Brantel
Well Known Member
Well I have to respectfully disagree with you.... You can have a higher than actual static pressure because I have this error in flight. Also, you can change the pressure quite easily by doing very insignificant changes to your static ports and their surroundings. The way I know this is because I have been doing a ton of testing in real life and in flight trying different things to reduce the error.
The other thing is that in cabin static pressure is lower than the true static pressure. The airstream over the fuse causes a negative pressure inside the aircraft. Alternate static sources in the cabin almost always cause your readings to go up not down and the only way to do that is to reduce the static pressure.
I have tested the pitot line from 30 to 230 knots using a manometer. No leaks. Minimal error.
I have tested the static lines by pluging one port and applying vacuum with a manometer to the outside of the other port. I have applied up to 35" w/c of vacuum for over 5 minutes and there are no leaks and the altimeter reads correctly at ~2500ft with 35".
Two other builders have tripple checked my work. There is definately something wrong as I have a huge error that I cannot get rid of. Finding it is the problem.
The other thing is that in cabin static pressure is lower than the true static pressure. The airstream over the fuse causes a negative pressure inside the aircraft. Alternate static sources in the cabin almost always cause your readings to go up not down and the only way to do that is to reduce the static pressure.
I have tested the pitot line from 30 to 230 knots using a manometer. No leaks. Minimal error.
I have tested the static lines by pluging one port and applying vacuum with a manometer to the outside of the other port. I have applied up to 35" w/c of vacuum for over 5 minutes and there are no leaks and the altimeter reads correctly at ~2500ft with 35".
Two other builders have tripple checked my work. There is definately something wrong as I have a huge error that I cannot get rid of. Finding it is the problem.
It is not easy to get an over pressure static by disturbing to flow over the port - the usual result would be a low static reading. I almost typed never, but thought better of it. Just think about it, the static ports are a little proud of the surface, so the air is accelerated slightly as it passes over them, so the pressure reduces - you would need some kind of dam behind the port to raise the pressure.
I think the most likely culprit is a leaky static in the cockpit, as cockpit static is usually higher than ambient. I know you have stated that the manometer testing ruled that out - but are you really sure (sorry haven't read all the posts)? If you pressuise the pitot it doesn't matter if there is a cockpit static leak - its all at the same pressure. Have you have an altimeter test guy put one of those fancy vacuum suckers on the static ports? Last time I had it done it was $90. Can you borrow a huff & puff ASI & Alt, hook them up and compare with the Dynon?
Failing that, have someone who has had nothing to do with your project come and do a pitot static check, and compare results. Perhaps there's something wrong, and because you have looked at it so often you're just not seeing it?
Pete
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