In article ,
"The Enlightenment" writes:
Those sorts of performances I think were achievable with piston
engines.

The Luft46 web site lists a few German pusher prop aircraft that were
projected as replacements for then current Lufwaffe aircraft.
Achieving as much as 584 mph on an ordinary 1750HP Jumo 213 V12 piston
engine seems to have been accepted.

Quite frankly, that's bat****.
cue the every 3 months lecture on the Speed/Power relationship for
the thrust of propeller driven airplanes.
To cut to the chase - a constnt power output engine, like a recip, or
the propeller side of a turboprop, produces less thrust the faster you
go. Assuming 85% propeller efficiency across the board, your 1750 HP
Jumo is producing 2790# of thrust at 200 mph, 1490# of thrust at 375
mph, and at 584 mph, 955# of thrust. (It's actually a lot worse than
that - the efficiency of the prop goes way down beyond about 450-500
mph at Sea Level.

This scimitar prop aircraft is one of the fastest at 584mph.
http://www.luft46.com/dornier/dop252.html

Even assuming that there are _no_ transonic effects on the airframe
(Which there will be), and two engines, the Equivalent Profile Area of
the drawing below is 3.55 sq ft. (That's Drag Coefficient * Reference
Area).
A P-51 works out to a profile area of about 4.66 ft.
This Dornier cattywampus is more that twice the size of a P-51.
The claims are rediculouss on the face of it. The SS Scientific Branch
might believe such horse****, but real life physics wins every time.


(And the Scientific Branch certainly _did_ believe such horse****.
They sent a specialist in Infrared Photography to Spitzbergen to
photograph the British Home Fleet at Scapa Floe through the Hole into
the Hollow Earth.)

The advantage would be fuel efficiency and the lack of refractory
alloys needed for the engine. The cost of making high octane fuel is
exorbitant compared to make Jet fuel.

I recall seeing GE tested scimitar shaped pusher prop engines, I think
it was on a 727.

And it wasn't operating at 85% efficency at that Mach Number, either.
The thrust numbers I posted above are best case.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster