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Hi Jeff,
You may be right; in fact, you're probably right.
But...
Keeping radiant energy away from the heat exchanger was really a
minor factor in my thought process. A data point: Every really
fast (on reasonable HP) plane I've looked at (both liquid &
air cooled) has used some form of exit duct to channel the heated
air back into the free stream. The stuff in the pic is the
beginnings of an exit duct for the oil cooler. It will be far from
an optimum shape because of space limitations; maybe so far from
optimum that I'll cut it away shortly after 1st engine start. But
I'm going to take a shot at it to see what happens. 'Education
& Entertainment', is why we get to do this, right?
I do have at least a layman's concept of why it might be a good
idea to use an exit duct. Everyone struggles with pressure
differential between front & back of heat exchangers. Everyone
pays attention to the inlet side to keep the air flowing smoothly
& to expand the area of the inlet so it slows down & gains
pressure. So what happens on the exit side of the core? It expands
again, into a massive area, where it slows down again, gaining
more pressure but now with totally chaotic flow. This begs the
question: What happens to the desired pressure differential across
the core?
If there's an Aero guy who can tell me that the *idea* of exit
ducts is bad, I'm willing to be educated, and to save some time,
money & trouble. But the empirical evidence of their goodness
is compelling, even with the torturous paths I've seen in Lyc
installations.
So I'd like to give exit ducts a shot. It's easier to do the ducts
now than after everything is built (I'll never go back once it's
finished), & if it doesn't work, 10 minutes on a band saw
& it will all be gone. :-)
Charlie
On 05/27/2013 07:18 AM, Jeff Whaley wrote:
Charlie, I used strips of 1/8” rubber the
same way Ed described.
I had to rotate your photo 90 degrees to
see the whole picture … it looks like you’re trying to
heat-shield your intake with a plate behind the cooler; I
think you’ll be more disappointed with the cooler’s
performance than you will the intake’s performance if you
leave that shield in place. Tightly diffuse the inlet side –
leave the outlet side open – my 2 cents worth.
Jeff
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I've started design/fabrication/redesign
of my oil cooler mount/diffuser. Just as I had a
'final' answer on the mount & was contemplating
the diffuser, it occurred to me that I didn't have
any shock mount provisions for the heat exchanger.
For those who have been flying for a while, have any
of you hard mounted the cooler to its support
structure? As the photo shows, the primary mount is
direct to the reduction drive plate. I would simply
add the shock mounts, but if I use this particular
cooler (a CX Racing 30 row unit like the one on
Tracy's 20B), I won't have any room. I do have the
option of buying a 25 row or using the 19 row I
already have on hand, but I'd rather have a bit too
much capacity & throttle the exit air than start
with too little & have to rebuild everything.
Thanks,
Charlie
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