size and install the ESC and to diagnose problems in the system.


What's Inside an Electronic Speed control?
http://www.youtube.com/watch?v=22CpR...ure=digest_sat

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Old 02-23-2008, 04:29 AM   #6
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The Low Voltage Cutoff Feature of your ESC
By Ed Anderson
aeajr on the forums

Many electronic speed controls include a feature called the low voltage cutoff
circuit, the LVC. The LVC watches the voltage that is being delivered by the
battery. When it gets below a certain level, it will cut power to the motor to
preserve power for the radio system. This will allow you to keep control of the
plane and land it in a glide.

Power draw by your receiver and servos is a tiny fraction of what the typical
electric motor draws. As the battery drains it will exhibit a voltage drop. You
may feel this in the way the plane flies. The plane may become sluggish or it
may not be able to climb under full power. This is a clear indication that the
pack is getting low.

A battery that can't sustain voltage when the motor is on, can still provide
plenty of power for the flight electronics and may be able to do so for quite a
while, but don't test it. If your motor cuts, enjoy the glide, but set up to
land as soon as possible. I always teach new pilots how to glide their planes
so, if the LVC cuts the motor, they don't panic.

If you practice flying your plane with the motor off, then an LVC cut will be no
big deal. You might even find you enjoy gliding, which can extend your flying
time. I often glide and thermal my electric planes just for fun.

LITHIUM BATTERIES CHANGE THE ROLE OF THE LVC

If you drain NiCd or NiMh packs too low, usually there is little damage. Just
bring them back to charge a little slower than normal. If you drain a lithium
cell below 2.5V resting voltage, typically the cell will be damaged. So, in
this case the LVC is protecting your plane and your battery packs.

Most lithium friendly ESC will cut the motor off if the pack voltage drops below
2.7 to 3.0V per cell under load. At this level there is very little useful
charge left in the pack and the voltage will continue to drop fast.

Note that when you cut the load of the motor the voltage will likely pop back to
3.1, 3.2 or even 3.3 V per cell. If you check your batteries after you land,
you may think that LVC has malfunctioned, but it has not. The battery may be
3.3 V/cell resting but it can't sustain it with the motor running.

One thing you might want to be aware of is that the voltage sag will be less at
lower throttle settings. If the LVC cuts the power at a particularly bad time,
you may be able to get a short burst of motor operation at a reduced throttle
setting. A short run at half or quarter throttle may be all you need to get you
over that fence, past that tree or properly aligned with runway. But don't push
it by trying to extend your flight with lots of short bursts. However if it
will help you avoid a crash, or two short runs, to save the plane, are worth the
risk to the battery pack.

CONCLUSION

The LVC was put there to protect the radio, but if you are using Lithium
batteries the LVC can protect them too. It is best to be sure your ESC/LVC is
lithium friendly. That means either that it can be set manually, or that it
senses how many lithium cells you have and sets automatically. Even if it is
not designed for Lithium cells, if you can set the cut-off at something above
2.75V per lithium cell, then you should be OK.

Understanding how the LVC works will make it your friend.

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Old 02-23-2008, 04:30 AM   #7
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WHO NEEDS A WATT METER?
A personal experience reveals their value.

I enjoy electric planes. They are quiet, convenient, can be fast or
slow and are fairly inexpensive to fly.

A few months back I picked up a Watts-up wattmeter.
http://www3.towerhobbies.com/cgi-bin...&I=LXLMV0&P=ML

I thought it would be a good investment as I was doing more in the area of
mixing and matching motors, props, and the like. It is small and simple to
use so I put it in my field box. It wasn't long before it started to show
its value.

We were flying one afternoon when one of the club members felt he was not
getting
good performance from a new plane he had built. I put he wattmeter on the
plane and determined he was pulling about 9 amps. Turned out the pack he
was using really was not up to the load and the voltage was dropping off
excessively. As a result he was not getting the RPM out of the prop that he
expected. Problem discovered and cause identified in a few seconds. He
needed stronger battery packs.

A few weeks later we did the same thing with another plane. There was a
concern that the LiPo being used might be getting over worked. However the
Wattmeter showed that it was working well within its rated capacity. Flying
went on with confidence.

I recently purchased an Easy Glider Electric from another club member. He
had upgraded the motor from the stock speed 400 to a brushless, a 27 amp ESC
and was using 2 cell 2100 MAh LIPOs. I bought the whole package.

The plane flies very nicely on the 2 cell packs, but I had a 3 cell pack
that I thought I might add to the rotation and REALLY boost the power. The
ESC could handle 3 cell LiPo so I did not see a problem. I assumed the
system was probably running at about 18 amps which was within the rating of
this pack. Should be a good fit.

Fortunately before I tried it in the plane I put the watt meter on the
system. I was surprised to see that the system was running at 26 amps on
the 2 cell lipo packs. That was much higher than I had expected. It turned
out that the 2 cell packs were an excellent match for the motor and speed
control. The amp load was well within the specs of the 2 cell packs being
used and the plane flew very nicely on this combo.

If I had blindly put a 3 cell pack in there I would have pushed well past
the ESC's 27 amp rating and probably burned out the speed controller. Or,
in the case of my 3 cell pack, it would probably have pushed over 30 amps
into the system due to the higher voltage, but it was not rated for that
high of an amperage and would probably have had a short life working at that
level. I would have thought it was just a crummy battery pack but in fact I
would have been over working it.

Operating in the blind I would have ruined the ESC, or the pack, or both. A
very expensive mistake. Certainly more than the cost of the watt meter. It
had just paid for itself.

A few days ago I pulled out my old Electrajet to prepare to sell it. I had
purchased it almost 3 years ago, but had never really been happy with the
plane and my interests have turned more toward gliders and slow flyers
rather than a pusher jet. When I purchased it I also bought some cells and
made up some 8 cell packs. However it really didn't seem to have the zip I
thought it should. I just attributed it to the speed 400 motor and the
plane being too heavy.

I put the watt meter on the motor/battery combo. The motor sounded about as
I had recalled. When I checked the meter, low and behold, those 8 cell
packs were duds! They were 9.6V 8 cell 1000 MAh packs rated for 10C. At
rest, fresh off the charger they were reading 11 volts, but when I hooked
them up they were both dropping to 7 volts while delivering 9 amps. That is
way too much drop! The problem was not the plane or the weight of the plane
but the quality of the cells I had used.

I tried one of my 15C Lipo packs and that held voltage well, delivering 13
amps. The motor screamed! Now that was more like what I had expected.
Hummm, maybe I won't sell it after all. I just need to put better battery
packs in it.

I also tried a 1000 MAh 2 cell lithium pack that is rated at 10 C. The
voltage sagged to 6.6 volts almost immediately. The motor ran but I was
clearly over stressing the pack. This pack would have been ruined in very
few flights if I had used it to fly the plane regularly.

I share this story only to help you understand that, without a watt meter,
or the use of a multi meter with knowledge and skill, we are working in the
blind. We really don't know what is happening in our power systems.


WHO NEEDS A WATT METER?

While the watt meter is a nice to have, some people don't need one. If you
are buying RTF planes, or ARF or kit planes and are using the manufacturer's
supplied motor and battery packs, I would say you can be pretty confident
that all is well.

However, if you start mixing and matching motors, gear boxes, props,
controllers, battery packs and the like, you are really working in the blind
if you are not measuring the energy flow in the system. In my case, I
started making my own battery packs but I was not measuring their
performance. Now I know the true results.

There are a variety of watt meters out there. This one is easy to use and
fits nicely in my field box, but there are other good ones. If you are
going to upgrade your power systems or make up your own packs, you need a
watt meter. You can perform many of the same tests with a millimeter if you
know how to work with shunts and the like, but if you want a simple to use
tool that does exactly what you need it to do, this is hard to beat. It has
other uses too, so read the instructions, but for this use alone it paid for
itself pretty quickly.

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Old 02-23-2008, 04:30 AM   #8
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WHY CONSIDER A GEARBOX?
by Ed Anderson

We are going to discuss why we would consider adding a gearbox to a brushed
electric motor.

I am going to get real loose with the words "gear ratio" for a moment, but try
to follow me. Think of gear and gear ratio as the way we adjust the load on the
motor. I can adjust the "gear ratio" on my motor/propeller set-up in one of two
ways:

1) change the propeller
2) add a gear box and change the propeller

The goal is to get the motor spinning, at full power, at its optimum watt range
so that we do not over burden it, but so that we get the power to the propeller
efficiently. We are trying to get the best balance between pitch speed, thrust
and current draw.

If I increase the diameter of the propeller while holding the pitch constant I
put a greater load on the motor. A 10X6 prop puts a greater load on the motor
than a 9X6 prop. It will cause the motor to draw more power, more amps. At the
same time, it may load it enough that it causes it to slow down. Its peak RPM
may will be less. This is similar to changing gear ratios on your bicycle.
You can feel the effect in your legs.

If I deepen the pitch on the propeller while holding the diameter constant, I
also increase the load on the motor. A 9X6 going to a 9X7 going to a 9X8. In
this case I am increasing the "pitch speed". Again, this is similar to changing
the gear ratio. As I go to a deeper pitch the current draw will increase, the
watts increase and we may again load the motor enough to decrease its top rpms.

If I go too wide, or too deep, I can overload the motor and burn it out.

So, on a direct drive set-up, no gearbox, I tune my propeller between pitch and
diameter to get the motor to the power range I want. Again, this is EXACTLY the
same as changing gear ratios, in practical application.

To some extent I can trade pitch for diameter and vice versa. So you will see
motors listed as accepting a range of propellers. Typically as diameter goes
up, pitch goes down.

9X7
10X6
11X5

For this sample motor, each of these props will probably produce a similar watt
output but they do it with different results.

The wider prop will provide more thrust but the lower pitch will produce less
speed. So I can tune for the application. Sailplanes typically want more
thrust for steeper climb but are not as concerned about speed. Pylon racers
are less concerned about climb or acceleration as they are about top speed.
Hopefully you get the idea. I am tuning the "gear ratio" by changing the prop.

