This group sounds knowledgeable on an engineering level, so I'll ask
here:
Are there equations to model/predict what air speeds a prop will
produce? I'd like to determine how much air flow will result from a 3
bladed warp drive prop through the 3 cowling openings, and at several
speeds including sitting still. The purpose is to find out if my
cooling capacity is large enough. AIUI, the exit openings also come
into play due to 1) major restriction in flow if the total exit area is
smaller than total inlet areas, and 2) when an 8 square inch inlet, with
wind entering at 100 mph, is opened via ducting to flow across the
radiator that the speed at the radiator drops to about 50-55 mph.
The air speed through the radiator is a function of the pressure across
the core and the air resistance of the core. Unfortunately we don't have
that flow data for any thin rad cores. We recently found some flow data for
3.5 inch thick oil coolers as a function of the pressure drop across
the core and I uploaded the web site address for downloading that data
in .pdf file format. This data indicates a 3.5 inch core is too
thick for cooling around 100 MPH.
Also, I was wondering if it is beneficial to install another duct
downstream of the radiator, between it and the cowling exit area.
It won't hurt but the air velocity is so low up until it tries
to exit the cowl that a complete exit duct will show little advantage.
It is very very important to smooth the exit opening however.
I've heard some people say that an electric racing fan behind the
radiator is a good idea even at 200 mph, and others say it is a
dangerous thing to do. What is your opinion?
Some people have experience that says the fan will spin at high speed
and burn out its bearings. Others seem to get away with it.
So 26 sq in inlet area widening to the radiator which is about 12x22
1/2, then narrowing down to say, 10 sq in exit area. Assume moderate
effeciency in duct shapes.
You are using a Ford so I cannot say if 26 square inches is too small.
For a rotary our experience would suggest that is way too small. Your
exit area should have a flap on it and be twice the inlet area when the flap
is wide open. At 100 MPH the dynamic pressure you have available to force air
through the rad is one quarter of what it is at 200 MPH so a large flap
is highly recommended to suck air through the core at 100 MPH. You
will be climbing out at around 100 MPH and max HP so you will need
max cooling at 100 MPH.
2 upper cowling inlets are 26 sq in each, and a bottom scoop (still in
prop wash) is about 10 sq in. My current idea is to use in of the top
inlets to feed baffling around the engine and exhaust pipes, the other
for the radiator, and the bottom scoop for the turbo intercooler.
Alternatively, maybe place the intercooler in front of (or behind?) the
radiator and channel the bottom scoop across the bottom of the engine,
or add it to the radiator inlet.
What do you guys think?
Thanks,
AI Nut
Still working on using that Ford 1.9L engine in a Mustang II.
An auto piston engine like that is a super light duty engine
(maybe 30 HP continuous). You are asking it to put out at least
150 HP all of the time. I thought it was a 4.1 liter V6.
You got a screaming hand grenade there :-)>
Good luck.
Paul Lamar
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