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Mustang
01-09-2006, 03:47 AM
What would be a good brushless motor fo a Sig LT 40?
The kit is still in the box and I will be starting the build in a week or so. I wanted to get an idea of what would be a good motor. I basicly think it should be an outrunner, use a 3 cell li-pol for power.
They say flight weight is 96 oz (tops) which would tell me that I want a prop motor combo that would provide 180 oz thrust. This is the second trainer for my wife so I want it to have a bit of zip.
If it were for me I'd just throw an OS .46 fx in it, but she does not like the whole glow fuel thing.

Any sugestions....

BTW also going to do a Senorita for my daughter any thoughts?
This would be her first trainer (other than the Easy Star we already have. Think I am going to put a himax brushless in the Easy Star, it has no guts period.

BradT
01-09-2006, 05:13 AM
WOW!!! Are you sure you meant to say 180 oz. of thrust? That would allow you to hold the model vertically, hit the throttle, and disappear straight up, VERY fast. You certainly won't get that kind of power out of a 3S li-po, you need 6S or more for this size model. Motors and cells are much happier giving you 1000W at 25Vx40A than they are at 12.5Vx80A. A trainer will fly well, including loops, rolls, and inverted, at 1/2 thrust/weight, or about 50 oz. for this plane.

A buddy of mine learned to fly on his E-conversion of the LT40. His set up was an Aveox 1409/3Y, geared 3:1, on 16 Nicads with a 13x10 APC E prop.This gave him 20Vx30A=600W, or 75W/lb, which is plenty for the model. I flew the model quite a bit while helping him out, and it was the equivalent of any of the .46 powered versions at the field. A 6S2P li-po would give even more power than his, being several volts higher, and would save close to a lb. in weight, as well. I think any set up that will give you 600 to 900W would be great here, as long as you do it with high V/low A, rather than the other way around.

Brad.

ragbag
01-09-2006, 07:16 AM
Go to the Hobby Lobby site and they have the LT 40 conversion that they did.
Call L A Johnston at tech support and he can set you up if you are serious about the over power.

Seems like you would want another type of plane for that setup, not an LT 40. Flatten the wing and some other mods and it might do though.

The fellow that got me to do the LT 25 conversion did the flat wing and over size tail feathers and 3D's his with a 2808-12 Axi.

http://www.hobby-lobby.com/g2e-sigkadetlt40.htm

By George:)

BradT
01-09-2006, 07:34 AM
Looking at HL's conversion, they've done a very modest one, getting about 350W out of that set up, I'd guess. That wouldn't be as aerobatic as my buddy's, but it shows that this plane doesn't need gobs of excess power to fly. That would be about 50W/lb, which is fine for a trainer.
Brad.

zappedalaskan
01-09-2006, 04:41 PM
I have one i built for glow and never got around to putting an engine in. I looked at the H-L one and have the AXI motor and a 6s battery. I might have to wipe the dust off of it and see what I can do with it! Great thread and thank's for the information and the link. George and Brad..
Take care,
Jay

Mustang
01-09-2006, 08:15 PM
Great info, I just used the 2Xweight to come up with the requirement of 180 oz thrust. I know that may a bit much but that is how I set up my glow planes. Yes, I do like to be able to go vertical if I like, but mainly like to be able to power myself out of trouble. Now I know she isn't going to fly the way I do, but to be honest, once in awhile I like to go to the field with out the glow fuel starter bat and alike. It's nice to just carry a charger, plane and radio out to the field, turn it on and go....
Yes I might "borrow her plane" lol...
I did not realize that I should pump up the voltage rather than, be able to dump a lot of amps into the motor. I just figured on 11 volts 75-80 amps for a controller for a output in the area of 800-900 watts of power. So I would end up with 150-200 watts per lb. To be honest I think that 350 watts is way underpower for the weight and size airplane and would look at 600 watts as an absolute minimum.
The GWS Mustang I built I has a power to weight ratio of around 150Watts per lb. It can go vertical no problem, and is very good for aerobatics. Keep in mind it only around 22oz, and has a setup which produces 48 oz of thrust. Given its light weight it was very easy to do with a himax brushless, phoenix controller, and a 3 cell 1500ma li-pol.
And while it is a trainer, it is her second airplane, so I wanted her to be able to get the feel of an airplane which has a lot of power. She has her heart set on flying my old top flite Razorback Mustand which has a .60 in it (as long as I start it and clean it up) because it is a real hot bird. And she not getting her hands on that till she really knows how to fly.

BradT
01-10-2006, 03:19 AM
Mustang:
Now we know the reason behind your handle:D . I wasn't saying that you couldn't get 2 times the weight in thrust, just that it's major overkill for this kind of model, but since you'll "borrow" it once in a while, I see where you're coming from;) . The way to go, then, would be one of the big 41xx AXIs, on as many cells as you can carry. The high V vs low A advice still holds, though. Think of it as the difference between a big-block V8 giving you 350HP at 3000rpm vs a 2L 4-banger trying to do it at 10,000rpm. You know which one has the legs to keep going for the long run.

Part of the reason for the high V is the output ratings of the cells. Modern nicads and nimh (round cells of sub-C size) can deliver amperages at up to 20C (20 x the rated capacity in MAH), and the latest gen. of li-polies are supposed to do the same, but all of them get hot at the high end of their abilities, so it's much safer to run them at 10C - 15C, therefore more of them, at lower amps. The motors also run cooler at lower A, even though the V may be higher. The upper limit for the motor is max. rpm, which is usually stated by the maker. This is determined by the voltage and the prop size, so check your set up with the same tach that you use for your wet engines, and stay a little below the max for your motor.

