The International Cessna^® 170 Association

I like turnips too. That's why I have a whole truck full of them.

I have a home made pitot tester consisting of a one pint surge chamber, a water tube manometer, and a squeeze bulb pump from a blood pressure test set. I can pump up the pitot system to any air speed for testing accuracy. My air speed meter does not leak down when locked off at any airspeed.

TX for all the info on this very, seems like, subjective subject. I am going back to have the A/S checked again. It was checked and found OK once. The "doughnut" fix is still working just fine. Before that fix I still feel that the static port was receiving some ram pressure...how?...I have no idea. Why the "doughnut" fix worked...maybe because it changed the airflow over the static port. I don't know. The beat goes on. I have no way to prove that my airspeeds are correct...just experience. However, the V/S and altimeter are operating normally under the present setup. More to follow.

JT

Tested the A/S indicator for leaks....none. Gonna try pulling the static line off the encoder in cruise and check for any changes in the A/S, VSI and Altimeter. Running out of things to try.

JT

Be certain to have the pitot/static system leak-checked AFTER all the instruments are re-installed. (like for an IFR certification)

If you have a venturi near the static port, it will cause bad readings. Also I have flown several aircraft that are checked and IFR certified. (CAP) I noticed once when I had to use the alt static valve, that the airspeed and everything settled back to normal once the thing was on a few minutes. I tried this in several of the other aircraft after that. Pull the alt air. Watch the airspeed go up for a minute or so then it would come back to where it was with the static port. Then close the alt air and the airspeed would settle down to what it was with the alt air on. I don't claim to understand all this, but it seems to me that these aircraft don't go fast enough or high enough to make that much difference with the static air. JMO

The venturis are on the right side of the aircraft and the staic port on the left. I do not have an alt static system or sw so can't do that but can do the next best thing, altho a bit archaic, and that is just pull the static source off the encoder. On a previous aircraft I did have the alt static source and sw and it did just what yours did when I would check it.
If the "doughnut" system works as well as the "alt" static system I believe I'll just stick with the "doughnut.....'til I'm questioned about by our federal friends. Who knows, maybe a new STC is in the making... "Thanks.

JT