William Robison
Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline
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John:
[QUOTE]Originally posted by john_89
It would be so much easier to do this electric. I think it would only take a 25 lb lead battery to power the thing for an hour using a 30 amp motor! What do you think could I swing it? [/QUOTE]
But 30 amps at 12 volts is only 360 watts. That probably wouldn't be enough power to taxi the battery alone, much less fly. But you can get a 360 watt motor for $10.
General rule for electric flight, with reasonable performance, is 50 watts per pound. With your 25 lb battery that means 1250 watts for the battery alone. You're getting into the $300- $400 dollar range for the motor without including the motor controller.
There are batteries with much higher power density than lead-acid, the airplane could be built using lithium-polymer batteries, for example, but you'd still have to add a lot of "Lightness" to get much more than 12-15 munutes duration under power.
For all of this you still read expensive. Piston power is much cheaper for the same performance.
Many large electric airplanes have been built and flown successfully, but you're opening another large can of worms. Small electrics, OK, but endurance and small electrics don't go together, except for sailplanes.
Can you count on thermal activity? If yes, a sailplane might work. BUT. An efficient sail plane is again, an expensive thing, whether bought or built, because of the materials required.
Pardon me for breaking in on your question to Bruce, but I do have several electric flying machines, including two helicopters.
Want to fly long? Twins make a nice song.
Bill.
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