Matt Kirsch
01-10-2006, 03:49 PM
Brad, you'd be surprised what a 6lb trainer can do on 400 Watts of BRUSHED electric power. I was running a Tower Trainer 40 on 10 NiCds and the classic geared Endoplasma setup.

I've since upgraded to a 4S Kokam BalanceProHD and an AXi 2826/12, and added floats for winter flying. Seems like it should have plenty of power, as soon as I figure out a speed control issue. The one takeoff I got was pretty nice, but the ESC went into thermal shutdown after about 30 seconds.

ragbag
01-11-2006, 02:17 AM
I am using the 2826 in my LT 25 conversion. Started wit a 40 amp Controller, 11x7 prop. Thought I had a ground clearance problem. Found I could use 13.5x8 and when I tried it had to go to a 70 amp Jeti.

Still have the 40 amp for the other 2826 on the shelf.

3s2p 4200 Polyquest 12c.

My thermal cutoff was on the bench fortunately.

Will work on the prop after we get it going, not sure where to go. Some tell me the APC is more efficient. I have a hand full of props, APC, MAS and MAS wood.

http://www.wattflyer.com/forums/showthread.php?t=1012

By George

Mustang
01-11-2006, 03:28 AM
Mustang:
Now we know the reason behind your handle:D . I wasn't saying that you couldn't get 2 times the weight in thrust, just that it's major overkill for this kind of model, but since you'll "borrow" it once in a while, I see where you're coming from;) . The way to go, then, would be one of the big 41xx AXIs, on as many cells as you can carry. The high V vs low A advice still holds, though. Think of it as the difference between a big-block V8 giving you 350HP at 3000rpm vs a 2L 4-banger trying to do it at 10,000rpm. You know which one has the legs to keep going for the long run.

Part of the reason for the high V is the output ratings of the cells. Modern nicads and nimh (round cells of sub-C size) can deliver amperages at up to 20C (20 x the rated capacity in MAH), and the latest gen. of li-polies are supposed to do the same, but all of them get hot at the high end of their abilities, so it's much safer to run them at 10C - 15C, therefore more of them, at lower amps. The motors also run cooler at lower A, even though the V may be higher. The upper limit for the motor is max. rpm, which is usually stated by the maker. This is determined by the voltage and the prop size, so check your set up with the same tach that you use for your wet engines, and stay a little below the max for your motor.
Thanks I never though about the cell temp, wouldn't want to cook her plane on her would never live that one down. She still a bit upset about her Next Star hitting the ground a the end of a series of loops (oops). She hates the oil all over the plane, so hence the journey into the electric realm. I did the GWS Mustang and kinda got hooked to the electric thing myself, lot easier than glow, just have to keep the li-pols away from the car when charging....
Hate to say gee the car caught on fire while I was at the field, don't want to sleep on the couch for the next few years...LOL
Anyhow thanks to you and all who have replied, had a wild thought on the way home from my club meeeting tonight. How about an lt 40 twin electric engine out shoud be rare.....
She'd kill me!
Thanks all got to go glue some parts together so I can start on her plane. She wants it this spring and I have yet to finish the glass on my latest creation.

BradT
01-11-2006, 08:40 AM
Brad, you'd be surprised what a 6lb trainer can do on 400 Watts of BRUSHED electric power. I was running a Tower Trainer 40 on 10 NiCds and the classic geared Endoplasma setup.
.

Matt:
Nope, wouldn't be surprised at all, my 3rd model was the 72" Unionville Beaver, built in '98, powered by a 6:1 geared MEC Turbo 10+ (13T car motor with 5x5 brushes), on 10 RC2000s, 12x8 prop. 12V x 35A = 420W. On wheels, it weighed 5.5 lbs., on floats, 6.5 lbs. Flew well either way, but not at the level Mustang is looking for here.

Mustang:
Cell temp is VERY important with li-polies, as you seem to get from your crack about burning the car:o . It matters for round cells too, but it's not quite as critical. I have got the temp of nicads high enough to melt the heatshrink off the pack and the cells (sustained 60A draw:eek: ), and they didn't perform very well after that! The twin LT40 has been done, as well as the twin Telemaster. I know a guy who did a twin electric Telemaster, and used it to haul a 2M glider aloft on a cradle, to release it for another pilot to fly. Worked great, and looked pretty cool, too.

Brad.

Mustang
01-12-2006, 04:58 AM
Many thanks to all who have replied, while I had some idea of what to do I still am new at the motor vs engine in rc airplanes. I knew what I wanted to do with my wifes new plane was a bit on the wild side, but it is also an experiment for me in the electric world of flight. I just looked at it this way, I have a proven and rugged airframe the lt 40, a bit heavy as far as most e flight aircraft go.
But I think given the noise problem that many have in dealing with the neighbors, to our flying sites in this area, it is the way of the future.
My little Mustang was an experiment to see how an electric with a thrust to weight ratio of two to one would perform. If I fly it normal without really going nuts I can get a good twenty minutes out of it. Doing aerobatics close to ten minutes not too bad just need to get another bat. so I can have one ready to go at all times just swap one out and put the other on the charger.
Well that all for now will post some info when I get to the "build" as far as modifications and equipment used. If anyone has any recomendations or sugestions of things to try please let me know....
For all the negatives li-pols seem to be the closest thing we have to Di-lithium crystals at this point.

BTW has anyone seen the electric plane that flew 48 hours with solar cells?

BradT
01-12-2006, 05:38 AM
I'm looking forward to the outcome of your "Hot Rod " LT40 conversion, Mustang, so I'll keep an eye out for your progress reports. Good luck.
Brad.