If you are not with me up till now, then ask because what comes next depends on
your understanding what is above.

ADD A GEARBOX

Now, suppose I have a given motor, say a brushed 550, and my prop choices don't
give me the thrust I want to take my 2 meter sailplane up at a steep enough
angle to make me happy. It takes too long to get to soaring height. Or,
suppose I want to fly a larger, heavier plane with the motor I have. My prop
choices don't give me enough thrust to handle the heavier plane. What do I do?

I can put in a gear box. The gearbox will have two effects. It will reduce the
top speed to the prop, but it will increase the torque available to turn the
propeller. This allows me to go to a wider propeller but my top speed will be
reduced. Now I can get an steeper climb, or perhaps I can fly a larger or heavier
plane. I am going to stay with the sailplane for the rest of the discussion, but it
applies equally to any kind of aircraft. We are talking gear ratios.

Again, using the bicycle example, you shift to a lower gear to go up the hill.
You can get up the hill in first but if you were to go to third you might not have
enough power in your legs to turn the pedals. So you tune the gear ratio to
match the available power.

A typical prop on a 550 motor in a sailplane, like a Goldberg Electra would be
an 8X4 prop. That is the widest prop, the highest thrust prop that this motor
can comfortably turn and provide enough speed to fly the glider. The motor will
likely pull about 18 amps on an 8.4V pack. It will fly the plane but the climb
angle might only be about 25 degrees. So it might take me 2 minutes to fly up the
height I want to reach. This plane isn't really made for speed, so going to a
7X6 prop, trying to get more speed, won't help.

But if I put a gear box on, say a 3:1 ratio, I can go to an 11X8 or a 12X7 prop.
Now I get a lot more thrust and the plane will climb at a 50 degree angle. Now
I get to height in less than a minute and the motor might only be pulling 16
amps. I climb in less time AND I may be drawing fewer watts to do it.

That is why we go to a gear box. Usually it is to allow us to swing a wider
prop at a slower speed in order to get more thrust at the sacrifice of speed.


WHAT ABOUT BRUSHLESS INRUNNER VS OUTRUNNER?

Because we have two motor types in the brushless world we add flexibility and
complexity. More choices means more to decide.

The gearbox discussion with a brushless inrunner is exactly the same as for the
brushed motor above, so I won't repeat it.

However if we look at outrunners vs. inrunners we see that outrunners tend to
spin slower/volt with more torque. This has a similar effect to having a
gearbox on an inrunner. So how do you decide?

1) Personal Preference
2) Mounting restrictions
3) Available motor choices

Some people don't like gearboxes. It is another thing to maintain and another
thing to break. Also gearboxes tend to make noise and some people don't like
that. However there is nothing spinning around inside the plane with a gearbox.
So you can mount the motor/gearbox without regard to clearance as long as you
have adequate air flow. You can just clamp a gearbox/inrunner to the frame of
the plane and you are done. I have seen motor/gearboxes left loose in the nose
of the plane. The Multiplex Easy Glider is set-up this way. No mount at all,
it just sits there.

Outrunners need space. You have a spinning can that must be protected from
contacting another surface, lose parts, wires, etc. Grass, string, stuff can
get caught on that spinning can. In some cases this could be a problem, so a
gearbox might be preferred.

I have read that brushless inrunners are typically more efficient than
outrunners. Even with the gearbox losses I have read that inrunners are still
more efficient at turning those bigger props. So, if that is true, and if that
matters, it could shape your decisions.

Summary

We can tune our power system by adjusting the "gear ratio". This can be done by
changing props to some degree. After that we go to gearbox systems to tune our
power systems to give us the performance we want.

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www.flyesl.org
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Old 02-23-2008, 04:31 AM   #9
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EXTENDING FLIGHT TIMES WHILE MAINTAINING BALANCE
by Ed Anderson
aeajr on the forums

Changing the type or capacity of your battery pack is typically done for one
of three reasons:

* You want longer flights
* You want to reduce weight.
* You want to do both

Here are some points to consider to get the most out of this change.

If you are currently flying NiCd packs, you can go to NiMh very easily. You
will gain about 40% in battery capacity at the same weight. The packs are
about the same size and shape so they fit easily and should not throw off
the plane's balance. NiMh and NiCd packs, NiXX for short, therefore can
typically be interchanged easily. I have eliminated virtually all my NiCd
motor packs and replaced them with NiMh packs.

If you go to lithium batteries you can either make your plane lighter or you
can maintain its weight but double, tripple or quadruple your battery
capacity. Lithium batteries have about 4 times the capacity per ounce as
compared to NiCd packs. Here are some steps to consider BEFORE you buy the
new pack:

Where is you battery pack located?

If your battery is forward of the CG, the balance point, then its weight is
helping to balance the plane. If you go to a pack of a different weight,
you MUST rebalance the plane or it won't fly well. For example, a lighter
pack will shift the CG toward the rear which may make the plane difficult or
impossible to fly. You must keep the plane in balance so that the CG,
center of gravity, the balance point, is in the right place.

This also applies to going to heavier packs as they will shift the CG
forward. A slight shift forward might not be a problem if you are adding
voltage as the more powerful pack will drive the motor faster which may mask
a slight change in balance and a more forward CG can make the plane more
stable. For Example I shift between 6 and 7 cell NiMh packs in my Aerobird.
The CG moves a little forward with the 7 cell pack but not enough to
seriously effect the way the plane handles. But optimally you want to keep
the CG in the same, the best location.

From here on I am going to assume you are going from NiXX packs to lithium
packs, as this is what many are doing and the one that takes the most
planning.

Before you buy that new pack:

* Weigh your current battery pack. A food scale or a postal scale is fine.
Many post offices in the US have self service scales. Great for weighing
stuff. Get it to the nearest .1 ounces. Write it on the pack so you won't
forget it.

* Now look at the space in the plane. Can the new pack go in the same or
almost the same place as your current pack? You can account for a location
shift by changing the amount of weight you add to the new pack.

Now decide on your goals based on what you can do in this plane and how much
money you want to spend.

1) Keep the weight the same and spend more money - Get a pack that fits in
the current space and weighs the same as your current pack - Now you can use
the new pack and your current packs interchangeably. Good deal! However
lithium packs are different sizes and shapes than NiXX packs so this might
be hard to do. If it is close, you might be able to modify the battery
space to allow the new pack to fit. A 600 MAh NiCd Pack weighs about the
same as a 2000 to 2400 MAh Lipoly pack, but the LiPoly may cost more.
Prices are dropping all the time and 4 times the flight time is definitely
cool!

2) Keep the weight the same and spend a bit less - Get a pack that is
lighter than your current pack and will fit in the same or close to the same
location, perhaps with minor mods to the plane. Maybe you go from a 600 MAh
NiXX pack to a 1300 MAh lithium pack rather than a 2400 MAh pack. This will
probably have a better chance of fitting where your NiXX pack fits. Great!
Add weight to the pack so it weighs the same as your NiXX pack. You can
still use both without serious modification to the plane. Good deal!

3) Make the plane lighter - If you can move stuff forward in your plane so t
hat a lighter battery can balance the plane, you can avoid the need to add
weight. Now you have a higher capacity battery pack AND your plane is
lighter. Lighter planes generally fly better. The only problem with this
approach is that your current "heavy packs" may not be able to be used
anymore unless you can leave space to adjust their position rearward.

If it won't fit, can you modify the space to make it fit?

If you remove foam, consider reinforcing the space with tape or glue and
light plywood as you have removed some of the structure of the plane. Can
you cut a hole in a former so the pack fits under it? Make sure you
reinforce to account for any cut away structure. By the way, tape, glue,
bals or plywood add weight so you so take these into account. Cut a little,
set some reinforcing in place but don't glue it. Position the pack and test
the balance of the plane; adjust accordingly. Be sure you pad the pack in
balsa or plastic planes so that a crash will not likely damage the pack.
Lithiums can not take the physical abuse that the NiXX packs tolerate.

If modifying the plane to move the pack forward won't get it done, then see
if you can move other things in the plane to shift their weight forward.
Some people have the receiver under the wings. Move it forward and it will
help to balance the plane and you won't have to add as much weight to the
lithium pack. Also see if you can move the ESC forward. Move any excess
wire that you have bundled to the forward area. Wire has weight.

If you have any components, like the receiver that sit behind the CG, moving
them forward will make a huge difference.

If you can move your electronics forward enough that you can balance the
plane without the battery pack, then you can set the battery directly over
the CG. Now it doesn't matter which battery pack you use as the weight of
the pack will not shift the balance of the plane. You can interchange packs
all you like.

When I rebuilt one of my sailplanes after a crash, I positioned my servos,
receiver and battery to more forward locations than the stock
recommendation. As a result I made the plane about 12% lighter with no
other modifications. That made a HUGE difference in how if flew.

I then made a removable motor for it and positioned it on a pod that sat
right over the CG so I could put it on or take it off without changing the
balance of the plane. Likewise I placed the battery right over the CG.
With the motor and battery mounted, the plane was much heavier, but it
stayed in perfect balance whether they were on or off the plane.

There are other considerations related to lithium batteries. You need a
special charger and charging procedures. You MUST protect them from damage
as they can not take the same abuse as NIXX packs. But these are covered in
other threads. This one is just about maintaining balance.

Clear Skies and Safe Flying!

* See if you can buy a lithium pack that is the same weight as your current
battery pack. If you can, and you can afford it you are all set and have
two to four times the flight capacity for longer flights.

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Old 02-23-2008, 04:31 AM   #10
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BATTERY BASICS
by Ed Anderson
aeajr on the forums
Revised January 2007

All RC planes use battery packs to operate their electronics. On planes
that don't have electric motors we call these receiver packs as they power
the receiver and the receiver then distributes the power to the servos and
other electronics in the plane. However for electric planes, we also use
the batteries to power the motor. They are the chemical fuel tanks and
fuel pumps that store and deliver the energy we use to fly.

