GFC500 problem

[rbp]

all of these unsolved GFC 500 issues raise the question of whether we need to go to garmin as a group

my feeling is that garmin is trying to treat each report as a separate issue — diving and conquering, and that some owners have just thrown up their hands

I’d like IAS mode to work as advertised in my plane

[rbp]

After having all the mechanicals checked and set to spec, they next step was the pitot/static system

IThey inspected and tested the entire static tubing and pitot tubing, and found no blockages, kinks, holes, or anything else.

The last possibility was a leak in the gear safety switch, which they disconnected and sealed off so I could test fly it, which I did late last week.

The IAS oscillations persist

I did try the trick of setting the VS and getting it stabilized and then switching to IAS. because there was so much lift, i kept having to set the ALT bug higher and climb out at 130 (instead of 120). I established a climb at in VS  @ 130, and then switch to IAS, which it held +/- 3 knots. then i rolled it down to 125 and 120, and the airspeed oscillations increased both times.

Last discussion I had with @TrekLawler was to bring my plane to Garmin, but they are looking for a J or K, not an M

at this point in time, I am at a loss as to what to do

[Fly Boomer]

2 minutes ago, rbp said:

at this point in time, I am at a loss as to what to do

So frustrating.  I can't even imagine.  It's one thing to spend a lot, and get a lot.  It even occasionally happens that we spend a little and get a lot.  But the worst is to spend a lot, and get something that doesn't work right.  Followed by more money trying to get it to work right.  I suppose if I look at it from Garmin's perspective, we are a small and shrinking market.  They will spend their resources chasing the biggest revenue potential.  It's a business.

[PeytonM]

Not a sustainable business model…or one to be proud of. 

[donkaye]

3 hours ago, rbp said:

After having all the mechanicals checked and set to spec, they next step was the pitot/static system

IThey inspected and tested the entire static tubing and pitot tubing, and found no blockages, kinks, holes, or anything else.

The last possibility was a leak in the gear safety switch, which they disconnected and sealed off so I could test fly it, which I did late last week.

The IAS oscillations persist

I did try the trick of setting the VS and getting it stabilized and then switching to IAS. because there was so much lift, i kept having to set the ALT bug higher and climb out at 130 (instead of 120). I established a climb at in VS  @ 130, and then switch to IAS, which it held +/- 3 knots. then i rolled it down to 125 and 120, and the airspeed oscillations increased both times.

Last discussion I had with @TrekLawler was to bring my plane to Garmin, but they are looking for a J or K, not an M

at this point in time, I am at a loss as to what to do

Does your elevator "glide like butter" when you move it during preflight?  Is there any resistance "at all" any place in the total movement?  If it doesn't "glide" or there is resistance at any time during the movement, then you will have pitch oscillation issues--at least with the M Model Mooney.  The KFC 150 was not so sensitive to resistance, but the GFC 500 is.

I personally was very embarrassed when I went to Garmin on my way to Oshkosh several years ago.  As one of the first M installations, I was experiencing pitch oscillation and they agreed to let me come to Olathe to look at it.  First, the pilot who did the flight testing for the M flew with me and acknowledged there was a problem.  Back on the ground they found the problem instantly when they opened up the O2 and number 2 battery inspection cover.  The installer had not installed the braces for the pitch trim servo, so the assembly was moving back and forth during flight.  I think Trek has said most of the issues are installation problems.

[rbp]

58 minutes ago, donkaye said:

Does your elevator "glide like butter" when you move it during preflight?  Is there any resistance "at all" any place in the total movement?  If it doesn't "glide" or there is resistance at any time during the movement, then you will have pitch oscillation issues--at least with the M Model Mooney.  The KFC 150 was not so sensitive to resistance, but the GFC 500 is.

I personally was very embarrassed when I went to Garmin on my way to Oshkosh several years ago.  As one of the first M installations, I was experiencing pitch oscillation and they agreed to let me come to Olathe to look at it.  First, the pilot who did the flight testing for the M flew with me and acknowledged there was a problem  Back on the ground they found the problem instantly when they opened up the O2 and number 2 battery inspection cover.  The installer had not installed the braces for the pitch trim servo, so the assembly was moving back and forth during flight.  I think Trek has said most of the issues are installation problems.