Mal Buckmaster
01-12-2006, 12:20 PM
Hi Mustang,

Somewhere in the middle range ot the suggested power systems is the 600W ND 30 from Oz. (this sounds like the number you first thought of)

How about you check out this little power-house at;

www.alphalink.com.au/~mkbuck (http://www.alphalink.com.au/~mkbuck)

Regards,

Mal Buckmaster

ASTROPOWER-LEISURE AUST.

RMFISH
01-16-2006, 01:28 AM
Hi There Mustang, Just a little more grist for the mill, to try to keep you out of trouble. Whilst we frequently hear about Amps and the number of cells needed to creat them, we very rarely hear about the MAX amps that motors are capable of taking before they burn up in smoke. For example, the Aviox 14/09 3Y brushless motor is a 28Amp motor, feed it more than that for any length of time and you can kiss the motor goodby. However, with a carefully selected gear ratio and the correct number of cells with the correct prop I was able to fly my LT40 for 10-13 minute lazy circuits and 8-9 minute aerobatic tearabouts. Brad and I used to see who could fly inverted for the longest, or who could do the roundest loops. Yes, she would do it all. It is the same for ANY motor. Select the motor after you have determined the number of cells and the Amps required to do the Job. Just to make it a little more complicated ALL motors also have a Maximum number of cells that can be connected to them. This is just like you knowing that you can not over prop a Glow engine, there is a manufacturers recomendation that you would not ignore, unless you wanted to replace the bottom end and bearings of the motor on a regular basis. Jane Austin had it all covered in the book Sense and Sensibility. There is more that you should know about controllers and how they do their job but if you want to know about that just ask.
Robert. :cool:

Mustang
01-20-2006, 01:57 AM
Hi There Mustang, Just a little more grist for the mill, to try to keep you out of trouble. Whilst we frequently hear about Amps and the number of cells needed to creat them, we very rarely hear about the MAX amps that motors are capable of taking before they burn up in smoke. For example, the Aviox 14/09 3Y brushless motor is a 28Amp motor, feed it more than that for any length of time and you can kiss the motor goodby. However, with a carefully selected gear ratio and the correct number of cells with the correct prop I was able to fly my LT40 for 10-13 minute lazy circuits and 8-9 minute aerobatic tearabouts. Brad and I used to see who could fly inverted for the longest, or who could do the roundest loops. Yes, she would do it all. It is the same for ANY motor. Select the motor after you have determined the number of cells and the Amps required to do the Job. Just to make it a little more complicated ALL motors also have a Maximum number of cells that can be connected to them. This is just like you knowing that you can not over prop a Glow engine, there is a manufacturers recomendation that you would not ignore, unless you wanted to replace the bottom end and bearings of the motor on a regular basis. Jane Austin had it all covered in the book Sense and Sensibility. There is more that you should know about controllers and how they do their job but if you want to know about that just ask.
Robert. :cool:

I found that out the hard way with my GWS Mustang which I built and modified. Using the original 300 motor I could barley get it into the air using the typical nicad cells that they recomended. Off to the local hobby shop grab a twenty amp controller and a three cell 1500 ma Li-pol Bat. Stuf that into her reset the COG and off to the field to have at it.

Well lots better response, the li-pols were lighter than the original plenty of ohmp. Still not all that much thrust overall so I am running about 3/4 on the left stick. All of a sudden I noticed I am trailing what looks like smoke. Hmm, no glow engine or smoke generator, this isn't good. Backed off the power and came in deadstick. Checked the bat nothing wrong here just a bit warm, same for the controller. Pulled of the spinner and noticed that there was still some wisps of smoke. Motor was still a bit warm after I pulled it out some five minutes after the flight. Not to mention it smelled a bit of cooked resistor, hmm I thought guess it could not take the 150 or so watts I was pushing into it. So I do understand about that limit, and have experinced the weakest link axiom. That is how it ended up with a HiMax brushless and controler that it has now. Needless to say the original motor is good for nothing other than a paper weight at this point. But it looked cool just before it died.
LOL
Thanks for the info, my real problem is trying to figure out what type of thrust I can get from a given motor prop combo. then set up the power system to drive it. The motor specs (in ads) that I have seen, for the most part realy do not tell you what the given thrust you can expect at ther max rated power. In a perfect world you would like to have a motor which would give you all the thrust you needed at 80% of it rated power, using only 50% of you what you could provide for power to it. (actualy 25% would be much better) lol

RMFISH
01-20-2006, 07:30 AM
Hi Mustang, download a copy of MotoCalc, it will give you loads of data about different props and the thrust they generate. I have been using the program since it first came out several years ago. If you realise from the get go that the program is a very good SIMULATOR and dont expect exact results, you will find the program invaluable. It will always put you in the Ballpark within a few percentage points and it will give you a great insight into how the electric motor generates it's power.
Robert.

Mustang
01-21-2006, 12:50 AM
Thanks, will do.

Mustang
04-01-2006, 02:36 AM
Well I am just now putting the covering on the Lt 40. It is you basic lt 40 build except the wingtips were modified to reduce the chance of tip stalls. Now as far as power I just ordered a axi 4120/18 with a 70 amp controller. Saw the post about the sale saw it ended today so orderded the hot rod powerplant. I was thinking of using the axi 2826/12 and a 40 amp controller but decided I could always downsize the powerplant and use this in a sport model as she progresses.

After the past couple warm days up here I am getting asked about how long before it is finished. I will have most of it covered tonight with the exception of the wing because I am still waiting to sand down the expoxy after fiberglassing the center of the wing.

Now one more question I am going to cowl mount the motor and was wondering about cooling for the motor. Given the small area on the motors themselves for airflow, how much opening do I need for the cold air intake?
I am going to use the standard 140% of the intake for exhaust of the warm air but was wondering about what size intake for an electric motor in an enclosed cowl. One other point to take into consideration is I plan to enclose the motor within a lite weight duct work to keep the airflow as close a possible to the motor, rather then just the empty box of the cowl. (As I do in my glow powered planes) I am guessing that around an 1/8 inch of clear space should be enough any thoughts about that?

