GFC500 problem

[PT20J]

1 hour ago, dzeleski said:

Because its allowed in the experimental world and they can tune it when it happens. Its specifically not allowed for certified installs.

But in the experimental world, each airframe can be somewhat unique because builders often make modification to the original plans or kit. Production airplanes should not have similar variation if they conform to the type certificate. Garmin optimizes all the parameters when it certifies the autopilot for a particular airplane. My Bendix King KAP 150 had two sealed plug-in modules within the KC 191 that programmed it for a specific airplane and I couldn't change them either. 

[dzeleski]

3 hours ago, PT20J said:

But in the experimental world, each airframe can be somewhat unique because builders often make modification to the original plans or kit. Production airplanes should not have similar variation if they conform to the type certificate. Garmin optimizes all the parameters when it certifies the autopilot for a particular airplane. My Bendix King KAP 150 had two sealed plug-in modules within the KC 191 that programmed it for a specific airplane and I couldn't change them either. 

I think you might be significantly over estimating the lack of consistency between each hand built 30+ year old airplanes. Then add repairs, new parts mixed with old, updated parts, etc. I have personally never flown two of the same model that felt the same or flew the same. Every single one had a bit of a different personality.

[carusoam]

Start with Trek…

The details supplied here are great for Big G and their product updates…

Best regards,

-a-

[Rmag]

The GFC500 in my M20J is rock solid on the pitch axis.  It holds altitude very tightly, in fact in smooth air, I can even feel the tiny micro adjustments being made to keep the plane exactly at its altitude without deviation.

Regarding IAS mode, I never use it in turbulence as the turbulence causes airspeed fluctuations as the plane is being pushed up and down by the turbulence.  The autopilot then tries to correct the fluctuations, so you play a game of nature changing your airspeed, and the machine trying to correct.  Forget about IAS in turbulence and use VS or Pitch.  In normal operations if I use IAS it is typically on a climb out after takeoff and I normally hand fly to the airspeed I want and then engage the AP and IAS.  Since it is already roughly at the airspeed I want, there is no oscillation.  Conversely if I am at 120 knots and I just engage IAS and quickly dial 100, the plane is going to pitch up very strongly to get back to the 100.  It is usually too strong and it will overshoot 100 and then rapidly pitch down to get to 100, and maybe have 2 more of these oscillations in lessening degrees until it stabilizes.  All this can be avoided if you establish your airspeed first, then engage the IAS within about 5 knots and use the wheel to adjust to your exact target airspeed.  When you engage IAS, it will engage at your current airspeed so you should not have any oscillation.  If you do this, just change your IAS in smaller increments if you want to change IAS.  Avoid large rapid IAS changes.

Regarding oscillations, I have experienced small intermittent oscillations in the yaw axis in smooth air.  Originally it would cause an abnormal disconnect.  Eventually Garmin recognized this, and it was fixed with a firmware update.  In smooth air I can still slightly feel some slight intermittent movement in the yaw servos that did not need to happen.  In mild to greater turbulence it works fine.  Now I just fly with the YD off when its smooth as the M20J has a really good yaw stability naturally. If I start hitting bumps I turn it on.

[Ragsf15e]

It’s interesting that ias mode causes large pitch changes even if it’s off airspeed.  You’d think there would be maximum pitch angles built into the system and the pitch change rates would be limited based on how far it wants to change the pitch.  The gfc700 ias mode is pretty calm and predictable even in turbulence.  Yes it hunts a little, but we’re talking a calm few knots and a couple degrees.  
If my autopilot gave me the +10 up wild ride you guys are talking about in IMC, I would not be happy as that’s a recipe for disorientation.

[PT20J]

1 hour ago, Ragsf15e said:

It’s interesting that ias mode causes large pitch changes even if it’s off airspeed.  You’d think there would be maximum pitch angles built into the system and the pitch change rates would be limited based on how far it wants to change the pitch.  The gfc700 ias mode is pretty calm and predictable even in turbulence.  Yes it hunts a little, but we’re talking a calm few knots and a couple degrees.  
If my autopilot gave me the +10 up wild ride you guys are talking about in IMC, I would not be happy as that’s a recipe for disorientation.

If you set IAS mode and then dial in a big change (say 20 kts) does the 700 capture the new airspeed pretty smoothly or does it overshoot back and forth a lot? I’ve flown the 500 in relatively smooth air in a C-172 and a M20J. In both it seems to overshoot and the oscillate back and forth for a few cycles before settling down.  I assumed it is the autopilot dynamic response interacting with the airplane’s natural phugoid. Since it did the same thing in two vastly different airplanes, I figured that's the best it can do.

