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
Peter Nunn wrote:
Thank you for the dissertation. I am looking at it and can fit a pair of
thin radiators vertically inside the tailcone with NACA ducts just behind
the wing trailing edge. You can check my web site at
http://www.users.bigpond.com/peter.nunn for some early drawings of my
project. It mostly covers the first prototype that was an ultralight but
the basic fuselage is similar. The first one used an RV6 canopy and EA82,
the one I am working on is heavier with a T-18 canopy on top. The tailcone
is empty and I think I can fit a NACA duct to carry the ir inside an
internal duct then out the back where you suggest. Do you have any idea of
the area that would be needed as a ratio of the inlet/outlet as some of the
data I have seen is 2:1 but a more scientific formula based on the
inlet/outlet velocities must exist. Excuse me if it is in the textbook you
talk of but it will take a while to find a copy.
The 115kw is based on the heat budget you sent me a copy of. As I had
indicated I want to try using oil/water and air/water intercooling. The
engine is a 13B with a Turbonormalizer. My estimations may be a bit
generous but I figure a margin of safety is worth it.
I would be guessing. Make the outlets as large as possible. You can
always adjust them with the flaps. You should always close the flaps
on final to insure you have plenty of elevator authority for flare.
Paul Lamar
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