These battery packs are made up of cells which act as chemical storehouse
for electrical energy. When multiple cells are joined together we call this
a
battery or battery pack. There are a variety of battery types. Each has
advantages and disadvantages that we will discuss.


Battery Types

At the time of this writing, there are three commonly used rechargeable
types of cells. They vary by the chemical mix that is used to
hold and deliver the electricity.

Nickel Cadmium, NiCd, have been in around the longest.

Nickel Metal Hydride, NiMH came in to use later and are very popular today.

Lithium cells are typically lithium polymer, LiPoly or LiPo, and the less
commonly used Lithium Ion. These are the newest breed of chemical cells.

NiCd packs have the lowest power to weight ratio. That is to say that, for
a given electrical capacity they will weigh the most of the three types.
However they have the ability to be charged faster than the other two and
will give up their power fast. While still in common use, the are dropping
in popularity as the other two types are improving and gaining on NiCd's
advantage of quick charge and quick discharge. Each NiCd cell is rated at
1.2 volts.

Nickel Metal Hydride, NIMH, packs hold about 40-60% more capacity per ounce
than NiCds. So, for example, a 800 mah NiCd pack might weigh 6 ounces while
an equivalent capacity NIMH pack might be 4 ounces. Except for very high
performance, NIMH packs can't quite match NiCds for how fast they can
deliver their electricity or how fast we can charge them, but they are
catching up. There used to be a big
gap, but the gap is closing fast. NIMH are far more popular today then they
were just a few years ago, and probably have passed NiCd in usage. Each
NIMH cell is rated at 1.2 volts, the same as NiCd cells.

In many ways NiCd and NiMh cells are very similar in their application. So,
as a shorthand, I am going to start to refer to NiMH and NiCd as NiXX when
what I am saying applies to both. I hope this does not lead to confusion on
the reader's part.

Lithium packs are the lightest for their capacity. They typically hold 4 or
more times as much electricity per ounce as compared to NiCd packs. For
example a 6 cell, 7.2V 2100 MAh NiCd pack might weigh 12 ounces while a 2
cell 7.4V Lithium pack of the same capacity will be about 4 ounces.

Because much of our RC electronics have been based on 4-5 cell NiXX packs
they are tuned for 4.8-6V receiver packs. However Lithium packs are 3.7V so
one cell is a bit low and two cells at 7.4V is a bit high. So Lithiums have
not been in common use for receiver packs used in gliders or glow powered
planes. Some micro plane electronics systems have been designed for 1 cell
lithium packs and the newer generation of electronics for the rest of the
market are being retuned to accept 1-2 cell Lipo receiver packs.

As a result, Lithiums have been used primarily as motor packs. Up until
recently, Lithium packs have been slower to charge and slower to deliver
their power. The newest generation Lipos can now deliver high currents but
still need to be charged at 1/3 the rate of NiCd or 1/2 the rate of NiMH
motor packs. However over time they are improving. They are growing in
popularity as the charge/discharge rates improve and the prices come down.
Each Lithium cell is rated at 3.7 volts.


Pack Configuration

Unless stated otherwise, we join the cells into packs by joining them in
series. In series we add the voltage of each cell so that a 6 cell NiXX
pack will be rated at 6 X 1.2 volts or 7.2 volts. With lithium packs, which
are rated at 3.7 volts per cell, it would take two cells to create a
comparable 7.4 volt pack. When you hear people talk about 4 cell, 6 cell,
however many cells today, they are usually talking about NiCd or NIMH cells.
However, with the rise of Lithiums, you should ask to be certain that they
are not talking about lithium cells.

Clearly if your instructions say that your motor can use a 7 cell pack, it
would be important to know if that is 7 NiXX cells or 7 Lithium
cells as the voltages would be very different. A 7 cell NIMH or NiCd
pack would be 8.4 volts. A 7 cell Lithium pack would be 24.9 volts.

While it is unusual to combine NiCd or NIMH packs in parallel to increase
capacity, it is quite common with Lithium packs. This has spawned the xSyP
designation, were x is how many Lithium cells are connected in series and y
is how many groups of these cells are connected in parallel. So a
3S2P pack would have two groups of 3 cells. This allows us to deliver
higher amperages at the same voltage, or to provide more capacity for
longer flights at the same voltage. The xSxP designation is most commonly
used with Lithium packs. I don't recall ever seeing this used with NiXX
packs.


Battery Chargers

When charging your battery packs you MUST use the right kind of charger or
you will damage the cells. Using the wrong charger, especially with lithium
cells, can actually lead to a fire or an explosion. So be sure that you
have the right charger for the kind of cells you are charging. Some
chargers are specific to one kind of cell while some can charge two kinds
and
some can charge all three. Make CERTAIN you know before you charge or
you could put your model, your car, your home or your personal safety at
risk.

I hope this has been helpful. Below are some additional resources for
further reading.

Excellent overview and safety information on Lithium Batteries
http://www.rchobbies.org/lithium_battery_breakthrough.htm
http://www.rcgroups.com/forums/showthread.php?t=209187

Lithium Battery Balancers and Chargers
http://www.rcgroups.com/forums/showthread.php?t=599287

More on Batteries
http://www.modelaircraft.org/mag/FTGU/Part8/index.html

A123 CELLS - This is an emerging cell for large
electric plane use.
http://www.rcgroups.com/forums/showthread.php?t=618071#post6636651

The Battery Clinic
http://www.rcbatteryclinic.com/

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www.lisf.org
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www.flyesl.org
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Old 02-23-2008, 04:32 AM   #11
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LITHIUM BATTERY CHARGERS -
Balance chargers vs. external balancers

Lithiums are great, but they benefit from a little extra care. We have seen that packs
with two or more cells can get out of balance. That means that one cell tends to
rundown lower or tends to charge higher. Since charging through the power port
that connects to the ESC only reads the total pack voltage the charger will charge
the pack to the expected voltage. For Lipoly packs that would be 4.2V per cell.
Therefore, when charging through the power port, the charger will take a 3 cell Lipo to
12.6V, regardless of the individual cell voltages. But if one cell is low and one is
high, that could result in one cell perhaps being charged to 4.3V or one being charged to
4.1V, for example.

Over many cycles this difference will build up. The most benign outcome is a loss of
pack performance. A more serious outcome could be that the low cell will drop below
the critical 2.5V level on discharge and be damaged, rapidly degrading the pack.
The more serious issue could be that one cell gets seriously over charged getting
well above the desired 4.2V top charge. This can result in pack failure or can cause the
over charged cell to "vent with flame". This is ungood. :-O

Balancers

So, for the past 18-24 months we have seen a flood of pack balancers that will bring the
packs into balance to maintain an even charge across all cells. To use these balancers you
need a compatible balance plug on the pack. Assuming you have this arrangement,
a balancer can help prevent the above situation. If you are happy with your charger and
don't feel the need for a new one, a balancer is a good investment. They run from $20 to $50
with a variety of features.

The balancing benefit is significant but it need not be critical to every charge cycle. Packs
don't go out of balance THAT fast. It might happen over 10 cycles or 20 cycles and it builds
up over time. So using a regular charger that charges through the power plug is fine. If you
balance every few charges, that would be adequate. Just be sure to do it and you have to
have a way of being sure you are doing it across all your packs.

Note that a balancer can only drain power so it does reduce the overall charge level of the pack,
it does not bring up the low cells. But I don't think that is a big deal.


Balancing Chargers

There are two features being discussed here, charging and balancing.

Some are chargers combined with balancers. They charge the pack to the desired
level, then the built in balancer bleeds down the high cell and charging can continue.
This is a good combination. It saves you from having to do this with a separate device.
This type of charger provides the very significant value of keeping your packs in balance
automatically. This leads to longer life, and better performance. And it has some safety
benefits in that it prevents one cell from being over charged.

Balanced Chargers

Then there are balancing chargers that charge each cell individually during the charge
cycle. The CellPro 4S, for example, charges each cell individually during the charge cycle.
If one cell is a little slower than the others the charger compensates so higher rates can be
tolerated, or so the charger companies claim. The older CellPro 4S that I have has a safe
charge cycle that charges at up to 1.4C. This is a side benefit of the balanced charge process.
The newer Cell Pro 4S charges at up to 3C. If charging your packs faster,
safely, is important to you, then these types of balancing chargers are a good value. CellPro is not
the only one but it is a good example. So, from that respect, certain chargers, let's call
them balanced chargers, bring more benefits than just balancing.

Practical use

I have 5 lipo packs with CellPro balance taps. Most of the time I charge them on my CellPro
charger but I also charge them on my Triton charger and on an AC wall wart Lipo charger.
Only the CellPro balances, but the packs get on it every few cycles so they will be balanced
on the next charge cycle. And only the CellPro charges at the higher rate. The others are
limited to 1C and I will not push them.

Cold Weather Cycle

I don't know if this is a common feature but the CellPro 4S also has a cold weather cycle.
It actually detects the temperature of the surrounding air. If it is below a certain level, it only
charges the cells to about 95% of full charge. This has very little impact in practical use but
it provides a safety effect. If you were to charge a lipo pack at the field, say at 30 degrees,
then not use it and take it home, as it warmed the cell voltage would rise, potentially taking it
over the desired 4.2V level. I can not say how serious a concern this may be, but it seems
to make sense that it could present an unrecognized problem. This charger accounts for it
automatically. I am sure there must be others that do it as well.

I do feel the balancing chargers are better than balancers, BUT not enough that it should be a
big concern if you don't feel you want a second charger or the higher charge rates that some
of the newer ones can offer. But understanding the benefits of balancing IS important.

