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Question for all the static system guru's out there

Brantel

Brantel

Well Known Member
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 1/2" horizontal and dead on the vertical 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:

woims.jpg


149a8ar.jpg


zkr7zd.jpg


25u6ul1.jpg
 
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Let's rule out one more thing - pitot leak. Have you done a leak test on the pitot system? It would take a pretty big leak to give that large an airspeed error, but you never know.

Assuming your pitot system doesn't have a leak, it certainly looks suspiciously like you might have large errors in your static system.

I doubt the edges of the vinyl registration marks would have that much effect. For what it's worth, the aft edges of one of the letters on the side of my RV-8 end about an inch before the static ports, and my system is reasonable accurate - it has 0 error at about 130 KIAS, with the error increasing to about 2 kt at 180 KIAS. In my case, the error is such that the IAS and altimeter read high. My results are here.

I don't know if Van specifies a different location for the static ports on the -7 than he does for the -8, or maybe I screwed mine up, but my ports are located 2 or 3" lower than yours. A small location change might make a small change in the error, but I can't see how a few inches change in position could cause a large change in the error.

Once you have confirmed no pitot leak and confirmed one more time there are no static system leaks, the next step is probably to do some dedicated testing to quantify the errors you have. Find some smooth air. Fly at a constant indicated altitude and IAS. Fly a box pattern with the legs roughly 90 degrees apart, and record:

  • IAS,
  • pressure altitude (i.e. with altimeter set to 29.92),
  • OAT,
  • GPS groundspeed and
  • GPS track

On each leg, use power as required to achieve exactly the same IAS, as closely as you can do it. Stabilize on a constant IAS, altitude and heading long enough for the GPS data to stabilize before recording the GPS groundspeed and track. Do this at three or four different IAS.

Send me the data (kevin01 AT kilohotel DOT com), or post it here. Also send or post the results of your tests to determine ASI instrument error, as we need to account for that when crunching the data.
 
Thanks for the post Kevin, I was hoping you would catch this one...

The test I did to verify the ASI instrument error was using the pitot line all the way out to the pitot. I can't really test the pitot because the Dynon unit has a calibrated leak in it and that does not work too well with a manometer. If you plug the holes in the side, it will come out the AOA port since inside the calibrated leaks on both ports share a common chamber.

I would say that Van's does give different positions for the static port. The 6 is different from the 7.

I really think it is these darn static ports and their shape. I am tempted to shave them flush and do what Scott Will did and install the pop rivet over them.

There are no static leaks as I did this test three times. Twice with a vacuum pump and once with the manometer. Rock solid!

I will do the test runs as soon as I can get some smooth air.

The ground test on the Dynon were very impressive. It shows that it is well calibrated on ASI. I can only get two data points on the altimeter side (pressure altitude and -35"w/c) but those two points are accurate.

Here is the ASI instrument error results. As accurate as you can be with a manometer:

Manometer Chart in Knots/ASI on Dynon in Knots
230/230
220/220
210/210
200/200
190/189
180/179
170/169
160/159
150/149
140/140
130/129
120/118
110/108.5
100/99
90/89
70/69.5
60/60
50/49.5
40/40
30/Dynon quit

I am really suspecting the static issue since the Alt does not start rolling up on climbout. The ground test reveal that there is no lag in the system. It responds to changes instantly on the ground.
 
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Brantel said:
The test I did to verify the ASI instrument error was using the pitot line all the way out to the pitot. I can't really test the pitot because the Dynon unit has a calibrated leak in it and that does not work too well with a manometer. If you plug the holes in the side, it will come out the AOA port since inside the calibrated leaks on both ports share a common chamber.
Click to expand...
How long ago did you do the ASI instrument error check? Is there any chance a new pitot system leak has arrived since that time? It might be worth disconnecting the pitot line at the pitot, and doing one more leak check on that side. There could still be a small leak between the pitot tube and pitot line, but the air lost through any leak there would be quickly replenished by air coming in the pitot tube, and the effect on pitot pressure would be very small.

