Static Port Problem

[pwhaley6347]

I just began flying my RV7A after 10 years of building. I noticed that my ASI, Altimeter and VSI (all steam gauges) needles ?shake?. I figured it must be a static port problem. I have done a basic test by closing off one of the ports and applying suction to the other and then covering it with my finger. The ASI and Altimeter increase and remain in position for 5 minutes and return to where they began after releasing my finger. Any ideas for a solution would be greatly appreciated.

Paul

[Mike S]

Originally Posted by pwhaley6347

I just began flying my RV7A after 10 years of building.

Paul

Paul, cant help with the jumpy needles, but sure do want to send a big congrats for getting the bird into the air.

[gasman]

Did you use Van's parts for the static ports?

Are they in the location as on the plans?

block one port at a time first to see if there is a change.

If the answer is yes, yes, then try this...... splice a "T" into the static line and add a link of tube about 2" or so. Cut the small finger out of a surgical glove and tape it on to the tube with electrical tape really good leaving a bulb extending from the end....... go fly.
If this solves your problem, then you have pulsing at your static ports.

I don't know how long the glove material will last.

[GeneL]

Paul, My 7A has the same problem, when I leave the VSI open to cabin the pulsing is the same (in the VSI and other instruments)?? My system also is sealed and passed a static test. I have been working the problem for more than 2 years with no joy. Seems to me the glove method would only work if cabin has lower static pressure than outside, this seems to be the situation in most 7's, but variations in cabin venting/heat could change this. Hope we can find a solution to this. Gene

[Walt]

What brand of instruments do you have? I'm guessing they are the Falcon units.

[pwhaley6347]

Originally Posted by gasman

Did you use Van's parts for the static ports?

Are they in the location as on the plans?

block one port at a time first to see if there is a change.

If the answer is yes, yes, then try this...... splice a "T" into the static line and add a link of tube about 2" or so. Cut the small finger out of a surgical glove and tape it on to the tube with electrical tape really good leaving a bulb extending from the end....... go fly.
If this solves your problem, then you have pulsing at your static ports.

I don't know how long the glove material will last.

I did use Van's parts for static ports and installed per plans. The ASI, VSI and Altimeter were purchased from Vans. Interesting idea with the surgical glove. I'm assuming this will act as a buffer if there is pulsing at the ports.

[David Paule]

Would something like this, from Aircraft Spruce, solve this? It would go in series in the static line.



It's their part number 10-00630.

Dave

[gasman]

Originally Posted by David Paule

Would something like this, from Aircraft Spruce, solve this? It would go in series in the static line.



It's their part number 10-00630.

Dave

No, that's more of a moisture trap. You need something that will expand a bit.

[David Shelton]

I'm not an instrument expert, but it might be worth doing a little experiment. You could add a flask in line with your static system. That would increase the volume and make it less sensitive to short gusts and such. Of course, it might also make your instruments slower to respond.

In sailplanes, the variometer measures flow in/out of an insulated flask. A smaller flask provides a quicker response and a jumpy needle. A large flask gives more of an average climb rate.

[rzbill]

Originally Posted by GeneL

this seems to be the situation in most 7's,

Really? Sure there are plenty of examples of static error which I believe to be port shape related, but this is the first time I have heard of "pulsing static pressure". A search using the terms "pulse static" returns nothing and "pulsing static" returns this thread.

I use the stock position and port shape but fabricated internal connections for 1/8 NPT fittings. Passed statics test. No variation, even though my new Falcon POS altimeter did not pass (GRT did).

The comment in this thread about pulsing via internal cabin pressure is telling.