Other Reference Sources

CellPro discussion
http://www.rcgroups.com/forums/showthread.php?t=786192&page=2#post8863342
Notes on Lithium Batteries
http://www.rchobbies.org/lithium_battery_breakthrough.htm
The Battery Clinic
http://www.rcbatteryclinic.com/

Long Island Silent Flyers
www.lisf.org
Eastern Soaring League
www.flyesl.org
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Old 02-23-2008, 04:33 AM   #12
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This is not totally unique to electric flight, but since many new electric pilots are trying to self train, it sorta fits.

SIX KEYS TO SUCCESS
by Ed Anderson
aeajr on the forums

Whether you have a coach or you are trying to learn to fly on your own, you
will need to be mindful of these six areas if you are going to become a
successful RC pilot. After years of working with new flyers at our club,
and coaching flyers on the forums, there are a few things I have seen as the
key areas to stress for new pilots. Some get it right away and some have to
work at it. They are in no particular order because they all have to be
learned to be successful.

WIND
Orientation
Speed
Altitude
Over Control
Preflight Check

1) Wind - The single biggest cause of crashes that I have observed has been
the insistence upon flying in too much wind. If you are under an instructor's
control or on a buddy box, then follow their advice, but if you are starting
out and tying to learn on your own, regardless of the model, I recommend
dead calm to 3 MPH for the slow stick and tiger moth type planes. Under 5
MPH for all others. That includes gusts. An experienced pilot can handle
more. It is the pilot, more than the plane, that determines how much wind
can be handled.

The wind was around 10 mph steady with gusts to 12. That was strong enough
that some of the experienced pilots flying three and four channel small
electric planes chose not to launch their electrics. This new flyer
insisted that he wanted to try his two and three channel parkflyers. Crash,
Crash, Crash - Three planes in pieces. He just would not listen. Sometimes
you just have to let them crash. There is no other way to get them to
understand.

Many parkflyers can be flown in higher winds by AN EXPERIENCED PILOT. I
have flown my Aerobird in 18 mph wind (clocked speed) but it is quite
exciting trying to land it.

Always keep the plane up wind from you. There is no reason for a new flyer
to have the plane downwind EVER!


2) Orientation - Knowing the orientation of your plane is a real challenge,
even for experienced pilots. You just have to work at it and some adults
have a real problem with left and right regardless of which way the plane is
going. Licensed pilots have a lot of trouble with this one as they are
accustomed to being in the plane.

Here are two suggestions on how to work on orientation when you are not
flying.

Use a flight simulator on your PC. Pick a slow flying model and fly it a
lot. Forget the jets and fast planes. Pick a slow one. Focus on left and
right coming at you. Keep the plane in front of you. Don't let it fly over
your head.

FMS is a free flight simulator. It is not the best flight sim, but the
price is right and it works. There are also other free and commercial
simulators.

FMS Flight simulator Home Page
Free download
http://n.ethz.ch/student/mmoeller/fms/index_e.html

Parkflyers for FMS
http://gunnerson.homestead.com/files/fms_models.htm

Getting Started with FMS
http://www.wattflyer.com/forums/showthread.php?t=3893

The links below take you to sites that provide cables that work with FMS.
If your radio has a trainer port, these cables allow you to use the trainer
port on your radio to "fly" the simulator. This is an excellent training
approach.

http://www.allthingsrc.com/webshop/
http://www.simblaster.com/
http://www.customelectronics.co.uk/

An alternative is to try an RC car that has proportional steering. You
don't have to worry about lift, stall and wind. Get something with left and
right steering and speed control. Set up an easy course that goes toward
and away from you with lots of turns. Do it very slowly at first until you
can make the turns easily. Then build speed over time. You'll get it! If
it has sticks rather than a steering wheel even better, but not required.
Oh, and little cars are fun too.


3) Too much speed - Speed it the enemy of the new pilot but if you fly
too slowly the wings can't generate enough lift, so there is a compromise
here. The key message is that you don't have to fly at full throttle all the
time. Most small electrics fly very nicely at 2/3 throttle and some do quite
well at 1/2. That is a much better training speed than full power. Launch
at full power and climb to a good height, say 100 feet as a minimum, so you
have time to recover from a mistake. At 100 feet, about double the height
of the trees where I live, go to half throttle and see how the plane
handles. If it holds altitude on a straight line, this is a good speed.
Now work on slow
and easy turns, work on left and right, flying toward you and maintaining
altitude. Add a little throttle if the plane can't hold altitude.


4) Not enough altitude - New flyers are often afraid of altitude. They
feel safer close to the ground. Nothing could be more wrong.

Altitude is your friend. Altitude is your safety margin. It gives you a
chance to fix a mistake. If you are flying low and you make a mistake ....
CRUNCH!

As stated above I consider 100 feet, about double tree height where I live,
as a good flying height and I usually fly much higher than this. I advise
my new flyers that fifty feet, is minimum flying height. Below that you better
be lining up for landing.


5) Over control - Most of the time the plane does not need input from you.
Once you get to height, a properly trimmed plane flying in calm air will
maintain its height and direction with no help from you. In fact anything
you do will interfere with the plane.

When teaching new pilots I often do a demo flight of their plane. I get the
plane to 100 feet, then bring the throttle back to a nice cruising speed. I
get it going straight, with plenty of space in front of it, then take my
hand off the sticks and hold the radio out to the left with my arms spread
wide to emphasize that I am doing nothing. I let the plane go wherever it
wants to go, as long as it is holding altitude, staying upwind and has
enough room. If you are flying a high wing trainer and you can't do this,
your plane is out of trim.

Even in a mild breeze with some gusts, once you reach flying height, you
should be able to take your hand off the stick. Oh the plane will move
around and the breeze might push it into a turn, but it should continue to
fly with no help from you.

Along this same line of thinking, don't hold your turns for more than a
couple of seconds after the plane starts to turn. Understand that the plane
turns by banking or tilting its wings. If you hold a turn too long you will force
the plane to deepen this bank and it will eventually lose lift and go into a
spiral dive and crash. Give your inputs slowly and gently and watch the
plane. Start your turn then let off then turn some more and let off. Start
your turns long before you need to and you won't need to make sharp turns.

I just watch these guys hold the turn, hold the turn, hold the turn, crash.
Of course they are flying in 10 mph wind, near the ground, coming toward
themselves at full throttle.

6) Preflight check - Before every flight it is the pilot's responsibility to
confirm that the plane, the controls and the conditions are correct and
acceptable for flight.

Plane - Batteries at proper power
Surfaces properly aligned
No damage or breakage on the plane
Everything secure

Radio - Frequency control has been met before you turn on the radio
A full range check before the first flight of the day
All trims and switches in the proper position for this plane
Battery condition is good
Antenna fully extended
For computer radios - proper model is displayed
All surfaces move in the proper direction

Conditions - No one on the field or in any way at risk from your fight
You are launching into the wind
Wind strength is acceptable ( see wind above )
Sunglasses and a hat to protect your eyes
All other area conditions are acceptable.

Then and only then can you consider yourself, your plane, radio and the
conditions right for flight. Based on your plane, your radio and local
conditions you may need to add or change something here, but this is the
bare minimum. It only takes a couple of minutes at the beginning of the
flying day and only a few seconds to perform before each flight.

If this all seems like too much to remember, do what professional pilots do,
take along a preflight check list. Before every flight they go down
the check list, perform the tests, in sequence, and confirm that all is right.
If you want your flying experience to be a positive one, you should do the
same. After a short time, it all becomes automatic and just a natural part
of a fun and rewarding day.

I hope some of this is useful in learning to fly your plane.

Other resources you may find useful:


Books on RC Planes and RC Flying

http://www.stevensaero.com/shop/product.php?productid=16645&cat=262&page=1

http://www.amazon.com/gp/product/B00071VIGC/sr=8-1/qid=1140260256/ref=pd_bbs_1/103-2556298-8424625?%5Fencoding=UTF8

http://www.amazon.com/gp/product/B0006PBE2M/sr=8-8/qid=1140260256/ref=sr_1_8/103-2556298-8424625?%5Fencoding=UTF8

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Old 02-23-2008, 04:33 AM   #13
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THINGS TO CHECK ON AN RTF
by Ed Anderson
aeajr on the forums

I think ready-to-fly airplane packages are great. This is how I started flying.
If I had been required to build a kit to begin my flying experience I would
never have gotten into the air. Now, after thousands of flights and almost
years of flying, I have expanded to 20+ planes, multiple radios and all kinds of
tools and things. I am having a ball. But there are things I know today that
would have helped me with my first plane. Let me pass on some tips.

Regardless of the plane, RTF or not, it is the pilot's responsibility to insure
that the plane is flight ready. If you put a plane in the air without checking
it, without following the instructions, any problems that follow, any damage
that is caused is your fault and responsibility. It does not matter if the
plane is defective, if you did not check it, any damage that occurred is your
fault. I can't make it any clearer. No full scale pilot would takeoff without
checking everything. You should do the same.


READ THE INSTRUCTIONS!

There is a manual or instruction sheet that comes with your plane, read it! I
read the manual several times on anything I get. It took the manufacturer time
and money to create it. I contains important information. Some instruction
sets are poorly done and some are very good. In either case, READ! If there
is a video included, watch it. It was put there to help you. Take advantage
of that help.

If they have a web site about the plane or product you purchased, visit the
site. Sometimes there is an FAQ, frequently asked questions page. Sometimes
there are additions to the instructions that have been added since yours was
packaged and shipped. And sometimes there are coupons, or specials for owners.
Go, look and see, and benefit from the manufacturer's web site.

RTFM

I often post this in my notes on the forums, "RTFM". To put it politely, it
means, " Read The Friendly Manual".

I have read so many trouble reports by new flyers. They crash, they have
problems and are angry and upset. Why was this happening to them? Often, the
answers were all in the instructions.

We had one club member who used to buy RTF planes, show up at the field and ask
me how to get them set-up and flying. I would ask him for the instructions.
"Oh, I left those home." So I sent him home to get them. No matter how
experienced I might be, unless I have this plane, I check the instructions.