Another approach to a pitot leak check, given the design of the Dynon pitot, might be to somehow connect the test pressure to both the pitot and AOA ports, and cover the drain holes in the side. Would that work?
I really think it is these darn static ports and their shape. I am tempted to shave them flush and do what Scott Will did and install the pop rivet over them.
Click to expand...
It is quite possible that this shape is the cause of the issue. I suspect that the closer you can come to the shape of Van's specified static port the less error you will have. But, there is no point to making any changes until you have a good baseline test to compare future results against.

I'm going to be on the road for the next week, so I'll have limited web access. I'll keep an eye on this thread, but my replies might be delayed.
 
Bran, try a quick flight with the static hose off (cabin static). You'll have error still, but if your readings get more sensible you've narrowed it to your ports. I'm still having trouble visualizing why vans static location/port shape is so touchy. Lotsa ragbags don't even read external static. Is it the wide speed envelope? I dunno.
 
Moisture accumulation?

Brian,

I noticed that you T'd the left and right static ports to the top. Per Van's instructions, the two ports are to be T'd on the left side, close to the left port. Any moisture accumulation in the lines will have the opportunity to drain via the left port (at some point in time... steep climbs, un-coordinated turns, or just pushing the tail down when on the ground), especially if the static line run is kept under the longeron (horizontal run).

Just a wild stab in the dark .... but you may want to check if the static line has moisture in it, and needs to be drained.
 
Kevin,

The ASI error check was last evening.......very recent data.

I will try and get a run in before making any changes.

Thanks for all your willingness to help! The tools you have made available are awesome. I just don't know if I understand how to use all of them.

Best regards!


.
Kevin Horton said:
How long ago did you do the ASI instrument error check? Is there any chance a new pitot system leak has arrived since that time?

It is quite possible that this shape is the cause of the issue. I suspect that the closer you can come to the shape of Van's specified static port the less error you will have. But, there is no point to making any changes until you have a good baseline test to compare future results against.

I'm going to be on the road for the next week, so I'll have limited web access. I'll keep an eye on this thread, but my replies might be delayed.
Click to expand...
 
No moisture in the lines. Dry as a bone. Ground checks are fine. It is an in flight issue. Moisture would not be specific.

There are various different opinions on where the T should be on a dual port setup. Most agree that the most accurate place for the T is in the middle. I put mine up high to prevent any moisture from being able to get in there.

The plane has never been outside in anything but great weather.

Thanks!!

Lycosaurus said:
Brian,

I noticed that you T'd the left and right static ports to the top. Per Van's instructions, the two ports are to be T'd on the left side, close to the left port. Any moisture accumulation in the lines will have the opportunity to drain via the left port (at some point in time... steep climbs, un-coordinated turns, or just pushing the tail down when on the ground), especially if the static line run is kept under the longeron (horizontal run).

Just a wild stab in the dark .... but you may want to check if the static line has moisture in it, and needs to be drained.
Click to expand...
 
aerhed said:
Bran, try a quick flight with the static hose off (cabin static). You'll have error still, but if your readings get more sensible you've narrowed it to your ports. I'm still having trouble visualizing why vans static location/port shape is so touchy. Lotsa ragbags don't even read external static. Is it the wide speed envelope? I dunno.
Click to expand...

I think I may install an alternate static port as I have the parts to do it and see what happens....I will fix it so I can plug and unplug it while in flight. I know the inside pressure is going to be lower than the correct static pressure so I would expect to see a large swing up in both my ALT and ASI. Not sure what this will get me...It is almost a guarantee that it is the ports at this point.
 
Just as a data point Brian, I have had static leaks behind the panel a couple of times, and the airspeed error is significant. the good news if you test it with the line disconnected inside the fuse, the error will be fairly linear - not the erratic behavior that you reported in your first post.

