flyrotary@lancaironline.net Mailing List Archive

I would hazard a guess that Wendell is probably alluding to the better energy conversion efficiency of an electric motor over an internal combustion engine. Assuming the same energy input (whether in the from of electricity or gasoline) a typical electric motor is around 50% efficient where as the piston engine is around 25% efficient in converting input energy to mechanical energy. So for the same energy input an electric motor should give better conversion efficiency. So you might get 100 HP out of a motor for a 200HP (electrical energy) input - whereas to get 100 HP out of a piston engine you would need 400 HP of energy input (in the form of gasoline) - the rest being "wasted" in form of exhaust and cooling energy (and some friction).

However, I agree with Jarret 1 HP = 1 HP regardless.

Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW

----- Original Message -----

From: Jarrett & Heidi Johnson

To: Rotary motors in aircraft

Sent: Saturday, July 08, 2006 11:48 AM

Subject: [FlyRotary] Re: Nothing to do with Rotary Engines, but....

Wendel, I was always under the impression.. 1Hp was 1 Hp regardless of how it was created..

The only convertion's I've heard of were.. 1Hp= 2Dp [Donkey power] , and 1Hp=1.5Mp [Mule power] :-)

Jarrett
----- Original Message -----

From: Wendell Voto

To: Rotary motors in aircraft

Sent: Saturday, July 08, 2006 9:29 AM

Subject: [FlyRotary] Re: Nothing to do with Rotary Engines, but....

What is the equivalent hp conversion of electric to gas engines? I'm thinking it is about 2:1 (tried to look it up quickly, couldn't find it), so instead of 180 hp, you would only need 90 hp electric.

Wendell

Subject: [FlyRotary] Re: Nothing to do with Rotary Engines, but....
Think about how small the alternators on big HP APU's are and you get the picture on how small you can make a powerful electric motor if you are willing to work at it a bit. You can easily make a 100 HP electric motor that weighs 100 lbs. It would not likely be DC, however.

Electric motors for stationary use have no constraint on weight. The only reason you would want to make one lighter would be to save on materials and/or on shipping. If you make a motor of a given HP lighter, it will cost more, spin faster, or be less efficient than the heavier motor. If you are running on batteries, you must be careful not to save weight on the motor by compromising efficiency, only to add to the total vehicle weight by requiring more batteries to make up for the reduced motor efficiency.

Bill Dube'

george lendich wrote:
Hi Bill,

I'm relieved.  I won't have to mortgage the house until the technology
advances enough to reduces the weight by a factor of 5. Currently it
looks like I would need about 1400 lbs of batteries.  Get it down to
280 lbs and allow 100 lbs for the electric motor and my W&B will work
out about right. :)

I'm looking forward to seeing what you come up with for the aircraft
batteries.

Bob W.
    
Bob or Bill
I would have thought a 130hp DC Motor  would weigh more than 100lbs.
Any rule of thumb on weight of motor to power output ?- I guess there's a
lot of copper windings per HP!?
George (down under)



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