Hi,

 I know this is not rotary related but I know that this is the only place
 where I would get a professional answer to my questions.

 I?m in the stage of fitting the panel as well as the turtle deck. Seeing
 that it is a composite plane, it is quite airtight. I was thinking of
 placing two small NACA ducts in the cowling to provide fresh air in the
 cabin. However, I feel that this air must be expelled somewhere. Should
 I place two same size ducts on both sides of the vertical stabilizer, in
 the turtle deck? Another question. During flight, if I just close the
 vent inside the cockpit, would it cause a lot of drag? Last question.
 Does anybody have drawings for a NACA duct?

 Regards,

 Pierre Swanepoel

 South Africa

 Any outlet will work. Just a hole in the tail will work if the cockpuit
 is indeed higher pressure than out side air.

 However it is near impossible to seal a cockpit entirely.
 Usually you will find the cockpit air at a lower pressure than
 the outside air because of the bulge in the cross sectional area
 of the fuse. so just about any cockpit air inlet works that faces
 forward.

 Here is the NACA duct proportions.

 Paul Lamar

Pierre,

   Not sure what type of aircraft you, but the Diamond Katana has an
adequate in flight ventilation system and is composite in construction.
Midway up the fuselage, just atf of the engine cowling there are two small
(maybe 3" tall) NACA ducts, one on each side. These are ducted to ball vents
in the lower panel just above the crews outboard knees. The a/c has a bubble
canopy with a built in 4"X6" sliding window, on each side. The baggage
compartment is behind the seats and on top of the fuel tank. The fuselage is
narrowing at this point (picture a winged sperm) and there is one vent
opening there. All openinings have coarse fly screens in them.
   The only time the aircraft is inadequatly cooled is during ground
operations on hot, sunny days. This is due to the rear hinged canopy and the
lack of canopy catches that could secure the canopy with an inch gap. If one
is very careful you can hold the canopy just cracked open an inch and then
it is very cool and pleasant. Just don't apply too much power or you will be
short one canopy and one arm.

John



Thanks guys

Pierre