I am afraid that I have to agree with your conclusion that it is probably the shape of the ports. The truth is that one of the hardest things to do with a new airplane in flight test is finding a good, consistent static source - it can take hundreds of hours to do this in some cases.So once a designers says "make the static ports like this!", I pretty much figure I'll use his recommendation. The pop rivets look chincy, but field experience says they work.

Paul
 
aerhed said:
Bran, try a quick flight with the static hose off (cabin static). You'll have error still, but if your readings get more sensible you've narrowed it to your ports.
Click to expand...
One thing to keep in mind as you flight test various mods is that this may have an effect on the airspeed errors on approach. The IAS that was just perfect before for the approach and landing may now be completely wrong.

Whenever you fly after making a change to the static system, do a stall and check the stall speed before coming back to land. Based on the new stall IAS, pick an approach IAS, then try a simulated approach and flare at altitude. Confirm you have adequate controllability, and enough airspeed to easily get to zero rate of descent, using your normal throttle reduction in the flare.
 
Amen Kevin,

This is one of those things that causes me to pause before messing with the static system.

Last evening when I added the tape to fair in the ports, the first thing I did was climb up to altitude and do some stalls. I did not want that change to go way on the other side of the curve and cause me to stall on final. The good thing with an RV is that you can almost measure final approach speed by how fast you are sinking on final.

My errors at stall air speeds were about 10 knots estimate based on where most RV7's stall. I was indicating a stall speed of about 45kts clean and 38-40 knots dirty.

Kevin Horton said:
One thing to keep in mind as you flight test various mods is that this may have an effect on the airspeed errors on approach. The IAS that was just perfect before for the approach and landing may now be completely wrong.

Whenever you fly after making a change to the static system, do a stall and check the stall speed before coming back to land. Based on the new stall IAS, pick an approach IAS, then try a simulated approach and flare at altitude. Confirm you have adequate controllability, and enough airspeed to easily get to zero rate of descent, using your normal throttle reduction in the flare.
Click to expand...
 
I had thought the pop rivet ports seemed a little cheesy so I installed 2 machined ports from Cleaveland Tool.They were almost completely flush with the skin when installed but I went with them anyway. After a couple of flights it was clear I was indicating low and slow. The A/S was close during slow flight and stall but got progressively worse as A/S increased.

I drilled a couple of 5/32 AN470 rivet heads and bonded them ovet the ports to give them some protrusion. This was worse as the A/S and Alt. needles (steam guages) were bouncing around and completely unusable.
Next I shaved the bonded rivet heads down to about .20 - .25" protrusion. The end result looked just like a pulled pop rivet. This version proved to be accurate to less than 50 ft. error and about dead on airspeed at all speed ranges.

FWIW if you try venting the static system to cabin, I had a split static line behind the panel once and this caused an indicated A/S increase of 7 knots at what should have been 165 KTs.

Good Luck
Paul Danclovic
Jamestown NC
RV-8A N181SB
 
pauldan181 said:
FWIW if you try venting the static system to cabin, I had a split static line behind the panel once and this caused an indicated A/S increase of 7 knots at what should have been 165 KTs.

Good Luck
Paul Danclovic
Jamestown NC
RV-8A N181SB
Click to expand...

Thanks Paul. That datapoint will give me an idea on what error one would expect to see on an otherwise normal setup.

I have a feeling that I will see way more rise than that since I am way on the other side of the error curve now...In other words @ what should be 165kts say I am indicating 145kts, unport the static system and I bet it will indicate around 172kts or a rise of 27kts...
 
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Brian,
4 of us have RV8's equipped with D180's, Dynon Pitot's, and the same Safe Air ports as you. We all read identical airspeeds and altitudes when flying in formation. My airspeed also reads the same when I fly next to the RV8 that I built and sold that has the Vans pop rivet static port.
The SafeAir ports work well on the RV8.
Any chance that the AOA and Pitot lines got reversed?
Regards.
 
wrong position?

