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Steve,
At 06:49 AM 10/21/2004 -0400, you wrote:
Bill,
Actually, where the scoops are located, they are outside of the fuselage,
and the only thing in front of them are the wing strakes.
It was hard to tell in the photos, but are they 3 or 4 inches away from the fuselage?
I didn't measure
from the strake leading edge to the scoop inlet, but I would estimate that
it is between 3 to 4 feet. I guess that would mean that there is a boundary
layer of about .6 to .8 inches present at that location.
If the boundary layer air becomes an issue, I will either put a small air
dam ahead of the scoop, or as I did with the NACA, install a vortex
generator ahead of the scoop.
The problem is the difference in pressure/velocity between the boundary layer and the free air stream. The free air stream turns around in the scoop and air comes OUT in the portion of the scoop next to the wing. It's just like making a big slot in the back of the scoop, but results in much more drag.
A scoop like the one on the bottom of the P-51 is what you want to have.
An air dam will not be as effective as spacing the upper lip of the inlet away from the bottom of the wing.
I thought that I might have a photo that shows the scoop in relation to the
wing, but looking at the ones that I took, none really show it very well.
Regards,
Steve
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On
Behalf Of Bill Dube
Sent: Wednesday, October 20, 2004 8:19 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Cooling version 2.2
At 05:55 PM 10/20/2004 -0400, you wrote:
>Attached are a couple of photos of my lower cowling. It is minus 2 small
>armpit scoops, and plus 2 larger scoops.
I notice that these scoops include the boundary layer with the air
they scoop in. Isn't this a problem, especially near the fuselage?
The boundary layer grows at something like a 0.2 inch per foot of
length. This rule of thumb would imply that you would need to space the
side of the scoop about 3 to 4 inches from the fuselage. The upper lip
should be something like 1.5 inches off the underside of the wing.
If you don't space the scoop away from the surface of the
airplane, you create a lot of drag and you don't take in much air.
Perhaps there is some key point I'm missing.
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