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Rob, et al,



Static port position error is determined by testing a proposed site against a

site yielding true pressure.  Lacking any test equipment with true static

pressure available, such as CAFE uses, we try other techniques.  As you

pointed out, airspeed is only useful to determine that there is error in the

pitot/static system, not where it lies.  Flying formation with a buddy in a

certified plane helps check the static data (within FAA required sloppiness).

 It turns out that the Piper-style blade had position error for both ram and

static readings, but the readings were steady.  The giant chrome pitot/static

had static ports in the top and bottom of the tube.  It was very sensitive to

attitude and must have been operating in a slightly turbulent area beneath

the wing, leading to a very twitchy altimeter needle.  Those static ports

were definitely in the wrong place.  Lancair's recommended location,

utilizing both sides of the airplane, yielded no static "position" error.  

Then the pitot location was determined to be accurate at the speeds tested by

comparing true airspeed against the average GPS groundspeed resulting from

flying the legs of a triangle (120 deg turns, constant altitude).



Ask me what time it is and I will tell you how an hourglass works.



Scott Krueger

N92EX

  

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