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 talked to a guy at OSH and he differs with that conclusion.
In fact he added arm pit scoops. Here are some pictures.
The scoops you refer to there are also not of what we speak; I
have
no
idea about that configuration. The stock cooling scoops now
used, and are flying on a number of Velocitys (air cooled IO360s
and
IO
540s) are NACA scoops which begin in the top of the fuselage ahead
of
the cowling, with the entrance at the cowling cut line. No
augmenters
involved. The only photo I could find is attached. If you went
by
the
Velocity booth I imagine you saw them on their airplane, or if you
check
the parts list of what is included in the kit you will find "2
NACA
inlet scoops for engine cooling"
Al
So what? It is not a liquid cooled engine!!!! If Velocity wants to
violate the
application rules of NACA ducts that is up to them. I would just
like
to help people design a rotary engine liquid cooling system that
works.
Way too often people find that the cooling system they designed for
the rotary engine does not work well under all conditions. Tom
Parkes
is the most recent victim.
Paul Lamar
Paul;
Our goal is the same. I have no interest in just making
controversy.
Velocity made the change from armpit scoops under the strakes to the
NACA scoops on top of the fuselage because they worked better.
There
are other cases of EZ's that found what I might call a quasi--NACA
scoop
on top worked better than the prior armpit scoops. Analysis of the
pressure distribution on a fuselage typical of the canards show
relatively high pressure; about the same as on the bottom, when you
get
that far back on the fuselage. And because the pressure is
increasing,
the boundary layer is being squeezed out, flowing at an angle down
the
sides of the fuselage.
So; in the case under discussion, the SQ, it is reasonable to
believe
the external scoops on top, which are already there, would work,
and
may work better than armpit scoops. Maybe not better than a P-51
style
scoop underneath, that we don't know.
My personal opinion is that the reason the Velocity armpit scoops
didn't
work as well was because of a poorly designed scoop, not because of
the
placement. I chose to put a p-51 style scoop under the strake
(armpit).
I don't know yet whether it will work well.
Al
I find it really hard to believe that the pressure is increasing
on the top of the Velocity cabin. In fact I am willing to bet lots
of money it is not. If one does not have experience measuring
pressures
it is easy to make a mistake. I would like to see pictures of just how
the pressure was measured up there. Did they use porous foam for
example?
It would be real easy to use an air velocity rake to determine the
thickness
of the boundary layer and porous foam static pressure taps if someone
has
a flying Cozy or Velocity.<
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
Nope. But contrary to what one might expect, I would put one right
behind the canopy; or at the back of the fuselage just in front of the
tail feathers.
Al