Airfoil vs Flat

[stinkweed007]

I have a question.

When building a wing.. ho important is it to have an airfoil? I realize most aircraft have it, but some dont or its nearly nonexistant.

I use this rather durable foam for my planes, it is for exterior insulation. and I have found that it comes in a thinner version (4cm) and I want to use it to make wings.. I would rather not sand the heck out of it except the leading edge and ailerons.

I lack a few foam working tools.

so if I dont shape it to an airfoil.. what, from a performance and aerodynamic standpoint, should I expect?

will the control be bad or will will I just be more reliant on power rather than lift..?

[Biplane Murphy]

Definately dependant on power, with no lift.


like the flat foamies.... point them where you want to go......no real lift to speak of.....

[slipstick]

Do you really mean 4 cm (1 1/2 inches) ? That's awfully thick for a "flate plate" wing.

Without some serious shaping to smooth the airflow over it you'll find it has very poor lift and probably more important, it will stall very easily and sharply, snapping all over the place with any slight change in attitude.

BTW if you don't have hot wire cutting equipment you'll find that a fine saw blade (e.g. fretsaw) will cut foam quite well. I've even used a fine hacksaw blade in a simple wood handle. Either way it's easier and a lot less messy than sanding :).

Steve

[stinkweed007]

first... I overstated my foam... its actually 2.5cm.. the 4 stuff is the thick stuff I use for fuselages... sorry...

but aside from being sensitive and easy to stall.. if balanced right.. I could make it pretty stable... ?

[SaucerGuy]

Think 30 grit if sanding means something, zagi tape over after, if you use some finer grit and you will like the results even more. No need to kill yourself along that gambit at all, well, unless you are wanting to sand and fill, then paint.

The airfoil, line it up with the expected running speed of the plane and design accordingly. You have to gauge that into the final profile for it entirely from that area.

[pd1]

Stinkweed, My personal preference is an airfoiled section instead of a flat section.

That said, Flat sections will work. They have some quirks and drawbacks, but they will work.

If the model is light enough you can get away with quite a bit.
Look at flat foamies, not what I like, but they work.

I found, in my own limited tests, that flat airfoils tend to be pitch sensitive at their lowest positive angles of attack.

I even have a flying stop sign that uses a 1 inch thick flat airfoil.
It is stable, as long as you don't drop the nose too far.

Even without a hot wire, it doesn't take too long to come up with a basic airfoil shape using coarse sandpaper , or a saw blade.

Good luck
Paul

[HX3D014]

flat foamie's work because of the Thickness percentage of the chord.
Air has a chance to rejoin the Straight line after its initial seperation.

Not sure of the ratio of thickness-chord-span of a wing with Square edges over the lift ability. but you will reach a point of impractical or dysfunctional.

IE.

you could make a wing that was made with 1mtr thick foam. and it would still generate lift given a + AoA. but the chord and span would need to be way out there. (Not practical)

the thing is given you 2.5 cm wing thickness. just the slightest trim of the upper LE would improve the lift.

there are many different foil shapes. so without knowing what plane you are using it for. I could not comment on what foil shape to use.

try this. Mark 25% of the chord (a line span wise 10cm back from the LE if the chord is 40cm) put a steel ruler along this line. also do the same for 1/3 down The thickness of the foam along the LE. now with a fresh Stanley knife cut the top portion of the LE off.
Doing this will greatly improve the Lift ability and reduce the stall tendency.

(This is a very rough improvement. but the thing is, it would be better than Flat)

If you do see the point and do decide to try it.
Don't do it just yet. It is easy to improve on that example I gave. and worth improving on :)

Foil wins hands down.

[MikeMc]

Airfoil or not has nothing to do with power. Lift is going to be generated by an airfoil or by a flat wing. The question is going to be how much drag is created or how efficient the airfoil or non-airfoil will be at a given speed and AOA.

That stuff we all learned about how the air has a longer distance over the top than over the bottom creates a low pressure on the top so it generates lift. Well you can pretty much throw that out the window. It's about as accurate as our history books that show Columbus feasting with Native Americans on Thanksgiving. It only attributes to about 10% of the lift in the best conditions. Most of the lift is from AOA.

In overly simple terms, if you fly slow to moderate it doesn't matter. It starts to matter when you start to care about how fast you can go.

There's one good reason to have a big thick airfoil. You can hide your structural strength inside it.

And now we have the flame fest. hahaha

[Biplane Murphy]

Airfoil or not has nothing to do with power. Lift is going to be generated by an airfoil or by a flat wing. The question is going to be how much drag is created or how efficient the airfoil or non-airfoil will be at a given speed and AOA.

That stuff we all learned about how the air has a longer distance over the top than over the bottom creates a low pressure on the top so it generates lift. Well you can pretty much throw that out the window. It's about as accurate as our history books that show Columbus feasting with Native Americans on Thanksgiving. It only attributes to about 10% of the lift in the best conditions. Most of the lift is from AOA.

