The drawings are really nice, particularly the transparent one. The
first one really communicates the shape.
I can see why the scoop on a pedestal is attractive for space reasons.
I still have to wonder about the drag. I can live with the looks.
Looks are important but not as important as efficient function. I
have seen pictures with a rectangular opening(s) with ramps on the top
of the cowl that I assume to be for induction air. What are the
considerations? Is there enough room for a female scoop, if I can call
it that. Is a female scoop less draggy than a male one?
The lower cowling looks rather bulbous. It that why James uses the
shark mouth? Which would be less drag?
Drag goes up with the 3rd power of speed. I am no speed demon, but
less drag means less fuel burned for a given speed. Ahh, that Scottish
blood again! And on a long trip faster is better.
Doc Custer
Retired software engineer and sometime Audiologist
Building RV9-A. Fuselage
The rectangular opening with ramp is probably pretty close to
this Me109-P38 type scoop in recovered dynamic pressure.
I was serious about negative drag at low speeds. The reason
this happens is there is a negative pressure drop on the face
of the scoop that pulls the aircraft along. There is no
free lunch of course so this cost the engine a slight amount
of HP sucking the air in. At higher speeds the dynamic pressure on
the scoop over comes the need for air by the engine so a positive
pressure will develop on the face of the scoop. This is more HP
and slight drag increase of course. Never the less the net result
is thought to be positive by the Me109 and P38 aerodynamic engineers
and our man Dave Leonard. However a ramp is easier to build
and less in your face :)
Unfortunately we need that bulbous shape to accommodate modern,
high efficiency, large frontal area, thin heat exchangers.
This is all explained in Kays and London's book Compact Heat
exchangers. The book was written after 30 years and 20 million
dollars of US Navy money at Stanford University.
Also read this.
http://www.rotaryeng.net/how-to-cool12.html
Hang on to your hats. I think I have a breakthrough in cowl shapes.
The next cowl iteration will accommodate and unprecedented volume
of modern thin heat exchanger. 700 cubic inches
of rad core and 250 cubic inches of oil cooler core. It is
a little Hurricane and a little P40-P38 in appearance.
IMHO experimenting with 3D program is the only practical way to find
the optimum cowl shape for the liquid cooled rotary engine.
Paul Lamar ...No rotor no motor.
Doc, slight correction on drag vs speed. Drag increases by the square
of the velocity, not cube. Double your speed and the drag goes up by a
factor of four, not eight. I guess this means that going fast is not as
bad as you thought!
Dave Detty
I think what Doc was thinking of is top speed is proportional
to HP cubed. Drag is indeed proportional to speed squared.
Paul Lamar ...No rotor no motor.
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