GFC 500 Low Speed Engagement problems?

[John Mininger]

Is anyone who has had a GFC 500 installed in their Mooney having issues with the Low Speed Engagement (LSE) “feature”. For those that aren’t aware of what this is, the LSE in the GFC 500 will automatically lower the nose when the airspeed gets below a pre-programed number; whether the autopilot is engaged or not. The LSE is set to disable when the GPS altitude is below 200 AGL, so as not to interfere with the landing flare. I’ve talked to a couple friends of mine who have recently had a GFC 500 installed. One has said that it’s a real problem in his Grumman Cheetah on short final. Another friend with a Grumman Tiger said that he notices it, but it’s not a problem. A friend with a Cardinal said that he doesn’t notice it at all.

Another friend, Mike McNamara, wrote an article about the GFC 500 and the Electronic Stability Protection for the September 2021 issue of the America Bonanza Society magazine. Apparently, Garmin certified the 500 so the LSE would activate at the same minimum speed for the entire Bonanza/Debonair series. The 33 series, the 35 series, and the 36 series. According to Mike, that speed is about right for the 36 series, and OK for the 35 series. But way too high for the 33 series. Garmin’s response was that they grouped the entire Bonanza/Debonair family together to speed up the certification process and keep the costs down. And then provided instructions on how to disengage it on each flight.

So, I’m wondering, did Garmin certify the GFC 500 so the Low Speed Engagement would activate at the same minimum airspeed for the entire M20 line? Short body through long body? And is anyone having problems with the LSE activating on final in the lighter weight models?

Thanks

John

 

Correction: I talked to my friend Mike McNamara who wrote the piece for the Bonanza Society magazine. The Low Speed Engagement on the 33 series and the 36 series are set with the same minimum airspeed of 70 knots. The V35, V35A, and V35B are set at 65 knots. John

[201Mooniac]

Not sure what the setting is for the entire Mooney line but the short, medium, and long bodies were separately certified so they could have setup the vallues differently.  On my M20J I never have a problem with it on short final.

[Skates97]

I have a M20D (short body) and it is set for 80 mph (1965 is in mph). When I first flew after having it installed I had it pushing the nose down as I was on short final about to come over the fence. I was fighting it as I don't come over the fence at 80 mph if I am alone and light. I would get below the altitude where it cuts off and the yoke would "pop" and fly normal. At first I thought there was something wrong with the install and then realized what it is. Fortunately it is easy to over-ride by just holding the AP disconnect button on the yoke. Now if I am feeling it pushing the nose down on me as I am getting ready to land I just hold the button down with my thumb and complete the landing.

[kpaul]

My GFC500 was factory installed as it was the certification aircraft for the F/G.  I have never had any issue with the autopilot engaging while landing.

[ArtVandelay]

If it’s not disabling under 200’, I wonder if that functionality is only available in the GNS navigators, not the old GTN or Avidynes?

[201Mooniac]

I checked the STC setting on my M20J and it is 69 kts.  I come over the fence typically between 72 and 75 so I guess that is why I never had it engage.

[PT20J]

I'm usually light and cross the fence at 65 KIAS in my J, but I generally don't get that slow until short final so I'd be below 200' AGL. It'll be interesting to try it out. It's part of the ESP so it can be disabled with a few button presses and knob twists depending on the display. The G3X Touch Experimental version can have a discrete ESP disable switch, but that got left out of the certified version.

I've flown a GFC 500-equipped C-172N several times for familiarization. I usually cross the fence at 60 KIAS which is what the underspeed is set for in that airplane, and I've never felt it.

Skip

[MisfitSELF]

My POH for short field for my M20J says to fly it at 65kts.  I'd be concerned if the set point for the GFC was set to 69 as I'd likely be established and stable at 65kts above 200 AGL.  I'm surprised it wouldn't have a gear down or flaps down switch to either lower the set point or disable it.

 

Edited October 14, 2021 by MisfitSELF

[Mooney in Oz]

On 10/14/2021 at 7:18 PM, ArtVandelay said:

If it’s not disabling under 200’, I wonder if that functionality is only available in the GNS navigators, not the old GTN or Avidynes?

If the functionality is available in the GNS navigators, it should also be fine for the Avidyne IFDs. A mate of mine who owns a K with a G3X, G5, 2 x IFDs and the GFC500 has not mentioned such an issue, only that the ESP works as advertised.

[Skates97]

18 minutes ago, Mooney in Oz said:

If the functionality is available in the GNS navigators, it should also be fine for the Avidyne IFDs. A mate of mine who owns a K with a G3X, G5, 2 x IFDs and the GFC500 has not mentioned such an issue, only that the ESP works as advertised.

It works as advertised in my plane. If I am getting slower than 80 mph and I'm 200'+ AGL it starts pushing my nose down. As soon as I cross through the 200' mark it turns off. It caught me off guard the first couple times because if I am light I am slowing through 80 mph on short final and suddenly it was pushing my nose down. Once I realized what was going on it's an easy thing to avoid by holding down the disconnect button on the yoke.