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This REALLY has nothing to do with rotary engines, but...
If you are trying to do back of the envelope type calculations to figure the size of the battery pack, you can figure that it takes about 90 lbs of high-energy Li-Ion batteries to replace a gallon of gasoline. This is figuring the typical efficiency of a gasoline engine and a typical electric drive package in a vehicle.
If it takes 6 gallons per hr to keep you at cruise speed, it will take 6 x 90 = 540 lbs of Li-Ion batteries to run the plane at cruise for the same amount of time. Since you will be carrying 500 extra lbs, you will have to adjust the speed or duration downward a bit to account for the additional induced drag.
540 lbs of traditional laptop "road flare" type Li-Ion cells will cost about $11,000 if you shop around for the very best deal. You have to add the expense of connecting them together and also the expense of the electronic battery monitoring system (BMS) that you need to keep these cells in balance (and to help keep them from becoming road flares.)
As I said earlier, this can work well for a motor glider, but not well for a cross-country airplane.
It would cost about $3.50 to fill this 540 lb Li-Ion battery pack with electricity, here in Denver. That works out to about $0.60 per electric "gallon of gas".
Makes a LOT of sense for a commuter car. That is for sure. That 540 lb battery pack will take a compact car 200 miles.
Absolutely nothing to do with rotary aircraft engines, like I said. :-)
At 09:58 AM 7/8/2006, you wrote:
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
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
<mailto:eanderson@carolina.rr.com>eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
----- Original Message -----
From: <mailto:hjjohnson@sasktel.net>Jarrett & Heidi Johnson
To: <mailto:flyrotary@lancaironline.net>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: <mailto:jwvoto@itlnet.net>Wendell Voto
To: <mailto:flyrotary@lancaironline.net>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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