Skip

[Ragsf15e]

5 hours ago, PT20J said:

If you set IAS mode and then dial in a big change (say 20 kts) does the 700 capture the new airspeed pretty smoothly or does it overshoot back and forth a lot? I’ve flown the 500 in relatively smooth air in a C-172 and a M20J. In both it seems to overshoot and the oscillate back and forth for a few cycles before settling down.  I assumed it is the autopilot dynamic response interacting with the airplane’s natural phugoid. Since it did the same thing in two vastly different airplanes, I figured that's the best it can do.

Skip

I’d be interested to hear from a Mooney with the gfc700, but the one I fly in a Meridian captures airspeed pretty well.  It hunts a little in turbulence, but I’m talking +\-3 knots and 1 degree of pitch.

I use it in both climb and descent (typically I’d want to use VS or VPTH in a descent, but the airplane has a low Vne and so IAS works well to keep a set margin from Vne).

In level flight, it’s common to be at 180kts, get a clearance to climb, push FLC (IAS mode) and just dial it back to 125kts.  It will pitch up to roughly 10 degrees, and then slowly start the nose down around 135 to capture 125 around 7 degrees nose up.  

Possibly the extra power and weight of the airplane make a difference, but the way the pitch oscillations are being described above seems a little troublesome in IMC.  But then I haven’t flown one…

[PT20J]

Today was continuous light turbulence and I took a couple of videos using IAS mode on the GFC 500. Excursions were not uncomfortable, but the autopilot did seem to be chasing the dynamics of the airplane when nearing the selected airspeed. 

 

 

 

[donkaye]

It's said that IAS would be preferable in climb to prevent possible stall and V/S should be used in descent.  Mine works pretty well, but I think it is touchy and requires attention.  In fact it requires so much attention that you might as well use V/S because with that much attention you are unlikely to get in an attitude where the airplane will stall.  V/S just seems more stable.

However, if IAS is used, then I think it should be used carefully.  By that I mean, as mentioned either on Beechtalk or here earlier, establish the IAS desired, then and only then, engage IAS.  If an oscillation should start, I would "lock" the pitch trim servo with the trim wheel, so pitch oscillation wouldn't occur.  When the excessive pitch tries to engage the servo, the force of hold on the wheel momentarily disengages the trim servo and effectively damps the oscillation.  Not a good solution, but it works.  You're basically simulating changing the gain on the servo manually.  I haven't heard of that to be illegal, yet.

[rbp]

here's 10 seconds of @PT20J's video that shows what i saw -- a lot of over compensation. it appears that the FD is using the prediction algorithms for AS and VS to determine where the nose should be, and its predicting too far into the future in turbulence. if its predicting 6 seconds out in turbulence that only has 2 second cycles, the this would be the behavior we see

 

 

 

 

[PeytonM]

89 M20J. I’ve been flying w/a new panel for about 20 hours, including G3X and GFC500. I’ve experienced what others have reported regarding IAS climbs: best used when IAS is engaged from an airspeed you are already flying, e.g departure climb. Ride can be interesting if engaging from cruise and then trying to dial it down to 100 KIAS!  In those cases, I agree VS is a better choice. 
 

About 90% if my initial flying was in choppy air, so I was surprised (read ‘disappointed’) to see the slight oscillations with ALT Hold when I recently finally found smooth air! Only about 10 feet up, then down, but you could feel it. However, trim wheel did not move. WT_!!   (My old Century2000 was solid as a rock in ALT Hold until the trim servo quit.)

We did the Alt Static Source experiment today and it did seem to reduce/eliminate it (or was it “placebo?!”)  Installer is leaning towards static line issue. He stressed changing Gain is a big no-no!  It goes back in in a couple weeks. I’ll let you know what happens.

Regardless, it’s unacceptable. 

[PeytonM]

Why can’t I see the videos?

[Tom 4536]

15 hours ago, PeytonM said:

Only about 10 feet up, then down, but you could feel it. However, trim wheel did not move. WT_!!   (My old Century2000 was solid as a rock in ALT Hold until the trim servo quit.)

Like yours, my 231 pitch varies only 10 feet but the pitching is very noticeable and my trim wheel definitely does not move when the pitch changes. I can't see the yoke moving. My old Century 41 was rock solid until it died. I am interested in what you find as a solution.

