What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

G3X pitot static help

Flyyak

Well Known Member
Friend
Still having trouble trying to calibrate AOA with G3X. I have a GSU73 and GSU25. I can calibrate the Minimum Visible and the Caution Alert but when calibrating the Stall Warning, I get a message that calibration is successful but when getting back to main screen by use of the back button, I get 0.000 as the value and a message AOA calibrations not valid. I have cleared the calibrations and started over on several separate flights and retried today about 4 separate times. Always the same, calibration of Stall Warning initially successful but then 0.000 value an not valid message.

Our great friend Steve, longez, has suggested that I may have inadvertently damaged an AOA sensor during a pitot static check. I have had 3 pitot checks since 2016(1st flight).

I understand that there is a “caution” when performing the pitot check that may not have followed but I do not know.I am hoping that one of our other installation guru’s may be able to tell me how to check to see if there is damage to my AOA sensor. Thanks
 
No real reply at this point except to re-emphasize the procedure. I have indicated that it would appear that the procedure and initial system appears to work, only the final calibration is successful until the “Back” button is selected, then it becomes invalid.

I am waiting to hear and hopefully g3xpert’s may have something to check.
 
I have seen blown AOA sensors on the GSU25 from folks having the P-S check done by shops not familiar with AOA ports, failing to tie the AOA into the system will blow the sensor.

There are P-S test boxes out there that can separately control the AOA pressure, but they are not in my budget. So I just tie the AOA port to pitot when testing. The AOA indication comes up when I do this on a calibrated system as the brains thinks the airplane is at a very high AOA (P and A pressure are the same).
 
No real reply at this point except to re-emphasize the procedure. I have indicated that it would appear that the procedure and initial system appears to work, only the final calibration is successful until the “Back” button is selected, then it becomes invalid.

I am waiting to hear and hopefully g3xpert’s may have something to check.

There are a few areas where you have to hit a done or save button instead of the back button. It sounds like that may be the case here. Maybe trying hitting enter instead of back or look for a different button, like "done" or "save."

Too many years ago to remember what I pressed in that step.
 
Make sure you following the cal procedure/order in the manual:
34.4.6.2 AOA Calibration Procedure
 
AOA calibration

I completed a leak test and discovered two leaks where connectors had loosened. After determining that all the tubing and connectors were secure, tight and leak free, I discovered that the Pitot/AOA probe was leaking. I taped/blocked the AOA probe hole just underneath the probe for the test with a manometer and our test probe covered the front of the probe an the AOA inlets. The probe was leaking but the system was leak free from the probe tube connectors just aft of the probe connectors. I could not determine the origin of the leak except when I connected the probe. I removed the probe from the RV and secured the probe pitot tube and the AOA tube and injected air in the front of the probe via a syringe. The AOA hole underneath the probe remained blocked/sealed.

I discovered leaks coming out of the probe at the top where the Pitot and AOA tubes and heating wires exited the epoxy filled body where the probe attaches to the pitot mast. As far as I can tell the pitot system has operated accurately on my G3X non touch system without the AOA operational. Maybe as a result of the air pressure received in flight. We discovered the leak by placing the probe in a bucket of water to observe the leaks coming from underneath the epoxy and some air bubbles coming out of the screw holes that are used to attach the probe to the mast.

I cannot imagine how the probe leaks could have become defective when the probe is attached to a rigid mast and the tubes are secured to a wing rib to prevent vibration or movement. Without a diagram of the probe, I do not know how the pitot and AOA tubes are connected underneath the epoxy filler.

Has anyone had or discovered a leak like this. Maybe the g3xperts can help with a diagram of the pitot/AOA probe or if this has happened on other probes.

I would assume that this is the reason the AOA calibrations will not be accepted by the GSU25 but the airspeed works. No leaks with the static system.
 
