I think your
conclusion about the missing ram air at the intake is the major reason why
the oil cooling did not improve at higher air speed. A second point may
be the air outlet. It looks like a turbulence could form where the back
scoop protrudes from the wing surface. This turbulence could produce
vorticies over the edge at the outlet, reducing the effective area of
the outlet. A more continous transition from the wing surface to the scoop
surface would reduce the possibility of this to happen.
Thanks, Richard
and all for comments and suggestions. Originally I had a more simple
up-sloping fairing (I guess that’s what you mean by “more continuous
transition”?). After some study and consulting with an aeronautical
engineer, the conclusion was that it would cause too much turbulence
behind. The current airfoil shape was the recommended approach in
order to keep the flow attached, have minimum turbulence behind, and least
amount of drag. So what’s right?
I think those
suggesting more of a ram inlet scoop, and those suggesting a less shrouded
exit fairing are both correct. The net change needed is more pressure
differential between inlet and outlet, and either change will likely
accomplish that, and either change will result in more
drag.
As I see it now;
the inlet was designed on the basis of a more negative pressure at the
outlet, alleviating the need for a ram scoop. The outlet was designed
based on an assumption of an inlet air flow equivalent to a ram scoop, so
the end result was a combination that is not effective. The exit
fairing is designed to speed up the exit flow so it will merge at something
closer to free stream velocity (reduce drag), and simply to protect the core
from things being dropped in. With too little inlet pressure to
produce the flow there will likely be very turbulent flow aft of the
fairing, increasing the pressure in that area. More flow should help
alleviate that issue – agree? Cutting back the fairing (moving forward as in
the Rutan case) increases the negative pressure but brings the air out at
much less than free stream velocity (more drag).
So, which is
better for cooling and drag - scoop or unshrouded exit?
An extended scoop
is an easier thing to try. Of course, I may still be missing the
target entirely.
Also, regarding
boundary layer and scoop, keep in mind that this inlet is in the wing aft of
the strake, so there is only about an average 4-5’ of buildup, and then only
in the case of gear up. For a very wide narrow scoop as this, there is
no effective way of diverting the B.L.; so the best bet is to mix it (VGs),
and ingest it.
Meanwhile, I have
another problem to deal with - a fuel leak(s) through the inner skin of the
foam core strake into the foam. Bummer!
Al