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hookedonflyin
12-07-2006, 11:01 PM
I have a rcm gas 40. trainer and i was wondering if anyone knows how to convert it to electric?

MTwallet
12-08-2006, 05:40 AM
I have a rcm gas 40. trainer and i was wondering if anyone knows how to convert it to electric?


Yeah, put an electric motor and some batteries in it.:rolleyes: :)


MT

MTwallet
12-08-2006, 05:45 AM
Seriously though, how big is it?
How much does it weigh?
What kind of flying experience do you have (how good are you)?
What kind of performance do you expect from it?
Do you have any experience with electrics?
What's your budget??


MT

d_wheel
12-09-2006, 12:15 AM
Go here:

http://www.hobby-lobby.com/glow2econ.htm

You can get a good idea of what might be compatible with your setup and budget.

Later;

D.W.

jeholliday
02-16-2007, 07:57 PM
MTWallet hit the nail on the head. It can be done with a lot less effort than going going the other way. Just need to get right power combination. Change the motor mount to accomadate. Change fuel compartment to put batteries in and out easily. Then the important part, provide cooling for the motor and the batteries. DOC Holliday

jrb
02-16-2007, 08:55 PM
Here’s an article that might help: http://www.rcgroups.com/links/index.php?id=4485 .

balsadust
02-17-2007, 02:24 AM
Hookedonflyin,
I noticed lots of help but no answers, I have a Great Planes Trainer 40 converted to electric. The Trainer 40 is Great Planes version of the RCM Trainer 40 which I think was designed by Joe Bridi so my setup should work for you.
Motor; AXI 2826/12
Speed Control; Castle Creation 45 amp
Batteries; 12 3300nimh, or 4S lipo 4400mah

The motor is mounted directly to the stock firewall with 1 1/2" standoffs.
I drilled 4 1/2" holes in the firewall for cooling air as well as two 1" holes in the bottom just behind the firewall.
The batteries mount on a flat tray glued to the bottom of the fuselage that lets me shift the batteries front and back to balance the plane.
No effort was made to lighten the plane and all up weight with nimh batteries is 6.5 lbs.
The plane flies just fine with a 12x8 APCe prop and will fly for over 12 minutes of relaxed flying or about 8 with some aerobatics.
It should really be flying with a 13" prop but I dont have enough ground clearance since I fly off of grass.
I dont have any completed pics but here is one just before I finished covering the wing.

Hope this helped,

balsadust

hookedonflyin
02-17-2007, 05:35 AM
wow, great help it will go a long way. Thank you

flypaper 2
02-22-2007, 02:59 PM
Pretty much the same as Balsadust. Done a couple, the Pulse XT and the Twist 3D. Both of these are made convertible from glow to electric. Motor is the Himax HC 50 swinging a 13-8 prop and Makita li-ion batts. Batt. is permanently installed where the tank goes with a 1 1/2 in. hole in the bottom where the tank goes where the wires hang out for connecting power and charging the batts. The batts can be pulled out if need be. If I want to put up a second flight I take the wing off and put another batt. in. I don;t usually bother as the li-ion batt fast charges in about 35 to 45 mins with the FMA Balance Pro charger. Batt and ESC cooling is done with holes in the firewall and the hole in the bottom just behind the firewall. I use a UBEC as I'm running 4 servos and the CC 80 amp can only handle 3. Hope this helps.

orionRider
03-05-2007, 01:00 PM
I have had very good results with a setup similar to the Axi mentioned, but much cheaper, on a 170cm (66") Pilatus. Here it is:

https://www.unitedhobbies.com/UNITEDHOBBIES/store/comersus_viewItem.asp?idProduct=666
https://www.unitedhobbies.com/UNITEDHOBBIES/store/comersus_viewItem.asp?idProduct=2062

Note that the ESC is for 4 to 6S LiPos and has no BEC circuit, so you need a separate rx battery or UBEC. Anyway, at 4S or more a separate rx power source is required for safety's sake.

I turn a 12x7" or 11x7" 3-blade prop on this motor @ 29Amps.
Any 4S LiPo between 3000 and 4500mah will do if it has at least a '12C' continuous rating.

http://users.telenet.be/Les_Busards/images/pilatus3.jpg

With any outrunner motor you really need to balance the prop and the spinner, especially if the motor is attached from the rear (with the rotating bell front). I found 3-blade props to cause less vibrations than 2-blade, but they are also less efficient.

jrb
03-05-2007, 08:29 PM
“found 3-blade props to cause less vibrations than 2-blade, but they are also less efficient.”


Check out the image below; you’ll see that a multi blade prop gets closer to the calculated “pitch speed” for the same rpms compared to a two balder.

