Diesel aircraft engines and are the light jets pushing out the twins?

"Mike Rapoport" wrote in message
nk.net...
I don's see that I've overlooked something relative to the Caravan. The
Caravan has a 940hp engine. There is currently no suitable piston engine
to
power such a large, single engine airplane. It couldn't be anything other
than a turbine.

As you yourself pointed out, that 940hp engine is derated to 675hp. You
don't need a 940hp piston engine to provide the equivalent power, and a
675hp piston engine is not out of the question (for example, the Orenda V8
turbine replacement engines are in that ballpark, if I recall correctly).

Of course, the Orenda design is a good example of the general philosophy
that piston engines are more efficient, and cheaper to own and operate.
After all, why would anyone replace a turbine with a piston engine, if the
piston engine weren't cheaper? So I'm not saying this somehow disproves
your point...I'm just saying that you need to make sure you compare apples
to apples (and claiming that you need a 1000hp piston engine to do the same
thing a 1000hp turbine does is not comparing apples to apples).

[...] The engineers designing airplanes
are not totally stupid, if it made sense to install 400hp turbines they
would do so.

I agree the engineers are not totally stupid. I disagree that just because
it hasn't made sense so far, that it will not make sense in the future. It
really just depends on what factors influenced the original decision.

Am I saying that I think it will make sense in the future? No...I don't
know enough about the technology to be able to answer that question myself.
But so far, the people who do know about the technology haven't provided any
information that would suggest to me that the future will be completely void
of lower-power turbines.

[...]
horsepower the diesel will always be cheaper and more fuel efficient than
anything else. There probably isn't an economic crossover point for
gasoline engines either unless the fuel price spread is artificially
raised
even higher than it is now. You have to remember that the HSI and
overhaul
costs on turbines is much greater than the cost of overhaul on a piston
engine. [...]

Would a HSI cost the same on a smaller turbine? Does a HSI cost the same
for the PT-6 as it costs for whatever gargantuan engines the 777 uses?

Inspections and overhauls for piston engines generally scale up with engine
size, so it seems to me you need to compare apples to apples by comparing
the cost of a HSI and/or overhaul with the cost of an inspection on a
similarly powered piston engine.

Turbines will be used in applications where cost is a secondary
consideration to high power and high reliability. The gas turbine is a
mature 60yr old technology, huge improvements in cost or efficiency are
somewhat unlikely.

The same thing could theoretically be said about piston engine technology.
I suppose, in fact, that's one of the most compelling arguments in favor of
your claim: all of the engine technologies are relatively mature, so it's
reasonably safe to compare cost/benefit ratios at this time and assume that
they will remain similar in the future.

But can we be *sure* of that? You might think you can, but I'm not going to
claim that I can.

Pete