RMFISH
04-01-2006, 05:16 PM
Hi Mustang,
Wish I had known that you were worried about tip stall and about to go to the trouble of changing the wing, could have saved you all the work. The LT40 wing is so stable, you can hardly force it to stall.
As for enclosing the motor in a tube, I do not think this would be a good idea. Heat accumulates in an enclosure and although it may seem like a good idea to place a tube arround the motor, it will only restrict the volume of air available to carry away the heat. Put holes in the front of the cowl, one large or several smaller, in all about 1.25" diameter. Drill as many holes in the fire wall as you can get in there comfortably, enough to allow a free flow of the input volume into the fuse. This air will now keep the batteries cooler. Place two 1.25" holes in the bottom of the fuse at about the servo tray area and cover them with screen door nylon mesh to keep out any grass clippings and goose poop on take off and landing. These two holes will be the exhaust ports for the cooling air. You can experiment with the inlet holes in the cowl, make them bigger if needed. If the airflow inside the cowl is enough to keep the air therein cool and carry away the heat of the motor you have got it made.
Robert.

Dereck
04-01-2006, 07:04 PM
Well I am just now putting the covering on the Lt 40. It is you basic lt 40 build except the wingtips were modified to reduce the chance of tip stalls.

Now one more question I am going to cowl mount the motor and was wondering about cooling for the motor. Given the small area on the motors themselves for airflow, how much opening do I need for the cold air intake?
I am going to use the standard 140% of the intake for exhaust of the warm air but was wondering about what size intake for an electric motor in an enclosed cowl. One other point to take into consideration is I plan to enclose the motor within a lite weight duct work to keep the airflow as close a possible to the motor, rather then just the empty box of the cowl. (As I do in my glow powered planes) I am guessing that around an 1/8 inch of clear space should be enough any thoughts about that?

Hi there Mustang
A flying buddy of mine had a Kadet Senior a couple of years back - it flew on 24 2000mA NiMh cells - that's about 42oz battery weight - as well as about a pound or so of metal tubes, steel rods, ply and epoxy in the wing to make it two-piece. Let's just say we let him carry it out to fly and no-one ever suggested weighing it.

Despite all that, it was an absolute puddycat to fly and almost impossible to get to a stall, power on or off. We had his wife flying it, and she barely knew which end of an aircraft went first - we briefed her on which stick to push and then just told her stuff like "half left", full right, or whatever we figured she needed to do.

Cooling. Yes, you need it. Snag is, with a battery, there's every chance even if you pull a computer blower fan in the fus playing on the battery, you couldn't cool a flight pack that was under heavy load within the time of a flight. You really need to get air around your motor though, and your ESC - possibly the latter is the most important as it hasn't got the metal parts of a motor that ease heat transfer somewhat.

Your approach of cooling baffles directing air over the motor is good - if you let it wander into the cowl, the airflow will mostly stagnate against the firewall and the backpressure the firewall will push forward with against the incoming. So, arrange your baffling to allow, I'd guess, a 1/4" around the motor, with an easy flow into the fuselage through the firewall. You really need a bigger hole for outflow than inflow, but your world shouldn't explode in flames if you don't do masses of math calculations to prove it. Just apply some commonsense and err on the side of caution.

Your ESC - I cut a big hole, larger than the ESC in the fus bottom ahead of the UC, place a couple of 1/4" spruce strips across the hole and Velcro my ESC, component side down, onto them - so that side is exposed to the outside airflow. It works on my somewhat fast 5.5lb, 700W pattern bird... The topside of the ESC is covered by airflow from the cowling.

To get the lot out the back, I leave an entire fuselage bay open in the back end, just aft of the wing - this is maybe 3 - 4" long, and the width of the fuselage. Inside of that, I place a piece of 1/16" balsa sheet, the width of the fus, starting at the back end of the hole and sloping upwards at maybe 30 degrees towards the front of the model. This ramp helps ensure that air outside the model stays out there and air inside on its way back from cooling duties leaves when it hits this ramp. Done right and filmed/painted to match the bottom, it is hardly noticeable.

Otherwise, airflow will tend to wander off to the tailend and make that work like a small drag parachute ...:eek:

The trick to not cooking your batteries - which, on the whole, are basically dying from the day you buy them, more so with lipos - is not to beat them to a pulp by running them flat out. In a trainer, this is hardly necessary, after all. If you overpower a trainer, you just get a lousy aerobatic model that's not all that fast.

Have fun, really must get back to seeing if Saphions can outdo lipo - but I do actually have a 3S and 4S lipo for my new Sig 1/6th clipwing conversion for a straight drive Mega...

oops, did I mention that?

D

Dereck
04-01-2006, 07:05 PM
PS - did you know that if you type in a common pet name for a domestic feline, the censor software changes it to "*****cat" ?

Don't we live in a laced-up world?

D

Twmaster
04-01-2006, 07:37 PM
PS - did you know that if you type in a common pet name for a domestic feline, the censor software changes it to "*****cat" ?

Don't we live in a laced-up world?

D

<Mike nods in agreement>

Twmaster
04-01-2006, 07:40 PM
Hi there Mustang
A flying buddy of mine had a Kadet Senior a couple of years back - it flew on 24 2000mA NiMh cells - that's about 42oz battery weight...

Darn you D!

I just got home from Hobby City. There is a Kadet Senior hanging in the rear of the store. It looks lonely.

Now you've planted some silly ideas in my head!

<Mike shakes fist toward Potomac. Darn you Dereck!> :D

Mustang
04-02-2006, 01:34 AM
Darn you D!

