> Mike is right about the fact they are relacing a lot of recips with 
 > turbines in ag and STOL work, but the cost is over 80K dollars 
 > (U.S.) or so. Even if the price is tripled because it goes into an 
 > A/C, a turbine is not cheap and the Allison 250 is about as simple 
 > of a turbine as you can get.
Gerry,
 The day is probably coming when turbine engines will be affordable in many 
applications that now use recips. Hybrid autos, light airplanes, and even 
home power operations all come to mind. For that to happen, we need a bit 
better material for the hot sections, perhaps more development in auxilary 
stuff like fuel handling, controls, etc. and higher production rates.
Williams International is working very hard on developing inexpensive (by 
today's standards) turbine aircraft engines. NASA is footing part of the bill 
in an attempt to develop something suitable for small jet aircraft. Even at 
that, Teledyne Continental Motors has a NASA contract to develop a new Diesel 
recip engine for smaller planes. So it seems obvious that they don't feel a 
small turbine will be cost-competitive in the very small engine arena (300 hp 
and down) for a long time.
York recently developed a small air conditioning unit that is powered by a 
Briggs & Stratton engine; it supposedly will operate for about half the cost 
of electrically-powered A/C. The B&S is a recip, of course, albeit bearing 
little resemblance to your lawnmower engine.
I've seen several co-gen units, from home-scale (both commercial and 
homebrew) to quite large (one megawatt) and THEY use recip engines. Some are 
Diesel, some are natural-gas fueled. I've also seen some decent-sized standby 
generators that the phone company uses that are powered by some sort of 
turbine engine, although most are either gasoline or Diesel recips.
The Toyota hybrid uses a small recip engine, of course. One thing that's 
sometimes forgotten by the folks who think turbines are 'the answer to our 
prayers' is the gear reduction that's normally required. Those turbines are 
often spinning at 50,000 RPM or more, and it gets costly to step that down to 
useable speeds. A typical recip engine might well be direct drive to the load 
(generator, airplane propeller, pump, etc.). This difference alone will often 
offset the inherent simplicity of the turbine.
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