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Static Port Error - A Journey

avrojockey

Well Known Member
Patron
Like many RVs mine is unique in many ways, but the static port was not one of the items that was ever noticed. It's just a hole.

My RV always seemed slow compared to others published numbers and Van's. This always bothered me...did I buy a dud? Ultimately I was happy with real performance, ie the gas milage being better than my car and my commute taking 1/3 the time. However, I searched for every bit of aerodynamic issue with the aircraft - wing, flight control, and gear fairing rigging, all to no avail. The pilot static and altimeter test also good.

Then I see a thread in the -9 forum about someone in like circumstance. The community to the rescue! Everything pointed to the static port! I remembered it was pointed out in my pre-buy that I didn't have the Van's pop-rivet port, so I took a 4-leg WOT test drive at 8500', captured G3X screen shots of my metrics and then plugged my data in the NTPS spreadsheet provide here. Well...I was indicating ~10 too slow...what was 148 KTAS was actually 158! Within 2 knots of the published Vans numbers!

So...how do I fix? Well, I'm not smart, but I can copy! I just modified the flush port to install a unset large flange 1/8 rivet like the one Van's provides. Retested, and my IAS and indicted TAS are now within 1 knot. Happy Days!

However...my IAS, and to a larger extent, my ALT and VS is jumping around a tiny bit. Very small deviations, but not very agreeable with my autopilot. Any idea what would cause this?
 
Could water in the static line(s) cause that?

Should be easy to test by disconnecting the static line before it reaches any instrument and blowing in out with air.

Finn
 
However...my IAS, and to a larger extent, my ALT and VS is jumping around a tiny bit. Very small deviations, but not very agreeable with my autopilot. Any idea what would cause this?

Since the IAS is usually more sensitive to static leaks than the other two instruments, I would look for a static line leak-maybe intermittent- close to the vsi and altimeter, but not close to the ASI.
Of course if all 3 are in the same efis box, then I don’t know.
 
I suspect it could be a leak around the new static port modification...I’ll report back.

What is weird is how jumpy it was. A leak should be constant not variable
 
When you get all your leaks sealed there is a quick way to check your static system. On ground note the field elevation. No go do a circuit with a low and over the runway at what you estimate to be 100 feet above the runway. Check your altimeter in the steady flyby.
If your system is good the altimeter should read 100’ above runway elevation.
If it is off experiment with some layers of tape either ahead or behind the static port and do the fly by again.

A few passes should get you close and you can make the appropriate final dam
 
I made the same “modification” to an aftermarket port about 10y ago.
I assume your modification was to drill out the old port and install the unset rivet into the old port with some adhesive?
This was also very unsatisfactory for me as well. Creating the same symptoms you describe.
I ended up removing the old port in its entirety and replacing with the Cleveland one that is shaped like the vans pop rivet. This fixed all problems and the accuracy was excellent.
Cheers
Richard.
 
I made the same “modification” to an aftermarket port about 10y ago.
I assume your modification was to drill out the old port and install the unset rivet into the old port with some adhesive?
This was also very unsatisfactory for me as well. Creating the same symptoms you describe.
I ended up removing the old port in its entirety and replacing with the Cleveland one that is shaped like the vans pop rivet. This fixed all problems and the accuracy was excellent.
Cheers
Richard.

This is exactly what I did! Looks like I have some Cleveland static ports to install.
 
Something similar...

If you don’t mind, I’d really like to jump your post with a question of my own...
I’m having a similar issue, but my 6A indicated airspeed is reading around 7 kts FAST compared to an 8A and a F1 rocket in formation. After some research, I thought an error on the high side was due to a static leak. Did I misunderstand where the leak would likely be? I have the standard unset rivet heads.
I’d appreciate any suggestions.
Thanks!
 
The static error due to the source shape/location can either read high or low. Not saying you don't have a leak, just that source errors can go either direction.

Larry
 
If you don’t mind, I’d really like to jump your post with a question of my own...
I’m having a similar issue, but my 6A indicated airspeed is reading around 7 kts FAST compared to an 8A and a F1 rocket in formation. After some research, I thought an error on the high side was due to a static leak. Did I misunderstand where the leak would likely be? I have the standard unset rivet heads.
I’d appreciate any suggestions.
Thanks!

