[Doug Rohrer]

I bought a flying RV-9A with the full complement of Van's steam gages. The ASI, VSI and altimeter are, of course, connected to the pitotstatic system. These three gages have a small amount of needle bounce, about +/- one needle width, even in steady flight. Is this normal? If not, is there a way to put a snubber in the system to smooth out the fluctuations? Where should it go?

 

[airguy]

Sounds like laminar turbulence next to the skin rolling over the static ports. Do you have dual static ports Tee'd together?

 

[Dmadd]

Not to hijack the thread, but mine does that too. And yes, mine are two ports tee'ed together... Been looking for the leak forever... :-/

DM

 

[Doug Rohrer]

Yes, the static ports on the fuse are tied together.

As an aside, after I bought the plane, I found both the static ports were plugged with the partial mandrels still in the rivets. There was enough leakage that the instuments worked, but reacted very slowly. I drilled out the mandrels to open up the ports, and got instant relief, but now I have more fluctuation than I would like. Makes you wonder how this got past the FAA inspection...

I can't remember what drill size I used to drill out the mandrels. It was no bigger than the hole already in the rivet. Is it critical? Would this be part of the problem?

 

[Doug Rohrer]

A bump for the evening shift.

 

[DakotaHawk]

Try disrupting the airstream

Use some duct tape and create an airdam either in front of, or behind the static ports. Do the same on both sides. Test fly to see if it helped. Make a couple of different airdams to see if you can steady out the flow of air near the static port.

Just a suggestion - can't guarantee that it will work...