Not sure I follow you about exit larger than = inlet being=20 gospel. IF you mean subject to translation errors and the cumulative=20 alterations of many scribes I might see your point. Everybody going = fast has=20 smaller exits than inlets.

As I stated that is because the inlet must be = sized for=20 WOT climb where you are moving a lot of air. At that point the outlet = must be=20 larger as well like 150% to draw the air through and allow for = expansion. OR=20 you must use an exhaust augmenter-take your pick.

As the speed increases and the power level = drops in=20 cruise you need to close the outlet down (unless you want a large drag = penalty). Ideally you should close the inlet down as well. Since it = really=20 doesn't matter much on a Tractor (because of external diffusion and an = ugly=20 front end aerodynamically anyway) and variable inlets are more = complicated it=20 does not typically make sense to fool with closing the inlet=20 down.

So ideally you should have an inlet sized to = cool the=20 thing in climb, followed by an exit that is variable from around = 150%-70% or=20 so depending on how you plane to operate the aircraft.

You want the minimum air flowing through the = cooling=20 system at any cruise operating point to create the least drag. Unless = you are=20 in full power climb, and then you just want to cool the = thing.

A single size for your outlet is a point = design and will=20 create excess drag or inadequate cooling at other operating points.=20

Monty

To many replies already, all mixed up, mission = acomplished! :)

I don't know wether the mentioned airplanes = had=20 cowl-flaps, and if yes, wether they are big enough to accomodate = 150-70%, but=20 they do use exhaust augmentation, but I don't think it figures that = big - it=20 seems it is more aerodynamic streamlining within the cooling ducts, = using the=20 proper pressure differentials/building the ducts in a way that they = take=20 advatage of the existing differential pressures around the=20 cowling/airframe.

Basically it looks like a real thorough = clean-up=20 according to Hoerner, K&M and K&W.

In the Kitplane article it is mentioned that = the Mustang=20 II does use the exhaust to augment, but it does sound like "just to = milk the=20 last bit out of it".

If you are able to eliminate around 30% of = total drag=20 just by cleaning up the cooling act - hell, I will be doing everything = possible to make it slick!

When I get to the point I will try to = interview both=20 guys in detail - if no one else gets to them first:)

Thomas J.

PS: Another study in smooth cooling is Cory = Birds=20 "Symmetry" - Scaled Composites.....