On Jul 26, 9:05*am, nurflugel wrote:
On Jul 25, 8:54*pm, Tim Taylor wrote:

I still think a reversed NACA duct will work better than the Butler
and much better than the Mandl. *The Mandl throws the low speed air
out into the faster air stream. *The JS design accelerates half the
air over the airfoil but what happens to the air under the airfoil?

The NACA duct was designed such that the edges create vortices
which force the air into the duct. Reversing the flow through a NACA
duct is an inefficient way to exit fluid from a body.

Actually a "modified" NACA duct with an extended top cover that also
adjusts the angle of the exit stream and only allows about the last
third of the length to be open will accelerate the air back to proper
speed to match the outside air and place it gently into the air-
stream. It will have a smaller opening than the butler design and not
put the air out at about a 45 degree angle like the Mandl. It would
be very easy to modify the standard inlet design to be a very low drag
air exit. The NACA duct is designed to allow laminar flow of the air
through the duct and it will work both directions to accelerate as an
exit as well as decelerate when used as an inlet.