There is no discernible stickiness
 

the shop has inspected and tested and adjusted every thing in the airframe that Garmin has asked for. 
 

——

6. Trouble shoot Garmin GFC500 autopilot for having a pitch oscillation when selected to indicated airspeed mode. Go through Garmin supplied autopilot troubleshooting checklist. Adjust bridal cable tension for roll, pitch and yaw servosto the top ofthe spec. Found leaks in pitot and static systems. Repair leaks in pitot and static system. Confirm addendum gain settings are correct as per Doc. 005-01470-17 Rev. 4. [12 hrs.]
7. Inspect pitot line from mask all along to ADC and G5 connection for blockages or kinks. Inspection of line is OK. [5 hrs.]

 

[PeytonM]

I’ve been thru the rigamarole, including 4 guys from Garmin out to look at the install. They found nothing. I’m almost a year into this with no solution in sight. I’m guessing there are a dozen of us on MS with the same issue across many models. And that’s just MS. 

[ArtVandelay]

I did try the trick of setting the VS and getting it stabilized and then switching to IAS. because there was so much lift, i kept having to set the ALT bug higher and climb out at 130 (instead of 120). I established a climb at in VS  @ 130, and then switch to IAS, which it held +/- 3 knots. then i rolled it down to 125 and 120, and the airspeed oscillations increased both times.
Last discussion I had with [mention=12081]TrekLawler[/mention] was to bring my plane to Garmin, but they are looking for a J or K, not an M

I’ve never tried changing the IAS after enabling IAS mode, but the +/- few knots is normal for me and barely noticeable. I will try that next time.
I have a J but not going to Minnesota anytime soon and unless it’s abruptly changing airspeeds I wouldn’t care as long as it stays within reasonable range (+/- 5 knots).

[TrekLawler]

3 hours ago, rbp said:

After having all the mechanicals checked and set to spec, they next step was the pitot/static system

IThey inspected and tested the entire static tubing and pitot tubing, and found no blockages, kinks, holes, or anything else.

The last possibility was a leak in the gear safety switch, which they disconnected and sealed off so I could test fly it, which I did late last week.

The IAS oscillations persist

I did try the trick of setting the VS and getting it stabilized and then switching to IAS. because there was so much lift, i kept having to set the ALT bug higher and climb out at 130 (instead of 120). I established a climb at in VS  @ 130, and then switch to IAS, which it held +/- 3 knots. then i rolled it down to 125 and 120, and the airspeed oscillations increased both times.

Last discussion I had with @TrekLawler was to bring my plane to Garmin, but they are looking for a J or K, not an M

at this point in time, I am at a loss as to what to do

Hello Bob,

   I did receive your email and will respond to it as well, but figured I'd take this opportunity since you mentioned our conversation. we're not just sweeping this under the rug so to speak, we're going to investigate it more closely but as I mentioned and have discussed with a couple of Mooney owners, we're looking at a "J" or "K" model to re-evalaute. so if there are any of these models that are seeing these oscillations and would be willing to allow us to look at your plane, please send me a personal message and I'll be happy to get everyone needed in sync on this so we can try and get these problems resolved.

[rbp]

33 minutes ago, TrekLawler said:

we're not just sweeping this under the rug

I definitely feel like you + G want this resolved!

[rbp]

2 hours ago, Evan said:

Wanted to give another data point for this thread. I have the 500 with a G3x. I too noticed that I had some pretty major pitch oscillations, especially during bumpy air. In smooth air, it was ok but never as good as the GFC700 planes I've flown.  

The first thing I did was put some LPS silicon spray on the control shafts, on both sides, The before and after were pretty crazy. My yoke now glides like butter. I went out and flew on a smooth day and sure enough, IAS mode held within a couple of knots and did so by changing pitch only a couple of degrees. 

I know you've said you've tried but maybe try silicon spray? My IAS still doesn't work the greatest in turbulent air but I believe that is to be expected. I usually use VS mode until a couple of thousand feet and then switch to IAS. Hope this helps. 

thanks -- I emailed my A&P about this

[philiplane]

It sure seems like the GFC500 needs perfection in order to work properly. Dozens of reports from owners of all brands of airplanes too. 