In overly simple terms, if you fly slow to moderate it doesn't matter. It starts to matter when you start to care about how fast you can go.

Hmmmm........I don't want to start a "Flame Fest" but........

Power doesn't relate to generated lift and airfoil type?
so a flat bottom airfoil doesn't generate more lift than a flat piece of foam?......Do you have some kind of proof to back up such statements.....

For instance... A Dr1 with 4 flat bottom airfoils, set at 0 degrees incidence, at level flight will climb proportionally to the airspeed it is travelling at....More power=more lift.

A flat foamy with it's wing, set at 0 degrees incidence, will just fly straight proportionally to it's airspeed.....more power does not = more lift

Symmetrical airfoils create the same amount of lift for the top and bottom.... this is why aerobatic competition planes use them....

I am very interested to hear how you came to your conclusions.....

[slipstick]

Mike makes one or two valid points though they are a bit hidden in the over-the-top confrontational style ;).

Flat plates do create lift due to AoA (basic Newtonian physics) as do airfoils. No symmetrical airfoil, however smooth and aerodynamic it looks, can create lift without having a +ve AoA just like a flat plate (which is just a special case of a symmetrical airfoil).

At a give AoA cambered airfoils create more lift than flat plates though not as much more as you might think. The major difference between them is not the lift it's the much lower drag a good airfoil has to go along with the lift (i.e. greater efficiency).

There's also a major difference at extremes of AoA. A normal airfoil stalls (stops creating lift) relatively slowly. Flow over a flat plate breaks up and thus loses lift very rapidly once it gets to a certain AoA....hence the terrible stall characteristics. A thick flat plate i.e. with a 2.5cm surface at 90 degrees to the airflow will make this worse and obviously will have much more drag (and so will need more power to fly at any given speed).

BTW murph your conclusions are wrong I'm afraid.....a cambered air foil like on a DR1 (which should only have 3 wings not 4 ;)) creates more lift with more SPEED not more power. Power is just the way you choose to gain speed, you could just as well leave power the same and put it into a dive to pick up speed....neutralise the elevator and it will zoom into the sky until gravity causes it to slow down. If it didn't work like that gliders wouldn't fly ;).

Steve

[SaucerGuy]

Mike makes one or two valid points though they are a bit hidden in the over-the-top confrontational style ;).

Flat plates do create lift due to AoA (basic Newtonian physics) as do airfoils. No symmetrical airfoil, however smooth and aerodynamic it looks, can create lift without having a +ve AoA just like a flat plate (which is just a special case of a symmetrical airfoil).

At a give AoA cambered airfoils create more lift than flat plates though not as much more as you might think. The major difference between them is not the lift it's the much lower drag a good airfoil has to go along with the lift (i.e. greater efficiency).

There's also a major difference at extremes of AoA. A normal airfoil stalls (stops creating lift) relatively slowly. Flow over a flat plate breaks up and thus loses lift very rapidly once it gets to a certain AoA....hence the terrible stall characteristics. A thick flat plate i.e. with a 2.5cm surface at 90 degrees to the airflow will make this worse and obviously will have much more drag (and so will need more power to fly at any given speed).

BTW murph your conclusions are wrong I'm afraid.....a cambered air foil like on a DR1 (which should only have 3 wings not 4 ;)) creates more lift with more SPEED not more power. Power is just the way you choose to gain speed, you could just as well leave power the same and put it into a dive to pick up speed....neutralise the elevator and it will zoom into the sky until gravity causes it to slow down. If it didn't work like that gliders wouldn't fly ;).

Steve

hmm.... care to re-write your post before I rebuttle? :) I can edit/delete your quote in my response as well.

[slipstick]

hmm.... care to re-write your post before I rebuttle? :) I can edit/delete your quote in my response as well.
No thanks. Such is my ignorance that I can't see anything wrong with what I wrote (other than it's rather simplified in places). If you believe you can actually rebut (the verb is "to rebut" not "to rebuttle" ;)) any particular points bring on your rebuttals. Then I can either try to correct your misunderstandings or learn something myself and we'll have a discussion going. Discussions are a good thing, they're what discussion forums like this are all about ;).

Steve

[Biplane Murphy]

Hi Slipstick.... I should have used Speed not Power.....Thanks..:)

The Dr1 has 3 wings and an airfoil between the wheels...4 lift creating airfoils total.:)

I was refering to level flight and 0 degree wing incidence in order to eliminate variables.....(such as angle of attack)

It seems to me that changing angle of attack doesn't necessarily mean the wing's shape creating lift.....It seems that the angle of attack would be creating the lift....with enough power and speed, anything can rise vertically......Rockets for example...

[MikeMc]

Mike makes one or two valid points though they are a bit hidden in the over-the-top confrontational style ;).
Sorry. You're 100% correct. It's because I've already seen and been involved in this topic a dozen times and know exactly how it's going to go down.

