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Static Port Question

Which Static Ports

  • Stock

    Votes: 34 39.5%
  • Cleaveland

    Votes: 29 33.7%
  • SteinAir

    Votes: 5 5.8%
  • other

    Votes: 18 20.9%

  • Total voters
    86
Performance comparison available ?

I custom machined flush riveted ports with 1/8? npt hose connections inside on my first RV and they look very upscale. I read many references on VAF that Vans rivet works fine. So I just used rivets on my second project. Does anyone have facts to compare the two extremes ?
 
I installed the Cleaveland, but if I was to do it again I would installed the Van's optional port rv9builder mentioned. Wished Van would just ship it in the standard kit.
 
Have the stock Vans kit option and no issues after 20 hrs and when tested for avionics accuracy by certified tester.
 
Location

Just curious.

Decades ago the "best" location was determined experimentally.
Anyone know how?

Has the location later been verified by fluid dynamic modelling?

Finn
 
SafeAir1 + Vans

I used the Vans port outside and SafeAir1 port inside. It allows the use of the reliable Vans port on the outside and the SafeAir1 fittings inside.
Not flying yet.
 
Just curious.

Decades ago the "best" location was determined experimentally.
Anyone know how?

Has the location later been verified by fluid dynamic modelling?

Finn

The location choice was based on a lot of prior experience and the verification was by flight testing to show that airspeed indications (the one most effected by static pressure error) are correct.

Side note - In my opinion a poll such as this without also asking whether the ports being used have been verified with detailed flight testing, is not of much value. It could just show indications of the blind leading the blind.
A lot of different ideas are used by experimental aircraft builders. Many of them are adopted by others. Sometimes in large #'s. And often times when the originator of the idea hasn't even made their first flight yet.

I am not saying that any in the poll list are bad. They are probably all fine because the tribal knowledge in the RV community has spread wide enough now that it is pretty well known that there are some specific details regarding static ports that need attention.

Bottom line..... following a popular trend based on numbers alone is rarely a good decision when it comes to experimental aircraft.
 
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+1

I used the Vans port outside and SafeAir1 port inside. It allows the use of the reliable Vans port on the outside and the SafeAir1 fittings inside.
Not flying yet.

Flying and it measured within 1.5 kt overall, just a tick low.

I used the stock rivet and was looking at the hole, it had some raised material due to the size of the pull anvil. I sanded off with fine grit and reduced the GPS TAS delta from 2.4 to 1.5. Don't let the decimal imply accuracy, this is an average of several runs, altitudes and temperatures.

If doing it again I would use the Vans unit with 1/4-20 thread and hose barb. Much less trouble for install and would expect same accuracy.
 
I am the blinded one who posted this to begin with. This is not a new topic. It has been kicking around for al long time. Furthermore, I have been on the this forum long enough to know that people would also post with their thoughts on what they put in, why, and how they work for them. I do tend to ask some dumb question at times, but someone has to ask them.

I put in the stock one because I was concerned about not using them for accuracy reasons. Today, I went into pull out the stock Van's static ports. The only thing holding the lines in place was the silicone I used to make sure they stayed in place. I am glad that I pulled them out.

In addition, Van's must sort of know that the stock static ports suck because they offer better ones. And I am truly baffled by why they aren't standard with the RV-14 kit.

I am putting in the SafeAir ones that I have had kicking around the shop for a while.
 
The location choice was based on a lot of prior experience and the verification was by flight testing to show that airspeed indications (the one most effected by static pressure error) are correct.

Side note - In my opinion a poll such as this without also asking whether the ports being used have been verified with detailed flight testing, is not of much value. It could just show indications of the blind leading the blind.
A lot of different ideas are used by experimental aircraft builders. Many of them are adopted by others. Sometimes in large #'s. And often times when the originator of the idea hasn't even made their first flight yet.

I am not saying that any in the poll list are bad. They are probably all fine because the tribal knowledge in the RV community has spread wide enough now that it is pretty well known that there are some specific details regarding static ports that need attention.

Bottom line..... following a popular trend based on numbers alone is rarely a good decision when it comes to experimental aircraft.

To Scott's point which I whole heartedly agree, I have verified my airspeed at slow, cruise and fast cruise and all have been verified by the three way GPS method.
 
Don't understand why you think the original stock ports "suck". Thousands of RVs have been flying with them for many years with no problem. My RV-6 has been flying since early 1993 with the originals and they work perfectly.
I suspect the reason Vans sells a different one is because so many people think that something that simple can't possibly be the best. i.e. More cost = better quality!
 