I sure am happy with my Century III and would never switch if the Garmin AP can't perform well without constant attention to details. Servo failures, cable tension drama... too much work for a new digital autopilot that will likely be obsolete in 15 years, while I can maintain my Century III forever with standard parts from Radio Shack. Well, maybe not Radio Shack, but Mouser or Allied Electronics.

[PT20J]

I have posted about this before and I have sent information to Trek.

The pitch control/trim system changed between the J and K models. M20Js and before had trim assist bungees which are elevator centering springs with the center point adjustable depending on the trim setting. M20Ks and later had a elevator bob weight and a down spring that is adjustable with trim setting. I don't know how this might affect the autopilot, but there is a difference.

Starting with mid M20Js and continued on subsequent models, the control shaft bearing at the control panel is an eyeball and cup assembly machined from Nylatron. The M20J service manual specifies lubrication with Triflow. Later model service manuals say to keep it dry. The problem with lubrication is that the lubricant attracts dust and that forms an abrasive and the whole assembly gets sticky. It is easy to replace the eyeballs when the panel is apart during an upgrade and rather arduous to replace them when the panel is assembled. I had mine replaced when I upgraded the panel on an airplane that only had 1200 hours on it. I felt the motion of the new and old eyeballs and the old ones were considerably stiffer. This is important because the control shaft does not move linearly back and forth, but rather moves in an arc, and so sticky eyeballs will cause stiction in the control system. Sometimes lubricating the control shafts helps some because when the eyeball sticks it slightly binds the shaft. But, I would use silicone spray and wipe it off so that no oily film is left behind.

Lastly, in my M20J, I noted that the GFC 500 pitch control dynamics in IAS is extremely sensitive to bridle cable tension. The Garmin turnbuckle uses safety clips so the adjustment is limited to half turns of the barrel. In my airplane, half a turn went from the low end of the spec to the high end of the spec. and made a noticeable improvement in the IAS mode. I would recheck cable tensions after a year because the new cables may stretch some.

So, in summary, my M20J GFC 500 performs well, but I replaced the control shaft eyeballs and had the cable tension tightened to the max. 

Skip

 

 

 

[donkaye]

13 hours ago, philiplane said:

It sure seems like the GFC500 needs perfection in order to work properly. Dozens of reports from owners of all brands of airplanes too. 

I sure am happy with my Century III and would never switch if the Garmin AP can't perform well without constant attention to details. Servo failures, cable tension drama... too much work for a new digital autopilot that will likely be obsolete in 15 years, while I can maintain my Century III forever with standard parts from Radio Shack. Well, maybe not Radio Shack, but Mouser or Allied Electronics.

I love the GFC 500.  It is so much better than the KFC 150.  The brushless servo design is so much better than the BK servos and much less expensive should they have to be replaced at some point.  We're hearing a lot about issues with the GFC 500 and I hope those issues get resolved for those having problems with it.  However, for me, with all of its functionality the GFC 500 is worth every penny I paid for it.  Knock on wood, 3 years and going strong in all phases of its operation.

[Pinecone]

I have read several reports where a slight adjustment to the gain solves the problem, but not allowed under the STC.

I wonder why the STC is not changed to allow a slight gain tweak.

[PT20J]

2 hours ago, Pinecone said:

I have read several reports where a slight adjustment to the gain solves the problem, but not allowed under the STC.

I wonder why the STC is not changed to allow a slight gain tweak.

I have seen posts speculating that, but I have not seen a post that had any specifics of a gain setting change that actually made a difference. But, I probably haven’t seen every post on the subject and I would be interested if you can point to the ones you have seen.

The gain settings would have been determined as part of the certification process.

[Pinecone]

I don't recall if any gave specific numbers.  And sorry, not sure of where to find the exact posts.

Yes, I understand that, but if there is a wide spread problem, find the gain setting that works, or test a range of settings and get them approved.

