> Paul,
 >
 > Let me add my two cents to the cooling exit discussion.
 >
 > While there may be a theoretically optimal inlet/exit ratio for drag,
 > wouldn't it be more important not to put more cooling air through the
 > cowling than is needed? I assume that liquid-cooled engine have
 > thermostats, and so the engine getting too cold is not a problem. But
 > the inlet has to be sized for the most adverse hot-day climb condition,
 > and so it will be able to admit far more air than is needed for, say,
 > economy cruise at altitude on a cool day. If you determine the outlet
 > area by some rule of thumb, say 80% of the inlet area, then you will be
 > on the thermostat and will be pumping air through the cowling for
nothing.
 >
 > There is a sort of mania these days for small inlets, but I think you
 > would agree that there is no harm in a large inlet, provided that it has
 > a well-formed lip. Pressure recovery occurs before the inlet, and
 > un-needed air flows smoothly around it. That's why radial-engined planes
 > still go fast. Opening and closing the outlet moves the stagnation line
 > on the inlet lip, and in the case of maximum spillage it actually yields
 > some duct thrust, just like on your inflatable shrouds.
 >
 > My plane has about 60 sq. in. of inlet area (200-hp engine), and the
 > outlet area can be adjusted from 98 to 18 square inches. I normally
 > cruise with the cowl flaps fully closed.
 >
 > Peter Garrison
 >
 > http://www.melmoth2.com/texts/NACA%20inlet%20sizing.htm
 >
 > I agree Peter. In fact I suggest a thermostat NOT be installed and the
 > engine temperature controlled with cowl flap alone. I too cruise the
 > C182 with the cowl flaps fully closed. Of course there is a lot of
leakage
 > around the crude C182 cowl :)
 >
 >
 > Paul Lamar

Paul/ Peter,

I believe the largest exit opening suggest so far has been 140% of the Inlet
opening. I was wondering what surface area you have on your Rad Peter, how
thick the Rad is and how far is the cowl flaps closed during take off - if
closed al all. I am not looking for exact numbers just something to compare
to the 'rules of thumb' we have to date.
TIA.
George ( down under)

Peter's piston engine is air cooled.

Paul Lamar

It is worth noting to the group Paul, the rare updraft cooling which Peter
used. Peter used CFD to determine the outlet of the cooling air on the top
of the nose.  It is a very interesting system. It is also worth noting that
despite all the CFD work Peter still ended up with a variable cowl flap to
make it all work in the climb phase. Please understand this isn't a knock on
Peters' work, far from it, but rather a FYI to every one that even with the
best tools tweaking will usually be needed to get everything working as it
should. If you have some problems with your water-cooling system keep after
it and you will probably succeed.
Bill Jepson


Peter,

Can you give me a rule of thumb of what "a well formed lip" on an intake
that you mentioned would look like?

Sandy McNabb
Renesis in a Glass Goose.