Alternative engines

[Howard Wilkinson]

Joe:
    you seem to be somewhat well versed in the matter of turbine
engines.  I'm curious about one thing here.  Several folks in the
experimental aviation community have tried to use APU engines for
power in light aircraft and had poor luck..... engine troubles.  I
have a theory on this.  From what little I can gather about it, and
I've not communicated directly with any of these people, it appears
that they are attempting to control turbine speed.  It looks to me
like these turbines are intended to wind up to governor speed and
operate at constant speed, and that they must have some sort of
governor system to control RPM as load varies as it must in a
generator application.
    My thinking is that the correct way to use one of these is to have
a controllable prop and operate at a constant RPM.... forget about
controlling RPM.... let the system operate as it was originally
intended and use the stock fuel control / governor system.  I strongly
suspect that the problems people have had originated from changing
RPM.
    Any comments on this??            H.W.

-----Original Message-----
From: Joe Piche <pichej at shaw.wave.ca>
To: diy_efi at efi332.eng.ohio-state.edu
<diy_efi at efi332.eng.ohio-state.edu>
Date: Friday, April 23, 1999 2:25 PM
Subject: Re: Alternative engines


>> Maybe.  Don't most turbines spin something like 30,000 RPM?  It's a
lot.
>> And they don't really produce any torque at all until they get up
to a
>> substantial portion of that.  You'd need a 20:1 final drive ratio
to get
>> "normal" performance, so that won't do.  What I would recommend is
a
>> reduction before you feed into the transmission.  Before the
clutch, even.
>> I wouldn't trust most transmissions to take that much RPM on the
input.
>
>Using a standard jet engine is out of the question. Using a
turboshaft
>engine is relativaly easy. Something like the PT-6 (variations on
>the engine produce 500 to over 1000 hp), with a low output speed from
>the reduction gear box.
>
>The allison 250, 400+ hp, has an output speed of 6000 rpm.
>
>As for exhaust size, these engines don't need very large exhaust.
Diesel
>truck sized.
>
>The most efficient way to run a turbine in a normal vehicle, would be
>to have the turbine at a constant speed, and use it to drive a
>hydralic pump with variable output, or an electric generator.
>
>Problems with turbines. Parts cost a fortune, and once a part like a
>turbine, or a compressors become time-expired, they tend to fly apart
>like a grenade.
>
>As well, turbine engines are fragile things. Doesn't take much to
>completely destroy a compressor (especially axial compressors). Small
>rock, dirt, etc.
>
>Just my 2 cents.
>
>Joe
>(I'm a AME (aircraft maintenance engineer). I just completed 4
courses
>on jet and turboshaft engines)
>