

Mar 07, 2012, 11:55 PM  
Hagerstown, MD  USA
Joined Jan 2009
27 Posts

You didn't say what the flight task is, but note that at 11 volts (~9*1.2) if you pull 20 amps you will need to dissipate close to 220 watts. That's input watts, but if your motors are only rated for 150 you will be limited to about 13 amps for long term running. You might get away with 20 amps for a short burst, but over 30 seconds of that may cook the motors.
Jim 
Mar 08, 2012, 07:44 AM  
USA, ME, Ellsworth
Joined May 2008
17,140 Posts

if the 18 NiMH cells are 25 grams each they will weigh 450 grams.
If the wing is 558 sq. in. (3.9 sq. ft.), and for the plane to have a favorable 15 oz./sq. ft. loading, it would need to weight about 58.5 oz. or 1660 grams (3.65 lbs). The two motors will have a combined continuous power of 300 Watts and, against the weight I mention above, that would be about 82 Watts per pound. And that is more than enough for basic flight. Here are some rules of thumb for electric flight power requirements: Approximate power requirements: 5070 watts per pound; Minimum level of power for decent performance, park flyer/slow flyer models 7090 watts per pound; Trainers and slow flying scale models 90110 watts per pound; Sport aerobatic and fast flying scale models 110130 watts per pound; Advanced aerobatic and highspeed models 130150 watts per pound; Lightly loaded 3D models and ducted fans 150200+ watts per pound; Unlimited performance 3D and aerobatic models To get the 150 Watts from each motor, the 9 cell packs would have to supply 15A at 10V and I think that might be were some problems start to show up. I've not used NiMH packs much at all and I'm not sure what discharge rate those cells will give you or for how long. Once in flight, you can reduce power and you may be able to maintain flight on as little as 1/3rd or 1/2 of the 150W so maybe you'll have a chance. But it looks like you have a chance if the batteries are up to it. Jack 
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