…. So I just tie the AOA port to pitot when testing. The AOA indication comes up when I do this on a calibrated system as the brains thinks the airplane is at a very high AOA (P and A pressure are the same).
Walt,
Do you have a picture or diagram of how you do this? Thx
 
Walt,
Do you have a picture or diagram of how you do this? Thx

Nothing more than a hose large enough to slip over the pitot probe then clamped at rear to effect a seal. Covers the drain holes at the same time.
Then some standard adapters to fit my pitot test hose.
 
The manual has some specs for acceptable leak rates of the pitot probe itself, not sure of an acceptable rate for the AOA side.
Minor leaks on the pitot side don’t usually have much effect on airspeed so my feeling are it wouldn’t effect AOA calibration.
A large leak on the AOA side would be a concern.
I think Garmin had some probes early on that exhibited some pitot leaking hence the manual reference.
 
Last edited:
Let's dive a bit deeper and try to isolate the sensor response. Assume that the pressure sensor for the AOA has a much smaller range of pressures it will tolerate, we know that it does.

I believe that the AOA ports sees pretty much the same pressure range that the pitot does and the sensor is likely the same one used for the pitot. At high angles of attack, the pressures will be pretty close. This is confirmed by the fact that guys like Walt apply the same pressure to the AOA and Pitot in testing. It is highly likely that if an differential calcs are done, it is in the software.

It is the S/W that is very sensitive. After doing calibrations, I notice that the Voltage readings displayed for each of the calibration settings go out three or four places to the right of the decimal point.

Larry
 
Last edited:
What is actionable for the OP here?

I believe that the AOA ports sees pretty much the same pressure range that the pitot does and the sensor is likely the same one used for the pitot. At high angles of attack, the pressures will be pretty close. This is confirmed by the fact that guys like Walt apply the same pressure to the AOA and Pitot in testing. It is highly likely that if an differential calcs are done, it is in the software.

It is the S/W that is very sensitive. After doing calibrations, I notice that the Voltage readings displayed for each of the calibration settings go out three or four places to the right of the decimal point.

Larry

While all you said may be correct, should the OP should not test his sensor?? Keep doing the same thing or send the GSU 25 back to Garmin??
 
While all you said may be correct, should the OP should not test his sensor?? Keep doing the same thing or send the GSU 25 back to Garmin??

Agreed. However, that fact that he can successfully calibrate the other 2 AOA settings would imply that the sensor is working. It could be defective and reading incorrectly, but the fact that the OP sees the calibration successfully complete before going back and losing it, would imply that the readings captured on the AOA are reasonable and in line with expectations by the S/W. This kind of feels like a S/W or configuration issue or readings that are too far out of the norm to calibrate. However, I don't believe there is a tool in the s/w for someone to observe raw pressure readings on the AOA, so no way for the OP to test it. Garmin only offers the calibration tool and displays the voltage point for each setting, post calibration.

Curious what the folks at garmin have to say about this issue.

Can't help but wonder if one of the other two settings was done incorrectly and when doing the last calibration it is seeing a number that is lower, but should be higher than the others and then dumps it, due to being illogical. Might make sense to delete the AOA settings and run all of the calibrations again and see if that resolves it. minimum visible should be the lowest pressure/voltage, with the caution next and the stall the highest. Pressures should increase as the angle of attack increases. Increased angle of attack exposes more of the angled hole and therefore pressure reads higher, relative to the pitot pressure.

Larry
 
Last edited:
I sent the OP my AOA values which differ quite a bit from his, my thoughts are still, unless he had a large AOA leak the sensor was probably the culprit.
A lot of back and forth but no way to test the sensor that I’m aware of.
 
I have emailed my data logs of the calibration test to Garmin along with videos of my leaking probe. I have tried the calibration procedures on 4 or 5 different flights using the procedures set forth in the manual. On each flight I started by clearing the prior calibrations and following the procedures again. The last flight I used the autopilot for minimum visible and caution alert then hand flew through power off stall. (Tried 4 times, clearing each time) Same result each time. The calibrations accepted for minimum visible and caution alert and stall warning. Stall warning indicated calibration successful but then AOA indicates calibration not valid.

If data logs or pitot probe videos do not help Garmin, I guess the next step is to return the GSU25 for inspection or repair.

