On Sun, 10 Aug 2003 23:45:26 +0000, B2431 wrote:
Folks - When I bought my Tcraft, all that existed of the static port
was a length of rubber tubing running parallel to the ram air port
(which was there). Do I need to terminate that piece of hose in a static
port of a precision size? - Mike
The only requirements for a static port is the hole(s) be flush to the
aircraft such that there is no air forced in or sucked out by the local
airflow in flight. You don't want the hole too small or you will get lag
when changing altitude. You may not ever notice the lag, but it's there.
You don't want it too big or critters my think you built them a home.
The static ports on big aircraft such as C-130s have a salt shaker
appearance and have half a dozen or so holes around .032". Helicopters
like the H-1 and H-60 don't have static ports. They leave the static
holes on the ASI, VVI and altimiter open to cockpit pressure.
Aircraft Spruce sells a single hole port.
You want a smooth surface within a few inches of the port.
That's as complicated as they get
Good luck with your project.
Dan, U. S. Air Force, retired
The location of the static port(s) is also very important. Ideally they
would be located such that they would be subjected to the ambient
pressure. I.e. the pressure that is present a long ways away from the
aircraft. But the pressure changes as the air goes around the aircraft.
So it is pretty much impossible to find a single location where the
pressure at the aircraft's skin is the same as the ambient pressure for
all airspeeds.
So the designer has to find a compromise location for the static port that
works as good as possible over the aircraft's flight envelope. The errors
in the pressure sensed at the static ports (position error) drive the vast
majority of the airspeed error that you will note in the POH, and of
course the static source error causes altimeter error too. This can be
significant - the Canadian S-2s that I used to fly had about 80 ft of
altimeter error in the landing configuration at the recommended approach
speed. This is a big deal when you are shooting an ILS down to 200 ft
AGL, using the barometric altimeter to define the decision height.
--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/