Byron Brandon Ward wrote:

Paul wrote: 
Yes that would seem like a subtle factor. My guess is the *hotter*
lower density air in the duct would tend to be at the top of the
duct somewhat impeding the overall mass flow. My guess it is not
a strong effect but I could be wrong. Would be great for heat soak
after you land however.

BTW if you can arrange the duct in such a way so that the controls
go through a tunnel close to the rad the air velocity will be lower
and hence so too will be the adverse effect of the control tunnel
on drag. I guess we need a sketch on that

All right here's two more questions then. My first question has to do with
your high wing setup. Just to confuse the issue a little more, don't you
have to worry about the effect of dumping all that air right under the
horizontal stab. (i.e. doesn't it increase the pressure in that area).
Maybe the added drag due to the effects of this exit on the horizontal
stab overcome the benefits of putting it there. I would guess that putting
the exit a little ways away from the stab would be a better idea...the
stab will influence the air (lower the pressure) at least a chord length
below it and probably in front of it too. A static port would quickly tell
you how far away you could put the exit.

Look at the diagram for the P51 I just uploaded. The low pressure
area drops off rather rapidly as you get away from the stab.

The amount of air going out there is no more than is coming in
the intakes. If you take 20% of the core area which is 17 by 13
from Neils example a 6.6 by 6.6 opening will have enough air.
If you divided that by two one for each side of the fuselage
you have roughly a five by five inch intake area.

You might notice it as a slight trim change. The cooling might be 
somewhat self regulating as I suspect slightly more down force is
required from the tail while climbing hence a lower pressure.

My second question is, if it could be fabricated, would it be an advantage
to first pump the coolant around the duct (i.e. have a double-walled duct)
before running it through the rad. Maybe just in the area where the duct
is actually hanging out in the airstream. Seems like you'd get more
cooling for nothing...then you could reduce the size of the duct and get
more speed for nothing :)

Byron

I don't think it would be worth the fabricating effort. Remember it has
to take 30 psi internally.

PL

 
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