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