Paul, this would have no use in a tractor but in a pusher it might do some
good..
Put a can on the prop hub coming back a bit into the cowl, put impeller fins
on it. Some ducting around the impeller takes care of the flow.
Why not resort to an active air system and create a bigger pressure
differential?
...Chrissi

Also I might add any simple mechanically driven blower system is
indiscriminate
in its use of HP. It uses too much HP at high speed where you don't
need the cooling. Cowl flaps on the other hand taylor the air flow
to the cooling requirements of the engine as a function of speed.

I cannot emphasize that enough. If you are not using cowl flaps
you are burning too much fuel at any given cruise speed.

Paul Lamar

The biggest problem with pushers is cooling while taxiing or waiting for
clearance on the ground. We don't have the big fan up front to force air
under the cowling. If the plane is not moving, the flaps  positioned below
the center line on the boat tail will do very little to move air out of the
cowling. I still think we need some active hot air extraction system, on
demand or constant (ex. augmentation)
Bulent

I don't agree. I think the flaps down there will work well to extract
the air at takeoff and climb. At idle the engine is not generating a lot of HP so
a lot of cooling is not needed. If you need more cooling at idle use electric fans. 
At least you can turn them off. 
 
Paul Lamar
 
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