I'll just say a couple things:
- A plane that has extreme thrust to weight ratios (3:1 is not uncommon) are not good examples. Although the rules still apply one can be confused between lift generated by thrust and lift from the wing. Airfoil or flat it's still the same.

- The important part here with flat vs airfoil shapes is Laminar vs Turbulent flow and drag, and almost nothing to do with lift.

[Biplane Murphy]

Sorry. You're 100% correct. It's because I've already seen and been involved in this topic a dozen times and know exactly how it's going to go down.

How about some links to these previous discussions then.:)

And Slipstick related what I was trying to say, but phrased it better.....

With 0 degrees angle of attack, a symmetrical airfoil (Flat plate included) creates no lift.
And a Cambered Airfoil does.

[stinkweed007]

let me add something to my own question...

I am not researching the build of a little flat 3D. Although they have there place.. I have no real desire for one.. not a cut, just preferance.

I am speaking of a plane with a wingspan of about 2m. and a slightly heavy fuselage (nice little 560g video cam I have always wanted to send up) power will already be an issue due to weight..

so lets assume I will have the power to travel such a plane at 1:2 T/W. what should I expect from the wing without the airfoil.. will she be uncontrolable? will I need a gross increase in T/W or will this just be a wee bit more sensitive?

[MikeMc]

With 0 degrees angle of attack, a symmetrical airfoil (Flat plate included) creates no lift.
And a Cambered Airfoil does.
Yes, but no where near enough to sustain flight. On a full size Cessna 150 it's about 20-40 lbs of lift. As you can see that won't get it off the ground.

I wouldn't give my worst enemy those links. Search RCU if you really want a headache that bad. Try wikipedia and search airfoil, lift, drag, etc for some basic info.

[Biplane Murphy]

Yes, but no where near enough to sustain flight. On a full size Cessna 150 it's about 20-40 lbs of lift. As you can see that won't get it off the ground.

I wouldn't give my worst enemy those links. Search RCU if you really want a headache that bad. Try wikipedia and search airfoil, lift, drag, etc for some basic info.

:Q:Q:Q.... RCG gives bigger headaches....but I don't mind sifting through threads like that....I still wouldn't mind a link or 2.:)


If I ignore theory and go with actual observation of planes I own and fly regularly....

So...... I have an Ultimate Biplane(Symmetrical airfoil) and an SE5a Bipe(cambered airfoil) With the same Wingspan, weight and Power systems(Prop,motor,ESC,Batt)-*.....

In level flight and at full throttle, the Ultimate Bipe flies straight, and the SE5a climbs.

In inverted flight the Ultimate flies straight... the SE5a loses altitude....

In Knife edge flight...the Ultimate flies straight(with appropriate rudder input).... the SE5a pulls toward the top wing (also with the obligatory rudder input)....

[Biplane Murphy]

let me add something to my own question...

I am not researching the build of a little flat 3D. Although they have there place.. I have no real desire for one.. not a cut, just preferance.

I am speaking of a plane with a wingspan of about 2m. and a slightly heavy fuselage (nice little 560g video cam I have always wanted to send up) power will already be an issue due to weight..

so lets assume I will have the power to travel such a plane at 1:2 T/W. what should I expect from the wing without the airfoil.. will she be uncontrolable? will I need a gross increase in T/W or will this just be a wee bit more sensitive?

IMHO....I would use some sort of lift enhancing airfoil with some dihedral to help haul around the extra weight, and help with stability..... especially since you do not have a lot of thrust to weight ratio....But that is only what I would do.:)

[stinkweed007]

Kool... because my wing building really bites...

[fdix]

If I ignore theory and go with actual observation of planes I own and fly regularly....

So...... I have an Ultimate Biplane(Symmetrical airfoil) and an SE5a Bipe(cambered airfoil) With the same Wingspan, weight and Power systems(Prop,motor,ESC,Batt)-*.....

In level flight and at full throttle, the Ultimate Bipe flies straight, and the SE5a climbs.

In level flight both aircraft fly... level! :Q
No seriously: they won't gain or loose altitude, they will just fly at different angles of attack.
If one climbs it is due to wrong trim, down thrust of the motor etc..


I would use some sort of lift enhancing airfoil with some dihedral to help haul around the extra weight, and help with stability..... especially since you do not have a lot of thrust to weight ratio....But that is only what I would do.

Dihedral makes a plane more stable on the roll axis and has quite a few other effects but it does not create lift.
In my opinion also an airfoil would be a good idea!

[MikeMc]

IMHO....I would use some sort of lift enhancing airfoil with some dihedral to help haul around the extra weight, and help with stability..... especially since you do not have a lot of thrust to weight ratio....But that is only what I would do.:)
Now knowing the type of plane I'd do the same.

Murphy, It's been quite a while since my days at RCU. I wouldn't be able to find them. Here's a link to a wiki page (ignore all those formulas). Check the links to the related topics too.
http://en.wikipedia.org/wiki/Airfoil

[Biplane Murphy]

In level flight both aircraft fly... level! :Q
No seriously: they won't gain or loose altitude, they will just fly at different angles of attack.
If one climbs it is due to wrong trim, down thrust of the motor etc..



