I'm really glad that you are flying and getting such
good numbers Al. I can't wait to get my 20B in the air. By the way that
Spal fan IS one of the good ones. Do you remember what you paid for it? You may
have a chaotic enough exit on your plane (exhausting through the prop) that the
turbulence and any restriction is moot? It seems to me that the typical tractor
exit will be harder to blend with the airstream, but I may be incorrect in
that thought.
Bill;
The price of the fan was on that link I sent
– I think it was $118 from Jaycore. And I mistakenly said it had 4
blades – it has 5.
You raise an interesting point about the
drag effect of the air exit. It is a different story having the exit into the
prop. Normally when we dump the air out of the back of a rad into the cowl we’ve
pretty much lost it’s energy and it hard to get it back in any efficient
way when putting it back into the air stream. If you exit into the prop you
give the prop some lower energy air to accelerate, so maybe it improves prop
efficiency? Or maybe not.
One of the interesting things I learned
in the recent air flow measurements came unplanned. In the second run we had
left open a couple of manometer connections inside the cowl. I was surprised
to see that they were reading about 5 ½” at 150 KIAS. So that is
pressure left over after passing through the in-cowl radiator that is
accelerating the air out the ports at the back; where there is already negative
pressure created by the prop. That could help reduce the cooling drag.
Al