GFC-500 Automatic Pitch Down?

[John Mininger]

I know two friends who installed Garmin GFC500 autopilots in their aircraft. Coincidently, they're both Grummans. One is a AA5A, and the other is a AA5B. They both say that whether it’s turned on or off, the GFC500’s Underspeed Protection Mode will pitch the nose down while they’re flaring to land. One says that it’s barely noticeable, the other says that it’s rather disconcerting.

Has anyone with a GFC500 installed in their Mooney noticed this pitching down while landing?

And with a GFC500 installed, would one still be able to run the trim back while flaring?

Thanks

[ArtVandelay]

Disconnect should be the only button needed to stop this I think.
What does he mean by “off”?
I thought ESP is the one that will activate unless AP disc button is held?

[John Mininger]

Just now, ArtVandelay said:

Disconnect should be the only button needed to stop this I think.
What does he mean by “off”?

By off, I think what he means is the autopilot is not engaged.

[201Mooniac]

I definitely don't get a pitch down while flaring.  The underspeed protection should be off below some threshold, maybe it is 200ft AGL, based on the information from the navigator.  Also, running trim up while flaring works fine.  I would think there is some installation or configuration issue.

[carusoam]

There are also different methods of disconnecting the AP…

One method doesn’t turn off the yaw damper either…

Be sure of the method being used, does what is Expected…

In the Mooney case… the red button on the yoke is a complete disconnect verses turning functions off on the control box…

PP thoughts only, not a big G guru…

Best regards,

-a-

[PT20J]

ESP only comes into play when the autopilot is not engaged.

ESP can be enabled or disabled via whatever device is driving the autopilot (i.e., G5, G3X, GI 275).

If enabled, it is activated when climbing above 500' AGL and deactivated when descending below 200' AGL (as determined by GPS altitude and terrain database). 

The min/max speeds for airspeed protection are set in configuration mode by the installer.

I have only flown a GFC 500 in a C-172 to become familiar while awaiting my M20J installation next month. I have not experienced any issues with ESP during flare.

Skip

[RobertGary1]

2 hours ago, carusoam said:

There are also different methods of disconnecting the AP…

One method doesn’t turn off the yaw damper either…

Be sure of the method being used, does what is Expected…

In the Mooney case… the red button on the yoke is a complete disconnect verses turning functions off on the control box…

PP thoughts only, not a big G guru…

Best regards,

-a-

I don’t think that is the case for the esp protection. It’s purpose is to correct pilot induced errors only when the autopilot is off. 

[PT20J]

Just now, RobertGary1 said:

I don’t think that is the case for the esp protection. It’s purpose is to correct pilot induced errors only when the autopilot is off. 

ESP only works when the autopilot is off, but it uses the autopilot servos. Holding down the AP disconnect on the yoke will disable ESP by disconnecting the servos.

[donkaye]

In 2 years of operations with the GFC 500 I have never experienced that situation, and that is to be expected because the ESP is not supposed to operated (no matter what) if the GPS altitude is below 200 feet AGL.

Per my AFMS:

The conditions that are required for ESP to be available are:

•  Pitch and Roll servos available

•  Autopilot not engaged

•  The GPS altitude above ground is more than 200 feet (for low airspeed mode)

•  Aircraft is within the autopilot engagement envelope (+/-50° in pitch and +/-75° in roll)

[John Mininger]

Is the 200 feet AGL that ESP is not supposed to work based on GPS altitude? Or baro from the G5?

Thanks

[JimB]

7 hours ago, donkaye said:

In 2 years of operations with the GFC 500 I have never experienced that situation, and that is to be expected because the ESP is not supposed to operated (no matter what) if the GPS altitude is below 200 feet AGL.

Per my AFMS:

The conditions that are required for ESP to be available are:

•  Pitch and Roll servos available

•  Autopilot not engaged

•  The GPS altitude above ground is more than 200 feet (for low airspeed mode)

•  Aircraft is within the autopilot engagement envelope (+/-50° in pitch and +/-75° in roll)

Don,

You are correct. That is what the AFM supplement states. However, I am struggling to understand how this is possible. With just a G5 and GFC 500 (minimum needed) installed there is no database to reference. How exactly does the system know where it is in relationship to the ground to be able to determine 200 feet AGL??? I get there is pretty neat PFM in these boxes but I don't get that. 

With that said, I have had it installed for about 6 months. No issues on flare. The lower limit of the ESP is set at 76 mph 

[RobertGary1]

1 hour ago, John Mininger said:

Is the 200 feet AGL that ESP is not supposed to work based on GPS altitude? Or baro from the G5?

Thanks

With baro it would need a position and database to know agl ?

[RobertGary1]

8 hours ago, PT20J said:

ESP only works when the autopilot is off, but it uses the autopilot servos. Holding down the AP disconnect on the yoke will disable ESP by disconnecting the servos.