Dihedral makes a plane more stable on the roll axis and has quite a few other effects but it does not create lift.

I clearly mentioned Dihedral and stability in the same sentence.:)

The SEFa is trimmed for medium throttle ( It does indeed fly level)... at full throttle it climbs....as does my Fokker DVII....And the Kadet I used to own...And several others....:)

How about a reference to a Kadet 42ep then.... alot of downthrust is needed to counteract all the lift created by it's airfoil even at medium speed.....

How about STOL planes that rely on generated lift to sustain flight at low speeds?.... A flying buddy built one that floats and floats along.....It takes off with very little throttle, and it isn't from angle of attack.

[pd1]

"I am speaking of a plane with a wingspan of about 2m. and a slightly heavy fuselage (nice little 560g video cam I have always wanted to send up) power will already be an issue due to weight.. "



I now take it that aerobatics is not a primary concern.
Also, a slow flight speed is not a disadvantage.pd


"so lets assume I will have the power to travel such a plane at 1:2 T/W. what should I expect from the wing without the airfoil.. will she be uncontrollable? will I need a gross increase in T/W or will this just be a wee bit more sensitive?"


I would definitely stay with an airfoil for slow flight or a free flight type.
A lot of lift without much speed.

Under cambered or clark Y would give good lift and lift reserve.
I wouldn't consider a flat airfoil.

I have an article on airfoil sections for planes of this size by Alexander Lipitsch. I'll copy it if you care to read it.

I hope I spelled his name correctly.
This article is based on actual data from wing sections about this size.

Paul

[HX3D014]

I am speaking of a plane with a wingspan of about 2m. and a slightly heavy fuselage (nice little 560g video cam I have always wanted to send up) power will already be an issue due to weight..

so lets assume I will have the power to travel such a plane at 1:2 T/W. what should I expect from the wing without the airfoil.. will she be uncontrolable? will I need a gross increase in T/W or will this just be a wee bit more sensitive?

You may need to make the wing out of two of those 2.5 cm flat foam pieces.
and then do some serious shaping. (a nice thick slow foil with maximum lift)

My suggestion of the ruler may need to be changed. 1/ you could use a length of steel or something. but I am wondering what the length of the Cutting blade may need to be.

anyway.

if you add shape and do some additional sanding. you will reduce drag( thus aiding lift) and increase controllability. especially over the control surfaces.

What other methods of getting a shape could other suggest (While we are looking for suitable foil to use)

[SaucerGuy]

Mike makes one or two valid points though they are a bit hidden in the over-the-top confrontational style ;).

Your' response is confrontational, don't you think?


Flat plates do create lift due to AoA (basic Newtonian physics) as do airfoils. No symmetrical airfoil, however smooth and aerodynamic it looks, can create lift without having a +ve AoA just like a flat plate (which is just a special case of a symmetrical airfoil).

Let's see plain english, zero lift is generated by a symmetrical airfoil, be it flat or otherwise, the air passes along both sides equally, this means there is no change in pressure on either sides. The angle of attack is not creating lift either, it's simply diverting the airflow downwards, similar to directing thrust.


At a give AoA cambered airfoils create more lift than flat plates though not as much more as you might think. The major difference between them is not the lift it's the much lower drag a good airfoil has to go along with the lift (i.e. greater efficiency).


There's also a major difference at extremes of AoA. A normal airfoil stalls (stops creating lift) relatively slowly. Flow over a flat plate breaks up and thus loses lift very rapidly once it gets to a certain AoA....hence the terrible stall characteristics. A thick flat plate i.e. with a 2.5cm surface at 90 degrees to the airflow will make this worse and obviously will have much more drag (and so will need more power to fly at any given speed).

BTW murph your conclusions are wrong I'm afraid.....a cambered air foil like on a DR1 (which should only have 3 wings not 4 ;)) creates more lift with more SPEED not more power. Power is just the way you choose to gain speed, you could just as well leave power the same and put it into a dive to pick up speed....neutralise the elevator and it will zoom into the sky until gravity causes it to slow down. If it didn't work like that gliders wouldn't fly ;).

Speed/power are the same in my book, when you are taking off, there isn't as much lift which means you are pulling a heavier object through the air, once the airfoil kicks in to full efficiency, you now have a lighter plane, so what power you were using, now is more efficient. At the same time, too much lift, ie. thicker airfoil will create drag because the profile is larger, so you have a threshhold along how much power you can put into a plane and still keep it practical.

Along the undercamberd airfoil, the reason why it works so well is that it's taking full advantage of both elements, we have an airfoil which creates lift on it's own, we also are diverting the air downwards along the bottom of it, pointing downward at the same time. You can go with a nuetral angle of attack with that airfoil and it will create lift on it's own, yet the air will curl into itself along the lower leading edge, this creates a pocket of turbulence and essentially turns it into a flat bottom airfoil since a portion of air get's trapped underneath for a brief amount of time while the rest of the air passes over the pocket.