I could be wrong (as I am not flying yet) but I installed the same ports you have and if I recall, the ports are to be mounted on the exterior of the skin. I started to do mine on the inside until I did some research. This would make the port inlet further from the boundary layer of the fuselage. In my interpretation of theory, this is to eliminate boundary layer sampling which is air that is moving slower and turbulent, therefore at higher pressure than true ambient therefore indicating lower altitude and lower airspeed. I have read here years back that someone else had a similar problem with these ports mounted on the inside as you have.

Another observation, I would spin your tee around so that it tees "up" instead of "down". This way if any moist air gets going side to side between the two ports, and condenses in the crossover tubes, the droplets will not drop into the tee and begin it's travel forward.

my .02

Bevan
 
Nope,

Double checked that the pitot was on the correct line.

The altimeter also reads low which is static only so it all points to the static system.

jthocker said:
Brian,
4 of us have RV8's equipped with D180's, Dynon Pitot's, and the same Safe Air ports as you. We all read identical airspeeds and altitudes when flying in formation. My airspeed also reads the same when I fly next to the RV8 that I built and sold that has the Vans pop rivet static port.
The SafeAir ports work well on the RV8.
Any chance that the AOA and Pitot lines got reversed?
Regards.
Click to expand...
 
The older design of these did not have a protrusion on them that was long enough and when people mounted them on the inside, it resulted in a flush port with the side of the skin.

Now SafeAir makes em with a protrusion on them and this was suppose to solve that problem.

They stick out about the same as one with the pop rivet but they are not shaped like the pop rivet.

It is hard to imagine that this is that critical but it sure enough is....

Bevan said:
I could be wrong (as I am not flying yet) but I installed the same ports you have and if I recall, the ports are to be mounted on the exterior of the skin. I started to do mine on the inside until I did some research. This would make the port inlet further from the boundary layer of the fuselage. In my interpretation of theory, this is to eliminate boundary layer sampling which is air that is moving slower and turbulent, therefore at higher pressure than true ambient therefore indicating lower altitude and lower airspeed. I have read here years back that someone else had a similar problem with these ports mounted on the inside as you have.Bevan
Click to expand...
 
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I bonded a pop rivet head onto the earlier flush static port.
It looks and acts like the Van's port.
I did not test it to the 9th degree.
It can be removed easily.

Tom
 
What's this "pop-rivet" mod? Are you installing the pop-rivet into the static port opening. I assume the hollow shank becomes the new port?

Interesting.
 
I removed the stem and bonded the
rivet head on, aligning the hole with the
existing port. I got the info from this
site in 2006 when I was in phase one
and picked up the error.
I'm not good at searching, but it's in
there somewhere
Tom
 
I agree with Rivethead. Disconnect your static lines from the port fittings and go fly. You will be basically operating as you would if you were using "alternate" static. from my experience alternate static is rarely off by more than 50ft or so on the altimeter. I don't know how the ADAHRS processes the A/S input. I can't imagine it uses static, but maybe.

I have the same static set up as you so I am interested in your results. How did that EGT issue turnout?
 
Just a thought...

....but are you absolutely sure that your static line is entirely clear?
No reading on the runway sounds strange.

A blockage could be acting as a diaphragm/restrictor in the system.
 
Pitot does not effect ALT readings...Dynon has been tested as of late yesterday to be spot on with a manometer.

I installed an alternate air port today that I will be able to access in flight to see what the results are.

My readings are not erratic, just wrong...Info in the original post.

Rivethead said:
MTC, Why don't you just disconnect the static port from the Dynon (take it out of the system) and go fly with it. You're going to get a wrong reading but it won't be as wrong as you're getting now nor as erratic. My vote is there's something wrong on the pitot side or in the Dynon.
Click to expand...
 
yep.... Manometer test are instant reactions. My theory is the error increases with increased airspeed and that counteracts the altitude gain until the alt gain overcomes the error.

