SafeAir Static Ports

[rvbuilder2002]

Originally Posted by RV7A Flyer

In other words, it can tell you that if the static ports "see" pressure equivalent to a certain altitude, that that altitude is what is being reported. But it can't tell you that the installation will actually "see" that pressure in flight at that altitude...

Correct.

Most any static port (shape or location ) can pass a ground test as long as the system has no leaks and the the EFIS/Instruments are working properly and are correctly calibrated.

The true test of a system accuracy is in flight. That is when the location and /or shape of the ports come into play. The desire is that with the dynamics of flight and high speed airflow, the system is still able to sense what the "static" pressure of the air is at a given altitude.

[Bavafa]

Originally Posted by rvbuilder2002

Correct.

Most any static port (shape or location ) can pass a ground test as long as the system has no leaks and the the EFIS/Instruments are working properly and are correctly calibrated.

The true test of a system accuracy is in flight. That is when the location and /or shape of the ports come into play. The desire is that with the dynamics of flight and high speed airflow, the system is still able to sense what the "static" pressure of the air is at a given altitude.

To add a bit more, based on my experience, the inaccuracies are seldom liner and more noticeable in IAS than indicated altitude. Although I have seen it in a few Planes that when the static port is not of the correct type for that plane, right after take off you see an altitude drop maybe even lower than the field altitude before it raises up.

[Richard Connell]

To add another 2c,
I spent probably a year getting this right after installing non standard static ports. Dozens of test flights. Experimenting with fences / ramps / tape etc.
Hours and hours with the NTPS spreadsheets.
I generally found it interesting and knew what I was trying to achieve and I needed it to be accurate to get an IFR cert here in OZ.

All of this would likely have been circumvented with 2 pop rivets.

I'd strongly suggest that anyone considering deviating from the factory design understand fully what influences IAS / CAS / TAS / PALT / PEC etc . Else it just won't be accurate which may or may not be important for your mission.

Seasons greetings all.

[Lynnb]

Since it depends on the position of the ports on the plane, do some RV's work and others don't because of where they are placed?

Lynn

[RV7A Flyer]

Originally Posted by Richard Connell

I'd strongly suggest that anyone considering deviating from the factory design understand fully what influences IAS / CAS / TAS / PALT / PEC etc . Else it just won't be accurate which may or may not be important for your mission.

That is assuming, of course, that the Van's-specified pop rivets are *themselves* somehow designed in such a way that they are always accurate.

I have a hard time believing that they're any better or any worse than numerous other types of static ports, simply by virtue of coming from Van's.

[bjustus]

The thing I don't like about the pop rivets is that's not much for the very small plastic tubing to hold on to and the tubing tends to come off or develop leaks. I had problems with them on both my RV-4s that I outfitted for IFR and ended up going with SafeAir ports on the second one; (they were very accurate with my Dynon.)

[Vac]

Static source error can only be determined through flight test. Ground test (including normal pitot/static checks) does not measure static source pressure error. Each aircraft is different, but systems installed in accordance with the drawings and using pop rivets have been shown to generally give good results. However, that can only be verified by flight test. The Cleveland ports mimic the geometry of the rivet. Anicdotal evidence in previous board discussions on this topic may indicate that ports flush with the skin on RV-types induce more error into the system than ports that protrude a bit. The most efficient way to test static source pressure error is in conjunction with using GPS to test airspeed performance. A simple manometer can be constructed to conduct ground test required to gather data that will support flight test.

Paper hole reinforcements can be cut in half, or layers of masking tape can also be used ahead or behind the existing port (depending on perceived airspeed error). Once an appropriate thickness has been determined, an appropriately thick washer can be glued in place to bias flow around the port, if desired.

Kevin Horton has an excellent write-up on his site regarding appropriate test techniques:

http://www.kilohotel.com/rv8/index.p...d=3&Itemid=218

Most of the modern EFIS systems minimize actual instrument/sensor error, but system (i.e., "installation") error is always a factor, and actual system error can only determined through a combination of ground and flight test along with appropriate data reduction. Although it sounds complicated, the basic test techniques are straight forward, and a good spreadsheet will take care of the math and make the analysis/hardware tweaking fairly easy.

By and large, I would estimate most homebuilders don't perform static source testing and it's not something that all pilots are aware of, so in many cases, the first time folks in the RV community run into the topic is on this board. There are also several other threads on this topic that will turn up in a search--it's a fairly common question that pops up at regular intervals.

Hope this sheds some helpful light on the topic.

Happy New Year,

Vac

[wjb]

Hi Folks,

I picked up a SafeAir kit from Avery about 1.5 years ago .. and was curious what configuration I received based on this thread.

Here's a photo of the static port .. it's 0.25" in diameter and is shaped similar to a LP 4-3 pop rivets -- which are slightly smaller in diameter, at about 0.23".



Looks like a close approximation of a pop rivet to me.

[N941WR]

Originally Posted by N941WR

Back in 2007 I mounted mine on the exterior of the skin because of some reported issues and after seeing them mounted in a similar manner on a business jet. In this configuration, they have worked great! (When I had the plane painted, I had them leave the entire fitting unpainted.)


(Click to enlarge)

To clarify, the early SafeAir static ports were designed to sit flush with the skin, which caused problems. By mounting them as I did, eliminated the issue.

Later SafeAir ports stood proud of the skins, also eliminating the problem.

[Jrskygod]

WJB - those are the exact vents I used as mentioned in post #11. I mounted them per the instructions on the inside of the airframe in the location set by the plans. The vent protruded through the skin and set proud of the surface. I had to use some crescent shaped pieces mounted in front of the vents to get my airspeed correct. FYI your results may vary - only detailed flight test will tell.