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All of the Van's demonstrator aircraft have the sucky :)rolleyes:) static ports because they are light, cheap, and work just as well (and sometimes better) than any of the other options available.

An upgrade option is available because some people just don't like the simplicity of the design of the standard ones.
Nothing wrong with that, but that doesn't mean the standard offer is inferior either.

Edit.......Looks like Mel typed a little faster than me with basically the same answer.......
 
My complaint about the original port provided by VANs is that it does not provide a positive and long lasting seal. As airplane ages, the tube that is simply inserted into the pop rivet loses its seal and will leak.
Of course much more important if you fly IFR and get your altimeter certified or not.
 
Tube security

The potential to leak is obvious with the rivet/ vinyl tube. So I invented a high tech insurance policy and sealed with silicone rubber and .031 safety wire. Hindsight suggests I might have used Fuel lube as sealant.
 
My complaint about the original port provided by VANs is that it does not provide a positive and long lasting seal. As airplane ages, the tube that is simply inserted into the pop rivet loses its seal and will leak.
Of course much more important if you fly IFR and get your altimeter certified or not.

The entire fleet of company demonstrators (some well past 20 years old) are still operating with zero leaks. Pretty good evidence that if installed per the instructions (including proper application of sealant) they will work for a long time.
 
I really like the idea by Larry and Tom is a great idea. So it is meaningless if the SafeAir is off. I can take 10 minutes to fix it with the Van's pop rivet. If needed. Thanks again for the useful answer.
 
Vans port

Just to be clear.
The SafeAir Static port(s) is riveted and prosealed to the inside of the fuse where Vans plans recommend each side. It may be a hair off to allow the flannge to clear the bulkhead.
The side skin and SafeAir port are drilled to the size requied for the Vans port (rivet).
The Vans port (rivet) is installed with proseal from the outside. No possibility of a leak and the port is, for all practical purposes, flush to the skin as Vans intended.
On the inside, the SafeAir port is plumbed with SafeAir fittings and tubing.
I elected to put the "T" at the top of the bulkhead.
As I mentioned, mine has not flown yet.
 
Just to be clear.
The SafeAir Static port(s) is riveted and prosealed to the inside of the fuse where Vans plans recommend each side. It may be a hair off to allow the flannge to clear the bulkhead.
The side skin and SafeAir port are drilled to the size requied for the Vans port (rivet).
The Vans port (rivet) is installed with proseal from the outside. No possibility of a leak and the port is, for all practical purposes, flush to the skin as Vans intended.
On the inside, the SafeAir port is plumbed with SafeAir fittings and tubing.
I elected to put the "T" at the top of the bulkhead.
As I mentioned, mine has not flown yet.

I keep quoting you Larry :) My safe-air is machined to a flat disc, drilled for the rivet and then pro sealed to the inner skin. Then the rivet was pro sealed and installed from outside engaging the safe-air through the skin. No leak.

It flew the calibration run several times and it ultimately was only 1.5 kts off averaged for speeds, altitudes and temperatures.

A builder can do what they want, but why have the inside connections perfect only to pooch the airspeed accuracy? What, exactly, is gained?
 
The standard location and supplied parts work well. You still have to verify when flights begin. A very simple way to check your static system is to set your altimeter to 0 on the ground. Now go for a flight and do a pass at normal airspeed about 100 feet above the runway. The altimeter should read 100 feet. Check two or three different air speeds. The static port can be ?tuned? with layers of tape in front or behind the static port. When you get the right combination add a layer of pro seal/ glass etc to replace the tape. (Another good reason for not painting your plane before first flight)
It is a fun process.
 
Just to be clear.
The SafeAir Static port(s) is riveted and prosealed to the inside of the fuse where Vans plans recommend each side. It may be a hair off to allow the flannge to clear the bulkhead.
The side skin and SafeAir port are drilled to the size requied for the Vans port (rivet).
The Vans port (rivet) is installed with proseal from the outside. No possibility of a leak and the port is, for all practical purposes, flush to the skin as Vans intended.
On the inside, the SafeAir port is plumbed with SafeAir fittings and tubing.
I elected to put the "T" at the top of the bulkhead.
As I mentioned, mine has not flown yet.

I mounted my SafeAir1 ports outside with rivets, so they stand proud in the recommended location, after reading all the issues people have with erroneous readings and after seeing one mounted externally like that on a business jet.

As near as I can tell, it is spot on.

PS. when I had the plane painted, I made sure they didn't paint any part of the static port.


