Question for the static system gurus????

[Brantel]

I seem to have a large static position error... I think that is what you static system guru's call it.

1. I have the SafeAir static ports that are of the new design.
2. They are mounted inside the fuse by the way of Pro-seal around the flange to the inside of the fuse skin.
3. The ports extend from the side of the fuse .051 on the left and .053 on the right.
4. The ports are within 1/8" of the position as specified on the plans.
5. The SafeAir ports are round with square corners on the OD and the ID. There is no radius or chamfers on these ports. They look like an exact cylinder sticking out from the skin of the fuse with a hole in them.
6. I used the SafeAir tube and fittings and the static ports are cross connected with a "T" in the exact middle between them. The static line is connected to this "T" and runs up to the D100.

The indications are:

1. On takeoff and climb out I noticed that even though I am climbing, the altitude seems to stay pretty much at field elevation until I get to around 200ft then it starts to roll up normally. ( I think as the airspeed comes up, this is increasing my error and the error is canceling out the fact that I am climbing until the higher altitude overcomes the error)
2. When flown beside an airplane that has been proven accurate, my altitude indicates almost 200ft low and the airspeed was also low by at least 20 knots. I did not get the exact numbers but mine was low on both. This was with me running around 2350rpm @ 3500ft.
3. I popped a flap fuse while landing which may be because I was above flap speed at some point and did not know it since my ASI is reading low.

The test:

1. I have performed a vacuum leak test on the static system where I applied 1000ft of elevation change for at least a minute and there were absolutely no leaks. I taped over one port and used a vacuum tool to suck it down.
2. I made a manometer and downloaded the chart from the "Fly EZ" site and performed an ASI instrument error test on the Dynon. The Dynon ASI was within 1 knot from 230 knots all the way down to 40 knots so I know the Dynon ASI sensor is accurate.
3. I compared my Dynon's pressure altitude reading on the ground while set to 29.92 to an airplane that is known good at the same elevation. His airplane has both a mechanical Alt and a D100 like mine. I only have the D100. Both our pressure altitudes were the same.
4. I used the manometer to apply 35" w/c vacuum to the static system after setting the Dynon to report 0ft altitude and I got exactly 2500ft.
5. I tried a test flight where I applied a 2"x2" square piece of aluminum tape to the side of the fuse and allowing it to ramp up and fair in the front edge of the static port without covering the hole. I honestly think this made it worse instead of better.

These test seem to indicate that on the ground the Dynon is very accurate. I also know that I do not have a leak. It all seems to point to a static system error where I am getting too high of a static pressure for some reason.

One possible theory is that I have my vinyl N numbers right in front of the static ports and that these are causing some sort of turbulence creating the error?

What says the guru's???

Here are some pics of the install and ports:

[Spike]

You could alternate plugging one of the ports to see if they are both consistent with each other.

Spike

[bullojm1]

I am thinking the vinyl N-Numbers are definitely causing some turbulence in the air before the static port. Maybe you could cover them in clear packing tape as a test to smooth out the air before the static port.

[captain_john]

I seem to recall users of the SA ports echoing this type of problem before.

The error (as I recall it) stems from the ports protruding from the side skin of the fuse.

The resolutions were varied and I seem to recall 2 of them.

1) Place a chunk of metal ahead of the port (.051 on the left and .053 on the right in thickness) in order to smooth out the airflow across the port.

2) Shave them down flush with the airframe.

Not sure why the phenomenon was occurring but this is what I recall from the conversations.

Hope it helps.

CJ

[Spike]

Actually John you just reminded me of something. I have a friend that had some issues on his 8A. He actually took a 960 washer and attached it to the airframe around the static port and it fixed a bunch of his errors.

That idea of trying to smooth the airflow might really help out. If you think about it tubular projects create a lot of drag and turbulence. That might really be skewing what that port is sensing.

[Thermos]

The only sure-fire static source method I've heard of is the one specified by Van's - that pop rivet with the stem removed, located per the plans. Since you're pretty much right-on with the position, it's probable that the shape of the port or some local "flow trip" in front of the port is causing it to sense an incorrect static pressure.

I've read of other folks having static source error issues with the SafeAir ports. As John mentioned, you might try shaving it down. But since Van's specifies a protruding rivet as a port, the sharp edges could be a more direct cause of the problem than the fact that it protrudes a bit into the airstream.

HTH

Dave

[Brantel]

My plan is to shave the ports flush and drill them to accept the pop rivet that Van's specifies. I will glue it in with JB weld. The end result will be the same as Van's recomendation.

[BSwayze]

My plan is to shave the ports flush and drill them to accept the pop rivet that Van's specifies. I will glue it in with JB weld. The end result will be the same as Van's recomendation.

Brian,

If you're going to shave them flush, why not try a test at that point before drilling and inserting the pop rivet? I'm curious about the effect you'll get when they're flush. Maybe that's all that's needed. ???

