"Peter Stickney" wrote in message
...
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.

You make one oversight though it is perhaps mine:

1 There are actualy 2 Jumo 213Js on this aircraft driving coaxial
contra-roting props so this automatically doubles the thrust.
2 I believe the Jumo specification is incorrect. Takeoff power is
1750 but with MW50 water methanol injection to allow overboost it is
someting like 2250hp. Likewise at high altitudes a Nitrous Oxide "Ha
Ha" system can bring power up to about 2150 hp because of the extra
oxgen in the NO and its anti-knock properties. Both systems were
fitted to the TA152

(for some reason I can get onto google but certainly the TA152H Jumo
213 could produce 2250hp I don't know if it was a J though)

Thus without boost an equivalent thrust of 900kg - 2000lbs is
available and that would presumably be maintained to quite a high
altitude where the atmoshere is at least half of sea level density and
probably less. With boost more like 2500lbs.

Incidently Anthony Kays book lists the following thrusts of the Jumo
004B1 jet as used in a Me262.

900kg sea level static
730kg seal level 559 mph (a test chamber result I suspect, German
test chambers were excellent and so good they were used by the allies)
320kg at 10000m




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

It DOES have swept wings and 584mph is not at the high end of
transonic. The AVA at Goetingen (German Equavalent to NACA) did a lot
of supersonic research in the mid 30s.

(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.

A pusher aircraft has less drag becuase there is no high velocity
airflow over the airframe that is turbulent to boot. This on its own
suggests higher speed.


(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.)

Sounds like the one where a Jewish doctor cut of Hitlers testicals
that was circulated in the war.


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.

85% for a scimitar shapped contra-rotating prop is good but I think
achievable.


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