GFC500 yaw damper vs. factory S-TEC yaw damper

[Marc_B]

I have my M20K Encore at the shop for a GFC500 install with  pitch trim and yaw damper.  Sounds like they've run into a hiccough regarding the yaw damper. 

This Encore came from the factory with an S-TEC yaw damper (see original W&B sheet below).  I found a reference from AOPA mentioning “Except for the addition of an S-Tec yaw damper/rudder trim system — greatly appreciated in those long climbs to the flight levels, the Encore's flight control system is pretty much unchanged from the 252.”

The avionics shop mentioned:   Mooney  with electric rudder trim with third party YD are to typically work as independent systems together in the flight regime.  Your plane however was rigged somehow when the STEC was installed they removed the factory rudder trim motor and rigged the STEC YD trim pot to the rudder indicator assuming to replace the rudder trim system factory installed.  STEC has no provision for this and you are now missing the original factory rudder trim motor and rocker switch.  GFC500 goes into these Mooneys with rudder trim no problem and they remain separated systems that is why there are no special instructions in the installation for doing anything with the Mooney rudder trim.  The issue still arises that the Garmin YD does not operate in this way and will not act as your rudder trim and your YD.  We can discuss more tomorrow at the office but options right now are no electric trim or add the Mooney rudder trim motor and switch to the aircraft.

Are there any Encore pilots out there with the GFC500 and yaw damper?  How did you address this?  Is it accurate that I'd need to reinstall a Mooney rudder trim motor in order to install the GFC500?  Currently I have a rotary knob for rudder trim L/R and below that a 3 position switch for On/Auto/Off for yaw damper.  Verified on old pictures, came from the factory with same.

Thanks,
Marc.

[Will.iam]

I’ll be interested in what you find out about this as i have the exact same yaw damper to my kfc-150 so would be something additional i would have to address if i went the gfc-500 route. 

[PT20J]

The current S-Tec yaw damper appears to include rudder trim and is a stand alone system. https://sarasotaavionics.com/Manuals/STEC/yaw-damper.pdf. 

Assuming that this is what you have installed and that it is working properly, the simplest solution might be to just leave it installed and install the GFC 500 without the yaw damper option.

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[Marc_B]

So I guess short and mid bodies don’t have rudder trim but long bodies do. And for the Encores (maybe others?) Mooney added a STEC yaw damper that doubled as a rudder trim.  However this won’t play with Garmin YD. So options are:

1) keep STEC yaw damper so I still have rudder trim and YD. 

2) take out STEC and install Garmin YD and loose rudder trim (but have YD integrated with AP).

3) take out STEC, install Garmin YD and see about adding rudder trim motor and rocker switch ala long bodies. 

anyone have an idea on YD comparison between Garmin and STEC? Don’t really want to give up rudder trim but also know most mid bodies don’t even have it. #1 vs #2???

marc. 

[carusoam]

Marc,

How old is your STec?

I think one of the things we are seeing with newer APs…. Is there incredible computing skill and speeds….

Real time yaw damping using an 80s PC… may not be as good as a new millennium PC… 

It may be possible to use some of the older STec hardware…

but sounds like more incompatibility challenges…

Even is using a new STEC AP, with old servos….

Mixing hardware sounds like a problem looking for an unexpecting person….

Unless you are a strong electro-mechanical kind of guy…

If it sounds too good to be true…

PP thoughts only, not a mechanic… or electrician.

Best regards,

-a-

[LANCECASPER]

1 hour ago, Marc_B said:

So I guess short and mid bodies don’t have rudder trim but long bodies do. And for the Encores (maybe others?) Mooney added a STEC yaw damper that doubled as a rudder trim.  However this won’t play with Garmin YD. So options are:

1) keep STEC yaw damper so I still have rudder trim and YD. 

2) take out STEC and install Garmin YD and loose rudder trim (but have YD integrated with AP).

3) take out STEC, install Garmin YD and see about adding rudder trim motor and rocker switch ala long bodies. 

anyone have an idea on YD comparison between Garmin and STEC? Don’t really want to give up rudder trim but also know most mid bodies don’t even have it. #1 vs #2???

marc. 

I had the Yaw Damper in an Encore that I owned (Serial #12) that served as a Rudder Trim. If it was me, I'd leave the S-Tec in and proceed.

[Marc_B]

1 hour ago, LANCECASPER said:

If it was me, I'd leave the S-Tec in and proceed.

@LANCECASPER and @PT20J Would it change your mind if the S-Tec had already been taken out and the Garmin YD already installed?

[PT20J]

21 minutes ago, Marc_B said:

@LANCECASPER and @PT20J Would it change your mind if the S-Tec had already been taken out and the Garmin YD already installed?

Personally, I would find the rudder trim more useful than the yaw damper if I regularly climbed to high altitudes. But, if the S-Tec is already removed and the GFC-500 yaw servo installed, I would not go back. 

[LANCECASPER]

31 minutes ago, Marc_B said:

@LANCECASPER and @PT20J Would it change your mind if the S-Tec had already been taken out and the Garmin YD already installed?

That would change things - no reason to go back.

The big bore engine Mooneys (Bravo-270hp; Ovation280hp stock, 310 on the one I had; Acclaim 280hp) all really benefit from rudder trim on take-off, The Encore (220hp) not nearly as much.

[PT20J]

Here’s a thread on BeechTalk that may be of interest

https://www.beechtalk.com/forums/viewtopic.php?f=21&t=201755&start=0

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[Marc_B]

@PT20J I saw that thread.  I think that most agree that the modern integrated YD makes sense.  So the follow up questions are can the S-tec be set up as a stand alone rudder trim along side the GFC500 YD and if not, can a standard Mooney rudder trim motor be installed in a M20K? (and what would be entailed with that...)  Working with my avionics shop and sent an email to Mooney to see...  Of course the underlying base question is will I even miss a rudder trim?

As an aside, the S-tec YD has 3 settings (on-off-auto) and I didn't realize til now that the auto was supposed to kick on when the AP was activated and off when it was off.  But with the move to the GFC500 I'm not sure that would even still be the case if I kept the S-tec YD.

[carusoam]

Let’s invite Don Kaye @donkaye to the discussion…

He is both a fan of the Garmin equipment, and has a Bravo that came with rudder trim….

 

I get the feeling rudder trim sets the zero point where the yaw damper works around….

We have three basic areas the rudder trim sits at depending on how you fly…

1) Climb

2) Cruise

3) Descent

These three settings are always different depending on speed and power settings and angle of attack…. Setting the rudder trim is simply centering the ball each time…

Sounds like the rudder trim and yaw damper are two different systems like elevator and elevator trim…

Best regards,

-a-

[PT20J]

44 minutes ago, Marc_B said:

@PT20J I saw that thread.  I think that most agree that the modern integrated YD makes sense.  So the follow up questions are can the S-tec be set up as a stand alone rudder trim along side the GFC500 YD and if not, can a standard Mooney rudder trim motor be installed in a M20K? (and what would be entailed with that...)  Working with my avionics shop and sent an email to Mooney to see...  Of course the underlying base question is will I even miss a rudder trim?

As an aside, the S-tec YD has 3 settings (on-off-auto) and I didn't realize til now that the auto was supposed to kick on when the AP was activated and off when it was off.  But with the move to the GFC500 I'm not sure that would even still be the case if I kept the S-tec YD.

I doubt you can mix and match the two systems. Even if it worked mechanically, it may violate the STCs. Good question for the installer.

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