GFC500 Update

[donkaye]

11 hours ago, Mooney in Oz said:

Hello Don.

Don't know if this means anything; I noticed -1000 is constantly displayed in the VS window whilst the VSI is fluctuating between 200 fpm and 1000 fpm. 

Hi Victor.  No that doesn't do anything unless you are in V/S mode.

[donkaye]

1 hour ago, Bob - S50 said:

Don,

I notice you are flying final at 100 - 110 KIAS.  How does it do if you fly final at something closer to your VFR final speeds?  Something like 80 KIAS or so?

The Oscillations would be much worse.   Notice near the end of the video when the speed was little higher that the oscillations were less.

[donkaye]

5 hours ago, MIm20c said:

To be honest we’ve been dragging our feet on the GFC upgrade since November.  The 225 flys the plane so well it’s hard to spend the money to get the performance shown above.  Finally planning on installing the new AP next month, I really hope Garmin gets their software tweaked before then. 

If you're having one installed in a J Model, you can feel comfortable that it won't behave like mine.  I have flown in a J on approach with the GFC 500 and it is rock solid.  At least one other  long body Eagle is exhibiting the same oscillations as mine.  I just need to find more long bodies that either exhibit it or don't to confirm the problem, or if not, start spending the money to track down the issue.

[Emmet]

Have you tried to swap servos?

 Is the trim moving during the oszillations? 

Have you tried it with disabled autotrim ?

[JohnB]

2 hours ago, donkaye said:

If you're having one installed in a J Model, you can feel comfortable that it won't behave like mine.  I have flown in a J on approach with the GFC 500 and it is rock solid.  At least one other  long body Eagle is exhibiting the same oscillations as mine.  I just need to find more long bodies that either exhibit it or don't to confirm the problem, or if not, start spending the money to track down the issue.

That is very interesting Don and great video to demonstrate.  Looks like it does get better the closer you get to DA. Could it be a sensitivity change issue with the g5 not switching to precision altitude correction soon enough?
 

I had a somewhat similar issue with course changes on my autopilot with wide Back and forth oscillations in course on AP corrections in GPSS mode( was actually less in NAV mode) , which my avionics shop fixed by altering the sensitivity. He said it was something to do with going from the previous analog autopilot input to digital one with the Garmin installed units. 
 

Hope you get this fixed, this looks annoying!

[Bob - S50]

3 hours ago, donkaye said:

The Oscillations would be much worse.   Notice near the end of the video when the speed was little higher that the oscillations were less.

It could be reduced oscillations due to distance to runway rather than speed. Have you ever a actually tried an approach at a lower speed?

[bradp]

It looks like a student instrument pilot chasing the vertical needle and then can’t decide whether to prioritize returning to selected airspeed, vs, or continuing to prioritize the vertical needle.  Ie if you’re trim is constantly moving during a stabilized approach I’d think it shouldn’t.  If you are Hand flying you should have a trim set for that phase of flight pretty much and you control rate of descent with pitch alone of power is not in the equation.  Seems like it would be a gain or frequency response issue between pitch trim response and pitch servo response.   Oshkosh isn’t too far away - can they look at it again and “tune” it during the summer? 
 

it would be interesting to dig into the settings to be able to compare yours with a J/K versus an A36 bonanza (if that finally made it on to the AML).  

[aviatoreb]

15 hours ago, donkaye said:

I'm still looking for a long body airplane that has had the GFC 500 installed.  After the installation issue I had with the pitch trim in my airplane, I don't think Garmin believes there is an issue with the GFC 500 on approach in the long body Mooney.   I've checked cable tensions and even spent 3 hours checking the spring cable tension on the elevator, which is independent of the autopilot.  I have reached out to them with no success.  What do you think?  Here is a video I made yesterday in smooth air.  VNAV works perfectly as does V/S with no oscillations, but approaches, that is another story as you can see.

 

I am sorry to hear you are still dealing with this.

I see a stable but not asymptotically stable control law.  Not stable (meaning unstable) would mean the oscillation is diverging - getting bigger and bigger.  Asymptotically stable it should be quickly getting smaller and smaller to nothing.

[Davidv]

It just seems ridiculous to me that Garmin seems to have abandoned Don.  He spent all of that money on something that was supposed to work as designed, it doesn't, yet Garmin won't make it right.  I'm not sure this would be tolerated in any other industry.

Think of buying a $20-25k Ford and it won't drive straight.  Ford suggests a few fixes that don't work and then won't return your calls.  Then you go on the internet to solicit the advice/help of other Ford owners on ideas to fix the problem.  Something isn't right here...

[donkaye]

3 hours ago, Emmet said:

Have you tried to swap servos?

 

No.  Interesting thought.

3 hours ago, Emmet said:

 

 Is the trim moving during the oszillations? 

Have you tried it with disabled autotrim ?

