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Yeah I'll be keeping a sharp eye on the GPS. It might be detectable in a high speed taxi.

Best way to correlate the static reading is with a cone test.

lakespookie wrote:Best way to correlate the static reading is with a cone test.

what is a cone test?

I think he means a trailing static probe. That seems like overkill. We used to do something similar in flight test at Sikorsky for new aircraft designs. Why not just see how your static system works? Fly with somebody's Cessna and do altimeter checks. If your static system is off either try moving it or do like we did at Schweizer - tweak with fences in front of or behind the port.

Now that we have GPS, using a trailing cone to determine static system error seems a bit outdated. My Sonex has the homebrew pitot-static system as shown on the plans. Initially the airspeed indicator read about 10% high at cruise speeds due to the static pressure being too low. The cure, through trial and error, was to add a collar of varying dimensions behind the static ports on the static tube until just the right combination was found. Subsequently, the airspeed indicator reads correctly (IAS / CAS) within 1 or 2 mph from 90 mph to 190 mph. Can't do much better than that but I'd still like to move the static ports to the sides of the fuselage and get rid of the ugly static tube beneath the wing especially since there is also a pitot tube and AOA tube there as well.

Art,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

Bryan Cotton wrote:I think he means a trailing static probe. That seems like overkill. We used to do something similar in flight test at Sikorsky for new aircraft designs. Why not just see how your static system works? Fly with somebody's Cessna and do altimeter checks. If your static system is off either try moving it or do like we did at Schweizer - tweak with fences in front of or behind the port.

You are right it would be a bit overkill but it is effective and pretty much spot on in most cases.

I wish some of the plans provided a little more exact information but as long as I have access to all you guys, I'll be fine. Besides, the worst that can happen is moving them or using the fence approach. If I move them I get to plug the holes with disco lights!