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Date: Tue, 03 Jun 2008 22:44:44 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: combined starter alternator
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Richard Sohn wrote:
> I do not have the direct answer to your question, it would be too long, however, the first two cars I owned had a starter-generator set up. The first one was a 700cc DKW model 1938 and the other one was a 1949 DKW, sort of a post war successor. Both were two cylinder two strokes. It had an outside armature on the crank shaft with a set of brushes on a disc type commutation. Once the engine was running, it worked as a generator through a separate exciter winding in the stator, controlled through the voltage regulator. The windings on the armature were used as starter and generator. 
> There was frequently a problem with cranking, because it was loosing torque with the slightest voltage drop in the system.
> I do not believe that such a system could be built competing, at least weight wise, with a gear reduction starter motor. As a mater of principle, a high torque electric motor is always heavier than a high speed motor producing the same torque through gear reduction. And, of course, at the same hp.
>
>   
I'm not disagreeing, Richard, but I'd like to point out that the system
isn't just competing with the gear reduced starter, weight-wise.  It's
competing with the starter, an alternator, and all the pulley, belts and
mounting hardware.

The last few years have produced some substantial advancements in
permanent magnet motors.  Mostly the introduction of neobyium (sp?)
magnets, that have given them useful power output.  The biggest problem
is that you need multiple horsepower from a starter to crank an engine,
but only need the generator to produce fractional HP.  I think the
problem could be solved by a PM motor that used relays to energize
several coils for starting, but only utilized a fraction of those for
charging.  Getting the requisite torque from a motor can be accomplished
by gearing it down, or by giving it a larger diameter.

Here is what I think is the start of the solution.  A Harley generator.
The stator is bolted up to the rear of the PSRU.  I still need to build 
an adapter to match the rotor to the flywheel/clutch-plate.

http://ernest.isa-geek.org/Delta/Pictures/EnginePSRUInitialMounting.jpg
http://ernest.isa-geek.org/Delta/Pictures/EngineGeneratorFitting.jpg

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