Standing still everything is very accurate and checks great with the manometer.

az_gila said:
....but are you absolutely sure that your static line is entirely clear?
No reading on the runway sounds strange.

A blockage could be acting as a diaphragm/restrictor in the system.
Click to expand...
 
Thanks Jim, I am almost positive that it is the ports or the N numbers at this point.

Others have their N numbers there at almost the same spot so it is most likely not the smoking gun.

It may be a combination of several things..
  1. Shape of the ports
  2. N numbers right in front of them
  3. How far the ports protude from the side of the fuse
 
What about a high speed run over the runway?? I live at an 8000 foot runway and can easily make a safe pass at 10 ft and 140kts. If it's a speed related issue I would think it would reveal itself in a test like this?? Make passes at the same altitude and different airspeeds to assess the effect on altitude indications? Or if that doesn't feel safe do something similar at altitude with another airplane acting as the altitude reference. Use that plane to set a stable altitude reference and vary the speed to see what kind of altitude variations you get with speed. You wouldn't have to fly very close to each other to maintain altitude reference.
 
Brian.
Here is a photo of my DIY static port cut from a 10-32 stainless screw. Not a whole lot different than yours.:eek:
k9ge94.jpg

Yesterday I flew a couple of boxes and entered the numbers in Kevin's sheet.
My error was -0.5 & -1.8 not to bad.
My manometer test was not as good as yours.:eek:
2lt4y6q.jpg
 
Frank,

How far do your ports extend from the fuse? Are the edges more rounded over or square?

Where are the ports located on the 9, are they the same as the 7?

Looks like over all your Dynon beats the Van's ASI on accuracy....I bet if you wanted, you could reset the Zero Pressure on the Dynon and get better accuracy on the low end. I would not mess with it though with that small error.

I have not been able to do any runs yet since the wind has been howling around here and most of the time crosswind. I have not honed my crosswind skills yet with the wheel in the back....I need to ease into that!
 
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Brantel said:
Frank,

How far do your ports extend from the fuse? Are the edges more rounded over or square?
.032 0ut, slight rounding.

Where are the ports located on the 9, are they the same as the 7?
Same place as the 7

Looks like over all your Dynon beats the Van's ASI on accuracy....I bet if you wanted, you could reset the Zero Pressure on the Dynon and get better accuracy on the low end. I would not mess with it though with that small error.
Hmmm?? better read the book again....:confused:

I have not been able to do any runs yet since the wind has been howling around here and most of the time crosswind. I have not honed my crosswind skills yet with the wheel in the back....I need to ease into that!
Click to expand...

123456789 10
 
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???????
 
isolate static to just dynon...

do you have your static split to other instruments beside the dynon? if so perhaps there is an internal leak or other failure that only reveals itself with flight... it might be worth it to isolate your static supply one instrument at a time.
 
Brantel said:
What is different on my install???????
Click to expand...


Maybe because you're actually doing TESTING during Phase 1?! :eek::D

Couldn't resist, but it's a little bit true. Many RV guys just bore holes in the sky during Phase 1, and never test or calibrate a thing....
 
I have been following this conversation on and off with interest because I have a not dissimilar problem, though my speed and altitude read high.

I very recently, and serendipitously, finally confirmed the problem. I mounted a camera in the cabin to make a short video and the altimeter shows up in the picture.

At the start of the ground roll, when you put all the power in there is a distinct increase in altitude. Because of the vibration it is hard to be exact, but perhaps 30 or 40 feet. Interestingly, the landings do not show the same change. At low power, on approach and to the point of touch down, the altimeter appears to be reading about correctly. It is back where it started before the roll out is complete.

My assumption is therefore that the error is due to high speed air over the ports, which are by the way the standard VANS pop rivets. At this stage I am not sure what if anything I plan to do about it. I would like perfect statics but perhaps I will just end up frustrated and chasing my tail. I have mostly learned to adjust for it.