He brought a computer radio to a meeting and asked me to show him how to use it.
"Sure, where are the instructions?" He left them home. I could not help him as
I had never seen that radio before.

Needless to say, he crashed and crashed and destroyed things. Fortunately for
him he had the money to do this. But he occasionally created a safety situation
and we had to "advise" him to change his ways. He has yet to become a
successful flyer. He is still a nice guy and I hope some day he will be
successful, but he needs to follow instructions.


THINGS TO NOTE WHEN YOU READ THE MANUAL

1) Does the plane need to be balanced, or does the balance need to be checked?

2) Are there linkages to be connected? Do they need to be adjusted? How do you
adjust them?

3) Is there tape or glue to be added. Is there covering material to be removed?

4) Do the batteries need to be charged?

5) Do they recommend some kind of "break-in" procedure?

6) What is the proper range check procedure for the radio system?

7) What is the working range of your radio system?

8) How do you adjust the surfaces to get the plane to fly correctly? Are they
moving in the correct direction?

9) What is the proper placement of the battery and how is it moved to adjust
balance?

10) Is there a maximum recommended voltage that can be safely accepted by the
ESC?

11) What wind speeds are recommended for new flyers?

12) How much space is recommended to fly this plane?

13) Who do you call if there is a problem? Do you call the hobby shop or the
manufacturer? Is there a web site?

14) Are there repair tips? What kind of glue can you use? Where can you get
replacement parts?

15) What channel is your plane using and how do you avoid channel conflict?


ASSEMBLY TIPS

Often, in order to meet a packaging goal or to keep the shipping weight down,
the manufacturer will expect you to do something or to add something. These are
usually common household items like tape or glue. In some cases the plane's
balance has to be checked and/or adjusted. They may include weights, or you
may need to buy weights, but coins work too. A dime is about .1 ounces and a
quarter is about .2 ounces. Coins can actually be cheaper than buying weights.

It is common to have to mount the tail and the wing. Are there alignment marks
or procedures that you are to follow? Do you have to remove covering material
so the glue will hold properly? How many rubber bands are needed to hold the
wing properly? Don't use less than the recommended number of rubber bands.

My Great Planes Spirit 2M glider came RTF, including the radio system. This was
my second plane after my Aerobird. The Aerobird did not need to be balanced,
the Spirit did. If I had tried to fly it without balancing it first I would
likely have broken it badly on the first flight. It took four ounces of weight
in the nose to get to balance properly.

A friend's RTF was brought to the field so we could help him. Following the
instructions we did a range check and found there was a problem with the radio
system. No problem! He packed it up, took it to the hobby shop and they
exchanged it immediately. He was back at the field in an hour. It was clear it
had not been flown so there was no question of flight damage. If he had flown
and crashed it, they could have easily refused to replace it, and they would
have been right, as crash damage is not covered under warranty. It was the
pilot's job to make sure the plane was flight ready.

FLYING TIPS

Often RTFs come with flight instructions and tips. One of the most important to
follow is related to wind. Many planes, especially two channel planes, do not
handle wind very well, especially in the hands of an inexperienced pilot. If
you don't know this, you could loose your plane, or worse, you could hit someone
or cause damage. What wind speeds are recommended, especially for new pilots?

Sometimes the plane will "porpoise" or tend to roll, or want to dive. Is it you
or is it the plane? The instructions may tell you.

Once the pilot has become comfortable with the plane, there may be adjustments
that can be made to make the plane more responsive. Sometimes it is that switch
on the radio, or a button you need to push, that goes from mild to wild. Or
maybe you have to turn something on the linkage, or move the linkage to a
different hole. Go back and read the manual for the proper procedures to make
those adjustments.

SUMMARY

Just because the plane says ready to fly, don't take that literally. Compared
to a box of sticks and a tube of glue, it is ready to fly. However there are
often set-up procedures, or assembly steps that needs to be done. It is best
to read the instructions to see how to do them correctly. You will have a much
better flying experience and your plane will last longer.

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Old 02-23-2008, 04:34 AM   #14
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Now its your turn. Post your articles, ask your questions, share your knowledge!

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Old 02-23-2008, 06:46 PM   #15
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Sticky! Sticky! Sticky!!!

"Give a man a plane and he'll fly for a day.
Teach a man to build a plane and he'll fly for a lifetime"
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Old 02-23-2008, 10:17 PM   #16
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Thanks! We will see if anyone agrees with you.

I have other article in the works. A more detailed discussion of the ESC will be next.

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Old 02-23-2008, 10:23 PM   #17
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Ed, this definitely needs to be a sticky in the proper forum so it is easy to find to and newcomers can be easily referred to the e-book.

Thanks for all the good work you do on WattFlyer.

Jim
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Old 02-23-2008, 11:06 PM   #18
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Originally Posted by AEAJR View Post
Thanks! We will see if anyone agrees with you.
Oh, I have little doubt about that. And I wouldn't worry about your "book" becoming obsolete either. Only products do that, and from what I've read so far, this mainly covers the basic rules of the game. Electronic formulas, aerodynamics, power. These are physical laws, if they become obsolete you won't be getting too many complaints, trust me!

"Give a man a plane and he'll fly for a day.
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Old 02-24-2008, 03:50 AM   #19
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Ed, Great Job! This needs to become a sticky!

The one question every beginner wants to ask but won't voice is "Why do you guys pay so much for your RC equipment? You must just be crazy! Joe's Discount House of Junk will sell me a complete RC system, airplane, radio, motors and all for $10. Isn't that good enough?"
In other words, I think you should address the "cheap is not better for these reasons" kind of issues.
Oh, please feel free to delete this post after you've read it, so it won't clutter up your great "How To".

Dennis Fishback AMA# 162410 AKA# 120592
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Old 02-24-2008, 06:00 AM   #20
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Thanks for all the work of writing the E-book. I'm just getting into Electric model planes and the timing of the article couldn't be better.
Another vote for a sticky! Thanks again.....Dick S.
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Old 02-24-2008, 11:39 AM   #21
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Wow what a great read,Has really helped with my knowledge of things and with my RTF plane hopefully coming next week i will know now what to look for.
Another vote for this being sticked in the beginners section as well so it nice and easy to find

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Old 02-24-2008, 11:52 AM   #22
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OK, I have enough requests to make this sticky, but I am going to keep it in the general forum. There are plenty of sticky threads in the beginner section.

Beginners will find it here, but I hope non-beginners will find it useful also, so I would prefer it to be in the general section.

Note that I added an article on the ESC and placed it at Post 5 where it made more sense. I moved the BEC article to 23. I also added an article on First Planes and what to look for in terms of design and materials.

The table of contents has been updated.

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Old 02-24-2008, 01:03 PM   #23
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THE ROLE OF THE BEC IN YOUR ELECTRIC PLANE
by Ed Anderson
aeajr on the forums

In the world of electric motors the electronic speed control, ESC, takes the
place of the throttle used on fuel powered planes. It regulates the speed of the
motor by pulsing the power to the motor to achieve the desired motor speed.
However most ESCs also have two other functions, the LVC and the BEC.

The LVC, low-voltage-cutoff circuit, will cut power to the motor and preserve
power to the radio system so you can land your plane safely when the motor
battery is getting too low. In the case of lithium batteries, the LVC, can also
save your battery packs by preventing them from getting too low. If you started
with NiXX packs and have switched to lithium packs, be sure your LVC is set
properly or you could damage your lithium packs.

The BEC, the battery elimination circuit supplies power to the receiver and the
servos. It is the BEC that will be the main focus of this discussion.

The name, battery elimination circuit, comes from the fact that, in the "old
days" of electric planes, you had a battery pack to power the motor and another
one to power the receiver. In order to save weight, the BEC was introduced to
eliminate the need for that receiver battery pack.

In most of our radio systems, the receiver is designed to operate between 4 and
6 volts. To match this, the typical BEC supplies power to the receiver at about
5 volts by stepping down the motor battery voltage. However the higher the
voltage of the motor battery, the harder the BEC has to work to get the voltage
down to 5 volts. In doing this work the BEC generates heat. The greater the
voltage reduction, the more heat the BEC generates. As a result most BECs have
to be disabled if the motor battery pack is over a certain voltage. ESCs that
are designed specifically for high voltage use often do not have an integrated
BEC.

BECs are also rated by how many amps they can deliver to the receiver. The
greater the number of servos installed the greater the amperage the BEC must
deliver and the more heat it generates in the process. However, with most
integrated BECs, the higher the voltage of the motor battery pack the lower the
amperage the BEC can deliver. This is often where problems occur. It is this
heat load that leads to the need for a compromise as to how many servos an
integrated BEC can support.

For example, if the motor pack is 8.4V, then a given BEC might be able to
support 4 servos. If the motor battery voltage is higher, say 11 volts, then
the same BEC may need to be derated to handle only 3 servos. Since more heat
will be generated by the larger step down from 11 volts to 5 volts, the amp load
has to be reduced or the BEC will overheat.

Note that the voltage rating for the ESC may be different than the voltage
rating for the BEC. Your ESC may be rated for 14.8 volts but the BEC may have
to be disabled over 12 volts and you will have to power the receiver separately.
If you don't take note of this and pop in a four-cell lipo, your ESC may be fine
but your BEC may be heading for a failure, resulting in a crash.

According to Dimension Engineering, a maker of BECs, "Many people don't realize
that their ESC's BEC rating is misleading. With the linear BEC built into most
speed controls, the current rating decreases as pack voltage increases. For
example, several popular 25A ESCs with "3A" BECs are only capable of supplying
0.5A when running from a 3s pack".

If you are flying an RTF or "receiver ready" model, there may not be ESC/BEC
documentation included. As an example, the manufacturer of the plane may
designate that the plane takes an 8.4V pack. At that voltage the included BEC
may be fine. However, if you decide to pop in a three cell lipo, a problem may
only be a launch away. The BEC may do fine for a couple of flights, or maybe 5
minutes or may fail 100 feet out, and down you go.

