IAS Issues at Stall- No static port (Airspeed wrong)

[Cardiff Kook]

OP again.

Interestingly this stall IAS came up again today.

I had some work done from cub and pulled out all the stuff from baggage. Took it out flying and it was stalling at 50 MPH indicated- used to stall at 43 MPH indicated. Hmmm.

Thought it was CG- loaded up the plane and moved CG back a few inches. Went flying, still stalling at 50 MPH IAS. That's odd (My GPS was dead so no ground speed.)

Thought about it for a minute and realized I always used to fly with my window open- mostly due to CO. Had the CO issue resolved and it is cold here so I had the window closed.

Opened the window and repeated the test- now I was stalling somewhere below 43 MPH on the AV30 (stops reading at 43.) It's a static port issue.

I would say a 7-10 MPH IAS difference between window open and window closed is alot.

 

[BC12D-4-85]

I had a similar issue for IAS in my PA-11. Varied with cockpit openings. I removed the LH wing fairing and ran a piece of plastic tubing inside the wing some, then attached the other end to the AS and Alt. Seemed better.

Gary

 

[dgapilot]

These airplanes were built with no static system and the ASI was never anticipated to be “accurate”. Open the window and indication changes, open the door and indication changes, turn on cabin heat and indication changes, slip either direction and indication changes. Not a big deal, learn to fly pitch, not airspeed.


Sent from my iPad using Tapatalk

 

[BC12D-4-85]

OP: Info from FAA Handbook of Aeronautical Knowledge, Ch.8

"Due to the venturi effect of the air flowing around the fuselage, the air pressure inside the flight deck is lower than the exterior pressure.

When the alternate static source pressure is used (from inside the cockpit), the following instrument indications are observed:
1. The altimeter indicates a slightly higher altitude than actual.
2. The ASI indicates an airspeed greater than the actual airspeed.
3. The VSI shows a momentary climb and then stabilizes if the altitude is held constant."

Gary

 

[arborite]

Did the technician checking the ASI confirm that there was no obstruction (water) in the pitot line?