One of the ways to quick check for a static leak - open and close your air vents, this will change the cabin pressure and you'll see a change in ALT,IAS,VS. A more detailed leak check includes a manometer attached to the static system, adding water to produce WC pressure and IALT decrease, then watch to see if WC or IALT changes after awhile. I'm doing this this afternoon.
 
Would a pitot/static leak test shed any light, maybe?

No, the pitot static leak will only show if you have a leak but not if there is any abnormal pressure at your static port during flight.

This has been well documented, for all RVs, the pop rivet shape yields the most accurate. For a better fitting and leak proof in a long term, the cleaveland static ports are the same shape but can be used with the fitting that makes them leak free in the long run.
 
So static system has a leak...somewhere.

It's a minor leak with 24"WC applied (~1800' below field elevation), it was dropping about 40'/min. I can only assume a proper test with vacuum to 18000' the rate would exceed 100'/min.

I'm going to get a hand vacuum pump from HF to do a proper vacuum test, find the leak and report back
 
So static system has a leak...somewhere.

It's a minor leak with 24"WC applied (~1800' below field elevation), it was dropping about 40'/min. I can only assume a proper test with vacuum to 18000' the rate would exceed 100'/min.

I'm going to get a hand vacuum pump from HF to do a proper vacuum test, find the leak and report back

The limits for an IFR cert (non-pressurized) are 1000' AGL with <100'/min.
 
how to calibrate

Some EFIS have airspeed calibration ability, some do not. Best way to determine accuracy is to
Fly heading 360, 135 knots or 155 mph indicated, write down your ground speed and true airspeed; do this again for heading 120 degrees, then for 240 degrees. Total both, divide both by three, and if there is a difference between the average true and average ground speed, check for pitot and static leaks first. Also, if you have an airframe static port, and you have a heated pitot, make sure the pitot does not also have a static port. In my case, with a Garmin G3X (no airspeed adjustment) was brought into "nuts on" indications with a .063 dam in front of the static port.

Regards,

Gary
 
So I got to beat myself up a little in the tail of the airplane. I decided that if I'm going to check for leaks I might as well replace the crappy vinyl tubing the builder used with 3 different splices. Also, I decided to add the second static port per plans. (builder only had one on left side)

When everything was finished, it leaked about 200'/min at 1000' AGL. I spent a couple hours trying to trouble shoot and find the leak, and you know what it ended up being? The tape I used to cover the other static port! :eek: Aluminum speed tape does not work! Once, I replaced it with another tape the altitude didn't budge a single foot....tight!
 
Update...

I drilled down my airspeed error after several test flights, and figured out I needed the pop rivet shape and the depth of an extra washer to get my static ports correct. Good news is after several speed runs and number crunching using Kevin's and NTPS spreadsheets my airspeed is within 0.2-0.3 knots of actual.

Im still having the issue of jumpy VS, pointing to spikes in static pressure. In the following video you can see it. https://youtu.be/7iFLKqXmxAw - Sorry about my vid skills (not stable) but I was hand flying. The AP was doing a terrible job because of the VS jumping.

You can plainly see the airplane is rock steading the VS just jumps up and down for no reason. This happens for both the left and right static ports when I isolate them, but the left port is a little worse. When I switch to the alternate static source, which is the cabin, the VS is normal and rock solid.

What would cause this? Any recommendation to troubleshoot?
 
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So what exactly does your static port look like now? Rivet glued inside washers or some such?

It looks exactly like the SD42BSLF rivet (standard Van's static port) with .375 dia washer (nearly same diameter as rivet flange) placed under the rivet flange prior to installing. Just think of standard Vans static port but sticking out another .050"

I actually did a test flight with just a washer under the flange before I fabricated a solid piece.

I don't think its the shape of the port because I was getting this VS variation throughout all my testing with different sized ports

How's summer in Oz? I was suppose to be there today to start quarantine but the contract with RFS got pushed to Dec 1.
 
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The static error due to the source shape/location can either read high or low. Not saying you don't have a leak, just that source errors can go either direction.

Larry

It looks exactly like the SD42BSLF rivet (standard Van's static port) with .375 dia washer (nearly same diameter as rivet flange) placed under the rivet flange prior to installing. Just think of standard Vans static port but sticking out another .050"

I actually did a test flight with just a washer under the flange before I fabricated a solid piece.