[stinkweed007]

relax ya'll this is just a thread about the DIFFERENCE between flat and round. both will fly... just one flys a bit different.. not the WWF between Newton and Hughes...

I understand that an Airfoil produces lift, while the flat is more directional. I only wanted to know how that translated into flight performance. In the form of a P-51, lift was very important in the overall performance, where as an SR-71 uses its wings just to direct that rocket..

[slipstick]

Let's see plain english, zero lift is generated by a symmetrical airfoil, be it flat or otherwise, the air passes along both sides equally, this means there is no change in pressure on either sides. The angle of attack is not creating lift either, it's simply diverting the airflow downwards, similar to directing thrust.
The AoA causes the the air to be diverted downwards....O.k. so far. And the diverted air pushes the wing up by a simple reaction which Newton explained centuries ago. A wing being pushed upward is what we generally call lift. So in what sense did you say lift is not due to the AoA ?

Speed/power are the same in my book
Sorry but if you really can't tell the difference between speed and power you've lost me, there's really no point continuing. Here's a hint, Oil tanker, power 50,000 hp, speed 18mph. Speed 400 pylon racer, power <0.2 hp, speed 100+mph. Power is not speed.

Along the undercamberd airfoil
And why suddenly bring up undercambered airfoils which I never mentioned ? You can't rebut an argument by talking about something completely different :(.

This is too bizarre to even be funny. I give up ;).

Steve

[SaucerGuy]

Slip, you are now on ignore, it's easier that way.

Stink, I came up with a killer airfoil on my latest flying wing creation, it's a real floater, I'll bounce you the specs if you are looking around for something to give you maximum lift without sacrificing it to drag.

[HX3D014]

Kicking it in the butt.

The lift formula dose not involve power anywhere. it uses V (Wind speed from LE to TE)

Chord line is the line along the Max distance between LE and TE

AoA is the difference in A between Relative Airflow and that Chord line.

Most Non-Symmetrical wings produce lift even with a - AoA.

Stink;
What are you other dimensions etc?
Chord? (If you go for double plate now 5cm thick @ 15% that would give a chord of 33cm.
how fast do you want to go?
what is the expected AUW?

A thick foil will produce more lift at a relatively slower speed and generally have a slower stall speed. (Ideal for camera flying) when I say thick I am thinking no more than 15% may be 16% depending.

Use a thick foil if you do not want lift and don't care about speed. (And a reserve for lack of stall, easy recovery, it is a camera ship ? )

the drag and lift formula are similar. the are both increase by (VxV).

[slipstick]

Slip, you are now on ignore, it's easier that way.
Easier than getting your facts straight ? Yeah, I guess so :(.


stinky, you really do need an airfoil of sorts on that plane. The last thing you want when taking video is a plane that tends to snap and stall every time you try to turn it. Just cutting wedges off the top of the foam to make it a flat wedge shape and rounding the LE will help a lot...and for that size you're probably best using the 4cm thick.

Steve

[watt_the?!]

very interesting thread fellas... please hang in there with it...very useful and excellent read...SS is there anything you dont know about flight?...SG is there anything you dont test/analyse/engineer?...great to have you guys at WF...keep it coming!
im sure that all these Qs&As and debates are on everyone's lips..

Tim

[HX3D014]

Easier than getting your facts straight ? Yeah, I guess so :(.


stinky, you really do need an airfoil of sorts on that plane. The last thing you want when taking video is a plane that tends to snap and stall every time you try to turn it. Just cutting wedges off the top of the foam to make it a flat wedge shape and rounding the LE will help a lot...and for that size you're probably best using the 4cm thick.

Steve

Good call using the 4cm (I forgot about that :)

I would also suggest that he round the top. (the pic you posted has a reasonable camber and it is relatively easy to do.

Another thing that could help is if he did use a rough sandpaper. he could always cover it with some film to bring it back to Smooth. though this is not a thing I would suggest doing without getting a pic of the foam after a little test. those little bubbles may cause a Golf ball effect even if covered with film. so I wonder on the methods available to round the top.

(One good point I was thinking with the doubled 2.5cm layered is being able to inlay bracing and bearers etc. (not a planker so not familiar with the terms of structural reinforcement) wonder if he could use two 2cm layers, (I know, he has what he has and so far we know it is either the 2.5cm stuff or the 4cm stuff)

Another thing I was thinking was;
To use some 3mm foam and lay that over the top surface. and fill in any gaps with Space filler (That stuff that expands, test its weight first) Hmm still thinking on that one.
But The result should be a smooth and gently accelerated curve creating a uniform lift and also helping the CP distribute smoothly during different AoA changes.