[Mooney in Oz]

3 hours ago, Tom 4536 said:

Like yours, my 231 pitch varies only 10 feet but the pitching is very noticeable and my trim wheel definitely does not move when the pitch changes. I can't see the yoke moving. My old Century 41 was rock solid until it died. I am interested in what you find as a solution.

My advice to everyone who has a problem with IAS oscillations and pitch changes in cruise is to advise your installer and follow it up with an email for them to on-send to Garmin to make it official. A mate of mine who owns a 231 is having the same problems and has also advised Garmin via his installer. I also know of a 252 owner and a Piper Saratoga owner with the same issues.

It would also be helpful to video these occurrences and download the logs to include with your email. I have already done this myself and have been advised by my installer that Garmin tech support Australia have sent all the information and are liaising with Garmin tech USA.  The issues are still under investigation.

Please don’t just leave it for the other guy to do as the more aircraft owners advise their installer of these issues in writing together with evidence then there is a greater chance of Garmin to take the issues seriously that could hopefully result in software updates or other appropriate solutions.

[PeytonM]

Mooney in Oz has some great points! It sounds like there are several of us who are observing the phenomenon of IAS oscillations in climb and slight pitch changes in cruise. I’ll bet there are many who are seeing these issues and chalking this to normal ops. In fact one poster writes “in fact in smooth air, I can even feel the tiny micro adjustments being made to keep the plane exactly at its altitude without deviation.” These 10 ft +/- pitch changes are what we are describing and IMHO are NOT normal given my experience with the Century2000. After spending $$$, unacceptable. 
 

MSers who do not see these issues, please post!  I know of Arrow and Skylane operators where these phenomena do not occur. What’s going on over in the Beech world?

Garmin needs to hear from us, and as Oz suggests, include videos and flight logs.  My installer with be at Garmin the week of June 13 and he will have my data. (Maybe it’s a “Dealer Conference!”) Hopefully, Garmin is reading our posts.   

 

 

[Tom 4536]

2 hours ago, PeytonM said:

Mooney in Oz has some great points! It sounds like there are several of us who are observing the phenomenon of IAS oscillations in climb and slight pitch changes in cruise. I’ll bet there are many who are seeing these issues and chalking this to normal ops. In fact one poster writes “in fact in smooth air, I can even feel the tiny micro adjustments being made to keep the plane exactly at its altitude without deviation.” These 10 ft +/- pitch changes are what we are describing and IMHO are NOT normal given my experience with the Century2000. After spending $$$, unacceptable. 
 

MSers who do not see these issues, please post!  I know of Arrow and Skylane operators where these phenomena do not occur. What’s going on over in the Beech world?

Garmin needs to hear from us, and as Oz suggests, include videos and flight logs.  My installer with be at Garmin the week of June 6 and he will have my data. (Maybe it’s a “Dealer Conference!”) Hopefully, Garmin is reading our posts.   

 

 

During a recent flight review my CFII said the porpoising I was experiencing during cruise was totally unacceptable. As a result of your request, I have sent my info to my installer and asked that he contact Garmin. Maybe if enough of us have our installers contact Garmin, they will come up with a fix. Thank you.

[donkaye]

23 minutes ago, Tom 4536 said:

During a recent flight review my CFII said the porpoising I was experiencing during cruise was totally unacceptable. As a result of your request, I have sent my info to my installer and asked that he contact Garmin. Maybe if enough of us have our installers contact Garmin, they will come up with a fix. Thank you.

When Garmin certified the M20M airframe for the GFC 500 they had to completely redo the flight control system.  Even a little "sticking" on the yoke can cause oscillations.  Have you all extensively lubed all hinges on all flight control surfaces and especially lubed the yoke inside the airplane?  Have you slowly moved the yoke back and forth to make sure there is no point on the movement where the yoke is "sticking" even slightly and requires a little more force to move it?

Before complaining to Garmin make sure all movement of all flight controls is smooth as silk.

[Tom 4536]

Just now, donkaye said:

When Garmin certified the M20M airframe for the GFC 500 they had to completely redo the flight control system.  Even a little "sticking" on the yoke can cause oscillations.  Have you all extensively lubed all hinges on all flight axis' and especially lubed the yoke inside the airplane?  Have you slowly moved it back and forth to make sure there is no point on the movement where the yoke is "sticking" even slightly and requires a little more force to move it?

Before complaining to Garmin make sure all movement of all flight controls is smooth as silk.

Yes to all your questions. Even replaced the servos. The new lubrication had no affect on the problem. 

