Howard wrote:

Didn't we just do this Paul??

......  working with 80% prop efficiency 375 mph becomes 300 mph where one
horse creates 1 lb thrust ......   or one hp makes .8 lbs thrust at 375 mph.
Do we rate jet engines in actual thrust and internal combustion engines in
horsepower?   Perhaps we should rate jet engines 25% higher in horsepower
than the thrust calculation if we are to compare between jet thrust
horsepower and internal combustion BHP.
    This is like comparing BHP to Net HP....... we need a conversion factor.

                             H.W.

Yes. I guess so. Never the two shall meet. Thrust from a jet is constant
with speed and thrust from a prop is not.

That big hole in the front of a jet engine gets more and more air the faster
and faster it goes. The ram jet is the logical conclusion. You can remove
the mechanical guts and just pump in a bunch of fuel. 

I also think that is why a ducted fan is more suited to very high
speeds while a prop is not. It will be very very interesting indeed when a high 
HP rotary is successfully mated to a ducted fan. It might take a gear box to do
it well.

The HP numbers give us just an intuitive feel for what an airplane will do over the
speed range. It is based on years of experience. Most prop pilots understand it
when you say airplane x has y HP. They subconsciously adjust for the fact that
the thrust drops off with speed.

Constant thrust, on the other hand, is much more quantitative and easier to work with
IMHO.
HP increases with speed.

Trust in thrust :-)

Paul Lamar
 
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