[SaucerGuy]

Good call using the 4cm (I forgot about that :)

I would also suggest that he round the top. (the pic you posted has a reasonable camber and it is relatively easy to do.

Another thing that could help is if he did use a rough sandpaper. he could always cover it with some film to bring it back to Smooth. though this is not a thing I would suggest doing without getting a pic of the foam after a little test. those little bubbles may cause a Golf ball effect even if covered with film. so I wonder on the methods available to round the top.

(One good point I was thinking with the doubled 2.5cm layered is being able to inlay bracing and bearers etc. (not a planker so not familiar with the terms of structural reinforcement) wonder if he could use two 2cm layers, (I know, he has what he has and so far we know it is either the 2.5cm stuff or the 4cm stuff)

Another thing I was thinking was;
To use some 3mm foam and lay that over the top surface. and fill in any gaps with Space filler (That stuff that expands, test its weight first) Hmm still thinking on that one.
But The result should be a smooth and gently accelerated curve creating a uniform lift and also helping the CP distribute smoothly during different AoA changes.

The 4 cm is too thin to do much with material wise, shaving it down, you could go symmetrical, but that's about it, flat bottom really will only produce a sharp leading edge which is counterproductive.

[MikeMc]

Speed/power are the same in my book...
We get our own book to make-up and re-write the laws of physics? Awesome!!! Where do I buy this book?

[HX3D014]

The 4 cm is too thin to do much with material wise, shaving it down, you could go symmetrical, but that's about it, flat bottom really will only produce a sharp leading edge which is counterproductive.

Actually if anything. I would have made the Foil's LE a little more round.

As it is, The LE on the Foil that SS posted is a little square, but it is easy to produce.
Getting that LE a little more round will help, so if you can do that, you will benefit.
SaucerGuy. Not sure is you can see the Pic I was Talking about.
last post by Slipstick. above watt_the!?'s post

Oh. and why would you go for symmetrical? he has no need to go inverted (I think?). I'm not following you reasoning there. Please Explain.

Mick MC; hehe.
saucer guy already admitted that Power dose not directly and always translate into speed. but generally. in a given aircraft, when one increases power,. the speed usually follows. (We know what he meant)

[MikeMc]

To be completely anal (it's pretty much required now. hehe), drag goes up exponentially as speed increases. This has a lot to do with why I said it doesn't matter if it's a flat plate or airfoil at low to moderate speed/performance applications. Stall characteristics withstanding.

Speed = Constant * Drag ^2

[slipstick]

Actually if anything. I would have made the Foil's LE a little more round.

As it is, The LE on the Foil that SS posted is a little square, but it is easy to produce.
Getting that LE a little more round will help, so if you can do that, you will benefit.
Yep it's all a matter of compromise....you can put in as much work as you like to get nearer and nearer to a genuine clean airfoil shape. But what I was proposing was taking a rectangular block of foam, 2 cuts to make the wedge shape and a few strokes with a sanding block to round the LE. You don't end up with a brilliant airfoil but you do have something very much better than the original rectangular block and for very little time and effort ;).

saucer guy already admitted that Power dose not directly and always translate into speed. but generally. in a given aircraft, when one increases power,. the speed usually follows. (We know what he meant)
It may be that I spent too much time with gliders in early life.....in a glider the elevator controls the speed and there ain't any power to play with. And then when I was learning to fly full size powered stuff my instructor drummed into me "Elevator for speed, throttle(power) for altitude". The equation power = speed just doesn't make any sense to me in terms of flight dynamics ;).

Ah well, there's an awful lot I don't know about these things. I'm still hoping to learn a bit more (but not that speed and power are the same thing or that downwash lift somehow isn't "real" lift :().

Steve

[HX3D014]

Cool.
Now we just gota wait till stinkweed007 gets back to us.
Re if he can manage to do the Shaping etc.

[SaucerGuy]

I'm going to unsubscribe from this thread, glad Stink is in good hands, I wish him well on achieving his goals. This and many other projects, he's going to do very well with.

[Eric_N57105]

try this. Mark 25% of the chord (a line span wise 10cm back from the LE if the chord is 40cm) put a steel ruler along this line. also do the same for 1/3 down The thickness of the foam along the LE. now with a fresh Stanley knife cut the top portion of the LE off.
Doing this will greatly improve the Lift ability and reduce the stall tendency.


I think what is being described here is an airfoil that is used on a lot of small free flight hand launch and catapult gliders. Mine are in the range of 12-18", and use this type of airfoil. Here's an article describing them. Check out Figure 5 which I think is what is described above.

http://www.modelresearchlabs.com/hand_launch_glider_airfoils.htm

Eric

[HX3D014]

I like that:)
but the description was just to aid in how to Get the cut. IE how to make a foil shape out of a flat piece. (I paid no real attention to the measurements I gave, and so suggested that this is just an example :) )

I read a little of the article and I like the section"Bernoulli’s law for hand launch gliders".