The trim moves waaaay too fast during the oscillations, compared to the KFC 150 which moved very slowly.  I don't think you can disable auto trim.

[donkaye]

2 hours ago, JohnB said:

That is very interesting Don and great video to demonstrate.  Looks like it does get better the closer you get to DA. Could it be a sensitivity change issue with the g5 not switching to precision altitude correction soon enough?
 

I had a somewhat similar issue with course changes on my autopilot with wide Back and forth oscillations in course on AP corrections in GPSS mode( was actually less in NAV mode) , which my avionics shop fixed by altering the sensitivity. He said it was something to do with going from the previous analog autopilot input to digital one with the Garmin installed units. 
 

Hope you get this fixed, this looks annoying!

John, do you have the GFC 500?  If so, and it works, I'd like to know.  Setting cannot be altered.  They are part of the STC.

[donkaye]

2 hours ago, Bob - S50 said:

It could be reduced oscillations due to distance to runway rather than speed. Have you ever a actually tried an approach at a lower speed?

No, Bob, I haven't, but will next time I fly.  I would expect it to be worse.  I think there is a minimum speed at which the autopilot will work.  I think it is 80 knots, but will have to check.

[HXG]

Don, You’re probably aware of the BeechTalk thread regarding reported GFC500 oscillations  in the F33As, which Garmin reported they were working on. Some reported increased tension settings and replacing elevator control rod ends  as a possible fix. But, I don’t know why your oscillations only occur in approach mode. Hopefully, this will get sorted out as more Mooney long bodies get the GFC-500 install.  Hopefully, before my planned Bravo GFC 500 install this spring.  

[JohnB]

2 hours ago, donkaye said:

John, do you have the GFC 500?  If so, and it works, I'd like to know.  Setting cannot be altered.  They are part of the STC.

I have a KFC 150. Seems to work fine for now, no oscillations in any mode now, so haven’t yet upgraded it. Wow, didnt know you couldnt adjust GFC settings. I’m still wondering if it has something to do with the G5, as I have a separate analog to digital converter which is not the G5. Anyway, I’d like to follow this thread to see if this gets worked out before I have to start autopilot shopping. 

[Emmet]

3 hours ago, donkaye said:

No.  Interesting thought.

The trim moves waaaay too fast during the oscillations, compared to the KFC 150 which moved very slowly.  I don't think you can disable auto trim.

You should at least be able to remove the trim servo from the configuration. I will lok it up when I have more time

Do you have a G5 or G3X ?

[donkaye]

30 minutes ago, Emmet said:

You should at least be able to remove the trim servo from the configuration. I will lok it up when I have more time

Do you have a G5 or G3X ?

G5

[Emmet]

In the configuration mode  under Flight Controls,  Pitch Trim should be a configuration setting called Auto Trim which can be set to disabled.

This should do the job and you should now still be able to use the electric trim in Manual mode.

If I remember correctly this mode change can be done in the normal operation mode in G3X installations...

[carusoam]

FCH,

Your avatar needs a picture of one of your work birds!

TarBes Mooneys are pretty cool... 

 

Yaw dampers are interesting... reaction time... sensor speed, decision speeds, computer speeds, motor speeds... all interconnected...

They will have to be incredibly forward thinking to be able to eliminate the yaw...

Best regards,

-a-

 

 

 

[gacoon]

Dont know if you have tried it, but try an approach with YD off?

[donkaye]

30 minutes ago, gacoon said:

Dont know if you have tried it, but try an approach with YD off?

Why do you think that would make a difference?

[flyingcheesehead]

1 hour ago, carusoam said:

FCH,

Your avatar needs a picture of one of your work birds!

TarBes Mooneys are pretty cool... 

Well it's not my avatar, but here's a pic I took the other day. I call it "a losing battle."

[carusoam]

12 minutes ago, flyingcheesehead said:

Well it's not my avatar, but here's a pic I took the other day. I call it "a losing battle."

Try and cut and paste that in to your avatar area... that is awesome!!!

There are two places to put pics in MS... one is the avatar pic, the other is your data page... the data page pic is a rectangular header that would be perfect for this pic...

-a-

[flyingcheesehead]

15 hours ago, carusoam said:

Try and cut and paste that in to your avatar area... that is awesome!!!

There are two places to put pics in MS... one is the avatar pic, the other is your data page... the data page pic is a rectangular header that would be perfect for this pic...

-a-

What I really need to do is get the big French Mooney and the little American Mooney in the same place and get a pic with both of them!

[gacoon]

On 1/12/2020 at 10:02 PM, donkaye said:

Why do you think that would make a difference?

I dont, but it eliminates another variable.

[tmo]

15 hours ago, flyingcheesehead said:

What I really need to do is get the big French Mooney and the little American Mooney in the same place and get a pic with both of them!

Don't forget to add a Mustang and a CV2 to the set

You know, for balance...