I just got home from Hobby City. There is a Kadet Senior hanging in the rear of the store. It looks lonely.

Now you've planted some silly ideas in my head!

<Mike shakes fist toward Potomac. Darn you Dereck!> :D

One of the guys whom I work with, and is in my club is finishing up a Kadet Senior right now. He has one with a OS 60 size 4 stroke in it. And he is thinking of doing his new one with an electric. He waiting to see how the set up I am putting in the lt 40 works out.

Thanks for all the input about cooling guys, with glow the rule I go by is the inlet should be equal to the fin area of the motor, then size the output at 140% of the inlet and you get good airflow. I just was not sure as how to size the inlet for an electric motor.
Basicly I was going to provide to inlets for cool air. One for the motor the other for the Esc and Li-pol and provide seperate outlest for each as well. The logic here being the motor will prodce a lot of heat on its own, and why blow preheated air over the esc bat and rec/servos. Overkill perhaps but both will be cooled by outside air.
I like the idea of mounting the ESC as part of the skin, no problem with air movement over it in that configuration.

Now as far as the mods to the wingtips, yes I know it really isn't a big concern but figured it would make it a lot better for high AOA flight. Besides they look cool and it only took a few more minutes to do on each wing.

To be honest I made a few other changes to the wings also, such as extending the sheer web all the way out, and also the d tube part of the LE of the wing. Most of the time when I build a plane it has full sheathing, with fiberglass, or silkspan and dope for the skin. Back in the old days it was either silk or tissue over sheathing or just silk or tissue. As a mater of fact this is the first plane I have ever done monocoat on. Not in love with it but some trim tape should hide all of the rough areas, besides this is a trainer a second plane for her, but still a trainer, not a scale job for show. :D
One additional note:
I figure where I have plenty of motor, a 70 amp ESC, along with 6 Cell Li-Pol's that I should never really have to tax the batteries. So I hope to keep the temp down overall, well at least that was one of the thoughts I used, when trying to chose how to set it up, after all of the remarks and advice that has been offered. I did work in the electronics industry for years, working with instrumentation mostly, a bit of robotics. But had not really tried any E flight stuff other than the GWS Mustang that I modified. And haven read some of the post here since last summer have found that many others have way more experince with this stuff than I do.


I just wanted to say thanks to all that have taken the time to input both their ideas and experience regarding this project.

I will be posting some pics of the finished plane along with some comments about the flight test

Dereck
04-02-2006, 03:36 PM
Darn you D!

I just got home from Hobby City. There is a Kadet Senior hanging in the rear of the store. It looks lonely.

Now you've planted some silly ideas in my head!

<Mike shakes fist toward Potomac. Darn you Dereck!> :D

Like most Sig kits, it's an electric, but they keep selling them with only the glow conversion drawings in the box!

Maybe too much of a haul for you, but Hobby Hangar in Chantilly has some high time fliers in the electrocuted Kadet Senior BARF field. Tyler Ake has some real good ideas on electrocuting Kadet, which can be applied to all sizes usually, and even has developed a sort-of universal battery tray for the type. Tyler used to work part-time at HH, but the store usually hauls out a stand at the local e-flies - first up being the CASA Spring Sizzle on Memorial Weekend Sat/Sun - event info at http://home.comcast.net/~mkroese3/ (shameless plug, come along and get your pride and joy into the International Press [as long as you built it yourself ;) ] )

Sigs are one of the few kit ranges around where you really can get away with bolting a suitable motor into the nose, figuring out how to access its matching battery and you've got an electric that will really perform.

Recall seeing a photo in a recent mag - might have scanned through it in the book shop, see little point in most of the *buyer rags around these days - of a F3A pattern electric with a plywood cooling duct system around the motor, to take air from the cowl front intakes, around the motor and into the battery bay. Nice stuff, bet he paid someone a lot to figure it and make it, but I've found that some common sense can come up with cooling that doesn't add to the weight bill.

Maybe now the lipo can deliver glow standards of overpowering, all us who learned the game on round cells are behind the curve somewhat, but it strikes me that a lighter model is still the cheapest performance upgrade going. My E-Rotica weighs 5.25lb with a 16 cell 3000mA NiMh pack and its performance could be described as 'adequate' :eek:. Maybe if I win the lottery, I'll re-battery her with a 4 or 5S lipo (and a new charger, and a fireproof safe, and all the widgets to balance the cells, and a fire extinguisher, and a comfy chair to sit and watch it all charge while balancing my fire extinguisher on my knee at the field...) and see if it was worth the effort ;)

For my next trick, a Sig 1/6th clipwing Cub!

Regards

Dereck

Mustang
04-02-2006, 06:11 PM
Sigs are indeed one of the few kits that lend themselves to being converted to electric by bolting a motor on instead of a engine. I am also doing a Seniorita for my daughter. Now that will be much eaiser than the lt-40 in terms of power requirements and a lot cheaper. Good luck with your 1/6 scale clipped wing cub nice kit I have built a couple over the years. This time rather than the clipped wing I built the full wing and made many mods to it, to bad it one of those glow powered beasts. Next winter I have a 1/5 scale cub that will be built in the clipped wing version. Still have not thought about power for it, electrics would be expensive but I have grown to like the ease of starting an electric. lol
Doing that in electric might be a bit more than I want to spend, but if I wanted to go with a Saito twin in it, the price would be close.
I will have to save up for its power system so you never know...