I like the Genese 34 or 36
these .gif files found @ www.ae.uiuc.edu (http://www.ae.uiuc.edu)
http://www.ae.uiuc.edu/m-selig/ads/afplots/rhodesg34.gif
http://www.ae.uiuc.edu/m-selig/ads/afplots/rhodesg36.gif




I was actually trying to describe (Off the top of my head) some foil shapes I had seen In G3. Hang on I'll Post one (Make that 5) attached, not the two above in the body of this post.

[Bill G]

Why not go for the happy medium? A curved plate undercamber airfoil.
They don't look as nice as a semi-symmetrical airfoil, and won't do the aerobatics as well, but have advantages.
1. Massive lift at the expense of a bit of power.
Its kind of like having the benefit of flaps on.
2. Excellent slow flight and reduced stall and launch speeds.
As before, its kinda like the flap thing.

I've become a big fan of the undercambered wing:

I scratch built a number of EDFs with undercambers, with the idea of easier flying in mind, back when I had less flying skill. What I got was a bit slower of a jet that wasted a bit of power, but would fly much slower than full airfoiled jets. When I started building full airfoil jets, what amazed me was how much harder the were to launch, at much lower weights. I have 2 undercambered 20+ oz jets of only around 30" span that lauch like prop planes. The first full airfoiled one was much lighter than these undercambered jets, with much lighter wing loading, but was MUCH harder to get going at launch speed. I don't do insane things when flying my jets, so other than for looks, I'll take the undercambers for the park flyer jets, since they hand launch well and land much slower.

[pd1]

HX3DO14, Good airfoil choices. Your fourth airfoil section on the bottom, looks remarkably like the airfoil Goldberg used in his Falcon and Skylark series planes.
I don't think the differences in the two airfoils will make that much difference in Stinkweeds use.

I have been using this airfoil for over 40 years and it performs amazingly well.

Even when the wing stalls, it won't drop one wing unless a lot of rudder and elevator are applied and held.

Very good choice for Stinkweeds application.

Paul

[watt_the?!]

To be completely anal (it's pretty much required now. hehe), drag goes up exponentially as speed increases. This has a lot to do with why I said it doesn't matter if it's a flat plate or airfoil at low to moderate speed/performance applications. Stall characteristics withstanding.

Speed = Constant * Drag ^2

Mike,
not to nitpick...im sure you dont mind anyways...and i think you mean this anyways also...but you have shown a squared (not exponential) relationship in your formula.

what many people dont know is that speed (actually prop or blade rpm) is directly proportional to the square of thrust and the cube of power.

im sure you could derive that relationship from the aerodynamic's fundamentals...but actually its a very useful relationship especially when sizing power setups.

its one of those things you can virtually do on the fly..

someone at your field might say my plane doesnt fly well...i know it is at 10000rpm on such and such prop and thrust to weight is 0.75..my plane weighs 500g.

from there you can easily prescribe a new setup.

you might suggest a 1:1 thrust/weight...which, since it means a 1.35 or so increase in thrust then its the root of that for the new prop rpm and the cube of the prop rpm for the power required to get there..ALL RELATIVE

i.e. if you want to increase thrust by 35%...then thats a relative increase of 1.35. that would be a relative prop rpm increase of (sqrt(1.35) about 1.17 (estimate) and will need the cube of that (1.17) in additional power (est 1.6 or so). So right there you can tell your friend that he'll need 60% more battery to go where he wants (added weight excluded).

just an interesting correlation i picked up in your post and thought- if anyone already doesnt know this that this is also a useful relationship.

from what i understand the relationship comes from change in prop rpm (a single dimensional figure) then converting to a 2 dimensional figure in thrust (related to swept area), then converting to 3 dimensions (swept area x length per unit time (volume)).

a bit of a tangent i know...sorry guys carry on...my bad::o

[watt_the?!]

Why not go for the happy medium? A curved plate undercamber airfoil.
They don't look as nice as a semi-symmetrical airfoil, and won't do the aerobatics as well, but have advantages.
1. Massive lift at the expense of a bit of power.
Its kind of like having the benefit of flaps on.
2. Excellent slow flight and reduced stall and launch speeds.
As before, its kinda like the flap thing.

I've become a big fan of the undercambered wing:

I scratch built a number of EDFs with undercambers, with the idea of easier flying in mind, back when I had less flying skill. What I got was a bit slower of a jet that wasted a bit of power, but would fly much slower than full airfoiled jets. When I started building full airfoil jets, what amazed me was how much harder the were to launch, at much lower weights. I have 2 undercambered 20+ oz jets of only around 30" span that lauch like prop planes. The first full airfoiled one was much lighter than these undercambered jets, with much lighter wing loading, but was MUCH harder to get going at launch speed. I don't do insane things when flying my jets, so other than for looks, I'll take the undercambers for the park flyer jets, since they hand launch well and land much slower.

golden!

[MikeMc]

Mike,
not to nitpick...im sure you dont mind anyways...and i think you mean this anyways also...but you have shown a squared (not exponential) relationship in your formula.
More importantly, do I still get partial credit on this exam?

