I don't think you should find it hard to believe, and I'd hate to take
your hard earned money. It is not just true of the Velocity, take just
about any fuselage you like. Take a ride on an air molecule. Along
comes an airplane and you and all your neighbors get rapidly pushed
upward out of the way, and your momentum carries you a little way
(resulting low pressure) but you stop moving somewhere about the end of
the front cowling, and the pressure has increased a bit again. Then you
all get pushed again by the windshield, and there is low pressure again
along the top back of the windshield. But then you're not pushed
anymore and because of the low pressure, you start heading back down and
the pressure above the surface starts to increase. By the time you get
toward the rear of the fuselage let's say the cowl cut line on a pusher,
you've gotten back to about equilibrium, and, although you may still be
moving downward as the surface may be dropping away, the pressure around
you is about the same as was in the air before the plane got there.
Nice colored pressure distributions have been published in some of the
flying magazines for different fuselages, or you can find them in Ilan
Kroo's Applied Aerodynamics CD. The lowest pressure is always just
behind the highest part of the fuselage, and increases toward the rear.
One objective in design is to have the pressure at the top and bottom be
about the same at the trailing edge - least drag. Same is true for a
good airfoil design. The pressure top and bottom just at the trailing
edge of the wing is about equal at cruise.
Sometimes we need to change our frame of reference.
Al
Unless some one steps forward with a CFD or takes some measurements we
will never know will we? Here is a CFD on a P51. Would you put a NACA
duct on the top of the canopy just behind the peak?
Paul Lamar
Here's the quote from Al in an earlier post which seems to have been
misread.
Al Gietzen wrote:
It has been shown on the canards (certainly on the Velocity) that there
is good pressure recovery on the fuselage as you get back to about the
cowling cut line. Even NACA scoops at that location are effective, so I
would guess that those scoops on your Speed Queen would work well.
Velocitys are cooling IO540s with two NACA scoops at the top of the
going in at the cowling cut.
Al
I think that the 1st word of the 2nd sentence was overlooked in
subsequent postings. My interpretation (Al, please correct me if I'm
wrong) is that he was saying the pressure is high enough on the top at
that point that *even* with the wrong inlet it still works to cool the
engine.
It seems that this thread has wandered from inlet *location* to inlet
*type*.
I ain't no rocket scientist; I'm not even an internet newsletter editor.
But I'm pretty sure that the dark green/black shown where the canopy
meets the tail cone in the P-51 illustration isn't caused by a shadow on
the subject. In fact it looks suspiciously similar to what's at the base
of the windscreen.
Now, here are a few real world empirical observations to consider.
1. Stock Thorp T-18 homebuilts have the cabin air inlet placed at the
base of the back side of the canopy. I can tell you from personal
experience that the wind from this inlet will part your hair in the back
and almost blow a cap off your head.
2. Sliding canopies on T-18's, Nagle-canopied Globe Swift's, etc cannot
be forced open more than a few inches in normal flight attitudes & speeds.
3. Pushy Galore, an O-200 powered pusher used by Bruce Bohannon to set
many time to climb (can you say 'high angle of attack?') records before
he switched to a different class with the 'Flying Tiger', had cooling
inlets on the *top* of the wing/fuselage intersection similar to the SQ
2000 that started this thread.
It seems pretty obvious that there really is some high pressure
available on the 'back side' of a fuselage to work with.
Charlie England
In front of a vertical tail yes. With a pressure recovery fuslage
maybe.
Paul Lamar
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