Doc, What do you think of this scoop shape?
Makes the cowl easier to make and provides
a bit more room under the engine for the radiators.
--
Paul Lamar ...No rotor no motor.
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.
Here it is! The best I have come so far up with in seven years.
I am real excited about the new cowl.
--
Paul Lamar ...No rotor no motor.
OK, the Me109-P38 scoop it if I can make it, or it doesn't cost too
much. Since I have seen pictures of them in use I assume they are
available for purchase?
I have been adding up the prices of components. I am becoming
concerned that the 13B installation will ultimately cost more than an
O320 installation.
Yes, I have read your web article on cooling the wankel. Very nicely
done. Very persuasive. I understand the principles I think. I did a
search on Amazon for a copy of the book, but no joy.
I agree with your statement "experimenting with 3D program is the only
practical way to find the optimum cowl shape for the liquid cooled
rotary engine." My grandson is enrolled in Colorado State University -
Pueblo. I was going to have him get Rhino at the student rate, but his
ID card has no date (year) on it. And CSU-Pueblo doesn't use Rhino
(AutoCAD) and he is not an engineering student, so a transcript
probably won't work. So I am still working on it at a low priority.
Maybe it should be a higher priority. Would it expedite things if I
had a copy? I understand that it has a pretty steep learning curve,
although not as bad as some. I could enroll as an engineering student
in January, but that doesn't seem very timely. In any event I will
have my grandson contact Rhino to see what they will accept given the
circumstances. Maybe he could get a letter from CSU-P on their
letterhead. I would really like to eventually be able to model things
as you do.
Yes, I can see why you are excited about the cowl. Big improvement.
Very nice. I can also see why the tuned muffler will not fit. Rhino3d
sure does a nice job.
Doc Custer
Retired software engineer and sometime Audiologist
Building RV9-A. Fuselage
They are not too picky. A letter would work I suspect.
It is not the cost of the boat. It is the upkeep :)
Paul Lamar ...No rotor no motor.
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
Copyright 1998-2006 All world wide rights reserved.