Yaw Damper Test

[donkaye]

I couldn't find the thread where someone made the suggestion to run a test on the effectiveness of having a yaw damper, so am starting a new thread.  I ran the test a few days ago. With the yaw damper on I applied full left rudder (with difficulty because the YD was on and fighting the displacement), then released the rudder pressure.  With no oscillation the plane IMMEDIATELY straightened out and stabilized.  I then turned the YD off and did the same thing.  First, displacement was easy because the YD was off.  Then, there were several lateral oscillations before the plane became stabilized.

The test was irrefutable: the Yaw Damper makes a big difference in lateral stability.  For the price, it is worth every penny in my opinion.

[Ragsf15e]

The one I’d like to see is flying level in turbulence damper on/off.  It will likely have to be done with the autopilot off, but just trimmed level, seeing what turbulence does in yaw without it, then turning it on.
In the Meridian i fly with a gfc700, I typically turn yd back on after disconnecting the AP because it makes such a difference in passenger comfort by reducing/eliminating yaw oscillation.

 

[47U]

1 hour ago, donkaye said:

I couldn't find the thread where someone made the suggestion to run a test on the effectiveness of having a yaw damper, so am starting a new thread.

Was it this thread, Don?  And thank you for sharing your experiences on best practices flying the Mooney line. 

 

[ArtVandelay]

Why would a long body provide better lateral stability?

Vertical stabilizer being a longer arm, and lateral push from air currents will result in more yaw.

I noticed a little yaw in my J in turbulence, not enough for me to care, I’m more concerned of trying to avoid it all together.

[donkaye]

16 minutes ago, ArtVandelay said:

Why would a long body provide better lateral stability?

Vertical stabilizer being a longer arm, and lateral push from air currents will result in more yaw.

I agree and edited the above to correct.

[PT20J]

Don's test results should be no surprise, because the purpose of the damper is to make a slightly underdamped system critically damped. (An underdamped system when disturbed will oscillate about the equilibrium point with each oscillation decreasing in amplitude until eventually returning to the equilibrium point. A critically damped system when disturbed returns to the equilibrium point as rapidly as possible without overshooting.)

Keep in mind that aircraft dynamics are complex. The vertical tail volume (vertical tail area x arm) certainly has an effect, but the mass distribution also has an effect. Stick a heavier engine farther ahead of the CG, and perhaps put more weight in the tail, and the dynamics change because of the inertia of all that distant (from the CG) mass when it gets swinging. This is one reason longer airplanes tend to yaw around more in turbulence than shorter ones. 

Skip

[Will.iam]

Actually in turbulance or climb out is when i notice the benefit of the yaw damper the most. With it on i can ruddertrim for the climb so I don’t have to manually push on the rudder. And in turbulence there is far less swaying and you feel the corrections the damper is applying on the rudder pedals if you still have your feet on them. About the only place i turn it off is in gusty crosswind landings. I need to know I’m countering the winds and not the yaw damper itself.  

[BDPetersen]

Hmmm. Flashbacks of Dutch roll recovery training in the 707-320. Yaw dampers off, press a rudder to induce a yaw and hang on in hopes the recovery technique is timed properly. Good thing the Mooney doesn’t have swept wings.

[Jerry 5TJ]

Qualitative assessment / guesstimate of YD utility—in the shorter body Mooney the back seat passengers are close to the yaw axis.  In the long body they are about 2’ further aft and the yawing motion is more noticeable to them.  

In the PA46 those rear-most seats are even further aft of the yaw axis and noticeably more nauseating in yawing turbulence.  The passengers seated there find the YD is welcome indeed. 

The aerodynamics experts may weigh in on axis coupling, especially roll-yaw coupling where the ratio of wing span to fuselage length plays a role (pun…) as well in just how much yawing is induced to discomfort our passengers.  

[EricJ]

3 hours ago, Jerry 5TJ said:

Qualitative assessment / guesstimate of YD utility—in the shorter body Mooney the back seat passengers are close to the yaw axis.  In the long body they are about 2’ further aft and the yawing motion is more noticeable to them.  

In the PA46 those rear-most seats are even further aft of the yaw axis and noticeably more nauseating in yawing turbulence.  The passengers seated there find the YD is welcome indeed. 

The aerodynamics experts may weigh in on axis coupling, especially roll-yaw coupling where the ratio of wing span to fuselage length plays a role (pun…) as well in just how much yawing is induced to discomfort our passengers.  

Eons ago as a young engineer I worked on a DARPA program where we used a Gulfstream I (turboprop) as a test platform for an imaging radar.   During system integration and testing I'd go on the test flights, initially to debug my own stuff, and then to help with integration.   I was using some test equipment that was kinda big and heavy and they wouldn't let me keep it at my equipment station near the flight deck during takeoff and landing, so I'd have to stow it in the cargo space all the way back in the tail.   Once in the middle of a test flight my stuff broke in an unrecoverable fashion, so I went to put the equipment back on a shelf in the tail.   Holy crap it was like swimming in ocean swells back there, and we were just in the normal straight-and-level racetrack patterns we were using.   It took me forever to wrangle the test equipment back onto the shelves and secure them because everything kept moving around so much.    Since I had nothing to do for the rest of the flight I went up to the jump seat on the flight deck and it was totally smooth and stable there.   I told the pilots they needed to go ride in the back for a while.    They did not care. 

I don't have any idea whether that airplane had a yaw damper or not, but I'd guess there was none engaged at that time.

[PT20J]

If you want to go testing this be a little circumspect. I’m not sure exactly how strong the Mooney tail is (and I don’t want to find out ) but generally aircraft are designed to handle the loads from a full rudder deflection and release at or below maneuvering speed, but not a full deflection in one direction followed by a full deflection in the opposite direction. Such pilot inputs are what caused the vertical stabilizer to separate from an Airbus A300 years ago (American Airlines flight 587).

Skip

 

[carusoam]

If you like Process controls… and PID loops…

A Yaw Damper is going to be your thing…. 

Nice to have MSers that can put all of this into practice…

And demonstrate and explain at the MSer level!

Go MS!

…and thanks DK!

Best regards,

-a-

[Will.iam]

3 hours ago, PT20J said:

If you want to go testing this be a little circumspect. I’m not sure exactly how strong the Mooney tail is (and I don’t want to find out ) but generally aircraft are designed to handle the loads from a full rudder deflection and release at or below maneuvering speed, but not a full deflection in one direction followed by a full deflection in the opposite direction. Such pilot inputs are what caused the vertical stabilizer to separate from an Airbus A300 years ago (American Airlines flight 587).

Skip

 

Yes no “bicycling” of the rudders are allowed unless you have a death wish or suicidal. 

[ArtVandelay]

but not a full deflection in one direction followed by a full deflection in the opposite direction. Such pilot inputs are what caused the vertical stabilizer to separate from an Airbus A300 years ago (American Airlines flight 587).
Skip
 

I never liked that, the Airbus stabilizer is just held on by 3 bolts IIRC. I’d like to see it attached with additional support, like a tongue & groove arrangement. I wonder how Boeing does it?
The Airbus was climbing so it was going pretty slow.

[carusoam]

One of the lesser remembered accidents around NYC…

Shortly after 9/11…

https://en.wikipedia.org/wiki/American_Airlines_Flight_587

-a-