Wiggly Stick

In nav, gpss and hdg mode, we are developing constant small side to side excursions. Not sure if this is a problem or some sort of rough air dampening move by the autopilot. It does seem like it could really wear down the servos and relays…Is anyone else experiencing anything similar ?

I’ve noticed the same in my A/P recently. Usually starts after several hours of flying. I’ve hypothesized the A/P is constantly overcorrecting when exactly on course. I’m having the avionics shop look at it in the morning (Tuesday) when I take my SR20 in to get the broken exhaust bracket and cracked engine baffle replaced.

Similar, but different.

In HDG mode, autopilot would oscillate between +5 degrees and -3 degrees (NAV mode was okay). Cirrus factory maintenance (thanks, Chris) diagnosed the problem to weird settings in the Sandel EHSI. The settings were apparently affecting the Sandel interpretation of the remote gyro info, and with no known maintenance on the Sandel, I was at a loss to explain the change. (Although, it was after the COPA Bahamian Adventure, so it could have been the Bermuda Triangle thing!) Reset factory settings and problem cured.

Suggest that you have the “factory settings” checked on the avionics to ensure that they are setup and behaving as expected.

Cheers
Rick

Gary, I consider myself to be somewhat of an authority on this, having spent lots of time working with Cirrus on this.

My understanding is that the oscillations do not pose any long-term problem to the servos.

I also found that it happened most on a long trip, and on subsequent trips of any duration.

Ultimately, I took my plane up to Duluth and had them work on it. My understanding is that there are two culprits. One, and apparently the most important, is the spherical bearings in the ailerons. Apparently they’re supposed to be lubricated very regularly, and they recommend a lubricant made by Sherwin Williams (I have it in my plane, but can’t remember the name - I can get it if anyone’s interested). Also, apparently the aileron trim tab influences things, although I haven’t played with it fearing making things worse.

After I took my plane to Duluth, the problem was virtually completely fixed. Since then (January) it is coming back gradually. Lubricating the bearings doesn’t seem to help much. I didn’t start lubricating them until after the problem seemed to recur, and I wonder whether there isn’t some wear that made things deteriorate somewhat.

My theory is that the normal oscillation that takes place on autopilot just to keep the plane on course happens enough on a long flight to heat and distort the bearings, such that there’s a deterioration in them resulting in a new “norm” in terms of oscillation. Longer trip makes things worse around the new norm.

I plan to see if I can have the bearings replaced again, and this time I’ll lubricate them every month (as they now recommend) as well as before long flights. My bet is that this will help.

As you probably can tell, an A&P I’m not. Hope this helps you and the multitude of others with this problem.

Andy

Same problem with our new SR20. Is there a dampener? If you take a rubber band and put a slight pull on the stick sideways one can nearly completely stop the wiggely stick…
My 2c

You know, someone with a sick mind could get the wrong idea from the topic of this thread. Do Cirrus pilots really have Wiggly Sticks?? DOn’t think so.

John Kinsey

Just got home from my 3x per week commute from VKX to ACY…My CDI on the HSI went nite nite…Plane flew ok in HDG with minimal wiggle…any theories on a connection ??

This roll oscillation, almost unnoticeable by passengers but somewhat irritating to Yours Truly, has been with me since day one (~18 months / 560 hours ago), and nothing has fixed it. I’m afraid that this is one bug that I’ve removed from my squawk list not because it’s been fixed, but because I’ve either become resigned to it or just used to it. If anyone who has it wants to talk about it (perhaps to potentially save a lot of time by knowing what DIDN’T work for me), feel free to give me a call - 732.213.7905. I suspect this is the SR20 version of the SR22 vibration - it’s there, in varying degrees, on many SR20s I’ve heard about.

Mike.

PS - I squawked it at my Annual inspection in Duluth in January. Like all really GOOD bugs, it was gone - completely - when I did my post-Annual acceptance flight.

It re-appeared on my trip back home.

I had that problem in all modes but GPSS. The problem was not minor and was not only noticeable, but on a coupled approach (VMC) was scary. The oscillations were noticeable to all on board and growing.

Agreeing with Rick’s comments, my avionics shop said that the Sandel was set up to emulate some other sort of HSI, which evidently was not correct. (I’ll verify this with the avionics shop.) I don’t know when or how the Sandel’s settings were changed. the only time that I can think of was when the ARNAV EngineView was installed. I am not blaming this on ARNAV, their instructions or equipment, but to the best of my knowledge, my Sandel’s setting were never changed.

It would be interesting to see if everyone who has this problem has the ARNAV EngineView, or when the problem was first noticed. (Could the Sandel be changing its own settings?)

Marty

In reply to:


This roll oscillation, almost unnoticeable by passengers but somewhat irritating to Yours Truly, has been with me since day one (~18 months / 560 hours ago), and nothing has fixed it.