I don't think its the shape of the port because I was getting this VS variation throughout all my testing with different sized ports

How's summer in Oz? I was suppose to be there today to start quarantine but the contract with RFS got pushed to Dec 1.

That sounds remarkably similar to what mine looked like. Also that airspeed tape is exactly what mine looked like as well.
Even though the “shape” of the port is the right rivet, it seems like even the smallest ridge such as the washer (or even paint) at the base of the rivet can cause instability. It’s quite possible too that the instability is not fully described by the oscillation in the ASI because I’m sure the EFIS has some smoothing going on.
I guess it could be somewhere else in the system but I don’t think so.

Summer here will be interesting. Lots of back burning going on at the moment.
We’ve got a LaNina weather pattern setting in here which has already made spring much cooler and wetter than last year. Much of the central and eastern parts of the country have had their best spring rains in a decade.
So there’s little chance of seeing the same catastrophic fires as last year.
Maybe that’s why you’ve been delayed.
Where are you going to be based?
 
Snubber

Would something like this possibly dampen the static port pressure, acting as a kind of "snubber"? (love that word!)

https://www.mettleair.com/store/dis...arb-inline-air-partical-disk-disc-filter.html

IF_1.jpg
 
That sounds remarkably similar to what mine looked like. Also that airspeed tape is exactly what mine looked like as well.
Even though the “shape” of the port is the right rivet, it seems like even the smallest ridge such as the washer (or even paint) at the base of the rivet can cause instability. It’s quite possible too that the instability is not fully described by the oscillation in the ASI because I’m sure the EFIS has some smoothing going on.
I guess it could be somewhere else in the system but I don’t think so.

Summer here will be interesting. Lots of back burning going on at the moment.
We’ve got a LaNina weather pattern setting in here which has already made spring much cooler and wetter than last year. Much of the central and eastern parts of the country have had their best spring rains in a decade.
So there’s little chance of seeing the same catastrophic fires as last year.
Maybe that’s why you’ve been delayed.
Where are you going to be based?

I'll have to evaluate the shape of the rivet again. I was wondering if that ridge was causing problems.

I'll be at RAAF Richmond. Bomber 210 is there all year (owned by NSW now and we crew it until they hire and train enough AU folks) and Bomber 137 will be there end of Nov. My entire family was coming over for the summer but government approved our quarantine plan so I'm doing month on/off.
 
One of the ways to quick check for a static leak - open and close your air vents, this will change the cabin pressure and you'll see a change in ALT,IAS,VS. A more detailed leak check includes a manometer attached to the static system, adding water to produce WC pressure and IALT decrease, then watch to see if WC or IALT changes after awhile. I'm doing this this afternoon.

Sounds like a good place for me to start. Thanks Avro!
 
Hey Avro... I tried your advice... wierd...
Set up straight and level, autopilot on, and both outside air vents closed.
Opened up both vents and autopilot slowly pushed the nose down and started losing altitude.
I guess I need to find the leak... 🤪
 
Hey Avro... I tried your advice... wierd...
Set up straight and level, autopilot on, and both outside air vents closed.
Opened up both vents and autopilot slowly pushed the nose down and started losing altitude.
I guess I need to find the leak... &#55358;&#56618;

Interesting...I would test it. I got a hand vacuum pump from Harbor Freight, and was able to connected it directly to a spare port on my static line manifold. I taped the static ports closed and gently (doesn't take much hand pump movement) pulled a vacuum on the instruments so ALT was indicating 1000' AGL (~1900 in KATW). then I watched how long it would hold. Should be < 100'/minute decent rate for IFR. Mine didn't move.

Wish it was little warmer in WI to be messing around with this stuff.
 
Interesting...I would test it. I got a hand vacuum pump from Harbor Freight, and was able to connected it directly to a spare port on my static line manifold. I taped the static ports closed and gently (doesn't take much hand pump movement) pulled a vacuum on the instruments so ALT was indicating 1000' AGL (~1900 in KATW). then I watched how long it would hold. Should be < 100'/minute decent rate for IFR. Mine didn't move.

Wish it was little warmer in WI to be messing around with this stuff.
That will be my next step, thanks Tim!
 
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