GFC-500 Autopilot in mid body Mooney - Yaw controls needed?

[UteM20F]

Hi folks, we just got a quote for a GFC-500 to finish up our new Garmin panel in our M20F.  We've been without an autopilot since we bought the plane.  It had an old S-Tec that was inop and not worth repairing.

We've heard that some don't think it is worth the extra cost for the adding the rudder/yaw controls.  I really have several related questions:

1. What do the A/P yaw controls add to a plane?  BTW, we don't have a rudder trim.  Would this be a poor rich-man's rudder trim?
2. Is it only for coordinating A/P turns?  Or is it a damper to stop tail wagging?  Both?
3. The avionics shop claims that with a mid-body Mooney, we won't be happy without it.  Do any of you with a mid-body have the GFC-500 w/o the yaw, and if so, what are your thoughts?
4. Is it worth an extra 5 AMUs (estimate for the servos and labor) to have the yaw controls hooked up?

Thanks for your help!

Ute

 

[Marc_B]

Mid-body with a GFC500 with 4 servo / YD.  I find it keeps the AP rock solid with bumps and well coordinated with turns.  It sorta acts as a rudder trim, but not exactly.  I still use right rudder on take off, but it helps to relieve the rudder pressure and keep ball centered once I have it there.  To decrease the work the YD servo has to do I turn off when I'm leveling off and coordinate manually; then reengage the YD.

Do you absolutely need it...no.  But is it nice and makes flying more effortless when using the autopilot...yes.

For me it's like having electric pitch trim...something you can do without but is nice to have.  The telling thing is that I haven't heard from anyone saying that they wish they hadn't gotten the YD if they installed it.

As an aside, the Encore came with the S-tec combo YD/Rudder trim unit.  In this case there was a rotary potentiometer on the panel that you could swivel to engage the servo "left" or "right".  It worked great on takeoff to relieve all rudder pressure and you could completely ignore your right foot and stay coordinated.  The S-tec was in the location that the GFC YD needed to be installed so came out with GFC install.  The GFC YD works better as a yaw damper to keep coordinated with GPSS turn.  The only time I miss the S-tec is on takeoff for about 30 seconds.  Long body rudder trim is mounted differently than the S-tec so the long bodies can keep their rudder trim even with the GFC500 YD.

[hubcap]

Myrtle is a mid-body K Model 231 with a GFC-500 and no yaw damper. The autopilot has been rock solid since Day 1. With almost 200 hours on this configuration, I can honestly say I see no need for it. I don’t feel like I am missing anything.

[PT20J]

I have a M20J with a GFC 500. I made a conscious decision not to add the yaw damper because I wanted to minimize the stuff I have to deal with operationally (you have to turn it on after takeoff and off for landing) and I wanted to minimize unnecessary equipment which requires maintenance and can fail. The mid-body Mooneys don't have the Dutch roll tendencies like Beechcraft products (worst ride I ever had in turbulence was in a Duchess), there's not a lot of adverse yaw, and the aileron-rudder interconnect already aids in coordination of rudder and aileron. I don't regret my decision a bit.

What you will likely find is that those that have it like it and those that do not don't miss it.

[201Mooniac]

I have about 500 hours now on my 4 servo GFC 500 install and while I'm glad I added the yaw damper it isn't really needed, nice but not needed.  As to install cost, $5K for the servo and install seems very high, that is about double what I paid (though that was 4 years ago).

[UteM20F]

2 hours ago, 201Mooniac said:

I have about 500 hours now on my 4 servo GFC 500 install and while I'm glad I added the yaw damper it isn't really needed, nice but not needed.  As to install cost, $5K for the servo and install seems very high, that is about double what I paid (though that was 4 years ago).

This is great info, thanks guys.  Regarding the cost, we got a quote for the GFC-500 2 years ago when we did the panel, and decided to hold off because of the cost.  Bad choice in retrospect!  The price is about 6 AMU higher than it was just 2 years ago.

[Tx_Aggie]

+1 for no yaw damper and flies like it’s on rails. 1980 M20J

[ArtVandelay]

If you want to convince yourself if you need it, just a quick push on the rudder and watch how quickly it settles down, it’s like a second in my J.

Now the V tails need it.

[Pinecone]

Most people without YD don't miss it.  Most people with it, WOULD miss it.

I have it in my K and it does a great job.

Necessary?  No.  Desired?  IMO, YES.

1)  It does keep the ball centered in climbs and descents.  So sort of a poor man's rudder trim.

