Electric power for a 25 pound model... - RC Groups
May 22, 2002, 02:27 AM

# Electric power for a 25 pound model...

Hey guys!

Im working on a project where we hope to build a 25 pound model, capable of flying for a few HOURS on a charge! In just the little research Ive done, it most certainly looks possible! I know, I know, it would be much easier to use a glow or gas powered engine, but Id MUCH prefer to do this as an electric!

What motor(s), gearing, prop and cell count would fly such a monster for over an hour on a charge? Would it be possible to then lift an added 75 pounds of payload on this same power system (100 pound total flying weight!!)?

The design has yet to be finalized, but we expect to have a TON of wing area from current projections. With a 25 pound all up weight, the wing loading would only be 6-8 ounces per square foot! As you can see, it will have a LOT of wing area! Upped to around 100 pounds ready to fly with added payload (Added payload would most likely be more cells, run in parallel, to extend run times even more!), wing loading still remains only around 25 ounces per square foot.

I realize this is pretty vague, but where should we start? Brushless will definitely be the only choice as I can see, but whos motor will it be? Hacker, Kontronik, Actro, Aveox?

Thanks a lot guys, just looking for some basic inputs and ideas on power systems. We want the plane to ROG, and climb at a decent rate of say 200-400 feet per minute. Again, the goal is on one charge and a single pack to get at least an hour, if not more!

Jason
 May 22, 2002, 03:32 AM high-speed freak First, make sure this plane is not overweight/oversize for the AMA regulations! David Lewis (homefly). He consults on many different research-type cutting edge planes... would be an excellent person to consult with. is this for school?? it's gonna be expensive... you need the highest efficiencies possible if going electric, brushless motors if they can be had in large enough sizes/light enough for the cause. you may find it easier/cheaper to go to a multi-engine setup. also, you need power densities exceeding what nimh/nicad can deliver, and given you need long flights, li-ion or li-polymer is a real option. I will be selling li-polymer cells up to 3800ma starting in two weeks. they can be tied together in any series/parallel configuration and charged with an orbit pro charger. they are spec'd for 2C+ continuous and up to 5C pulse. say at 50 watts a pound, you need a 1250 watt-hour battery for an hour of full-throttle flight. say 30 amp draw, 12-cell li-poly (equivalent of 36 cells), a flight pack for 1 hour of full throttle will weigh 24 pounds. not a whole lot left for everything else, huh? that's why you need to consider a sailplane-type design, so that you can use a fraction of the battery weight and use throttle to climb, then glide...
 May 22, 2002, 08:32 AM Member Jason, Have you looked at Steve Nue article in the July SEM (pgs 65 & 75)? He wrote about the same AIAA project the group near him will be using the Graupner Ultra 3300/7. Good luck! UJ
 May 22, 2002, 09:33 AM AMA 697691 / FAA 13675 Hmmm...I'm not sure about the "few hours" part but MaxCim just came out with the MEGAMax3.7-()Y that packs over 2 kilowatts of power. Latest blog entry: Greg's Web Hangar
May 22, 2002, 11:47 AM
Registered User

# Battery

At that size/weight, could he get into some of the 12v gel cells for power? How do these cells compare in Energy deisity to the nimh's... also, what would be the safety concerns if the plane were to crash? (I.E. Is splitting open a Gell Cell as bad as splitting open an old fasioned Lead Acid Battery).

One other safety concern would be hydrogen gas accumulation.

Still, if they are safe enough to run kids toys (powerwheels) and my car (honda CRV), it should be ok, no?