Twmaster
04-02-2006, 11:16 PM
It's driving me sorta crazy. I have a new in box Sig 4 Star 40 kit and have plans to electrocute it. Just have zero time to build with my business taking off like mad. :(

Dereck
04-03-2006, 12:59 AM
Mustang - I've flown a 1/5th J3 at full span on 16 good old fashioned round jugs, into a very nice but slightly excessive MaxCim 13Y - still the finest sports electric motor around for many reasons, if somewhat unfashionable due to its sensored ESC - which is responsible for its remarkable speed control, from 'count the blades' slow, smoothly up to full power.

On 16 cells, it weighed 8-1/4lb, was off the ground too quick if I didn't pay attention to the take off and would handily loop and roll. On 3000 cells, I once got over 10 minutes of Cub-like low level flying. Big advantage was in field recharging - I'd prop a little computer blower fan in the cockpit to cool the pack, not that it got hot much, and hook up the charger with the pack in place. If you want to do that with a lipo, just keep your fingers crossed ...

Tw - now you are talking the #1 electric sports model. I've seen or heard of Four Star Forties with everything from 8 x 1000 to 24 big roundies, and have never heard from anyone who didn't like theirs either. Mine is now over five years old, but it really needs a re-cover and major checking over before I'd fly her again. One wing has a warp, and I reckon an aerobatic airframe with so much flight time really needs looking at now and then - mine's on its third covering job...

Of course, about all that's left of mine vs the kit is the airfoil section and most of the fuselage side sheets ... :)

Have a similar home-business problem to yours right now - know just what you mean!

Mustang
04-03-2006, 04:41 AM
Hi guys,
TW the Sig 4* is sweet nice plane, good design. Just open the box and start it.I basicly gave up on watching tv at all, and use any of that time for building.
You can still do it with the fifteen minutes at a time pick at it type of build. Your taking a "break" type of thing, it is surprising how a bit a a time can still keep you progressing. I have one plane I just finished building (over two years) although a good part of that time when in to research as well. I can not wait to get it in the air. But want to try to get a few weeks of flying again after the winter lay off before I do it's maiden.
Well with yard work season upon me, this is about the end of building season here.
Although there will be the ocasional rainy day.

I want to fly my 20 size sportster, before I fly any of the new stuff.

I have got to build the Seniorita for my daughter but that will be a quick build. The lt40 was a couple of weeks, with a 2-3 more nights doing the cowl and installing the electronics, ok maybe four nights...

Dereck- your cub sounded like a nice set up.

I have a set of plans for a extra that is sized for a .2-.36 engine that I think I may scale up from a four foot wingspan to a six as the next plane for myself. Before I do the Cub. And with the way my wife has progressed I will have to do a 4* for my wife in a 40 size, for her next plane. The power system from the lt 40 would drop right in to it.
Maybe I could borrow that one from her sometime, bet you it would fly real nice...

Mustang
06-03-2006, 03:32 AM
Well got the fuse all set up with cooling duct and mounted a Axi 4120-18 into the plane. I have gotten side tracked doing repairs on one of my planes which suffered from one of those hard landings. Anyhow, I will have some pictures of the finished plane in a week or two sorry for the wait.
The cooling setup uses the fuse for expansion of the heated air with the exaust being sent out about about a foot from the tail under the fuse.
Do you have any recomendations as how to mount the batts? Should I build a holder for them which is shock mounted, so I can get the best airflow and protect them from impact damage. I would think that to wrap them in foam would not allow them very good cooling.

Dereck
06-03-2006, 03:42 AM
Mustang

Hope these shots work - sized them down from some I took at the CASA SPring Sizzle last weekend. THey're of Tyler Ake's Sig LT25 - Tyler has spent a lot of time figuring out a good battery access and tray system for a high winger and this is about as good as it gets.

It's recently been adapted to lipos, which usually need to be further forward than BRJ (big round jugs) if nothing else is changed in a model. The tray is at an angle, higher at front than rear, angle and position determined by the shape of the model, how much space is available, etc. pack's held down by Velcro between pack and tray, plus velcro strap

The whole nose lifts off to access the packs, clips back on with magnets or screws to taste.

Hope that helps

D

jonnyjetprop
06-03-2006, 05:16 AM
Great idea.

John

ragbag
06-03-2006, 09:21 PM
Here is how I did the LT 25 battery box:

12403 12404 12405

One 1/4-20 screw.



.

Mustang
06-04-2006, 01:27 AM
Thanks,
That is a great idea, I've had a block on how to mount the batteries in this thing. The pics are great!

I can't wait to see the guys at our field reaction to this electric. We have a few fans of electric, but for the most part many are still die hard glow or gas guys...
Most of them feel that you can not get any real performance out of an glow to electric conversion. This should open their eyes to the fact that electrics can not only match the performance of glow, but go beyond it as well.
All I need now are some good lightning bolt graphics to dress it up with....

Twmaster
06-04-2006, 01:54 AM
There ya go Tiger!

I mostly love my 'leccy planes. I really need to get my butt in gear and finish that 4*40.

ragbag
06-04-2006, 08:30 PM
12452 12453 12454 12455



.:)

Mustang
04-14-2007, 03:47 AM
Do to other commitment and projects I have just now finished this plane. She had gotten a couple of other arf type of planes and I had to keep them in the air so this project was set aside for awhile.

I will try to take some photos of it tommorow and post them later in the evening.

Final details:
Motor: Axi 4120/18
ESC: Castle creations 90 amp brushless controller*
*note I had originaly bought a jeti opti plus 70 amp esc but it would not program with smart card and was total unresponsive with power applied.

Batteries: two lithium Ion 2300ma 3 cells in series made by A123 Systems these have a 30c discharge, weight is only slightly heavier than 2000ma li-pols, the voltage is just over 19 volts and I can dump 69 amps continuously out of them if need be. So the power available is on the order of 1300 watts.

This should be more than she needs in a trainer and she will have to learn throttle management from the start.