We also have the variable of which servos are being used. Different servos draw
different amounts of current. If the current draw gets too high, the BEC will
get too hot causing a thermal shutdown of the BEC. This protects the BEC and
prevents a fire, but cuts the voltage to the receiver. The net effect is that
you lose all power to the radio system and you lose control of the plane.

In the case of an overheated BEC, if there is enough cooling air going through
the plane, the BEC may come back quickly as it cools. This could look like a
radio glitch, but it could be the BEC operating on the edge of total failure.
If your ESC is very hot when you land, the cause could be the BEC operating at
the edge of its capacity. When we see these glitches, we often think the
problem is the radio system, but in fact the cause could be the BEC.

A CASE STUDY

This pilot was flying a new Spektrum 2.4 GHz system. All was fine till the plane
suddenly went dead and crashed. All sorts of speculation were offered about what
the cause could be and much of it was focused on the Spektrum 2.4 GHz system.
After the plane was recovered, everything seemed to work OK so it must have been
a radio hit, right? However, due to the diligent work of the pilot, it was
determined that the BEC had failed due to overload. You can read the actual
account at this link in posts 2986 to 3006.
http://www.rcgroups.com/forums/showthread.php?t=604621&page=200

This is not the only account of this type that has been reported, but this was
one that was worked out over a short time with a very clear outcome. Note also
that the pilot had to run his test for several minutes before the failure
appeared. Thus, everything seemed fine at first; it seemed that the BEC was
handling the load. But over several minutes' heat built up in the BEC. Combine
this with the heat from the motor and the battery and, perhaps not enough
cooling airflow and the BEC shut down.

BE COOL FOOL!

With good airflow a BEC overload may be avoided. Regardless of what radio
system you are using, make sure you have enough cooling air going through your
electric plane. This is especially true of foam planes as the foam acts as an
insulator. You may have a cooling air vent in the front somewhere, but the heat
can't get out unless there is an exit air hole large enough to allow good
airflow. If you are pushing the limit on any part of your power or radio system,
not enough cooling air can cause damage or failure to your motor, ESC, BEC or
battery packs. The receiver could overheat or you could cook your servos.

How you fly your plane can also cause heat build-up. For example, an Easy
Glider that is flown for 1 minute to get to altitude might have enough airflow
to eliminate the built up heat. But if you fly it constantly for 10 minutes,
the heat build up could be enough to cook your BEC, your battery pack, or some
other part of the plane.

Be cool fool, and make sure you have enough airflow in your plane. If your
battery is very hot, or if your ESC is very hot, you may need more cooling.

OTHER CAUSES OF BEC PROBLEMS

You could be configured properly. Your BEC may be rated to handle your servo
count and you could have plenty of cooling air but still have problems. If you
have a servo push rod that is dragging or is otherwise placing a high load on
the servo, this can increase the amp draw of that servo. If that servo gets
stuck, the amp draw will go way up!

Servo loads are expected to be variable. A servo will move, put a load on the
BEC then come back to neutral and the current draw will drop. In between loads,
the BEC has a chance to cool. However a jammed servo will draw a lot of power
and that draw will be constant. You can see why it is very important that your
servos move freely, without binding. Check those control rods for kinks,
obstructions or things that could get in the way.

ENTER THE COMPUTER RADIO

In the past it was common to have 2 ailerons run off of one servo, so three
servos were typical of a 4-channel electric plane. With more and more people
using computer radios, there is a tendency to put 2 servos on the ailerons
meaning more load on the BEC.

Also, with a computer radio it is easy to add a little aileron to rudder mixing,
moving 3 servos at once. Now add a little up elevator in the turns and all four
servos are pulling power. Go to a full house electric sailplane, with flaps
following ailerons, rudder mixed in and a little up elevator in the turn and you
now have 6 servos, all moving at once. We begin to see how the BEC can become
challenged to keep up.

WHAT IF YOU NEED MORE?

If you need more power than the integrated BEC in your ESC can supply, or if
your motor battery voltage is higher than the BEC can handle, you will need to
disable the integrated BEC and put in a separate receiver pack or a separate
BEC. Many companies make after market BECs that can handle these higher
voltages or higher servo loads.

Note that there are different kinds of circuits that are used to create the BEC
function. There are linear BECs, which seem to be primarily what is found
integrated in with the ESC. These seem to be low cost but are more affected by
the voltage of the motor pack. Then there are switch mode BECs that seem to
tolerate these higher pack voltages better than the linear BECs. It appears
many of the after market BECs are of this type.

Regardless of what type you have, follow the instructions carefully or risk
losing your plane. And be sure to provide plenty of cooling air.

Listed below are some examples of after market BECs.

For very large servo counts - 6 amps
http://www.horizonhobby.com/Products/Default.aspx?ProdID=SQBDBEC008V

Dimension Engineering has several BECs
http://www.dimensionengineering.com

The SMART BEC - Combines BEC and LVC that is Lithium aware
http://www.dimensionengineering.com/SmartBEC.htm

SUMMARY

The ESC is the heart of your electric power system. The BEC is the part of the
ESC that powers your radio system. Keep it cool and make sure you read the
instructions so you don't overload it. Forget these tips and you may be
picking up pieces of your plane, wondering what caused that crash.


What's Inside an Electronic Speed control?
http://www.youtube.com/watch?v=22CpR...ure=digest_sat

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Cool The Mythical Best First Plane

As many electric flyers are new flyers, I was asked to add a section on selecting your first plane. The next article is about what makes a good first plane and some of the issues to consider.

Note that I am only looking at electric planes or gliders. I have not taken other forms of power into consideration.

Your feedback and questions would be appreciated.

Ed Anderson
===========================


The Mythical Best First Plane
by Ed Anderson
aeajr on the forums

If you run a search on any of the RC forums you will find many posts that ask
for advice on the best first plane for them to get. The purpose of this
discussion is to show that there is no perfect first plane. But there are
things that can be taken into account to help someone pick an appropriate
plane.

Be advised that this discussion will be based on my personal experiences, my
bias, my prejudice, my research , what I have observed, and what I have been
told. That is exactly the basis that every one uses when they give you their
advice. So take this and mix it in with other advice you trust, as no one
person has the answer, only opinions based on our knowledge set.

Go and read, so you can build on what you read here. Then make an informed
decision and go with it. And when you are greeted by the first all knowing
guy who tells you that you made a mistake, you will be able to explain your
reasons, the considerations and the goals upon which you purchased that plane.
And if he doesn't agree? That's OK, we are all entitled to our opinions.

First Consideration - How are you going to learn?

An Instructor - The best, but not the only path to success

If you plan to learn to fly under the close guidance of an instructor, then do
NOT go and buy a plane. Go to your instructor and ask what they suggest.
Learning under an instructor is the best way to learn to fly. That
knowledgeable guide is going to take you through planned steps that will
impart skill and knowledge. So the best first plane is the one that allows
that instructor to do that. Your best first plane is the one s/he is most
comfortable using.

No one else's opinion matters as you have placed yourself in their hands and
should follow their lead. Otherwise why are you working with an instructor?
This opinion comes from a guy who has never worked under the close guidance of
a flight instructor but received much coaching from helpful and willing members
of the club I joined. But any journey of learning is best started with a
knowledgeable guide, and when you engage a guide, you follow them. Nuff said
about that!

A Coach - Much better than going it alone

A coach is an experience friend or club member who is willing to give you some
time, provide some assistance and point you in the right direction from time
to time. However they are not going to take on the close training
responsibility of an instructor. They will help, but you will be doing a lot
of the learning on your own. This is how I learned.

If you have not purchased a plane yet, be sure to ask your coach(es) for some
input as to the plane, or at least the design of the plane.

To be a coach, I feel the person has to spend some time with you on the field.
Perhaps they preflight your plane. Maybe they take it up for the first flight
to make sure it is OK. They may or may not use a buddy box. But the key is
that they will give you some help. Having a coach is a wonderful thing.
Things that are a mystery to you can be made clear in a moment by that helpful
coach.

The key is that you take on a lot of responsibility as you will be on your own
much of the time and there is probably no formal program that is being
followed. If you can't find an instructor, try to find a coach.

An Advisor

I and many of the people who post on these forums are trying to take on the
role of advisor. We can't be there with you but we can explain a few things,
and point you to good sources. We can tell you what has worked for us. A
coach is much better but you can have coaches and advisors and you can benefit
from the multiple sources of information. If you have an instructor, you can
ask for clarification from advisors but you should always take your lead from
your instructor. Whether a paid or not, they have made a commitment to you.
You have to do the same.


On Your Own

Here I mean that you bought something, read the instructions and tried to fly
it. Can you be successful? Sure! But the chance of success goes up as you
add levels of help. Find advisors, seek coaches and get an instructor if you
can. You are more likely to progress faster and your planes are more likely
to survive your progress. Flying is not a simple or obvious thing. It took
intelligent people thousands of years to learn how to do it. There is no
disgrace in you taking advantage of some of that previous experience and
knowledge. Get some help if you can.

If you have not purchased a plane yet, ask your advisors for some suggestions. ALWAYS
ask why they feel this particluar plane or feature is important. Sometimes their goals differ
from yours and you should factor this into your discussion.


WING DESIGNS

High, Mid or Low

Broadly speaking, airplanes have one of three wing locations. They are
either high wing, mid wing or low wing. This does not include things
like flying wings or delta wings. These don't have a fuselage in a
conventional sense. And, while there are people who learn to fly on
these designs, I don't consider them the first choice for
beginner/trainer planes.

Most people will agree that the better choice for beginner/trainer
planes are high wing designs. The reason is simple, with the wing high
and the fuselage hanging below, the plane tends to be more stable and
self righting. This can help keep a new pilot out of trouble.

