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GFC500 problem


Larry

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1 hour ago, PT20J said:

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 you Pilot's Guide for details.

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Thanks @PT20J.  I will look this up in the Pilot's Guide.

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I emailed a sample of flight data to Trek earlier this week, along with other info that Trek requested. I encourage all of you who have reported issues with the GFC500 on this thread do the same. Thank you in advance. 

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  • 4 weeks later...

I have read this thread and others with interest, as I have a KAP 200 presently, which I have chosen to replace with the GFC500. I discussed this issue at length with the folks that will be doing the installation and my concerns were addressed to my satisfaction. The owner of the shop doing the installation was a Garmin engineer for 10+ years and dealt with these issues while employed at Garmin. We shall see. 

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“If replacing a Century or King at the end of service life I can see going to a GFC500, it makeseconomic sense”

little off topic from Garmin issue. I flew my 1994 century 2000 to Mineral Wells last year. Had several issues which all were resolved. Have had other fixes over last 17 years altogether have not reached the new $10,000 cost of new Garmin economy model.

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  • 5 weeks later...
36 minutes ago, mike261 said:

I have this exact issue. IAS works fine the first time I use it during a flight, on subsequent attempts it lurches nose up, scary up. like peg the VIS up. had to disconnect. I was going to osh and it happened multiple times. I spoke in person with Trek when i got there and he suggested I try vertical speed mode on the way home. VS mode worked fine on the way back. Trek spoke of a known issue with a bracket on past installs in Mooneys as a possible cause. I have to get to the avionics guy and have him download a log to send to Trek, But I'm in annual now...anyone have any history with this issue and know the cause?

Mike

Where is the airspeed bug relative to current airspeed when you get the pitch up?

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1 hour ago, mike261 said:

I tried it in  various configurations. I even tried setting the IAS to my actual current airspeed at two values, 96 knots and 105 knots or there about. tried it on three legs of my trip. 

Mike.

 

I believe mine works “normally.”

When engaging IAS, it will attempt to hold current airspeed and does a reasonable job in smooth air. In turbulence, it hunts it pitch.

If I change the airspeed bug with the thumbwheel, I must do it very slowly so that the airspeed is never more than about 5 kts behind the bug or the autopilot gets behind the dynamics of the airplane and I see a typical phugoid response of about 2-1/2 cycles. If I abruptly move the bug significantly off current airspeed, I’ve seen an initial pitch up of as much as 15 degrees. 

i very seldom use IAS mode.

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  • 3 weeks later...

I’ve flown over 70 hours since I got the airplane back in April. I have the same issue with altitude oscillation that others reported. I’ve sent data log files to Trek at Garmin and exchanged pleasant emails, but without resolution. I’ve tried everything listed in all the posts above. My installer can’t find anything wrong.

I was looking forward to the Summit, but frankly I can’t imagine enduring a 6+ hour flight with an autopilot that continually oscillates. After a flight to Mackinac and back, Mary surely won’t won’t go. 

Since this thread has gone dormant, I assume I’m the only Mooney with this problem. I’m exhausted, and kinda sad.

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The springs are part of the control system as described in the TCDS, so changing them would change the stability and handling characteristics and render the airplane unairworthy.

Since most installations work fine, the issue has to be one of four things:

1. Something to do with the airframe control system (friction, slop?)

2. Something to do with the airplane pitot/static system (leaks, contamination?),

2. Something to do with the installation (cable tension, software setup?),

3. Some defect in the equipment.

Trek's team supports Oshkosh and they are probably just getting back to normal business. At the end of the day, it is the dealer's responsibility to solve your problem. 

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The springs are part of the control system as described in the TCDS, so changing them would change the stability and handling characteristics and render the airplane unairworthy.
Since most installations work fine, the issue has to be one of four things:
1. Something to do with the airframe control system (friction, slop?)
2. Something to do with the airplane pitot/static system (leaks, contamination?),
2. Something to do with the installation (cable tension, software setup?),
3. Some defect in the equipment.
Trek's team supports Oshkosh and they are probably just getting back to normal business. At the end of the day, it is the dealer's responsibility to solve your problem. 
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My understanding is there’s a torque setting and we require the maximum, so there is probably little margin for any extra resistance.
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30 minutes ago, ArtVandelay said:


My understanding is there’s a torque setting and we require the maximum, so there is probably little margin for any extra resistance.

I believe that it is only the trim torque that is set to 100% but I can check the next time I am out at the hangar, or perhaps someone else knows. The trim servo is clearly marginal. In order to meet the trim time spec from stop to stop they had to really gear up the servo which, of course, reduces it's torque. The B-K servo was geared about 1:1, but the sprocket on the Garmin servo is huge. 

Two problems can occur with the Mooney elevator system. First, it has a lot of rod ends in series, and as they wear, the lost motion in the control system creates a dead band. Second, the friction in the bushings where the yokes pass through the instrument panel can create a breakout force. I don't know if this causes GFC 500 issues or not.

I notice in my airplane that the autopilot is pretty aggressive at holding altitude. If I really pay attention, I notice very small (less that 1/2 degree) pitch changes almost continuously while the altimeter is rock solid. These pitch changes are too small to cause accelerations that can be felt, but they are there. 

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9 hours ago, PeytonM said:

I’ve flown over 70 hours since I got the airplane back in April. I have the same issue with altitude oscillation that others reported. I’ve sent data log files to Trek at Garmin and exchanged pleasant emails, but without resolution. I’ve tried everything listed in all the posts above. My installer can’t find anything wrong.

I was looking forward to the Summit, but frankly I can’t imagine enduring a 6+ hour flight with an autopilot that continually oscillates. After a flight to Mackinac and back, Mary surely won’t won’t go. 

Since this thread has gone dormant, I assume I’m the only Mooney with this problem. I’m exhausted, and kinda sad.

You are not the only one. I suspect Garmin did not investigate full envelope of stability on the Mooneys. 

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10 hours ago, PeytonM said:

Since this thread has gone dormant, I assume I’m the only Mooney with this problem. I’m exhausted, and kinda sad.

You are not the only one.  I too have tried all the suggestions offered here with no improvement.  I am resigned to going into VS mode every 15 minutes or so and setting it to zero to stop the oscillations.  It is hard to believe that Garmin can't come up with a software patch that looks for low level pitch hunting and damps it.

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For the money we’ve spent, we should expect better.

I took a volunteer flight Friday and put both passengers in the back. I was 20# under gross, and near aft CG. The oscillations were terrible. I put my finger on the control yolk shaft, bracing it against the instrument panel, and could feel the movement, every second or two, quarter inch or so. It was abrupt movement, but no change in trim.

Luckily both passengers slept through the 2.2 hr flight. I used 22 gal and took no fuel for the ride home. I estimate I was at least 470# under gross and now I was mid-CG.

The ride home was SIGNIFICANTLY smoother! (I don’t think it was my imagination, either!) I couldn’t believe it. I wonder what the data file will show. 

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