And, that it uses less power in for the same propulsive power out – meaning it is indeed more efficient.

All of the above is why you see 3 bladed windmills!

orionRider
03-06-2007, 10:01 AM
Well, the theory says that:confused: but in flight it is another story. In my experience, for the same power you always get better results from a larger prop. A trainer aircraft will fly better on a larger 2-blade vs a smaller 3-blade prop. At least for common props like Graupner, Master or APC.

For the same watts, my Pilatus flies better on a straight 12x8" than a 11x7" 3-blade. But then I don't care because 3-blade looks cool :cool:

jrb
03-06-2007, 12:53 PM
If by the same power you mean the same engine (gas or glow) a multi prop of the same diameter as a two will likely over load the engine more.

Hence the myth you describe.

But, when you can match the power system to the prop; you will get more propulsive power out for the same power in with a multi blade prop!

skiman762
03-06-2007, 02:02 PM
If by the same power you mean the same engine (gas or glow) a multi prop of the same diameter as a two will likely over load the engine more.

Hence the myth you describe.

But, when you can match the power system to the prop; you will get more propulsive power out for the same power in with a multi blade prop!


Are you saying you can get better performace from a 3 blade then a two turning the same rpm for the same amp draw ?
I don't see how that can be but if you've tested it I guess so

jrb
03-06-2007, 02:21 PM
Or, a synchronous motor as I used for the tests shown in the above image!

orionRider
03-06-2007, 06:08 PM
I mean that my Pilatus flies better with a straight 12x8" than with a 3-blade 11x7". Both props have the same profile (Graupner) and absorb exactly the same watts on the ground.

I think the 2-blade performs better because it is bigger. This is not a myth, but a well-known fact: larger props have a better efficiency. There is also less drag with a 2-blade prop than a 3 or 4-blade.

I have not seen many 3+ blade props on competition models, like F3A or F5D:confused:. But I have seen single-blade props on control-line and fast RC aircraft :cool:

All of the above is why you see 3 bladed windmills! ROFL:D

http://phizo.club.fr/Machines/Ferme_eolienne.jpg

(Windmill farm of Castellnuovo Della Duonia (IT). 2.6 megawatts since 1995)

The problem with Benchmarks is that they don't fly :rolleyes:

jeholliday
03-06-2007, 06:17 PM
I myself do not think a single blade prop would work for electric. They work in control line because of the high rpm engines. We are talking about in excess of 30,000 rpm. In electric I think also a prop depends on the airplane design and how it is to be flown. A low pitch prop is like driving in low gear, it excelerates better. It takes experimenting to find the ultimate prop for any given setup. My opinion, DOC Holliday

skiman762
03-06-2007, 08:00 PM
Your right about the bigger props the reason mainly is tip speed
I talked with a couple of prop makers and they all told me it's the outer 1/3 of the prop is where the thrust comes from I played with some large spinners and found that to be true
I also talkes to a full scale acro flyer about why they use 3 blades and he told me to reduce the disk forces on the crank shaft they do loose some effiecency but having your crank break off like has happens to a few acro flyers with 2 blade props isn't very effiecient either:eek:
I wonder if at higher elevations 3 blades would help overcome the thinner air

orionRider
03-07-2007, 09:19 AM
Skiman, at higher elevations using 3 or 4-blade props is a neat way to transform more power and get more speed without increasing the pitch.

Generally speaking, multi props are used on aircraft that have so much excess power that a 2-blade prop would simply be too large. A large diameter prop has many physical disadvantages: it requires a high landing gear to clear the ground, it tends to give more torque and at high rpm the tip speed reaches the speed of sound, which kills performance, increases noise and causes prop failures. Balance can also be a big problem and hub construction has to be stronger than for a smaller prop.

A good example is the F4U Corsair, which could use more than 2000HP thanks to it's huge 4-blade prop. The same kind of power would have been impossible to use with a 2-blade prop.

http://upload.wikimedia.org/wikipedia/commons/thumb/0/03/F4U_Corsair.jpg/250px-F4U_Corsair.jpg

Modern turboprop aircraft have the same problem, like the A400M witch will use 8-blade props! http://www.airbusmilitary.com/gallery/a400mdesertlanding1024.jpg

In model aircraft, the main reason to use a multi prop is ground clearance, followed by scale appearance.

I myself do not think a single blade prop would work for electric.
Jetholliday: control line aircraft have high rpm engines, but electric racers too. Their small props turn at 30.000+ rpms. That's why single-blade props have been used in pylon-racing F5d, which have basically 'on/off' motors. At such a high rpm, traction offset is less of a problem.
It works only with small props on high rpm motors and would be a disaster on a 'regular' model.

;)