Mid wing and low wing planes are typically less stable as the weight of
the fuselage is mounted around or above the wing. These planes are
typically more agile and aerobatic than the high wing planes. That P51
Mustang you saw at the hobby store is a good example. It may be a cool
looking plane but it isn't really the best choice for a first plane.
That is why the fighter pilots who flew it in combat started on
something else when they were learning to fly. It might be a good idea
if you did the same. They make good second or third planes once you have
mastered the basics of flight.

Dihedral

You will notice that some planes have wings that are basically straight.
That is, they come straight out from the fuselage. Others have an
upward angle where the end of the wing is higher than the root, the part
that attaches to the plane. This is called dihedral. On some planes
the upward sweep goes through two or three upward angles. In this case
we say the wing is polyhedral, or having many dihedral angles.

Wings with some dihedral tend be more stable and self righting than flat
wings. Wings with flat designs tend to be more responsive and will tend
to go where you put them, but also tend to stay there. This means that
if you bank the plane to make a turn, you better remember to bank it
back to level or it will stay that way. A banked wing will tend to lose
altitude if not managed properly. A plane with dihedral in the wing will
tend to return to level flight if you release the sticks.

In fact, when I am helping new flyers, if their plane has a fair amount
of dihedral, I will often advise them to release or center the stick if
they get into trouble. While not always the right thing to do, most of
the time the plane will right itself if it has enough altitude and
enough dihedral in the wing. It sounds funny but sometimes the planes
know better than we do when it comes to flying. We have to teach people
to let the plane fly.

Whether you are flying glow, gas, glider or electric, having some
dihedral in the wing of your trainer will help it to stay stable and
level during your early flights. To some extent dihedral will tend to
"fight" roll based aerobatics like inverted flight knife edges and the
like. However, when you are trying to master take-off, landing and
straight level fight, this is less of a concern.


ENGINE LOCATIONS

Many people expect the motor and propeller to be on the front of the
plane. However there are many places where the propeller can be
located. It can be a pull or push design. It can be in front or in
back. And while pure sailplanes don't have motors, e-gliders use a
motor as a launching system to get into position to look for lift.

There is much to be said for a pusher design on a first plane. On
take-off and during flight, the engine location may not matter on that
first plane. However when you come in for a landing, having the engine
and propeller high and out of the way can be very helpful. You are less
likely to hit the prop and, if you do come in hard on the nose, your
repairs are more likely to be restricted to fixing fuselage damage and
less likely to involve fixing or replacing the motor and/or propeller.

I don't have a problem with front motor designs as they are clearly the
most common. However I think that the pusher design has some advantages
for new flyers.


POWER SOURCE

Today RC aircraft are powered in a variety of ways, each having its
advantage. While there are good first/trainer planes in each category it
is worth a moment to explore the different ways to power your RC plane.


Gliders

Pure gliders or sailplanes have no motors. They achieve flight through
some sort of launching system. Once in the air they may simply glide
down or they may be designed for the pilot to look for natural sources
of lift such as thermals or slope lift. Clearly you have no fuel cost
and your battery needs are extremely modest. So the cost of fuel,
chargers, motor packs and the like just don't show up.

If this is a thermal glider, you will typically need some kind of
launcher. It might be a good arm toss for a hand launched/discus
launched glider or it might be a hi-start, an elastic system that
typically costs under $100 an lasts for years. If this is a slope
glider, then your fuel comes from natural air flow, but you have to find
the right location.

First gliders tend to be in the 1.5 to 2 meter, 60 inch to 80 inch range and
weight between 8 and 38 ounces. They typically fly fairly slowly.
This slow flight gives the pilot the advantage of having more time to
think and react to the plane.

The one down side of gliders is that they don't have the instant power
nature of powered planes. But their silent flight and low operating
costs can make them very attractive to new flyers.


Electrics

For electric powered aircraft, including e-gliders, you use a
combination of an electric motor and battery system to get your plane
into the air. Electric power has become very popular as battery and
motor technology has advanced. Today's sophisticated electric planes
can rival the performance of traditional fuel powered planes.

Electrics are quiet, clean and very dependable. On the other hand you have the
up front cost of battery packs, and battery chargers. If you allocate the cost
of these items over their useful life, electric flight is quite economical.

Electric power also lends itself to small planes and indoor use. Today you can
buy kits, ARFs or RTF electric planes that weigh 1 ounce or less. The broader
"parkflyer" weighs from 8 ounces to about 32 ounce and can be flown in areas
the size of baseball, football or soccer fields. Others require more room.

Some electrics can fly very slowly which allows them to be flown
indoors. Many of these "slow flyers" make excellent first or trainer
planes, even outdoors if you wait for calm weather.

Since you don't have the vibration inherent in internal combustion power
system, electric planes tend to be build lighter, however once you add
the battery system back in, an electric plane tends to be similar in weight to
comparable fuel planes, especially if they have modern brushless motors and
lithium batteries.

It should also be noted that over the duration of the flight, the available
power will start to drop off as the battery pack runs down. So maneuvers that
can be done
in the beginning of the flight might be difficult near the end of the flight.
This drop off will probably always exist but today's battery technology is
making this less and less of an issue as flight times extend from the 5 minute
flights of a couple of years ago to the more common 10-20 minute flights of
today.

One last point on electric power. Because it is clean and quite,
electric planes can sometimes be flown in locations where fuel powered
planes might be denied. This factor alone has probably been a key
contributor to the rise of electric power for RC airplanes.



CONSTRUCTION

Today you can select kits, ARFs and RTFs made from a variety of
materials. Which you choose is a matter of personal taste and your
desire to work with that material during a kit build or repairing crash
damage.

Balsa wood and light plywood construction is the tried and true material
for traditional kits. You can make very light strong structures that
fly extremely well. Add heat shrink polyester film covering materials,
silk or other covering materials you can construct almost anything using
simple tools and techniques.

First plane/trainers constructed in this way are fairly resilient, but
hard hits can result in breaks that will need to be taken to the work
bench to repair. A hard crash can produce serious structural failures.

A variety of foams have become popular. EPS, expanded polystyrene is
used in cups and packing materials. Major structures are often molded
from solid foam. It is light and fairly rigid. It can take a pretty
good hit and when it does break it tends to break in large pieces. A
little 5 minute epoxy can effect repairs in the field and get the flyer
back in the air fairly quickly.

However repeated impacts can cause permanent dents and damage that must
be fixed. Accumulated impacts that might not bother a balsa plane can
start to degrade the integrity of the foam causing a loss of shape.
Again repairs can be usually effected with pieces of foam and epoxy.

There are a wide variety of kits, ARFs and RTF planes based on EPS foam.
Because most of the structures can be molded to shape, the planes can be
built very inexpensively.

Elapor is a branded product of Multiplex. EPO, expanded Polyolefin and Z foam
are similar in character. These are more damage resistant than EPS, but not as
rigid so it sometimes requires more bracing than EPS. These foams will more
likely tear than shatter as EPS does. Using the right glue, each can be fixed
quickly so that the pilot will get back into the air quickly. In balance some
feel these are a better choice for models, so this group is growing in
popularity. Each has its own special character, but all seem to be a good
compromise between rigidity, weight and damage resistance. .

EPP, expanded polypropylene is another popular foam that has been around for a
while. It moves further from EPS in that it is less rigid than the rest of the
foams. In fact EPP is quite rubbery and tends to be heavier than the other
foams. As such it needs more bracing in order to maintain a solid wing or
fuselage shape. However for damage resistance EPP is the king. I have bounced
EPP planes off of hard surfaces and sustained no damage at all.

Planes made of molded solid EPS parts tend to be heavier than balsa or
EPS structures. EPP is so resilient that it has
spawned a new class of full contact combat flying. Popular with slope
glider flyers, EPP equipped pilots will intentionally crash into each
other to try to knock each other out of the sky. Since little or no
damage will result from the crash, the pilot can just relaunch for the
next round.

Molded Polystyrene and Polyethylene are also popular. Polystyrene is the
plastic typically used in plastic model kits. And Polyethylene is the kind of
plastic used in plastic milk bottles. Like the foams, these are inexpensive to
manufacture and can be quite resistant to damage. More commonly seen in small
electric RTF planes, these are growing in popularity.

Other forms of foam and plastic are also being used in first/trainer planes.
However the ones mentioned above cover the vast majority of models out there.
Their advantage over wood is resistance to damage and ease of repair. However
wood remains popular for the light and strong structures it can produce. The
foams and plastics just open up more options for new pilots.

Which you choose is up to you. If you like the idea of building with
wood, you will find a wealth of wood kit based first/beginner planes.

If you want to minimize the build, or minimize the chance of extensive
repairs, the foams may be more to your liking. And the plastics are
most typically seen in ARF or RTF packages rather than kits.

If we look at the electric plane market we see a much higher percentage
of foam and plastic planes as compared to the glow or thermal
gliders. This is especially true in the RTF part of the market.

While I have no statistics, I would guess that the sale of non-wood
first/beginner planes probably outnumber wood starters in the electric
market. That doesn't mean that the wood planes are going away just that
the market is expanding very rapidly and most of the expansion seems to
be in non-wood construction.

So, the good news is that you can have whatever you want to meet
whatever goals you set for yourself.


Channels of control - How many should you have?

Let's knock down some myths about channels and what can and can not be flown
and what can and can not be used to learn to fly. Today you can buy RC
airplanes with one channel of control and 12 or more channels of control.
They can all be flown and anyone who says they can't is wrong. Is that strong
enough?

Understand that each channel is used in some way to control the plane or some
function on the plane. From a flying point of view we will be focused on
attitude control. That is pitch, roll, yaw and speed. Broadly you can think
of them as up/down, left right and fast/slow.. This isn't correct,
but for the moment it will do. You can learn the true meaning of
pitch/roll/yaw and speed later.

The more channels of control you have, the more control you have over the
plane. Dah! However the more channels of control you have the more
responsibility you have in applying those controls. A 10 channel plane has
been designed with the assumption that the pilot knows how to use those
controls and has a sophisticated radio system to help them manage those
channels. Maybe it would be easier to learn if we had a plane that didn't
need our full understanding of 10 channels of control or a $500-$1,500 radio
system to fly it.