Dereck
04-15-2007, 12:47 AM
Hi mustang
As my dear old 4* never had more than 700W on board, and was responsible for a lot of slimer drivers stopping thinking things like "electrics can't do much in flight", I think your model will be 'adequately powered' :eek:

Lack of throttle management at 1300W could result in an instantaneous and huge increase in wing loading ...

Regards

Dereck

RMFISH
04-15-2007, 01:30 AM
You will never need more than 800 Watts, 900 at the most. I flew mine with a great deal of authority on 16 x 3000Ma cells and a 13x10APCe prop on a brushless motor that drew about 36-38 Amps full throttle Static. Just fooling arround with circuits and bumps I got about 10-13 minute flights. Throw in some aerobatics and the flight times came down to about 7-8 minutes. It was the perfect combination.
If you are going to prop for the 60 amp range, you will waste tons of energy in heat in both the motor and the cells and possibly throw a magnet or lose the smoke. Max current on the Axi 4120/18 motor is 55 Amps for only 60 seconds, Max constant at about 80% efficiency is 40 Amps, so I cant see the reason why you want to overload it!!.
Robert.

Mustang
04-15-2007, 01:43 AM
Hi mustang
As my dear old 4* never had more than 700W on board, and was responsible for a lot of slimer drivers stopping thinking things like "electrics can't do much in flight", I think your model will be 'adequately powered' :eek:

Lack of throttle management at 1300W could result in an instantaneous and huge increase in wing loading ...

Regards

Dereck
My wifes other plane is a wingdragon, which I added ailerons to and changed out the brushed motor for a Himax outrunner.
Pull out from a power dive tore the spar out of the wings, they just folded back. The good thing is that cutting power we were able to get it back and land it. Was an easy fix but the lesson was learned about high speed and sharp pullouts.

edit...
Forgot to mention....
The wing of the LT-40 has had the middle section, and the spars reinforced with carbon fiber; along with the entire center section fiberglassed.

Mustang
04-15-2007, 02:03 AM
You will never need more than 800 Watts, 900 at the most. I flew mine with a great deal of authority on 16 x 3000Ma cells and a 13x10APCe prop on a brushless motor that drew about 36-38 Amps full throttle Static. Just fooling arround with circuits and bumps I got about 10-13 minute flights. Throw in some aerobatics and the flight times came down to about 7-8 minutes. It was the perfect combination.
If you are going to prop for the 60 amp range, you will waste tons of energy in heat in both the motor and the cells and possibly throw a magnet or lose the smoke. Max current on the Axi 4120/18 motor is 55 Amps for only 60 seconds, Max constant at about 80% efficiency is 40 Amps, so I cant see the reason why you want to overload it!!.
Robert.

The motor is supposed to turn a 16/8 prop so I have put a 12/6 3blade Master Airscrew on it so it should not load up too bad. Hopefully the max current it should draw is on the order of 50 amps or so. I wanted to have the esc well overated as to keep the temp of the unit lower. If it can handle 90 amps it should be very happy outputing 25-30 amps which I feel should be more than it needs to cruise. But if one wanted to play a bit you could punch it up to 50 amps for a few seconds without blowing up anything. By keeping the supply voltage high this should also keep heat to a minimum, in theory at least. One other thing I may do is set a stop for max throttle, as insurance. Lets face it the Sig Lt-40 will fly on a .40, it is aerobatic with a .46. With a .60 you can 3D, the 4120 is equal to a .60 I do not see her ever using that much power. She, unlike many othrs I see fly understands that the left stick is not just an on off switch. Besides I told her I paid for the part to build it, she has to pay for any repair parts....

Do you think I am about right with the prop loading and current draw?

Fully loaded the plane weighs in at just under 6 lbs, this includes a separate battery for the radio and servos. Even if the motor power system fails, control should be maintained, just as a fail safe.

I forgot to add the main reason for the high power is flight duration, not speed or aerobatics.

RMFISH
04-15-2007, 02:25 AM
When the Max motor amps on the motor is ONLY 40 Amps. why do you want to overload it by loading it to 50 Amps????, and don't say you will control it by throttle mannagement, cos it can't be done.
Robert.

Mustang
04-15-2007, 03:08 AM
When the Max motor amps on the motor is ONLY 40 Amps. why do you want to overload it by loading it to 50 Amps????, and don't say you will control it by throttle mannagement, cos it can't be done.
Robert.


Robert,

The limit is not 40 amps.
Max. efficiency current15 - 40 A

Hopefully just using restraint should work.

Sort of like when I used to drive my 1970 GTO with a 500hp 400 cubic inch motor and only got 1 ticket.
I know she isn’t interested in speed or aerobatics at this point, so as long as we can stay off the throttle, we should be safe. Although, I am thinking about putting a hard limit into the equation, just to be safe.
I am a BSEE, trust me if I say I can limit the power, I will find a way do it.

Methods all ready considered:
1. Physical stop on the throttle
2. Setting the stops on the radio
3. Current limiting resistor on the power feed to the esc
4. Fuse the power to the esc.

Number 4 is one thing I am going to do before it is fired up again, just to keep the fire danger to a minimum.

Specifications for the motor
No. of cells16 - 20
5 - 7 Li-Poly
RPM/V515 RMP/V
Max. efficiency86%
Max. efficiency current15 - 40 A (>82%)
No load current / 10 V1,5 A
Current capacity55 A/60 s
Internal Resistance70 mohm

They claim that that you can punch 55 amps into it for 1 minute.
So if I fuse the battery output with a 50 amp slow blow, I should be safe.

