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Steve, here is an article which mentions the problem at
http://history.nasa.gov/SP-4302/ch1.12.htm
here is part of what the article states
...The rumble appeared in the wind-tunnel tests and its source was found to
be the belly scoop on the undersurface of the wing. More specifically, it
was soon learned, the rumble came from disturbances in the inlet airflow
when gobs of de-energized air from the boundary layer surged over the inner
lip of the scoop and into the air duct. Over the long expanse of wing and
fuselage lying ahead of the scoop, a considerable thickness of boundary
layer would build up and the thickness was all the greater as a result of
the blocking, effect of the scoop. North American engineers had considered
the boundary layer in the design of the scoop and had lowered the scoop
below the surface of the wing a little way to allow the boundary layer to
pass harmlessly by. But for reasons of maintaining cleanness of line, they
did not want the scoop to project downward any farther than necessary. In
fact, they had made it wide and shallow-thus, unfortunately, providing every
opportunity for the ingestion of boundary layer.
A number of minor modifications of the scoop were tried with little effect.
The ever-present Smitty DeFrance, who seldom failed to advance his own
recommendations, spoke forth on this occasion in no uncertain terms: "Lower
the damn thing!!" This measure was pretty obvious, of course, but Manley and
his boys were searching for a somewhat more refined method of accomplishing
the same end. Nevertheless the lowering idea was tried and it, together with
certain other modifications, was found to be a nearly perfect cure. North
American people were delighted. An easily applied cure had been found, and
that in a matter of only a few weeks. But above the pleasure of finding a
solution to the P-51 problem, both NACA and North American had learned a
valuable lesson. It concerned the importance of keeping boundary layer out
of air scoops. And a thoughtful observer might have taken time to reflect
that the boundary layer, so little appreciated by the layman, so infinitely
important to the aerodynamicist, had again got in its licks. Certainly this
was not the last we would hear from it.
There was another article (which I am currently unable to find) that
addressed the effects on cooling in more detail, but basically the
turbulent boundary layer ingestion caused flow separation from the diffuser
walls, eddies in the flow and blocking of flow through the cooling core
thereby reducing cooling effectivesness (as well as causing the rubmble
mentioned in the above article)
You may be able to find more on the internet
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From: "Steve Brooks" <steve@tsisp.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, June 30, 2004 7:52 AM
Subject: [FlyRotary] Re: Temps finally down
> Ed,
> I would like to have more information on the reason for keeping the
boundary
> layer air out. My current scoop is open, and lets in both. If the
boundary
> layer air needs to be excluded, then my next scoop will have to be like
the
> P51 scoop which does exclude it. I never really understood why.
>
> Looks like I may have to have another look at Bulents' scoop. His is made
> like the P51.
>
> Steve
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> Behalf Of Ed Anderson
> Sent: Tuesday, June 29, 2004 7:56 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Temps finally down
>
> Sounds like you are closing on the solution, Steve, congratulations. Its
> always nice when you get to the point where you can fly without one eye on
> the temps.
>
> The boundary layer (particularly with coolers to the rear of an airframe)
> appears to play a big role. The layer increases in depth as you go
rearward
> and it creates havoc with the operation of cooling ducts and diffusers.
One
> article I read indicated the American P-51 and German fighter designers
> figured out the significance of keeping the boundary layer out of the
> cooling ducts whereas the British supposedly continued to be plagued with
> cooling problems with the Spitfires due to their cooling inlets being
partly
> in the boundary layer. FWIW
>
> Keep us apprised
>
> Ed
>
> Ed Anderson
> RV-6A N494BW Rotary Powered
> Matthews, NC
> ----- Original Message -----
> From: "Steve Brooks" <steve@tsisp.com>
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Sent: Tuesday, June 29, 2004 6:37 PM
> Subject: [FlyRotary] Temps finally down
>
>
> > I made my eight flight today, and I'm happy to report that my inlet
scoop
> > augmentation on the Cozy did the trick.
> > I flew only about 1/2 hour because I had some other work that I wanted
to
> do
> > on it, but the temperatures ran at 190 coolant, and 200 oil.
> > I climbed up a couple thousand feet, and instead of throttling back and
> > watching my temperatures come back down from 210/220, I wasn't quite up
to
> a
> > stabilized temperature yet. That was a big change. I pulled power back
> to
> > what I had been running previously, and the temperatures stayed the
same,
> > maybe dropped a little. I then throttled up to zero boost, and the
> > temperatures held. YEAH !!!!! They used to climb up with the throttle.
> > On the decent to landing, I thought that I would have to chip the ice
off
> of
> > the engine. Coolant dropped almost off the gauge to about 140, and oil
> down
> > to 160. Actually when I touched down, they were even lower than that.
> >
> > Now that I know that I can cool it, I'm going to make another scoop,
> > narrower on the sides, but a little taller (actually lower) to get a
> little
> > further outside the boundary layer. The next scoop will have a smaller
> > inlet area compared to the current one.
> >
> > Steve Brooks
> > Cozy MKIV N75CZ
> > Turbo Rotary
> >
> >
> >
> >
> > >> Homepage: http://www.flyrotary.com/
> > >> Archive: http://lancaironline.net/lists/flyrotary/List.html
> >
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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