OK folks for all you people that want to use a NACA duct this MIGHT work.
I call it the NACA trigger. The small electric fan sucks enough air
out of the boundary layer to trigger the flow into the NACA duct.
Sort of a fluidic amplifier. You can turn it off at cruise instead
of using cowl flaps. If it works it could have a large advantage
over the P51 scoop in lower overall aerodynamic  drag because
of the reduction in overall aircraft frontal area and skin friction.
The air from the fan could be routed back to the rad.

What about using NACA ducts with exhaust augmentation.  I hadn't considered
NACA ducts until this latest exchange on cooling.  Could the vacuum
pressures created by the augmenter act as the fluidic amplifier to trigger
airflow into the duct?

Del Johnson

Absolutely and I just uploaded some picture of a Velocity so equipped.
You could also use both for a belt and suspenders approach.

I understand completely the desire to use NACA ducts. Potentially
they can drastically reduce the drag. My priority however is
sufficient cooling and most of what has has been said before has been
oriented to that end. This NACA trigger fan could be the key to getting
us over the NACA hump but it needs to be tested. 

BTW Too bad NASA does not get involved with
this stuff. We need a lot of help but all they do is waste millions
on paper studies of 3900 pound gross weight turkeys powered
by derated Chevy LS1 V8 ducted fan airplanes guaranteed
not to get off the ground in less than 8000 feet nor get
more than 10 MPG.

Paul Lamar
 
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