Couldn’t resist bring this back to the top. While reviewing my flight logs, I found a note to myself about a recent flight where this oscillation occurred, where autopilot was commanding very slight aileron roll. Brainstorm – what about rudder inputs? So I found that a slight amount of right rudder pedal pressure eliminated the oscillation (left didn’t seem to work). Interestingly, rudder trim didn’t help either (early SR22 only). So I suspect that there is some play in the linkages that the autopilot is dutifully tracking side-to-side. Next flight, not a problem.

Cheers
Rick

We also have a slight A/P roll oscillation in our -20 (~500 hours, no HSI), pretty much from day one. I notice it most during long flights, in both NAV and HDG modes, particularly if there is a good cross wind. A bit of right rudder seems to help, but the easiest solution for me has been to park my left knee under the stick to stop the right roll at level flight. The oscillation seems to stop after a few taps on my knee, and it is usually an hour or so before it starts up again. FWIW.

Phil

In reply to:


…they recommend a lubricant made by Sherwin Williams (I have it in my plane, but can’t remember the name - I can get it if anyone’s interested)…


In reply to:


Lubricating the bearings doesn’t seem to help much.


In reply to:


My theory is that the normal oscillation that takes place on autopilot just to keep the plane on course happens enough on a long flight to heat and distort the bearings, such that there’s a deterioration in them resulting in a new “norm” in terms of oscillation. Longer trip makes things worse around the new norm.


Andy,
I believe that LPS I or LPS II (either) is what was recommended to me, and what I now use.
That’s a big DITTO… my roll oscillation started on reaching cruise when I left Duluth; the bearings were brand new and freshly lubricated.
Possible, but doesn’t seem to fit what happened to me. My own theory is that the autopilot is using the trim motors, which are not the standard STEC motors, to fly the airplane; and those motors don’t match the system well enough. The result is that the feedback loop (STEC -> Motor -> Attitude Change -> STEC) happens at a different rate than STEC expects, so that by the time the STEC “realizes” that it has the wings level, they’re actually just PAST level, which results in the oscillation. I also think that just maybe that’s why we have a metal trim tab on the aileron - possibly an attempt to add some “load” to the system, to damp those oscillations.
All this is pure speculation, and probably worth precisely what you paid for it! I can’t even spell A&P [:D].

Mike.

Mike, the lubricant they recommend is not LPS - I specifically asked, because I already had some of the LPS, and was told it wasn’t as good for this job as the Sherwin Williams.

Regarding your theory on the oscillations, it doesn’t explain why it seems to happen more on longer flights, which has been my experience and according to Cirrus, common among those with the problem. Is is possible that your bearnings were not as aggressively lubricated as they should have been, in the first place, or would have been if there was an understanding then of the possible tie with the oscillation?

Andy

In reply to:


Mike, the lubricant they recommend is not LPS - I specifically asked, because I already had some of the LPS, and was told it wasn’t as good for this job as the Sherwin Williams.


In reply to:


Regarding your theory on the oscillations, it doesn’t explain why it seems to happen more on longer flights, which has been my experience and according to Cirrus, common among those with the problem. Is is possible that your bearnings were not as aggressively lubricated as they should have been, in the first place, or would have been if there was an understanding then of the possible tie with the oscillation?


Andy,

Yup - I wasn’t saying that the Sherwin Williams stuff is LPS, just that what they recommended to ME was LPS. I’m interested in trying the Sherwin Williams stuff.

I think the difference is that my oscillations do NOT seem to happen more on longer flights – they start pretty much as soon as I engage the autopilot in level flight (I think - I’ll double-check). In any case, your theory may be the right one. I don’t think it has anything to do with how aggressively lubricated my orbital bearings are, because I lube 'em myself, so I know they’re good and soaked. But, it may possibly have to do with the type of lubricant, since I’m using LPS II.

  • Mike.

In reply to:


Do Cirrus pilots really have Wiggly Sticks?? DOn’t think so.


John,
Of course they do; but it depends how you say it. Mine oscillates. Be proud, man, be proud!

[:)]

Mike.

In reply to:

    >Do Cirrus pilots really have Wiggly Sticks?? DOn't think so.

    >> Of course they do; but it depends how you say it. Mine oscillates. Be proud, man, be proud!

Mine’s CONVECTIVE, if ya know what I mean!

Hey, I saw you flying to the Bahamas! It’s that triangle thing, eh?

Cheers
Rick

Marty:

Do you have the recently released Sandel software update installed? To all of you reporting this problem, please chime in as to whether you have the new software or the original.

Could be. Maybe I got a little “Bermuda Triangle air” into the system.

In reply to:


Mine’s CONVECTIVE, if ya know what I mean! [;)]


Bill,

I’m not going to touch that one… if I did, I’d have to make some comment about a lightning rod, and you wouldn’t want me to do that! [:D]

Mike.