Thanks for contributing to the fray...

I wasn't really talking about cruise so much as I was talking about
climb-out: high engine output, low vehicle speed, high AOA. Arm test-
If you can feel pulsing 5 feet back from the prop, then you know that
there is air of varying velocities washing over your arm. And since
you also know that the distubance decays very quickly at first and
then more gradually as time (and airplane) goes by, the disturbance is
much higher a one foot behind the propeller. I'm sure its not total
chaos, and it isn't laminar either, something between the two.
Question is, does the amount of turbulence produced, boost the heat
transfer capability of that air enough for a surface radiator on the
front/under surface of the cowl to work for a 100-200HP engine?

And yes, the first step is to make sure that you've got reliable
cooling. Okay, check, you've done that. Now what can be done to
eliminate one of the largest sources of drag? If this actually
worked, it would be a huge incentive for more water cooled (AKA auto
conversion) power plants in aircraft.



"RJ Cook" wrote in message ...
Excellent answer A, in cruise flight, there is little difference between a
propeller's slipstream and freestream velocity.

Today's props are very efficient (near 90% max) and create little
turbulence, with the exception of the tip's vortex . I have opened the
window on a c-150 and put my arm out to feel the propwash, and other than a
slight pulsing the only substantial disturbance is where my hand penetrates
the prop's tip vortex ring. Try it some time. This is not to say the flow
across a fuselage behind a prop is laminar, I'm nearly certain it isn't as
laminar boundary layers needs very little disturbance to become turbulent,
but total chaos does not exist within the slipstream behind a prop.

The stagnation point can also be defined as the point on the leading edge of
a surface/component that the velocity normal (perpendicular) to the skin is
0.

The Meredith effect, and ramjets in general, create stream flow by
maintaining a negative pressure gradient (high to low pressure) streamwise
within the duct/engine. This gradient is created by area differentials,
fixed or variable, between the inlet and exhaust. The inlet area is smaller
than the exhaust area, and thrust is a product of the duct's massflow times
the inlet's and exhaust's differential velocities. In the case of a cooling
system, if the internal aero losses are to high, due to friction across
radiators, etc., then the net thrust may be negative.

RJ