I know a certain record setting RV-4 builder/racer that found speed by sealing up the elevator pushrod at the aft fuselage bulkhead. It seems that cabin vent air was working to the back of the fuselage and exhausting at the rudder and elevator hinge line - creating measurable airframe drag (about 2 knots IIRC). Got me to thinking about the extreme drag sensitivity the sailplane mafia has. The cabin air entry on a sailplane is generally right on the stagnation point on the nose - a low drag and high performing spot - but what comes in must also go out. What do the competition sailplane guys use for the exhaust? I assume this has been studied and perfected in that camp.