Jerry Hey wrote:
Before I spend a lot of money or do something really stupid, I
thought I let you guys shoot holes in my scheme. The basic problem
is installing the 13-B in a Tailwind. This all came to me while I was
sleeping, I guess, because I awoke with a start and knew all the
details. The prerequisite was months of worrying and pondering the
13-B cooling system, trying to get adequate separation from the
exhaust, fitting the entire package under a tight cowl, studying the
postings on this list.
What I am now planning to do is to place a HUGE radiator in the
fuselage behind the baggage compartment. The oil cooler (either
built in or stock RX-7) will go in the same area. By huge I mean a
radiator with around 1000 cu in of core. There is room for outside
dimensions of 28" X 20" to any thickness) Why such a big radiator?
Well, why not. The only penalty is a slightly greater weight of the
additional coolant.
Air will be supplied by NACA inlets on the side of the fuselage to an
intake plenum.
Big problem there Jerry. The sides of the fuselage aft of the wing
are neutral to low pressure. You need P-51 type scoops there. If
you put the NACA duct on the bottom you will pick up some higher pressure air
on takeoff and climb. Run the exhaust out to the side and down if
you wish to avoid ingesting exhaust gases into the rad air intake.
Exhaust will be though either an louvered aluminum
plate on the belly aft of the radiator or a hinged cowl flap in the
same location.
The louvers may not work for the same reason above. It may be a high
pressure area. The cowl flap will work of course but it is better to put
two of them under the stab where there is a low pressure area for sure.
I don't have a pressure map for a high wing airplane but here is one for
a P-51. Red is low pressure. Yellow is neutral and green is high pressure.
On a high wing airplane there is high pressure under the wing on
the fuselage sides.
The advantages are an extremely easy installation, with the radiator
vertical and perpendicular to the air stream. The radiator is away
from exhaust heat and vibration.
Plumbing will be via aluminum tubing to the fire wall and flex line
from the firewall to the engine.
C.G. is of no concern what so ever. I'll bet I have your attention
now. Here is the trick. I have designed a bed mount for the 13-B
which has a rail (7/8" x 0.49) running now each side of the engine
just below and outboard the pan flange. This ultimately will be
bolted the the engine using vibration dampeners made out of hydraulic
hose (copied from Jess Meyers). I am getting a digital camera soon
and will post pictures. Anyway, the important point is that the
engine can be moved forward or back on the rails until perfect C.G.
is obtained. Only then will the mounting brackets welded in place.
and the engine mount finished.
What do you think? Jerry
IMHO that much rad is totally unnecessary.
The motor mount sounds trick.
Have you no cowling? Making a custom cowling is not my idea of fun.
As Tracy said in his last news letter you'll probably ignore me.
If you do I will completely understand :-)
Paul Lamar
Thanks, Paul, for your quick response. I have no problem with
placing the exhausts under the stab. Excellent suggestion. Also, I
have no problem with cowl flap intakes on the sides.
Do you mean P-51 style intakes?
I don't think
they would have to stick out very much when wide open and would be
flush when closed.. Could it be combined with the NACA
inlets.....hmmm.
OK yes you could try a movable lip on the NACA intakes on the sides
of the fuselage. Might work but the boundary layer is quite thick
back there. IMHO the P51 style would work better to get the intakes
out into clean air.
The radiator is probably gross over kill. It can
be down sized, of course. Any idea what the capacity of the RX7
radiator is?
Might work with a perfect duct. Worth a try. With your set up it would
be easy to go bigger later.
I was so happy that the size was no longer constrained.
Still am. As far as making a custom cowl being fun. I think all of
this is fun. Why else would we be doing it? The most important thing
about making a custom cowl (I have never done it, I admit) is to make
it out of aluminum. The stock Tailwind cowl which I can buy is
gorgeous, by the way. And with the radiator in the fuselage, fitting
it would be no problem.
I have a friend who finished his beautiful, show quality, One
Design last month and has just flown off the first five hours. Last
night, he was looking at plans for a Celerity and he said he just
might cannibalize the One Design for engine, instruments, etc...He
wants to have some more "fun". Jerry
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