[PT20J]

The reason I don't think adjusting gains is the solution is that the vast majority of these installations work well using the certified gain settings. Some clearly have problems. So something is different. The hardware, software and settings are the same so that means that either there is an installation error, a defective servo, or something different about the airframe. Adjusting gains might just mask the real issue. I would systematically eliminate each possibility.

Appendix A of the G3X Experimental Installation Manual https://static.garmin.com/pumac/190-01115-01_aq.pdf has the flight test procedure for setting the gains. I am NOT advocating messing with the gains, but flying the specified test profiles while recording the data might give insights to the engineers into what's going on. 

Skip

[EricJ]

29 minutes ago, PT20J said:

The reason I don't think adjusting gains is the solution is that the vast majority of these installations work well using the certified gain settings. Some clearly have problems. So something is different. The hardware, software and settings are the same so that means that either there is an installation error, a defective servo, or something different about the airframe. Adjusting gains might just mask the real issue. I would systematically eliminate each possibility.

Appendix A of the G3X Experimental Installation Manual https://static.garmin.com/pumac/190-01115-01_aq.pdf has the flight test procedure for setting the gains. I am NOT advocating messing with the gains, but flying the specified test profiles while recording the data might give insights to the engineers into what's going on. 

Skip

At a minimum I think it all means that the GFC500 is sensitive to tolerances in the controls, either friction or slack or control force or whatever, it isn't particularly robust against typical variations in deployed systems.   Usually control systems have a lot of margin for design tolerance, but given Garmin's difficulty with their servo design I suspect that it's part of the problem.   King or Century or S-Tec or Brittain or whoever's autopilots don't seem to have the same issues with variations in Mooney controls.

I used to think my 45-year old Century III (when it was working) was a problem because it had a very slight oscillation in roll sometimes, until I started noticing how other autopilots or installations behave.   My Century was pretty solid in comparison.   I wish it hadn't crapped out.  :'(

 

[hammdo]

It seems these issues pertain to Mid-Long bodies. Curious if the short bodies with just the 2 servos experience any issues…

-Don

[ArtVandelay]

It seems these issues pertain to Mid-Long bodies. Curious if the short bodies with just the 2 servos experience any issues…
-Don

I assume you mean 4 servos with optional yaw damper, I can’t believe anyone wouldn’t install the trim servo that allows hands off flying.

[hammdo]

I’d have to see how that works with the manual trim setup I have. (don’t have the auto pilot yet). Just asking if anyone has the 2 servo install on short body…

-Don

[Ragsf15e]

6 hours ago, ArtVandelay said:

I assume you mean 4 servos with optional yaw damper, I can’t believe anyone wouldn’t install the trim servo that allows hands off flying.

I think I’ve read of a few people on here that have gone with just the 2 servos.  Especially for the older models that didn’t already have electric trim.  The g5 (g3x) will annunciate “trim” kind of like an stec 30a.   I do agree, by the time you’ve got someone opening up the airplane and installing a gfc500, go for the trim servo at least.

[pirate]

28 minutes ago, hammdo said:

I’d have to see how that works with the manual trim setup I have. (don’t have the auto pilot yet). Just asking if anyone has the 2 servo install on short body…

-Don

I removed my S-Tec 30 and had the GFC500 installed on my 70C for 3 weeks now. 

I had  the four servos installed  and I so far I have not experienced any problems during climbs, descents, ILS or GPS approaches. 

The only problem I had after install was the well known shop screwing up my tail trim position. I questioned them about this prior to my test flight and they said it was just fine, well I found out it was severely out of trim during rotation. I’ve heard this has happened a few times now from different shops. 

On my model I’m surely impressed with its performance especially while encountering turbulence. 

Im sure it’s frustrating  to some of the long body Mooneys with the problems listed on this thread but I think Garmin is a stand up company, I believe they will get this ironed out for them hopefully sooner than later. 
 

 

 

[ArtVandelay]

The only problem I had after install was the well known shop screwing up my tail trim position. I questioned them about this prior to my test flight and they said it was just fine, well I found out it was severely out of trim during rotation. I’ve heard this has happened a few times now from different shops. 

I had same problem as well but they fixed it before my first test flight.