[PeytonM]

Today I called Garmin Support… twice… about the pitch oscillations. On the first call, the gent told me this was a known issue with Bonanzas and SW ver 3.10 was released in Jan 2022 to fix that.  He said I could check my GFC SW version on the G3X: “Menu-Menu, LRU, look for Autopilot.” I went over to the plane and tried. Nope.  And of course I had hung up by then.

Being a glutton for punishment, I called back, and got a different guy.  “It’s a known issue.  There’s a fix and your installer will know what to do.”  He did not know what the fix was; he muttered something about “configuration.”  Hmmm.  I asked about accessing SW version, and he said that info was not pilot-accessible. Great. 

There are too many reports to assign the issues to manufacture, airframe, friction, iPads on the yolk, etc.  Like I said, my Century2000 was 45 yo tech and it held ALT perfectly. Bonanza drivers saw it, they complained and out comes a new SW version. MSers need to do the same thing.  It is the GFC500!

Send love notes, flight log data & videos to:  aviation.support at garmin.com 

[Mooney in Oz]

10 hours ago, donkaye said:

When Garmin certified the M20M airframe for the GFC 500 they had to completely redo the flight control system.  Even a little "sticking" on the yoke can cause oscillations.  Have you all extensively lubed all hinges on all flight control surfaces and especially lubed the yoke inside the airplane?  Have you slowly moved the yoke back and forth to make sure there is no point on the movement where the yoke is "sticking" even slightly and requires a little more force to move it?

Before complaining to Garmin make sure all movement of all flight controls is smooth as silk.

G’day Don.
I too did all of this.

[TrekLawler]

Good evening everyone,

   thank you to Skip for forwarding me a message on this thread. My apologies for not being available sooner on it, we're in the middle of our show season and have been involved with quite a bit of travel this spring which has limited my forum exposure the last couple of months.

in most cases when our team starts really investigating these reported problems we can usually narrow it down to an airframe issue, some of you I've worked with can attest to this with some of the installation issues we've had to address, a couple of them even with our team while flying into IXD which is our home airport. but I most certainly understand the concern on these issues and we're here to help. I've read where a number of you on this thread have indicated you or your installer has been in contact with Garmin, but what I'd like to do is organize this a bit, if possible could you please drop me a private message outlining the airframe details, who the installer/dealer is? I'd also like to know if there has been contact with our FSE team and if any assert logs have been forwarded to our teams. I will put this all together to get with our autopilot teams to see what more we can do to try and get to the bottom of these reports.

thank you for your patience.

[carusoam]

Thanks for stopping in Trek!

Best regards,

-a-

[whiskytango]

2 hours ago, TrekLawler said:

Good evening everyone,

   thank you to Skip for forwarding me a message on this thread. My apologies for not being available sooner on it, we're in the middle of our show season and have been involved with quite a bit of travel this spring which has limited my forum exposure the last couple of months.

in most cases when our team starts really investigating these reported problems we can usually narrow it down to an airframe issue, some of you I've worked with can attest to this with some of the installation issues we've had to address, a couple of them even with our team while flying into IXD which is our home airport. but I most certainly understand the concern on these issues and we're here to help. I've read where a number of you on this thread have indicated you or your installer has been in contact with Garmin, but what I'd like to do is organize this a bit, if possible could you please drop me a private message outlining the airframe details, who the installer/dealer is? I'd also like to know if there has been contact with our FSE team and if any assert logs have been forwarded to our teams. I will put this all together to get with our autopilot teams to see what more we can do to try and get to the bottom of these reports.

thank you for your patience.

Hi @TrekLawler, and thanks for your response.  

Your post made reference to "assert logs".  Could you provide detail on what that refers to, and how we can obtain them them to forward to Garmin?

[PeytonM]

Trek, thank you so much for your post! I will send flight log from EIS and vid. Br, Peyton 

[PT20J]

14 hours ago, whiskytango said:

Hi @TrekLawler, and thanks for your response.  

Your post made reference to "assert logs".  Could you provide detail on what that refers to, and how we can obtain them them to forward to Garmin?

The G3X, G5, and GI 275 log data that has a lot of useful diagnostic information for each flight. Files are in a .csv format so that they can be easily imported into a spreadsheet. This feature needs to be enabled and for the G3X and G5 an SD card must be present. I believe the GI 275 downloads via Connext to Garmin Pilot or to a USB drive if you have a GSB 15 installed. Check your Pilot's Guide for details.

Skip