(Click to enlarge)
 
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Regarding accuracy of various static ports, this is a more complicated issue than some may realize. The CAFE Foundation tested the RV-9A factory ship and published the table below (full report is here). They measured pitot and static pressure using a special probe mounted to a cuff on the wing, in order to minimize errors caused by airflow around the aircraft. The resultant CAS measurements may still not be perfect but are presumably better than any measurement made on the aircraft skin. They also used a calibrated barograph to measure errors in the airspeed indicator.

The result shows that there are errors of up to +7 mph caused by the factory pitot-static system. The error gets smaller at lower airspeeds, which is probably what you want (more accurate near stall). Interestingly, the instrument error does the opposite; it is up to +8 mph error on the slow end and very accurate at the high end. From the pictures in the report it was an analog "steam gauge" indicator, but digital isn't necessarily more accurate. The total error for this particular system runs up to 12+ mph (at speeds near Va).

One conclusion from this might be that the stock pitot-static system really is not all that accurate. Or, one might conclude that it's accurate enough, provided you have an idea of the indicated airspeed at Vso. These data also make it clear that getting accurate data takes a lot of work. As anyone who has been involved in racing will tell you, its difficult to get reproducible numbers at precision better than ~3 kts.


49805086873_ecd516f9c3_c.jpg
[/url]n129rv by Alan Carroll, on Flickr[/IMG]
 
Regarding accuracy of various static ports, this is a more complicated issue than some may realize. The CAFE Foundation tested the RV-9A factory ship and published the table below They measured pitot and static pressure using a special probe mounted to a cuff on the wing, in order to minimize errors caused by airflow around the aircraft. The resultant CAS measurements may still not be perfect but are presumably better than any measurement made on the aircraft skin. They also used a calibrated barograph to measure errors in the airspeed indicator.

The result shows that there are errors of up to +7 mph caused by the factory pitot-static system. The error gets smaller at lower airspeeds, which is probably what you want (more accurate near stall). Interestingly, the instrument error does the opposite; it is up to +8 mph error on the slow end and very accurate at the high end. From the pictures in the report it was an analog "steam gauge" indicator, but digital isn't necessarily more accurate. The total error for this particular system runs up to 12+ mph (at speeds near Va).

One conclusion from this might be that the stock pitot-static system really is not all that accurate. Or, one might conclude that it's accurate enough, provided you have an idea of the indicated airspeed at Vso. These data also make it clear that getting accurate data takes a lot of work. As anyone who has been involved in racing will tell you, its difficult to get reproducible numbers at precision better than ~3 kts.

Keep in mind that there are two factors in airspeed indicator accuracy at a wide range of speeds and AOA.

- static pressure (from static ports)

and

- dynamic pressure (from the pitot tube)

If either of these is incorrect, the indicated airspeed will be incorrect.

One of the benefits of a test probe like the one used by CAFE is the directional pitot probe mounted well fwd of the wing. This removes any influence of the flow around the wing as well as error induced by the changing pitot AOA in relation to relative wind.

I think the RV-9 wing shape has a bit more influence on the pitot pressure than the other RV models have , because flight testing (extensive... on all the models) over the years has shown that the static system documented in the plans is very good.

My theory is that the difference is caused by the pitot inlet being closer to the leading edge on the RV-9 than on all of the other RV's.

To some degree, mounting a pitot tube below the wing helps reduce AOA induced errors because the wing redirects the airflow at high AOA so that it is still entering the pitot inlet nearly head on (or at least more than it would be if the pitot inlet was well clear of the wing).
A good example of the use of this action is low wing Piper airplanes. The blade style pitot tube they use is rather short and often mounted about mid chord on the wing which keeps it located in flow that is always nearly direct into the pitot inlet.

With the RV-9 pitot located closer to the leading edge, I think it has a bit more of a variable in the angle that the relative wind hits the inlet at, depending on speed and AOA, but I have no specific test data to prove that.
 
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So I did a couple of quick tests on the stock tubing, which I think is Tygon flexible clear PVC, with some RTV sealants.

1. standard clear silicone does not adhere to the tubing
2. Loctite black 598 does not adhere to the tubing.
3. 3M fire barrier silicone 2000 adheres like crazy to the tubing.

As I side note, I tested the 3M stuff for gluing two flat pieces together to simulate gluing on the static port to the skin. So there is a thin film between the pieces of sheet metal. It does not setup, which is what I expected. A silicone RTV needs water the polymerization to go. This means that the edge of the seam will set up but the further you go in the less likely it is to set up (polymerize), since the water can't get in there. This is why you want two part adhesives to glue flat pieces together like fuel tank sealant.
 