I have separately computed the speed error in the cruise to be about 7mph. I wonder how that compares with 30 or 40'. I will have to dig that out.

If you want to see the video, it is the one referenced in my signature strip below. "Circuits"
 
I second the suggestion of high speed passes over the runway. This helped me to isolate and correct a static error in a few quick flights.
Set your altimeter to field elevation before take off and do a quick low and over circuit at cruise speed. Fly as low as you feel safe doing so and note the altimeter reading. Mine was reading about 250 feet high.
I landed and built up the area in front of my static ports. My static port is on the pitot tube but the theory is the same. I simply used a few wraps of stainless safety wire and then flew again. Better; but not enough. A few more wraps and I had it as close as would be needed for my missions. The altitude now closely matches the gps model and airspeed numbers are very close when I use the four leg gps system and work backwards to calculate TAS and CAS. They are at least as close as what I would call my personal pilot error.
In your case I would build a stack of electrician?s tape in front of the static port. Build it higher then the port. Before flight, make sure that you have an alternate static system that is easy to open and close and then go and see what happens.
It might take you a few runs to get the right combination and then you can make a beautiful little aluminium piece to replace the tape. The beauty of this system is that any time you feel like going a bit faster you can simply remove the dam.
 
Nope....One Dynon is it......both pitot and static is a straight shot to the Dynon...

Manometer testing on the ground has eliminated the Dynon as
the problem.

[email protected] said:
do you have your static split to other instruments beside the dynon? if so perhaps there is an internal leak or other failure that only reveals itself with flight... it might be worth it to isolate your static supply one instrument at a time.
Click to expand...
 
Thanks Paul. I actually thought this as well....

Ironflight said:
Maybe because you're actually doing TESTING during Phase 1?! :eek::D

Couldn't resist, but it's a little bit true. Many RV guys just bore holes in the sky during Phase 1, and never test or calibrate a thing....
Click to expand...
 
Brian,
Here is 50 seconds of my last take off, Dynon recorded at 1 sec interval.
(A reason to use glass):cool:
Something for you to compare?
352rgbt.jpg
[/IMG]
 
I did a ton of flight testing in this area a few years back, even had three altimeters hooked up at one point with different pitot/static combinations, and finally concluded it was impossible to get instrument readings that were totally accurate across the speed/altitude range of the aircraft. I did discover that the pitot tube could be offset by as much as 45 degrees and it did not seem to matter. A small moon shaped fence in front of the static port seemed to provide the most accurate information so it stayed.

This was all done on a different airplane. With the RV, I decided Van's had probably placed the static port in the best place and with the pitot out of the prop blast on the wing, it was about as good as it can be. I have Van's tube on the left and the Dynon on the right. The ASI's are within 2-3 knots with the Vans's gage always reading higher. The Dynon AOA has been calibrated and is used on every approach.

All that being said, accuracy of flight instruments is important and to illustrate how difficult it is to achieve such results, the heavy equipment I flew in a previous life had a computer system that corrected known errors determined from flight testing. Primary gages were electrically driven with that information and reverted to pressure instruments without power or there was a backup mechanical gage. The altimeter error could be 300-400 feet up high. Airspeed errors were minimal.

It is interesting doing the flight testing you are doing with regard to the static port but in all likelihood Van's has been down that road and the plan installation is probably about as good as it gets without additional equipment to compensate for the various errors present.
 
While I agree that the location of the port should not be questioned, the other variables around the static system in my case are too far off to ignore. I cannot accept that I will have to live with the amount of error that I have.

In the end, I bet I will end up with the SafeAir1 ports shaved smooth or drilled to accept the same Pop rivet that Van's provides in their static kit.


David-aviator said:
It is interesting doing the flight testing you are doing with regard to the static port but in all likelihood Van's has been down that road and the plan installation is probably about as good as it gets without additional equipment to compensate for the various errors present.
Click to expand...
 
