----- Original Message -----
From: Carrie Sparling <CarrieSparling@identicard.com>
> > Wouldn't a turbo-fan jet engine be considered internal combustion?
You bet -- and some of the small ones approach 100,000 rpm!
> Actually, this reminds me of something I was wondering about (and your
> question is helping to confirm my deduction)...
>
> Pardon my ignorance, here: In turbine-powered vehicles that are
mechanically
> driven (as opposed to being propelled by the exhaust of the turbine), such
> as the Chrysler Turbine car of the 60's, jet-powered tractor pull
> "tractors", and possibly Jay Leno's motorcycle... Where is the mechanical
> link to the drivetrain? Is it really just the fan of the turbine? What
kind
> of reducer must there be to translate that ridiculous RPM into streetable
> revolutions of something like a driveshaft?
This is actually a pretty common application -- not in cars, but in
helicopters and a few tanks. Technically, they're called turboshaft
engines -- a typical example has a one- or two-stage (stage = disk)
compressor and two sets of turbines -- one to run the compressor, and the
"power turbine," which drives the output shaft. Depending on the engine,
the compressor and turbines run at between 30,000 and 70,000+ rpm. A set of
reduction gears at the back reduces the revolutions by a factor of 10-20 at
the output shaft -- much easier to deal with!
Specific power for turbines is great -- normally better than 2 hp/lb. The
real downside is heat and inflexibility. Turbine exhaust temperatures for a
typical turboshaft engine are 1500-2000 deg F. And turbine engines don't
change speeds well -- lots of rotating mass to deal with. On aircraft and
helicopters, the engines tend to run at constant speed, with "gearing"
controlled by changing propeller or rotor blade pitch. On the M1 tank, the
engine's throttled normally (part of the reason it has a reputation for
thirst), and hooked to a very heavy-duty automatic transmission -- a 70-ton
tank can live with somewhat slower throttle response than a 2500-lb car.
The ideal solution, though, would be to control power to the wheels by means
of a CVT while running the engine at constant speed.
Jamie
'92 Prelude Si
Speed Demon Racing
http://www.mindspring.com/~jsculerati/sdr
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