Thanks Walt for your assistance which help me determine leaks and correct them and thanks Bill for your suggestion to attempt to determine if the sensor is operational but I doubt I could interpret the results. I will keep you posted.
 
AOA calibration and pitot static leak test

I am embarrassed to say that I have determined that the issues with my AOA were the result of my errors and not Garmin instruments or equipment. After spending multiple consultations with g3xperts and vansairforce builder supporters, I have located leaks in my pitot system which caused erroneous calibration information to the GSU25. I thought I had thoroughly tested every leg of the system and had secured or determined all legs were leak free. I still had leaks at the pitot probe. I read in the manual that the probe was allowed a certain amount of leaking but I was sure that had to be the culprit. As I removed the probe I thought I discovered a leak where I had allowed a flared aluminum fitting from the pitot probe to become loose where it connected to the flexible nylon tubing. I removed the probe and discovered leaks coming out of the epoxy filled area where the wiring and aluminum tubes exit the probe. I reinstalled the probe and made certain my flared fittings were secure. Fortunately, some of our experts (Walt and Steve, great guys) (which we are lucky to have on our forum), advised me that if a check of the complete system failed to hold airspeed constant or within the acceptable parameters, then I still had leaks. If I still had leaks, my AOA calibrations may not be accurate or valid.

I performed one last leak test with a manometer and by taping/securing the drain holes and AOA hole under the probe. I was surprised that even with the leaks that I found in the probe (videos available by email if desired), the airspeed held absolutely constant, indicating a leak free system.
The weather co-operated early in the AM with smooth air and I was able to calibrate all functions of the AOA. I still have to fine tune the settings and learn how the AOA will work best for me but it works. The heated GAP26 pitot/AOA probe and the GSU25 both operate correctly. I have learned a great deal about the G3X system and will be very aware of a technician that is testing my pitot-static and transponder on the bi-annual certification.

I am very thankful for the expertise, contributions and patience of our members to this forum.

HERE ARE A COUPLE OF SUGGESTIONS THAT I LEARNED IN THIS PROCESS .

BE CAREFUL WHEN PRESSURE TESTING. Read the manual to discover the cautions set forth before pressure or leak testing. I was afraid that I, or a technician not familiar with G3X or our experimental EFIS systems may have caused damage to my AOA sensor. I have had three calibrations and transponder bi annual test performed prior to installing a Touch system with AOA cababilities. I have learned that these are very sensitive. I also learned that the push to connect connectors can be very reliable. I purchased mine from SteinAir and a local company that sells Parker connectors (both stainless steel and quality plastic). None of my connectors leaked.

1. I constructed a very easy and cheap manometer using a ½'’ vinyl tube (lowes) after looking at the multiple post on this forum. I was not necessarily looking for precise measurement but changes which would occur from leaks.

2. I first disconnected my nylon tubing from instruments and tested each leg if the line had tees or connections to non instruments (GSUs and G5) to make sure all connections were leak free. It also helped me to make sure I was not over pressurizing so that when I connected legs with the instruments (GSU73 and GSU25) that I did not over pressurize.

3. When I determined that the all legs and connectors were leak free including all attachments to instruments, I reattached the tubing to each connector by cutting the end so that the nylon tubing at the connectors had a fresh end to be reconnected in the fitting. I previously had a two screen non touch and I replaced with single screen touch and added a G5 so the tubing had been removed and reinserted probably multiple times.

4. Be sure to tape/secure all drain holes or the hole under the pitot/AOA probe before any pressure is applied

This procedure is really not as hard as I had convinced myself that it would be.

Thanks also to g3xperts who have patiently helped me install, trouble shoot and configure all the garmin instruments.
 
Congratulations!

Good for you!! No one finishes an airplane with everything working without perseverance (and friends!!!) . Happy to hear it was the little things - they are the most difficult.

I wrestled with the leaks too, and found most were in my shoddy test rig - new fittings and care allowed the internal battle to be won. It took days.
 
Back
Top