air speed needle movement

[dan carley]

in my rv4, the asi needle bounces also a little movement in my altimeter. i've only had the rv a little while. i just replaced the asi and it still doing it. does any one know where to look? must be in one of the lines. would it be pito or a static problem

thank you
dan carley

[Mike H]

Sounds like a small slug of water in the static system. Remove the pitot and static lines from ALL instruments and blow them out from the cockpit side using low pressure dry air or nitrogen.

[dan carley]

i also have a angle of attack system and it has a static port on the top of the left wing. could that be causing a problem?

dan carley

[Mike H]

Not unless you tapped into the static system to run the AOA. The AOA system should have its own plumbing for the AOA sense port.

[dan carley]

i gave that a shot today. it didn't clear the problem. if i keep it about 150 mph it seems to go away

danny

[Marc Bourget]

Dan,

Curious, did you use the standard diameter tubing for A/S and Static?

If you used a larger diameter, it may appear more sensitive as there's less flow damping.

FWIW

mjb

[dan carley]

no it's standard tubing

danny

[Mike H]

Maybe turbulence at static port orifice due to damaged port or chipped paint/irregular surface up stream of port. Do have dual static ports? Have you tried slipping the airplane to see if it changes. Maybe a static leak inside of the airplane that is being affected by the positive pressure from the air vents? Time to carefully inspect the entire static system.

[dan carley]

i think i found the problem. (not) i have 2 static ports in rear of fuse, they are large rivets. one of the lines came off there for neither port was connected. i rehooked them up and tried it again. still same problem. when at 175 mph it shakes at 2500 rpm but at 2000 rpm 150 mph it's smooth. i'm thinking a vibration from the prop?? i do have one of those little pitto tube covers that open like a butterfly when your moving. could that be causing turbulence by the pitto tube?

dan carley

[Mike H]

I have never been a fan of those weather vane/flapper valve type covers, but I doubt it would cause an issue if it is installed and working properly. Do you feel vibration in the airframe when the ASI needle is bouncing?