So how many is enough?

One - Probably Not

Two - Yes and Maybe

Two Channel Gliders Gliders - Yes!

Many gliders are two channel. Based on their design you can have very
effective control. You can even fly wild aerobatics at speeds in excess of
100 mph. Two channel gliders can be very exciting and wonderfully enjoyable.

Typically the channels will control pitch and roll. This can be done with
elevator/rudder or elevator/aileron. With these two axis of control we can
have excellent command of the plane. Of course the plane needs to be designed
properly for the controls it has, but that will be a given here. We are not
trying to design planes.

There are hundreds of successful and effective glider designs made for slope
soaring, thermal duration soaring, hand launch, discus launch and other forms
of flying. Zagi slope wings, Gentle Lady thermal gliders, Gambler discus
launched gliders and others are examples of this kind of plane. They can be
exciting to fly and can really teach you about flying. So, when someone tells
you that you can't control a plane with only two channels, they are very
wrong! Go to the glider field or slope soaring field and you will see all
the evidence you need.

It is for this reason that many people feel the best plane to use to learn to
fly is a glider. They are typically simpler in design, lower in cost, easier
to understand and do not suffer from complicated, expensive and troublesome
power systems. You could fly for the next 20 years, have a fleet of planes
and never need more than a two channel radio. You can even enter national
competitions and win championships with a simple, low cost two channel radio
and a two channel plane.

So, two channel gliders are excellent planes to use to learn to fly. I often
recommend them.

Oh, you never thought of gliders? Maybe you should.


Two channel - Rudder/throttle control or differential thrust - maybe

If one channel is used to control the electric motor, then we can control speed
and duration of the flight. Usually these planes have been designed to climb on
power and glide down on reduced power. Rudder is used to control direction.
Planes, like the Firebird series are of this type. By placing the motor at the
right angle, the application of power will cause the plane to pitch up and
climb. What this kind of plane can not control is negative pitch. That is, you
can't push the nose down to go into a directly controlled descent or dive. This
limits your control in windy situations or where you need a more rapid descent
than gravity and glide path provide.

My personal experience with these planes are that they fly well and are easy but
they can not be safely flown in much wind by a new pilot. Since you can't dive
into the wind they are easily blown away with the pilot having little ability to
fly the plane back up-wind. If you have one, fly it in calm conditions.

An alternate design is the differential thrust models that have two motors.
These planes have no flight control surfaces. Like the example above, when you
apply full power they tend to climb and when you reduce throttle they glide
down, but you can't direct the nose down to fight the wind. These planes steer
left and right by changing the speed of the motors.

My personal experience with these is that they are even less wind worthy than
the Rudder/Throttle planes. In dead calm conditions they can be fun but
control is so limited that I can't recommend them as trainers. But they can be
a lot of laughs.

Thousands of new pilots have had their first taste of flying on these
throttle/rudder pr differential thrust planes. And you can do some pretty cool
things with them.
However, without the ability to control downward pitch, to dive into the wind,
these planes can be very easy to lose in any sort of wind, especially for the
inexperienced pilot.


Three Channel - Electric Power - Yes

We already achieved a yes for gliders with two channels. For unpowered silent
flight, two is enough. In my opinion, when we have three channels to work
with we have enough control for the new power pilot to have a good command of
a plane with a motor. They can control pitch, roll and speed. The plane can be
managed
but the controls are still quite simple. A plane designed around this channel
count, can be a great learning platform and can carry the pilot long into the
future.

In my opinion, the most important asset we gain is the ability to push the
nose down so that we can penetrate into the wind. If you have ever seen a
glider pilot fly you know that even though he does not have a motor, he has
the able to fly down wind and to come back against the wind. This is done
through a controlled dive where the plane picks up speed so that its air speed
exceeds that of the oncoming wind and progress can be made over the ground.

Whether it is throttle/elevator/rudder or throttle/elevator/ailerons, this
plane can be controlled and therefore gives the new pilot the authority to
command the plane as he wishes. In fact very exciting planes can be made with
three channel control. They can be highly aerobatic or they can be slow
flyers that can fly indoors.

So, in my opinion with three channels we have reached the minimum channel count
for controlled powered flight. We have enough control, yet we can use very
simple and inexpensive equipment to fly the plane. A single stick radio with a
slide, lever or switch can provide all we need. I prefer proportional control
of the motor, but even with only on/off motor control you still have enough
control. However I always recommend proportional control for the motor.

For some, this will be all the control they will ever need. They can have
slow flyers, high speed aerobats, beautiful scale ships and never lack
positive control of the plane. This is where I started my flight training and
it has taken me quickly into all kinds of wonderful flying experiences.


Four or more channels. - Yes Yes

So, if three is enough, why do we need more? The answer is more channels give
us more control. While we have positive control of a three channel power
plane, we can have more positive control with four or more. Now we can have
throttle, pitch, roll and yaw control and apply them all at the same time or
any time of our choosing. This normally translates into throttle, rudder,
elevator and ailerons. This can provide more controlled landings, or make 3D
flight possible. Aerobatics can be much more sophisticated.

While 2 channel beginner gliders are very common and three channel beginner
electrics are common, glow powered starter planes are much more likely to have
four channels. Part of this is a matter of tradition and part has to do with
the nature of the plane. Glow powered starter planes are typically larger,
faster and more powerful than the typical starter electric. While the gliders
might be larger they are normally much lighter and travel at much slower
speeds.

A typical glow powered starter plane might be 5 pounds and capable of 50 mph.
It represents a lot more energy than a 3 channel 1 pound electric that is
moving along at 25 mph or a 30 ounce glider floating along at 10 mph. When you
tell that bigger faster plane to turn, you want to make sure you have as much
control
as possible.

For this reason, while I do not fly glow powered planes, when speaking with
potential new glow pilots, I normally recommend they equip themselves for a
minimum of four channels. There is no question that you can fly a glow
powered plane on throttle/rudder/elevator but you won't find many around on
the shelves of your local hobby store. Where you will see three channel glow
planes it is more likely to be in the flying wings and pylon racer designs.
However these are not your customary first/trainer planes in the glow world.


Five Plus - what are they for?

Let's just finish up with a brief overview of why you would ever have more
than 4 channels:

Retractable landing gear - 1 channel
Flaps - one channel
Spoilers/airbrakes - 1 channel
tow release - 1 channel
Scale features -
Bomb doors
Powered canopy
and on and on
Show features
Smoke
Glitter
just imagine

And some functions can benefit from using more than one channel.

It is very common to put a servo on each aileron and assign them to individual
channels. Now you can trim them from the radio and you can set up different
up throws from down throws to tune the plane for less drag. Using this setup
you can also double duty the ailerons as flaps or spoilers.

Flaps are likewise often split between two channels for more flexible
control.

Less common is the split elevator that has two servos on two channels that can
be made to follow the ailerons to make the plane roll faster or perform other
stunts more effectively.

It goes on and on. It takes expensive and sophisticated radio gear to handle
some of these functions, but that cost is going down and the ease of set-up is
going up. Many beginners are now entering the hobby with computer radios as
their first radio, or their first upgrade from an initial 2, 3 or 4 channel
standard radio.


SPACE

How much space do you have for flying? If you have totally clear space of at least 600'X600', about 9 square acres, approx 4-6 squarefootball/soccer fields, then most parkflyer class planes should be fine. These are planes that are typically two pounds or less that typically fly at about 40 mph or less. These planes are commonly powered by Speed 400 or 480 brushed motors. They also fly well at partial throttle so that you can fly at less than full power and have more time to think and less rush to turn.

If your space is more like 200X200, one square acre or one football/soccer field, then a different plane is in order. Now you want something more akin to a slow flyer. These planes do ver well under 20 mph and some can fly so slowly that you can almost jog with them. Their main challenge is their light wing loading and wign designs make them challenging to fly in more than about 5 mph winds. However, for a new flyer with limited space, they make wonderful first planes.

These are my own designations and are based on my subjective
ranking of the space a new flyer should have when learning on
his own. An experienced fyer can fly faster planes in smaller spaces,
but a new flyer wants to have more space so you are not in a constant
state of panic trying to turn.

Of course you can get above the edges of the field and expand your space,
but if you lose control, you drop in woods, on top of kids or smash
someone's windshield. If that windshield is in a car is traveling
down a road when you hit the windshield, you could cause an
accident or worse.

So much for space. You get the idea.


Summary

So, if you made it this far, you should get an award! By now you should have
seen that there is no ideal best first plane. It is a myth. Many planes can be
excellent first planes.

What we have discussed are the characteristics of planes that would be better
suited for new pilots.

So, here is my mythical best first plane:

High Wing
Significant dihedral
2 or 3 channel glider
3 or 4 channel electric
Foam construction - EPP, Elapor, EPO, Zfoam or EPS foam
I love gliders and feel they make great first planes/trainers
If it is power, I think the pushers are outstanding

I hope you found some of this useful, helpful and perhaps interesting. If not,
how did you get this far?

The AMA

The AMA, the Academy of Model Aeronautics, is an outstanding resource to the
new and experienced flyer. I encourage you to become a member. Here is an
outstanding series of articles published by the AMA that will be really useful
to new pilots. It is called, "From the Ground Up" by Bob Aberle. I highly
recommend
it.
http://www.modelaircraft.org/mag/FTGU/Part1/index.html

RC Clubs in the United States:
http://www.modelaircraft.org/clubsearch.aspx


Good luck new pilot and welcome to RC flying!

Long Island Silent Flyers
www.lisf.org
Eastern Soaring League
www.flyesl.org
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Old 02-24-2008, 10:03 PM   #25
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Ed, Is ther a way to isolate individual posts/replies? I have printed up the first part, and would like to add the succesive articles (like the one above) alone to what I have as they come out.

"Give a man a plane and he'll fly for a day.
Teach a man to build a plane and he'll fly for a lifetime"
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