From: cantrell@seqp4.sequoia.com (Paul Cantrell)
Newsgroups: rec.motorcycles
Subject: Re: Faster 1100
Date: 29 Sep 92 13:44:03 GMT
Distribution: usa
Organization: Sequoia Computer Systems

In article <viking.717212125@vincent2.iastate.edu>, viking@iastate.edu (Dan Sorenson) writes:
> In <txd.717194809@Able.MKT.3Com.Com> txd@ESD.3Com.COM (Tom Dietrich) writes:
> >Hey Mark, I have it!!! We were at the Reno air races, and I gotta
> >believe that one of those supercharged P51 Mustang motors would be a
> >good starting place! Hell, it already has the NOX setup and
> >everything!
> 
> 	There is also a Ford 427 SOHC residing there.  Figure 450hp, 400
> foot-lbs of torque at your fingertips.  It's also light, being an
> aluminum block, and not as large as the W-24.

I've always thought that a turbo-shaft engine like that used on jet
helicopters and turbo-prop airplanes would be a great motorcycle or sports
car engine. They're quite small and light. You could just fit one inside a
sport bike frame. A small Allison puts out 300 - 450 shaft horsepower.

The way that a free-turbine turbo-shaft engine works is that you have a
regular jet engine which is producing exhaust gasses. Completely separate
from the jet engine, there is a turbine sitting in the exhaust. As the jet
exhaust blows by, it spins the turbine which is connected to whatever you
want to turn - in this case, the drive for the rear wheel.

You can start up the jet engine without the power turbine spinning, so you
could just hold your foot on the rear brake, light up the turbine, release
the brake and idle away. Throttle is then just rigged to the fuel control,
as in an aircraft. It would be very simple, mechanically. You'd have to
fit an extra-large brake to the rear wheel - getting the bike to stop once
it's moving might be a bit of a problem since even at idle, the engine is
putting out a significant amount of power. The brake would have to be
large enough to stop the bike, plus stop the free turbine despite the
fact that the engine is still trying to turn the turbine. I suppose you
could redesign the engine to allow bypass of the free-turbine, but now
you're talking about a significant change to the engine.

The biggest problem I see is fuel. Even a small turbo-shaft burns about 30
gallons per hour of jet fuel, so a 5 gallon tank is only gonna last 10
minutes. By the way, you can run limited amounts of gasoline, so for those
long squid runs to the next town, you could refuel at the local gas station
and then ride home again. There's a limit to how often you can do this.

Additional problems I can think of:

	1)	The exhaust gas is *hot*. It can't be pointed at anything
		you don't want to melt. You couldn't point it down anywhere
		near the tires. Ducting it to the rear of the motorcycle
		would be a sure cure for tailgaters. Actually, it's not
		*all* that hot - say, about 700 degrees. 5 or 6 feet
		away you'd only feel a hot wind. You could mix cool air
		in the exhaust system to decrease the output temperature
		to something bearable.

	2)	Turboshaft engines like to work at high rpm. When you let
		them "spool down" to low RPM, excess horsepower goes away,
		and it takes a long time for it to accelerate to full
		RPM/power. (Actually, this is true of pure jet engines as
		well - it can take several seconds for them to go from idle
		to full power) Still, even at idle RPM it can probably develop
		more power than a ZX-11 engine WFO.

	3)	They're pretty expensive to operate. Figure a hot section
		every 1500 hours for about $25,000, and an overhaul at
		3,000 hours for about $150,000. That's $58/hr to maintain
		the engine, plus about $63/hr for fuel == $121/hr to
		operate, pretty much independent of throttle setting (i.e.
		idle costs the same as WFO). Purchase price? I've never
		bought one, but I'd guess you could get a high time one
		nearing overhaul for a hundred grand.

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