I asked the mother ship where to get the rivets after telling them that my plan to possibly install the standard rivet head into the safair air.

The response was in a driven out SD-42-BSLF followed by the following links:


http://porcupinetech.com/rvproj/pitotstatic.htm

https://buildaplane.wordpress.com/tag/static-system/

http://smilinpete.com/wp/?cat=65

https://buildaplane.wordpress.com/2010/05/14/pitot-static-system/

http://rvplane.com/?dayid=506

http://www.vansairforce.com/community/showthread.php?t=8836

No other comments at all in the email.

cheers
 
Static port

I asked the mother ship where to get the rivets after telling them that my plan to possibly install the standard rivet head into the safair air.

The response was in a driven out SD-42-BSLF followed by the following links:


http://porcupinetech.com/rvproj/pitotstatic.htm

https://buildaplane.wordpress.com/tag/static-system/

http://smilinpete.com/wp/?cat=65

https://buildaplane.wordpress.com/2010/05/14/pitot-static-system/

http://rvplane.com/?dayid=506

http://www.vansairforce.com/community/showthread.php?t=8836

No other comments at all in the email.

cheers

I keep forgetting.
I ground the SafeAir port so it was flush to the fuse skin. Drilled the fuse and port for the Vans rivet port.
 
One thing I found a long time ago on the RV-10 model was that I purchased flush flat mounted ports by Cleaveland and they were not accurate. I can't remember the error but I think it was around 7kts in cruise. They later came out with domed ports, which were much more accurate. There were people around that time experimenting with air dams in front of ports, and other things to get the ports to be more accurate.

The takeway from all that was that on the RVs, a person may be better off with something domed, imitating Vans original rivet based port, if you want them to be accurate. The other takeways are, whatever port you use, don't believe it until you've flown the GPS course and calculated out the actual speed, because it's easy to just believe what the instrument tells you. Go find out for yourself. Also, I appreciate having a port that at least could be removed and replaced, or monkeyed with so that you actually can fix an error if you have one and its significant. A 7kt error will drive you nuts if you know about it. Another takeaway at the time was, make sure you paint the static port when you paint the plane, because you don't want to take a domed port and raise the surrounding aluminum with paint, but not also raise the port.

None of this necessarily will help you in your build, but, I would encourage people to definitely fly the GPS course and calculate their airspeed errors, so when you tell people speeds, they are accurate speeds.
 
Vans standard static port

Below is a copy of the section of my Phase 1 where I calibrated the airspeed. At the time, I had not installed wheelpants and my slow speed data was not completely stable. I found a cruise speed accuracy of within a knot and a slow speed accuracy of 3 kts. I later redid the low speed and the accuracy tightened. This is using the standard Vans supplied pop rivet static port. I have been flying 400 hours since 2017 without a leak. So I think the standard design is robust.

oCK.jpg
 
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One thing I found a long time ago on the RV-10 model was that I purchased flush flat mounted ports by Cleaveland and they were not accurate. I can't remember the error but I think it was around 7kts in cruise. They later came out with domed ports, which were much more accurate.

Tim - 7 knots too fast, or too slow?

FWIW I used flush ports on my my RV-8 and got a different finding. I did extensive testing at 5 kt increments using 4 way GPS stabilized groundspeeds. The temp and pressure corrected results showed my indicated speeds to be 1-2 knots too slow across the whole range. Either the flush static ports are acceptably accurate, or else I had other errors (ASI?) that were cancelling out static port error (quite possible).

To me the larger points are that there are multiple sources of potential error (see for example Scott's post, #34), accurate testing is hard (and maybe impossible without a calibrated ASI), and that its probably not worth worrying about the precise shape of the static port. The Cessna I used to fly had published IAS errors of several mph and no one seemed to mind. Van's ships that have been tested by CAFE do too. The RV-8A did a little better than the RV-9A, but still indicated as much as 5 mph too fast compared to data from the calibrated wing-cuff test gear.
 
Sorry Alan, I can't remember if it was too fast or too slow. Right now my IAS reads about 2kts slower than actual, but I don't know if it was 7 high or 7 low before. I think 7 low. It's been over 10 years since I dealt with it.

I know that the errors are acceptable from a flying standpoint. What sets a lot of us RV people apart from your average SPAM can flier though is that we tend to talk or brag or whatever about speed a lot more than average folk. So really the concern is that if people don't go and do a GPS course test to verify theirs, they probably shouldn't be spouting numbers on forums either. I mean data means nothing without validation, right, and all it does is mislead others when someone throws numbers out there that aren't valid. Other than that, sure, there's no reason you can't have some error.
 
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