On Dec 7, 12:47*pm, Don Johnstone wrote:
Do you blokes suffer from major flatulence problems? Seems a lot of effort
to remove air from the cockpit but I could understand if the air was
contaminated in some way :-)

At issue is that ventilation air tends to pressurize the cockpit, and
then leak out around the canopy perimeter. Anywhere that there is air
escaping through the canopy frame gap, that leak will trip the
boundary layer and increase drag. If you can keep the cockpit at lower
than ambient pressure, you run a good chance of maintaining laminar
flow across the gap between the fuselage and the canopy, which can
result in several more square feet of laminar flow than you had
previously.

I happen to think that many original designers got it right; that the
most effective vent is back at the base of the rudder, where it is
convenient to exhaust air around the rudder cable horns.
Unfortunately, something often got lost in translation, and most
production gliders allow too little exhaust area through the vertical
fin spar, causing inadequate ventilation flow and too much cockpit
pressure. They also offer many restrictions on the path from the
cockpit to the tailboom, which reduces the flow rate.

So I think that these trendy exhaust vents, while perhaps not the best
possible solution, are still a lot better than you can get without
removing the rudder and doing some relatively major surgery on the fin
spar.

Thanks, Bob K.
http://www.hpaircraft.com