My aircraft is fitted with a heated Piper blade pitot+static probe
under the left wing. The pressure at the port decreases with airspeed,
causing an altitude error that varies with speed. As others have
noted, this is worth fixing. Most of us have had no problem with the
standard static port locations below and behind the aft window, but then
I don't know anyone who has actually tested their system to see if it
is accurate. Even the CAFE tests did not calibrate the static system,
but rather the pitot-static difference.

Bob,

 

I didn't like my answer when I saw my reply in the LML echo in that it didn't respond your actual question.  This reply won't answer it well either, but I do have experience with trying to make a heated Piper blade work.  It doesn't.  I then tried using an enormous L-shaped heated pitot/static  (it had static ports on the top and bottom of the foot long pitot.  It didn't work either.  I currently utilize a standard sized L-shaped heated pitot and have located the static ports on both fuselage sides at the Lancair recommended position.  The pitot tubes have always been mounted on the aileron bell crank access door to avoid any possible influence from the prop.

 

My indicated true airspeed is within one knot of GPS derived airspeeds over a broad speed range and the altitude reasonably matches certificated aircraft flown on my wing at different altitudes.  It is good to know that I am flying with the same altitude indications as the spam can fleet that fills the skies around my airport.

 

Another way to test altimeter readings might be to fly horizontally parallel to the tops of known tall towers close to barometric pressure reporting stations to see if speed has any effect on static pressures (even if the speed is inaccurately reported because of static problems).  One more method could be to fly an ILS glide slope and note the altitude crossing the FA fix (as accurately reported by a GPS) with the needle centered to see if it matches the published altitude.

 

Of course, one must remember that even certified instrumentation has quite an error allowance and use of the static/transponder test data, recorded in the aircraft log, can provide useful correction data.