Frank gave me an idea to go plot my EFIS data... Here is the first four flights. I can only compare IAS to GS at this time since I did not have the GPS Alt sentence turned on on my GPS....therefore my EFIS did not log it.

I know GS and IAS will be different so I added a poly trend to the data and since all of these flights were pretty much circling the field, the average should be somewhat of a representation of what my error is.

As you will see, the error trends start to really seperate around 100knots. The average error between the trends is 12 - 14 knots with the IAS being low.

2mxk9s8.jpg


1z4wvb7.jpg


vf8555.jpg


2dgmjxs.jpg


Question for the math experts, if you have a 12-14 knot low IAS that was caused by a high static pressure error, what would the expected low ALT error be?
 
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Yep, My bad, you are correct...I was in a hurry...High Static Pressure causing Low IAS and ALT... Sorry, original post corrected.

Rivethead said:
It may be just that it's to early for me to think straight but shouldn't low static pressure cause a higher indicated speed reading. Please excuse me if I'm being stupid.
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Is your static tubing getting pinched somehow? and keeping the higher pressure in the line?
 
nope... Not possible. There are no kinks or pinch points in my lines. Straight up to the Dynon. There are no restrictions in my sytem as proved by ground manometer testing....instant reactions on both IAS and ALT

Radomir said:
Is your static tubing getting pinched somehow? and keeping the higher pressure in the line?
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The answer to your question is in your question. Obviously the "opening" of the ports are not in an area stagnant air. Assuming that the Van's recommended port location is the best location, either the shape of the ports or their extension from the side or the N numbers stuck on in front of them is causing interferance resulting in a higher than reality pressure in the static line which results in my readings being low on both ASI and the ALT.

Not sure what having a leak on the inside of the aircraft has to do with my situation other than if that happens, you get the opposite error that I have. There are no leaks in my system as proved by ground manometer testing.

Would one think that there is enough difference in the 6 vs the 7 that Vans has the 7's port one bulkhead further aft than that of the 6? I sure would not.

Rivethead said:
It seems a tad unreasonable that your ports are creating a high pressure at worst they should be creating low pressure. Given the variables in the airflow around our fuselages I would think it's only fair to expect an average. It's a bit like trying to catch a live fire hose after it's been dropped.
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Thanks for all the help guys....I have not had the chance to do much more flying. I hope to get some more in tommorrow.

I appreciate all the replies...I appreciate all the help! I hope one of you come up with the smoking gun! So far I have been able to list a bunch of items/issues that are not the problem...
 
Just a thought. Next time you fly, tape over one port and then the other to see if there's any difference between the two, or when using "both". Not sure what it would suggest other than to possibly isolate the problem, or rule something out. OK I'm really tired. :rolleyes:

Bevan
 
It is not easy to get an over pressure static by disturbing to flow over the port - the usual result would be a low static reading. I almost typed never, but thought better of it. Just think about it, the static ports are a little proud of the surface, so the air is accelerated slightly as it passes over them, so the pressure reduces - you would need some kind of dam behind the port to raise the pressure.

I think the most likely culprit is a leaky static in the cockpit, as cockpit static is usually higher than ambient. I know you have stated that the manometer testing ruled that out - but are you really sure (sorry haven't read all the posts)? If you pressuise the pitot it doesn't matter if there is a cockpit static leak - its all at the same pressure. Have you have an altimeter test guy put one of those fancy vacuum suckers on the static ports? Last time I had it done it was $90. Can you borrow a huff & puff ASI & Alt, hook them up and compare with the Dynon?

Failing that, have someone who has had nothing to do with your project come and do a pitot static check, and compare results. Perhaps there's something wrong, and because you have looked at it so often you're just not seeing it?

Pete
 
as cockpit static is usually higher than ambient.

Pete, I thought cockpit static is usually Lower than ambient. Caused by the airflow around the fuse pulling the the air inside the cockpit out and creating a slightly lower pressure inside the cockpit.
 
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