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Yellow Aicraft P-38 Conversion

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Old 03-22-2004, 03:11 AM
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voodoodb
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Default Yellow Aicraft P-38 Conversion

Need help converting YA P-38 from Gas to Electric. Would like to convert and get same power and flight times. Was going to use 2 G-45, 45cc gas engines. Can someone help me come up with motor, batteries, and speed controller to convert? Also gear box if needed. Also would new Lithium Batteries be better than Ni-cad?
Sorry, here are the specs for the P-38
Specs:
Length:......................72"
Wing Span:................100"
Weight:.....................28-32 lbs

Recommended Engine: Supertigre 3000 , Moki 1.8, 2.1,
OS BGX, Zenoah G-38, etc.




Thanks for the help

Doug
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Old 03-22-2004, 03:35 AM
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Default RE: Yellow Aicraft P-38 Conversion

I don't know too much about electric flite, but I don't think such a large
airplane can be successfully converted to electric power.


http://www.yellowaircraft.com/prop/p-38/p38.htm

100" wing span and 30lbs weight and two 2.0 glow engines.
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Old 03-22-2004, 09:23 AM
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Default RE: Yellow Aicraft P-38 Conversion

Ignoring the cost issues, it should be a given that such a conversion could readily be done, given that guys are demonstrating competitive performances in the world aerobatic champs, the eelctric power systems and models having a more than equal performance and duration to their pumped piped 120 FS competitors.

In the sport-scale world, there's at least one 80+ inch span World Models ARF Zero conversion flying - with Hacker C50 14XL Acro geared 6.7:1, 22x10 prop and 10s4p 8200 Thunderpower lipos - it flies knife-edge with no problems weighing 17.5lb. Tune in to http://www.rcgroups.com/forums/showt...hreadid=140665


Similarly there's Dave Grife's 1/4 scale around 84" span Travelaire Mystery Ship weighing around 15lb that does about 12 mins of huge aeros, on a similar geared Hacker, 22x12 and 9s4p 8200 lipos. Surf http://www.rcgroups.com/forums/showt...hreadid=122100 for a look at this one.

So putting a pair of these systems in a YA P-38 would make it really go with absolutely no problems at all beyond the cost.

Gordon
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Old 03-23-2004, 08:32 AM
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Default RE: Yellow Aicraft P-38 Conversion

Heck, you want large electric? Here:

http://www.rcuniverse.com/forum/Hist...1387209/tm.htm

Ain't no such thing as, "It can't be done." Now, AFFORADABLE? That's a different question
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Old 03-23-2004, 10:20 PM
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Default RE: Yellow Aicraft P-38 Conversion

Thanks Matt, but believe 2 of those setups would be overkill. Guess what I'm looking for is a conversion to electric that would, swing a 20x10 propat around 7500 RPM, produce about 4.5 H.P. and give me about 15 min flight times.

Thanks for the help

Doug
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Old 03-24-2004, 08:42 AM
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Default RE: Yellow Aicraft P-38 Conversion

Hmm, 4.5HP is 3357 Watts. A little over 100 Watts per pound. Not a bad idea. Mind you, this is all the power you need from BOTH motors, combined, to make the plane fly extremely well. I believe you got this figure from the ratings of the various recommended engines for this plane.

7500 RPM on a 20x10 prop is a 71MPH pitch speed. Pretty respectable, but we may need to compromise here to keep the weight from getting out of hand. The faster you turn a prop, the more power you need.

We can get the battery nailed down anyway. I generally like to keep currents at 40 Amps or less because the equipment is less expensive and there is more to choose from. However, this is a large plane, and

30 cells at 50 Amps is approximately 1500 Watts. Two of these, one powering each motor, will give you 3000 Watts total. Plenty.

For conventional cells, I'd use nothing but GP3300 NiMH. Each pack will weigh about 4.5 pounds, so 9 pounds of your final weight will be batteries. For LiPolys, I'd wait a bit. The new Kokam 2100 cells in a 9S4P configuration will power both motors, give you about 1/3 more flying time and save a bunch of weight.

Either way, you're not going to get 15 minute flights. I'd estimate the NiMH configuration would power your plane for 5-7 mintues, and the LiPoly for 8-10. If you want more duration, the only solution is to add more mAh. With the NiMH, it's not practical. You'd have to add another 9lbs of batteries. On the other hand, it's VERY practical to add capacity with LiPolys. Just add more packs in parallel. 9S6P would probably give you 15 minutes plus some reserve. The problem is cost. 54 cells at an estimated $30 each... $1620, just for the battery!!!!!
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Old 03-25-2004, 01:30 AM
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Default RE: Yellow Aicraft P-38 Conversion

Thanks Matt, what about engine and esc? Also Gear if needed? Don't know what your preference of motor is, but the Hacker brushless appears to be a favorite of many.

Thanks
Doug
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Old 03-25-2004, 09:33 AM
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Default RE: Yellow Aicraft P-38 Conversion

You've got the important information, 30 cells at 50 Amps. All you need to do is pick a brand and look up suitable alternatives in their catalog or on their website. ESCs are easy. Motors are a little more involved.

Really, any motor rated for 30 cells at 50 Amps can be made to spin the right size prop at an appropriate RPM, though some are more practical than others. Choosing a motor is where I would recommend bringing in the Motocalc program. You can program your cell count and desired prop size in, then try the various motors and gear ratios you found earlier until you find one that draws the right amount of Amps.
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