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In rec.aviation.owning Mike Rapoport wrote:

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The question remains, at what HP level, based on the physics of the
engines,
does the crossover from piston to turbine occur?

As additional criteria, assume specific fuel consumption is the most
important parameter and that the A/C spends the majority of its time in
flight not doing touch and goes.


I think that you can look at the market to see where the crossover
occurs.
THere are currently no production piston aircraft engines over 450hp and
there are no aircraft turbines under 400hp.

There's lots of ground turbines under 400hp so we know there's a market
there; i.e. they must be practical and competive with pistons or they
wouldn't sell.


A lot of them are used to power natural gas compressors way out in the
middle of nowhere and reliability is much more important than fuel
efficiency and you have a large suitable fuel supply availible.

So put it this way, if it were the turbine makers instead of the diesel
makers that jumped on this bandwagon, what would be their smallest
engine?

Given the high initial cost of turbines and the hgiher fuel comsumption, I
doubt that turbines would be competitive with gasoline engines given current
price differentials between the two fuels. The beauty of a diesel aircraft
engine is that it should cost the same as a gas engine, has fewer parts,
uses less fuel and lasts longer. The turbine engine is more reliable but
costs more and uses more fuel. The lower the hp the less competitive the
turbine gets against the diesel.

Mike
MU-2