2)  It stops tail wagging.  

3)  See my comments.

4)  I think so.

[pirate]

People would tell me I didn’t need a yaw damper on my short body but I thought since I’m pulling a S-Tec30 out and installing a GFC500 I might as well go all the way, very happy I did. 

Take regular trips say 2-4 hours and then have to return the same day in pretty bumpy air and you will have a much more relaxed / enjoyable ride with it. 

Like many others have said, the ones with it will say you need it and the ones without will say you don’t.  
 

My neighbor asked me if I thought the damper was needed so I took him for a ride on yet another bumpy day, we turned it on and off many times so he could make his own decision what worked best for him. 
 

[Yooper Rocketman]

I have the M20K/231 modified with the Rocket conversion (100 HP more).  I don't have it with my dual G3X and GTN750 panel and really don't miss it.  I never have any yaw issues but I do need to keep my right foot on the rudder during climb, since I have no rudder trim at all.  I DID have a yaw servo in my Lancair Prop Jet IVPT, and disconnected it. Too many guys with the 750 HP Turbines would get dependent on the rudder auto trim and then get in the pattern after a long cross country, A/P  disconnected, and would get uncoordinated and shift all the fuel out to the wingtip, resulting in a flame out.  That's a lot less of an issue with the gas engine, since you switch tanks and it relights.  Not the case with a turbine.  A flame out in the pattern will be a dead stick landing.  I find I am a lot better "coordinated flight" pilot as a result, which with the Mooney is not as much of an issue as the IVPT.

Tom

[dzeleski]

15 hours ago, PT20J said:

I have a M20J with a GFC 500. I made a conscious decision not to add the yaw damper because I wanted to minimize the stuff I have to deal with operationally (you have to turn it on after takeoff and off for landing) and I wanted to minimize unnecessary equipment which requires maintenance and can fail.

If you use the disconnect button it also disables the Yaw damp. If you press the AP button then it stays engaged. It also remembers the way it was configured last so I actually never touch the YD button, it’s always on if the AP is engaged.

 

Personally I wouldn’t go without it. In turbulence it makes a big difference for passenger comfort.

[UteM20F]

19 minutes ago, pirate said:

My neighbor asked me if I thought the damper was needed so I took him for a ride on yet another bumpy day, we turned it on and off many times so he could make his own decision what worked best for him. 

So what did your neighbor decide?  It seems like his decision would be a very good data point.

Also, is the yaw damper more important with a shorter body or with a longer body?

[MikeOH]

1 hour ago, pirate said:

... I’m pulling a S-Tec30 out and installing a GFC500 I might as well go all the way, very happy I did. 

As a very happy S-Tec30 owner, and assuming your S-Tec30 was working, what made you want to spend the money on a GFC-500?

[pirate]

2 hours ago, UteM20F said:

So what did your neighbor decide?  It seems like his decision would be a very good data point.

Also, is the yaw damper more important with a shorter body or with a longer body?

He decided to go for it, currently being installed. 

Not sure about short and mid body differences, I've only flown the GFC500 in a A36 (which opened my eyes to the GFC500) an Arrow and my Mooney. I’ll fly in my neighbors 231 once it’s finished,. 

[pirate]

1 hour ago, MikeOH said:

As a very happy S-Tec30 owner, and assuming your S-Tec30 was working, what made you want to spend the money on a GFC-500?

I originally had my my S-tec30 with gpss installed back in 2003.  I thought it was good at the time but never very precise, in the bumps it always wondered a bit plus it lacked many features I really wanted. It still worked when removed. 

THEN I went up in a A36 with a GFC autopilot  ( complete system ) and that did it for me. I was amazed how stable, smooth and precise it was. I also really liked the approach capabilities felt like I was in a biz jet. 
 

 

[Marc_B]

4 hours ago, UteM20F said:

Also, is the yaw damper more important with a shorter body or with a longer body?

Long bodies have a larger engine/more HP and longer lever arm so would probably benefit more from YD in general.  But for turn coordination and trimming rudder pressures, many more aircraft could benefit. 

[donkaye]

As I get older, I have a different perspective on money.  Whether it's a small improvement or not, if I'm going to spend the money on an upgrade, I want the best.  That means all 4 servos--and the improvement in the Bravo is not small.

[Z W]

I have the YD.  I can tell there's a big difference when it's on in stability.  It's a very nice feature to have and I use it on every flight.

