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Hi, Bill...thank you very much for taking the time to go into such detail
regarding the cowling pressurization/ram air scoop scenario. I hadn't
thought of putting a piece of aluminum under the ram air scoop with a 3 inch
tubing plumbed directly to the throttlebody. The only drawback there is that due
to the location of the ram air scoop, the hose would have to be a very tight "S"
configuration and more difficult to hook up the hose because it is on the top
cowling, which is the last cowling to be installed. By using this NACA duct on
the bottom cowling, I can install the bottom cowling, attach the hose, then
simply install the top cowling without any hoses to try to align or secure,
etc. It will definately be easier installing/removing cowlings with the
lower NACA scoop versus the ram air scoop on the top cowling. It's funny
that you mentioned that there might be some airspeed where no air would enter
the cowling through the radiator. It seemed that as the plane picked up speed
(at the same throttle setting), my temps were rising. Must be my imagination, I
thought. Maybe not. Temps did, however come back down as I
turned base and final, but I'm sure that was because I was at idle and therefore
producing less heat through horsepower. Oh, well....another lesson
learned. Fortunately it was only fiberglassing labor lost....no damage or
injuries. (except maybe to my ego). Because my cooling was so great prior to the
addition of the ram air scoop, I'm fairly confident that the removal of the
scoop and bringing in air directly to the throttlebody will give me the cool air
intake I need without inhibiting my cooling airflow. Take care, and thanks
again for your valued input. Paul Conner, waiting on NACA duct from UPS.
----- Original Message -----
Sent: Tuesday, April 12, 2005 12:15
AM
Subject: [FlyRotary] Re: SQ2000 flying
again
Thanks, Tracy....I should be able to find out in a few
days. Today I removed the ram air scoop and fabricated an intake plenum for
the 3 inch scat tubing. As soon as the NACA duct with the 3 inch outlet
arrives, I will install it and be ready for testing. Today I measured the
length of the scat tube that I will need....14 inches. Thanks again
for sharing your experiences. Paul Conner
Paul,
It is interesting that as you have noted your problem, there was on
the other list comment made about exactly the same phenomenon you are
experiencing. You have found the relationship between the effectiveness of the
cowl outlet, and inlets. The rules of thumb that have been discussed on the
list recently apply to pushers as well. You have some advantages, extraction
assisted by the prop usually, and some disadvantages, often turbulent air near
inlets often making flow paths difficult to predict. Ask Perry Mick to remind
us of the oil cooler troubles he had.
The real problem Paul is that when used without a sealed tube to
the throttle body your ram air scoop pressurizes the cowl. The fact that you
are seeing higher temps isn't so much a supprize, rather
it's expected. The better your "ram air" scoop works the worse your
problem. The pressure increase does help the engine make more power. That
heats up your coolant and the increase in pressure inside the cowl makes it
harder to get air through the radiator, making the engine run hotter. There is
probably a point if you could reach a high enough speed that the pressure
could prevent ANY air from going through the radiator! The fixes are to
re-plumb the scoop as you are doing, or to enlarge the exit area to prevent
pressure build up. Since enlarging the exit may be impractical, you should fix
the problem by replumbing as you are doing. It is a shame that you can't
keep the other scoop easily. The type of problems you are having would seem to
indicate that it is working well! I've been away for a while and couldn't
comment, but my suggestion would have been to put a sheet of aluminum under
the scoop with a 3" exit tube near the rear plumbed directly into the TB.
You would probably see a HP increase at cruise. The NACA duct will
probably solve the problem but you will lose some of the ram effect you
could recover with the other scoop. Should be less drag though. Hang in there
Paul.
Bill Jepson
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