I'm following this very carefully because I have installed them, too. I read somewhere that they're SUPPOSED to protrude into the airstream, because of the laminar flow of air. It's believed that the thin layer of air right next to the skin isn't flowing. Anyone else have any comments?

[jwyatt]

I know nothing, but I too have purchased these ports a couple months back, and was planning to install them in the next week or so, on the supposition that the newest (protruding) version of these had fixed the error problem.

One observation: the ports I received don't look the same as Brian's -- yours are cylindrical with a hard edge, whereas mine have a chamfer on the protruding bit, probably 30 degrees or so if I had to guess from a quick look this morning. For whatever that's worth; perhaps there are actually three versions of these floating about?

I'll definitely be watching this thread before proceeding with the installation here.

[Brantel]

I think there may be three versions...I saw another pic where someone said they were SafeAir and they were not square like mine either.

I think I will email the SafeAir guys and see whats up.

When I shave them, I will fly em first before inserting the pop rivet.

[Brantel]

I talked via email to Tony of Safeair1 and it seems I am the lucky one. Seems that I am one of 2 that have contacted him with static errors. I am #1 out of a 1000 sold that have an issue with the ones that stick out from the fuse....

What is different on my install???????

[hydroguy2]

my mom told me, it's ok to be different.

[Thermos]

[f you're going to shave them flush, why not try a test at that point before drilling and inserting the pop rivet? I'm curious about the effect you'll get when they're flush. Maybe that's all that's needed. ???

I'm following this very carefully because I have installed them, too. I read somewhere that they're SUPPOSED to protrude into the airstream, because of the laminar flow of air. It's believed that the thin layer of air right next to the skin isn't flowing. Anyone else have any comments?

Great idea on the test, Bruce. I've seen a lot of pitot and static source tweaking in the production flight test world...and one good flight test is worth a hundred analyses (or website posts ).

As far as laminar flow is concerned, you don't want the air at the static port to be moving much, if at all, so that thin area of non-moving air next to the skin - the boundary layer - is your friend. That's probably why a flush or domed static port works better; the sharp-edged port is more of an airflow disturbance.

HTH

Dave

[Thermos]

I talked via email to Tony of Safeair1 and it seems I am the lucky one. Seems that I am one of 2 that have contacted him with static errors. I am #1 out of a 1000 sold that have an issue with the ones that stick out from the fuse....

What is different on my install???????

Maybe you're just doing a better job of testing than everybody else!

[Brantel]

Have not had a good chance to fly all week. Most days were sunny but very windy and gusty.

Saturday looks like a real winner!!!!!

[BSwayze]

One observation: the ports I received don't look the same as Brian's -- yours are cylindrical with a hard edge, whereas mine have a chamfer on the protruding bit, probably 30 degrees or so if I had to guess from a quick look this morning. For whatever that's worth; perhaps there are actually three versions of these floating about?

I hadn't noticed this until you pointed it out, Joshua, that Brians' are cylindrical with 90° square tops. Mine are the beveled ones, too. Mine are the SafeAir1. I bought them not long ago from Avery Tools. It seems to me that the bevels might make the air flow around them a bit smoother. Which ties right in with what you're saying, Dave.

Brian, maybe you don't need to shave them flush after all. Maybe you just need a bevel to remove those sharp edges.

[Brantel]

We have a winner!!!

Last evening, I flew some test flights after the latest round of changes to my static system. I performed a few stall series and also flew several legs while being chased by a friend and his RV6A. This RV6A has very similar IAS and ALT indications that another friend's RV7 has as they have been compared many times to each other. I have been using both aircraft in my prior flights as a reference depending on which one was available.

The new IAS at stall is 44kts which is right at Van's published stall for solo weight of 1400lbs and that is right about were I was at during these test. As best I can tell, my aircraft and the RV6A are now displaying the same or very similar IAS and ALT. We compared readings at 100kts and 150kts and the results were great. I am now eyeball level with other planes in our pattern. My final approach speed now feel normal and not too fast. My TAS at 90° to the wind (light winds aloft) is now indicating almost exactly what the GPS GS is indicating.

I broke the rules and changed more than one thing so I am not sure what resulted in the major reduction in error:

• Moving the N numbers from in front of the static ports
• Drilling the shaved flush ports to accept Van's pop rivet, installing the pop rivet with a thin washer under it.

Here is a pic of the ports now:



Now that I am sure that I am not a mile off, I will do some GPS runs and see exactly where I am at various speeds. I feel confident that I am now withing the same narrow error band that most RV's have. GPS testing will confirm!

I am sure there are many people out there flying that have no idea how much error they have in their ASI and ALT indications. Passing a pitot/static check does nothing to confirm that you do not have in flight errors. Kind of scary really...

[cjensen]

Glad you got it figured out! I keep meaning to check mine, and have forgotten the last several times I've been to the hangar...

[hydroguy2]

good work Brian

[hydroguy2]

double post