Peter Nunn wrote:
I know someone has done it but is there any info / experiences on an
under-wing P51 style cooler?
I am thinking this is going to be the best solution to my problems as my
cowling is getting too full for comfort and I am stripping the aircraft at
present and can run some 1 1/4" pipes through the airframe easily. Does
anyone have one flying?
Regards
Lots of stuff on this in Hoerner. None of it very good.
The graphic is for a high speed airplane (ME109) so a thick rad
could be used as the dynamic pressure is proportional
the square of speed.
What kind of airplane do you have again Peter? Do you have room in the
aft fuselage?
Paul Lamar
Peter Nunn wrote:
The aircraft is a low wing 2 seat experimental. There is lots of room in
the aft section but I cannot just open the back due to a lower longeron
along the aft fuselage bottom.
The drawing is what I was thinking of. Roughly a scoop under the wing
center that is outside the boundary layer and a 600mm wide by 150mm high
dual core radiator like you were proposing, and a diffuser behind with an
automatic cowl flap (operated by the water inlet temperature).
What is the reference book this is from. I have printed the articles about
radiator position from the web site. Is there a definitive engineering text
that you can recommend on the size and performance of cores. I have located
several racing shops that can make the cores for me (at a price 8^) but I
need yet to design the core dimensions. I have figured that I will need to
disipate about 115kw at about a 60 knot climb, but there seems to be more
art than science to the rest.
regards
The bible on heat exchangers is "Compact Heat Exchangers" by Kays and London
available directly from the publisher Krieger Publishing Co. Malabar Florida.
they have a web site as I recall. Replace the word "header" with "intake diffuser"
through out the book. That confused me for the longest time.
Your are right about it being more art than science but here is the science
that I know about so far.
600 mm is 24 inches by 150 mm which is 5.9 inches. Apparently from all the
data we have you will need somewhere around 600 to 900 cubic inches of
rad to cool the Mazda. So with a rad only 5.9 inches high you are looking
at about 5 to 7 inches thick. At 70 MPH the dynamic pressure is 0.088 psi.
Not much. Assume your near perfect diffuser is 80% efficient that translates
to only 0.07 psi air pressure across your rad. Not enough to get the air
to flow much through a 5 to 7 inch thick rad. We had a guy try this with
a 5 inch thick rad and it did not work. He gave up. You might want to think
about what Brian Traube is doing with a thinner oblique rad mounting.
I would look at the structure in the aft fuselage and redesign it to
feed the longeron loads around the intake opening or use two round hoses 4 or 5
inches in diameter to feed a large area thin rad mounted in the aft fuselage.
You could use a P51 style duct or a NACA duct which would be lower drag as
it adds nothing to the overall frontal area of the aircraft. The air outlets
with flaps can be under the stab as that is normally a very low pressure area.
It may affect your pitch trim when the flaps are open or closed.
115KW is 154 HP Peter. What do you have in there a turbo three rotor? :-)
Paul
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