RMFISH
04-15-2007, 06:35 PM
Hi again, rule number one when selecting a motor for an aircraft is, if you can not get the power you calculated that you need from the motor you are thinking of using for the type of flying you are going to do, without going into the maximum powewr rating listed fot the motor, select another motor.
I know that it is tempting to think that you can control things by the throttle but think of this, if you are using a slimer, half throttle on the stick is half throttle at the throttle body, therefore you have half power on the motor. This is NOT SO on an electric powered aircraft. The reciever frame rate I believe, is about 500 Milliseconds. Let's try to think that your transmitter stick is linnear, 1/4 stick = 125Msec, 1/2 stick = 250Msec Etc. If your battery voltage is 22Volts, at 1/4 stick the moter will see 22Volts for 125Msecs, at 1/2 stick it will see 22Volts for 250Msecs, this is called the DUTY cycle. as you can see, at a stick position of only 3/4, the motor is seeing 22Volts for 75% of the duty cycle or 375Msecs. At anything over half throttle, if you have chosen a prop and voltage combination that places the motor into its max current rating, the motor will start to get hot. Ohms law can not be changed with throttle management.
Your 12x8 3 blade prop and six lyPo's should yeald about 41-42 Amps and give you about 900 Watts, more than enough for the airplane, if you want to reprop for more power, choose another motor.
Robert.

Mustang
04-15-2007, 09:43 PM
Hi again, rule number one when selecting a motor for an aircraft is, if you can not get the power you calculated that you need from the motor you are thinking of using for the type of flying you are going to do, without going into the maximum powewr rating listed fot the motor, select another motor.
I know that it is tempting to think that you can control things by the throttle but think of this, if you are using a slimer, half throttle on the stick is half throttle at the throttle body, therefore you have half power on the motor. This is NOT SO on an electric powered aircraft. The reciever frame rate I believe, is about 500 Milliseconds. Let's try to think that your transmitter stick is linnear, 1/4 stick = 125Msec, 1/2 stick = 250Msec Etc. If your battery voltage is 22Volts, at 1/4 stick the moter will see 22Volts for 125Msecs, at 1/2 stick it will see 22Volts for 250Msecs, this is called the DUTY cycle. as you can see, at a stick position of only 3/4, the motor is seeing 22Volts for 75% of the duty cycle or 375Msecs. At anything over half throttle, if you have chosen a prop and voltage combination that places the motor into its max current rating, the motor will start to get hot. Ohms law can not be changed with throttle management.
Your 12x8 3 blade prop and six lyPo's should yeald about 41-42 Amps and give you about 900 Watts, more than enough for the airplane, if you want to reprop for more power, choose another motor.
Robert.

Robert,
At 900 watts that set up will give 150 watts per pound, that shoud be more than enough to fly a trainer around, I hope.
You would go as high as an 8 pitch, I thought the 6 pitch would present less of a load.
I was going to originaly go with a 6 cell li-pol setup but opted instead for 6 cell li-ion batts. their voltage is a bit lower that li-ion but the have a lot higher discharge rate than li-pol 30c constant and 60c short duration. Given they are rated at 2300 ma the 30c rate should make them a good match for this motor, I hope. And like I mentioned before this set up could be used for a 40 size 4* or a SE after the trainer.

GravityHog
04-15-2007, 11:56 PM
Mustang
A good motor maybe the Eflite .46 w/castle creation ESC. I have two sigs, one is a scratch built foamie. Its powered with the eflite .32 but its the 70" LT 40 and weighs 6lbs. You can check it out on the (FOAMIE THREAD)
Good luck....GH

RMFISH
04-16-2007, 12:41 AM
Hi Mustang,
The 12x8 would give you a faster climb rate and a bit more pep and you would be in a good current range for the motor but even at these figures, MotoCalc warns of possible Motor heating. Check the temperature for the first few flights to be sure things are OK.

I would Be very interested in hearing a little more about the Li-Ion cells you mention. Do you mean the A123 cells or the other Electric drill cells that have been raising eyebrows recently??. I know of no Li-Ion cells that come even close to 30C let alone 60C, Wow. Cheers,
Robert.

Mustang
04-16-2007, 03:53 AM
Hi Mustang,
The 12x8 would give you a faster climb rate and a bit more pep and you would be in a good current range for the motor but even at these figures, MotoCalc warns of possible Motor heating. Check the temperature for the first few flights to be sure things are OK.

I would Be very interested in hearing a little more about the Li-Ion cells you mention. Do you mean the A123 cells or the other Electric drill cells that have been raising eyebrows recently??. I know of no Li-Ion cells that come even close to 30C let alone 60C, Wow. Cheers,
Robert.

The Li-ion cells I mentioned are the new ones that a123racing are producing.
Hypersonic™ 2300 9.9V (http://www.a123racing.com/racingpacks/hs3s1p.html)
2300 mAh, 9.9V, Lithium Ion, 3S1P
Dimensions: 70mm length x 55mm width
Weight: 230g
Output: Up to 30C continuous, 60C pulses
Max temperature: 160F/71C
Features: Balancing connector, Deans Ultra output/charge connector

I am glad I looked up the info, so the voltage I am running is 19.8 volts.
The wild thing about these is they can be recharge in 15 minutes or so, is what I was told. Aparently they can take a high rate of charge as well. Although they may be a bit heavier than li-Pols the power output is a big plus. Our LHS owner has been into e flite for some time and had got some for the car guys, he was telling me about them, so I decided to try them rather than Li-pols in my wifes plane. He got some for his planes as well, granted these are not going to work in smaller planes but for .40 and up I think they are an option.

Here is the website:
http://www.a123racing.com/html/hypersonic.html

I do think they are part of a123 systems which produces cells for hybird cars.

Mustang
02-19-2009, 09:32 PM
I am sorry I forgot to post some pictures of it as I had promised.
Flying on 6 a123 cells it flies like an LT-40 with an OS 55 in it.