I have wondered if there would be any advantage to using a set of those expanding bellows things they have on a VW.

They use them to control the amount of air passing over the fins on the cylinders.

 

I read somewhere that a builder had incorporated them in his cowl to vent the area after landing. Once things cool off they contract and close the vent.

I’m not sure whether or not it would fit this type of application.

 

T Mann

 

 

 

 

Great concept Ed.  Perhaps a spring load biased to open position to ensure that the flap opens sooner as speed is reduced.

Bryan

Passive, and no electricity required!