[watt_the?!]

More importantly, do I still get partial credit on this exam?

yes you do. :pim sure we all knew what was meant..as you used "exponential" to mean "increasing beyond linear"..right?

lol.:D

[HX3D014]

Why not go for the happy medium? A curved plate undercamber airfoil.
I included some Pics again from RFG3 but they still prove your point

How would he cut it in? (The undercambered part)
I could think of a few way.but.

I would have mentioned it myself. but the post with the pics is a further explanation to a post I made explaining how to cut.
in that post I mentioned that if he decide to do the Cutting. then he should chouse based on Performance requirements. I also did not want to cause to much effort. (The trick was to get him to believe that a Foil would be better than flat plate.)

we have some more information now. but I have not heard back from him on AUW or that he is interested in cutting it.

Could you elaborate more on how he would cut it.

PS. Go through the thread again and pretend you are me. IE look at the posts I posted and why.

Here is another.
the foils I posted here are not further suggestions for StinkWeed007 but just to elaborate more on your post :)

The Clark y looks good to. check out the lift.

PS. Anyone know exactly how to interpret the Moment line.

[BobbyDog]

Lol, holy crap people. Stinky arent you glad you didnt ask about how a wing works now? I'm pretty sure your like me and just want to fly a plane and dont really care why it works. I have all sorts of planes with all sorts of airfoils, my favorite planes to fly by far are my flat plate foamies. I have even built flat wings just by cutting untill I liked the looks of the shape. Still flew great. This morning I watched a video of a flying witch, and last month seen a video of a flying lawnmower. I dont think those guys read the books about physics. :) Good luck and let us know how you make out.

Bob

[HX3D014]

That’s some pretty good instructions there. LOL.

Cut the wing till you like the look of the Shape.

PS. The thread was a debate on Airfoil Vs flat. so tell me. Dose the color count on the Vote. >> ??

Hmmmm
Let me see. Should I cut the top part to look like a house roof. or maybe look like a Ferrari roof (Yeah. Ferraris go fast so that must be a good shape. Or a Lambo : ) ) or a convertible mustang. That looks like a good shape.

Now swing your video camera off of it.

Think about the Advice and what you base it on. Seriously.

I like the shape of a Nice woman. Maybe I should cut that into my wing foil. ;)

PS How do wings work?

[stinkweed007]

well, I had only really wanted to know if making a big flat wing was worth the effort (if it would fly). but to my amazement, I have received a welth of good info on how to build and airfoil!! :ws:

Right now though, my building and R/C in general is up on blocks. My mother is flying in for a visit from the states. had to "put away all my toys" I will get back with ya'll!!

[Airhead]

Hey Stinky,
Enjoy your Mom visiting you... Thats terrific..:ws:

[BobbyDog]

I have a question.

When building a wing.. ho important is it to have an airfoil? I realize most aircraft have it, but some dont or its nearly nonexistant.

I use this rather durable foam for my planes, it is for exterior insulation. and I have found that it comes in a thinner version (4cm) and I want to use it to make wings.. I would rather not sand the heck out of it except the leading edge and ailerons.

I lack a few foam working tools.

so if I dont shape it to an airfoil.. what, from a performance and aerodynamic standpoint, should I expect?

will the control be bad or will will I just be more reliant on power rather than lift..?



Now tell me %(*%(*, does this sound like Stinky wants to know the most effecient airfoil ever created? Or does it sound like he just wants to put together a cheap, easy to build wing so he can go FLY... Nobody but the three of you guys argueing could understand what you were talking about. Correct me if I'm wrong, but I'm guessing that you havent done any scientific studies on any of this stuff. Just regurgitating what someone who REALLY knows thier stuff told you by word or by mouth. That my friend makes you IGNORANT to the truth.

There I feel better... Feel free to get me going again. :p

Bob

[stinkweed007]

Although I understand the basics of what an airfoil does, I don't have necessary tools to make, creating and airfoil, an enjoyable experience.

as my esteemed fellow watthead from the great white north put it so eloquently put it. I was looking at putting a flat main wing into service, to which I have been told will work, but will be fun to control.

Ding, Ding... lets not get hot.. cool?

[HX3D014]

Cool.
Read Post # 7 and then Post #16.

I don't mind being called smart. And I do apologies for being an %^&. Just had to do it when ignorance to the thread was apparent.

Investigating the Requirements of Stinks Plane was my first intention. Post # 7. and Stink replied with further Information that Changed the Design Root.

Good thing I didn't tell him how to build it before knowing what it was being used for. I did not guess. I asked Specifically. and he Replied.

Stink.
I bet the Planes weren't all the things you had to hide :p
told the Girls to stay away for the time she is there.

Never had a mother myself. But I imagine them to be What a father is to his daughter. ? Over protective and Over judgemental

[Rugar]

Closed as requested by the Thread Starter.