I'll admit to failing to turn it off at least once and landed with it engaged.  Not recommended, but it's a non-event from a safety perspective.  Didn't even notice it until I'd cleared the runway.  Lesson learned and now I use the AP Disconnect button on the yoke to turn the autopilot and YD off for landing, and not the "AP" button on the GFC500 control panel, which leaves the YD engaged.

[PT20J]

22 hours ago, donkaye said:

As I get older, I have a different perspective on money.  Whether it's a small improvement or not, if I'm going to spend the money on an upgrade, I want the best.  That means all 4 servos--and the improvement in the Bravo is not small.

Gee, Don. If money isn’t an issue and you want the best, I think Mooney still has an Acclaim Ultra they’d sell you. 

[gevertex]

On 11/14/2024 at 10:40 PM, PT20J said:

I have a M20J with a GFC 500. I made a conscious decision not to add the yaw damper because I wanted to minimize the stuff I have to deal with operationally (you have to turn it on after takeoff and off for landing) and I wanted to minimize unnecessary equipment which requires maintenance and can fail. The mid-body Mooneys don't have the Dutch roll tendencies like Beechcraft products (worst ride I ever had in turbulence was in a Duchess), there's not a lot of adverse yaw, and the aileron-rudder interconnect already aids in coordination of rudder and aileron. I don't regret my decision a bit.

What you will likely find is that those that have it like it and those that do not don't miss it.

This is exactly my stance. I am sure it would increase the ride quality a little and help with other tasks, but that benefit probably doesn't outweigh the operational complexity of needing to manage it.

[donkaye]

14 hours ago, PT20J said:

Gee, Don. If money isn’t an issue and you want the best, I think Mooney still has an Acclaim Ultra they’d sell you. 

I bought my airplane 32 years ago before my "perspective" change.   I think my airplane may be one of the best equipped Mooneys in the fleet.  The G1000 and G1000NXi are great products, but I like the flexibility of being able to modify my airplane as new and exciting technology comes to market.  That can't be done with any G1000/NXi equipped airplane.  I happily accept the 20 knot speed difference between my airplane and the Acclaims for the extra benefits I have with mine.

[donkaye]

5 hours ago, gevertex said:

This is exactly my stance. I am sure it would increase the ride quality a little and help with other tasks, but that benefit probably doesn't outweigh the operational complexity of needing to manage it.

Complexity?  A complete non issue.  In heavy turbulence I turn the AP off because I can fly the airplane better than the autopilot, but the YD stays on because the multiple Garmin inputs* to it can better anticipate yaw changes than I can.  To me one of the most important inputs is Lateral Acceleration, which is the rate of change of lateral motion.  It's one thing to adjust to lateral motion.  It's quite another to adjust to the rate of change of lateral motion.   To me these multiple inputs make it better than other YDs with single inputs.

*Per Garmin: "The yaw servo provides Dutch roll damping and turn coordination in response to yaw rate, roll angle, lateral acceleration, and airspeed."

[mhrivnak]

In turbulence, I've turned the yaw damper off and on to feel the difference. It's significant. When off, there is some definite yaw happening, which is expected as the left and right wings encounter different bits of turbulence at different times. But press one button, and nearly all of the yaw motion stops like magic.

As pilots, the yaw motion in turbulence probably isn't that big of a deal. I'd be fine without the yaw damper, but it does marginally improve my quality of life in turbulence.

For inexperienced passengers though, yaw is perhaps the most unnatural dimension of turbulence. I'd also bet that yaw feels worse in the back seat where you're further behind the center of gravity, and thus swinging farther left and right.

If you don't fly much in turbulent air, it may not be of much value to you. But I'm very happy I have it, since convective turbulence is an issue a lot in NC.

If you're looking for ways to justify the expense, I think you could make an argument that it's also a speed mod! The natural yaw of turbulence causes the plane to briefly travel somewhat sideways through the air, and yaw is corrected by air flow hitting parts of the airframe that it normally shouldn't. If the tail swings right, air will hit the right side of the vertical stabilizer, and possibly parts of the plane's body, pushing it back into a straight position. That must increase the drag profile. Or you could use a yaw damper to keep the airframe pointed as straight as possible through the air flow.

[PT20J]

If you want the yaw damper but cost is an issue, keep in mind that the GFC 500 is a modular system. It’s very easy to add the yaw servo later if you decide you want it. The servo mounting will be there because it attaches to the same bracket as the pitch servo and the CAN bus and power are easily extended with from existing wiring. Installation is simply bolting in the servo and attaching the bridle cable and some changes to software configuration.