Is that a cws button?

[donkaye]

48 minutes ago, JimB said:

Don,

You are correct. That is what the AFM supplement states. However, I am struggling to understand how this is possible. With just a G5 and GFC 500 (minimum needed) installed there is no database to reference. How exactly does the system know where it is in relationship to the ground to be able to determine 200 feet AGL??? I get there is pretty neat PFM in these boxes but I don't get that. 

With that said, I have had it installed for about 6 months. No issues on flare. The lower limit of the ESP is set at 76 mph 

What GPS do you have?  The determination is from GPS altitude.

[donkaye]

24 minutes ago, RobertGary1 said:

Is that a cws button?

That would be nice, but the disconnect button is just that, a disconnect button.  Treating it as a CWS button you would first need to push the AP button on the 507, which would turn the AP on in the default ROL and PIT mode and then push NAV or HDG for lateral navigation and VS or IAS for pitch--not exactly like the simple release of a CWS button as in the KFC 150.                                                                                             

[PT20J]

29 minutes ago, RobertGary1 said:

Is that a cws button?

No. The disconnect button is wired to the GMC 507 controller and all GS 28 servos. Holding it down releases the servos so you can hand fly while pulling the AUTOPILOT CB in case of a malfunction. In the experimental version, it syncs the autopilot pitch and roll attitude when released without disconnecting the autopilot providing a CWS function. In the certificated version, however, it just disconnects the autopilot — there is no CWS. 

Skip

[JimB]

18 minutes ago, donkaye said:

What GPS do you have?  The determination is from GPS altitude.

I'm not sure what your asking. I can install a G5 and GFC 500 without a GPS unit. The G5 can certain determine GPS MSL altitude but it won't know if the ground elevation is 500 feet or 5000 feet so I still don't know how it can determine what AGL you are. You can be in a valley or on a mountain top.  

[PT20J]

33 minutes ago, JimB said:

I'm not sure what your asking. I can install a G5 and GFC 500 without a GPS unit. The G5 can certain determine GPS MSL altitude but it won't know if the ground elevation is 500 feet or 5000 feet so I still don't know how it can determine what AGL you are. You can be in a valley or on a mountain top.  

[Ragsf15e]

4 minutes ago, PT20J said:

Ahh, so it looks like the esp low speed function only works if there’s an appropriate gps giving it the terrain awareness for the 200’ function.  Otherwise, no low speed esp.

To the OP… what gps did he have? Is the terrain database current?  Maybe a config issue?

[PT20J]

There’s a lot of interesting info in the manuals. For instance, here is a description of how the autopilot will kill you if you forget to add power during a missed approach 

[Tom 4536]

10 minutes ago, PT20J said:

There’s a lot of interesting info in the manuals. For instance, here is a description of how the autopilot will kill you if you forget to add power during a missed approach 

On the go around what will determine the position of the flight director command bars?

[201Mooniac]

Just now, Tom 4536 said:

On the go around what will determine the position of the flight director command bars?

It is a configuration that is specified in the STC for the aircraft type.

[RobertGary1]

5 hours ago, donkaye said:

That would be nice, but the disconnect button is just that, a disconnect button.  Treating it as a CWS button you would first need to push the AP button on the 507, which would turn the AP on in the default ROL and PIT mode and then push NAV or HDG for lateral navigation and VS or IAS for pitch--not exactly like the simple release of a CWS button as in the KFC 150.                                                                                             

Thanks Don. I'm looking at adding a GFC-500 to my Garmin cockpit. I mostly teach in the G1000 with the GFC 700 and find the CWS very helpful. Is CWS an option in the 500? Seems like a notable hole in an otherwise exceedingly capable autopilot system.

 

-Robert

 

[donkaye]

Just now, RobertGary1 said:

Thanks Don. I'm looking at adding a GFC-500 to my Garmin cockpit. I mostly teach in the G1000 with the GFC 700 and find the CWS very helpful. Is CWS an option in the 500? Seems like a notable hole in an otherwise exceedingly capable autopilot system.

 

-Robert

 

I thought I was going to miss it, having used it with the KFC 150.  After over 2 years with the GFC 500, I find I haven't missed it at all.  Considering there is CWS in the experimental version of the GFC 500, it is apparent it wasn't an accident that they left it off with no current option to have it.  If someone knows the reason, I'd be interested in knowing what it was, since it is included in the GFC 600.

[Ragsf15e]

6 hours ago, Tom 4536 said:

On the go around what will determine the position of the flight director command bars?

 

7 hours ago, PT20J said:

There’s a lot of interesting info in the manuals. For instance, here is a description of how the autopilot will kill you if you forget to add power during a missed approach 

I see you wrote that with a wink, but it will enter the esp low airspeed mode and start pushing over the nose well before stall.  It’s pretty good at keeping the airplane from stalling… don’t worry though, the pilot can still find a way!