OK, I know this is off subject, but it IS on a rotary-powered RV-6.

 

My static system pressure is off to the tune of 100 feet at cruise speeds. 

 

Every airspeed indicator I tried (2) read 10 mph too high when calibrated using GPS triangulation.  One day I glanced at my altimeter while making a cruise speed pass down our home runway (close to the surface) and noticed that it read 100 ft higher than at rest.  My calculations show that would also account for the +10 mph on the ASI.

 

I have the standard hollow pop rivets at the standard Van's locations.  Can't imagine that the small rise on this rivet would drop the pressure that much!  I have asked other RVs to also do this test, and they come in anywhere from 50 to 80 ft. high.  I tried pulling the static line to let the instruments use cockpit pressure (which I already knew was lower than static) and the altimeter read 850 ft!

 

With all the brainpower available on this list, surely someone can suggest a method of attacking this problem.  I could just continue subtracting 10 from my indicated, but that is the easy way out.  I was going to drill out the rivets and use a hole in the flat skin, but I just can't bring myself to mess up a great paint job. (Yet)

 

Ideas?

 

Bill Eslick

N268BL