Russell Kent wrote:
The angle also appears to make the top of the radiator face somewhat
further from the cowl cheek opening face than the bottom of the
radiator (but not as pronounced as the left-right difference).
But since the lower positions (2-5 & 3-6) have more pressure
differential than the upper positions (4-7 & 1-8), I'm perplexed. The
prop appears to sweep bottom-to-top on the right side of the cowl
(where the radiator measurements were taken), therefore I
would expect the relative airflow to favor the upper positions
over the lower positions, causing the pressure differences on
the upper positions to be greater than the lower positions.
Are we certain of the manometer setup?
Alex,
Thanks for the additional overhead photo, along with the side shot and
the backside shot.
I think the pressure data indicates that you have an air leak at the
top, at the radiator & upper-cowl seal. Check this area carefully, as
air leaks can defeat even the best designed duct systems.
Also, you need a larger heat shield around those exhaust pipes. I see
that you have one on the close exhaust pipe, but it needs to be larger
(in area) and the further exhaust pipe also needs a heat shield.
I doubt that it's possible to make this change at this point... But if
the radiator were turned such that the face was closer to parallel to
the side of the aircraft, then a wedge diffuser (Kays & London) should
be possible, with the airflow drawn from the outside of the cowl cheek
opening, passing through the radiator towards the engine. The backside
photo shows what appears to be a cowl rib that would be problematic,
however.
Russell Kent
I think you are right Russell. Here is a good picture of the leak. We
have decided to build a new, better sealed, stand alone diffuser. More
on that later.
Paul Lamar
AUGMENTOR TUBE: It seems something I've flown a long time ago had a
lightweight SS tube around the exhaust pipe where it protruded from the
bottom of the cowling. The tube forms an annulus through which the
relatively high velocity exhaust gasses are expelled. The exhaust pipe
is substantially short of the end of the augmentor tube. The exiting
exhaust gases drag air out of the cowling, thus augmenting airflow
through that volume. The cowling should fit fairly well around the
augmentor tube. It could also serve to prevent heat radiation into the
engine enclosure. Rough sketch attached.
Do any of you guys employ this technique to enhance airflow through the
cowling? What are the pros and cons as you see them?
Jim Beckman
Austin
Yep. We covered that stuff in http://www.rotaryeng.net/cooling.html
Nice drawing Jim. Thanks.
Paul Lamar
Here is the fix for the leaks around the rad due to the top
part of the cowl being incorrectly used as part of the diffuser.
It will be sealed all the way around with RTV.
Also improves the shape and size of the air scoop.
Eventually it will be blended in with the rest of the
cowl.
Paul Lamar
Hi Paul,
That guy works fast! I was thinking that extending the snout forward
would allow more room for diffusion. I'm glad that idea is being tried.
Please let us know how it works.
Did you go to Reno this year? It was fun looking at the various airplanes
to see how the cooling systems were layed out. I thought Dave Hoover's
(Mike Arnold's?) Endeavor looked very elegant.. I like how the air
inlets are part of the lower cowling.
http://www.webpak.net/~mprather/Reno/2005/IMG_1565.JPG
At home, I have a pic of the engine with the cowl pulled. Very sanitary.
And notice how tiny the inlets are. That engine is probably making 150hp,
and by initial reports it runs too cool. The right kind of problem.
And now that I look around a bit, I see that Mike has posted more AR-6
pics on his web site..
http://ar-5.com/gallery/AR-6
If we want good performance we have to look at and understand what the
racers are doing.
Regards,
Matt-
That guy is me. I spent all morning trimming and fitting the diffuser to to
the rad and clearanceing the old intake:) I carved the foam, Alex sanded
the foam and taped it up with duct tape to act as a parting agent
and Dan Grey's (turboprop powered Legends) employee laid up the epoxy
fiberglass. We got a lot of talent here at SZP.
Paul Lamar
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