My ASH-25 was emitting a very loud squeal as I went through the finish
gate at
redline (above 500 feet of course). I removed the rudder and found no way
for
vent air to get out, so I drilled a 1" X 2" hole in the tail wheel fender.
Worked fine and the cockpit ventilation got a bunch better. As you know,
the
exit hole should be 1.5 times the entry hole size.

On my nimbus 3, I enlarged the hole in the vertical fin spar and also
polished
out the rudder cable exit guides with a sanding roll on a rod, driven by a
drill motor. Unfortunately, some major sailplane manufacturers don't do
much,
if anything, about providing an efficient airflow exit system and if we
don't
let it out in the tail area, the vent air will go looking for a way out in
other places, like the wings, landing gear doors and canopy seal.

JJ Sinclair