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Operation Tips

Free wheeling trim wheel
Author Last Post
Hi Tom,
 
I've written about this before in a thread a number of years ago.  I would not recommend drilling a larger hole in the shaft so you will need a new shaft.  This wear or oversized hole in the shaft will cause the roll pin to flex, work harden and eventually fail.  It happened to me once and initiated the process of going through the whole system.  My very experienced mechanic convinced me that the failure was a symptom of lots of other potential issues with the trim system.  He was right.  We pulled the tail, replaced worn and bent jack screws, bushings, etc.  This was a fairly high time airframe but it had been meticulously maintained, except for the trim system which had been neglected.  Since then, I have found this to be the case on most 180/185's.  During the pre-purchase inspections I did before settling on my current airplane, the trim systems were the first thing on the my list.  My reasoning is that if the owner properly maintained the trim system, everything else will probably be in good shape.   As I said before, the trim wheel operates very easily and smoothly when everything is in order back in the tail.  The whole job takes about 2 days.  That airplane will likely fly another 4000 hours before the trim system needs another overhaul. 
 
Safe flying,  Joe
 
I don't want to steal the thread but an issue I have was mentioned specifically here.
 
The trim operates fairly well but there is some slop in the area where the pin connects the wheel to the shaft. 
How is this wear normally addressed? can it be drilled slightly larger for a larger pin?
 
Tom

 
Hi Guys,
 
I have written several posts on issues with the 185 trim system a number of years ago.  Please remember that we are discussing a system comprised of numerous components.  It is impossible to adequately troubleshoot this system without inspecting all of it including stab bushing wear, jack screw condition (many are bent or worn), cable tension, worn trim wheel axle/roll pin fit and friction button condition.  Without pulling off the tail and going through all of the components, you may be chasing your tail.  It is likely on our aging airframes, that there will be a number of components that need attention, replacement, lubrication, etc.  Without looking at all of it, replacing one component may mask a more serious issue.  I have experienced a runaway trim and it is a serious issue that may result in a loss of control.  I would encourage all owners who have done so in recent history to pull the tail and go through this system.  You will get many hours of safe, confident flying from your efforts and you won't believe how nice your trim wheel operate after you overhaul the system.  Safe flying,  Joe
 

A similar runaway trim happened to me in a '72 180H a couple of years ago.

 

I was light and trimmed for a fast decent speed coming over the Oregon Coast Range to get fuel and all of a sudden the trim wheel sounded like a fishing reel getting the line stripped off by a huge fish as the Skywagon headed for the sky! Straight up in fact before I pushed the yoke forward to level off.

 
It took a tremendous amount of force as the trim was maxed out in the accent direction. After I got my wits I trimmed back to level
but could feel the trim wheel was getting tight or ready to let loose again toward the neutral. I flew a few more minutes when it happened again, although I was ready for it this time, the Skywagon then headed straight up again.
 
Well by now I was sweating and trimmed again getting close to neutral but I backed off when I felt the trim wheel getting "loaded". I flew with my elbow jammed between the pillar and the yoke to keep in level flight. (When landing with flaps I realized I could have put a notch of flaps in to "trim"). I got the Skywagon on the ground okay and the partners and I promptly got to investigation, they didn't want to do a test flight to see if it was something I was doing wrong.......
 
We totally disassembled the trim wheel assembly and the only thing we could see was the spring plungers were a bit weak and the notches worn a bit, but not a definitive conclusion. However when testing the trim wheel cable tension it was loose, and out of spec. I can't remember the actual amount but it seemed like it was only half the amount it should have been. After the cable was tightened we did not have any more problems.
 
When researching the runaway trim, I did find some other pilots who had been in the same flight profile of light, and fast decent when it happened. There were various other issues, like sheared pins, worn detents and weak spring plungers as well as too slack of tension.
 
I feel very fortunate being a low time pilot I reacted appropriately and didn't panic and have an accident. I read of others who had passengers and did a complete loop or ended inverted before they got on top of it.

Quoted Text
i was 20 minutes hand flying my 1979 185 well trimmed for level flight. S-tech auto pilot on standby. Suddenly plane went into severe nose up attitude. i fought the yoke with forward pressure then noticed trim wheel had moved to a nose up position. I reset trim and returned to airport without issue. A post flight check did not detect anything obvious. 
Has this happened to anyone?
Could the trim wheel change position on its own?
Did the S-tech on standby have anything to do with it?
Trim wheel clicks when rolled but does move fairly easily. 
 
I posted the original with an incorrect word ("still") in the last paragraph.
The Correct word "stiff" is in red. . .
----- Original Message -----
Sent: Sunday, November 01, 2015 10:21 PM
Subject: re: Free wheeling trim wheel <<$137096833477$>>

Hi Steve,
Some thoughts on your run-away pitch trim.
These are based on the floor mounted pitch trim system.  I forget what it is in a '79.
That whole trim system relies on system frictions and gear ratios mainly in the jack screws in the back.
A run-away sounds like it lost some of its friction required to hold a pitch angle. 
 
The worst is when the shear pin in the axle of the hand trim wheel shears.  But it sounds like it flew Ok after the incident. 
Next, the clicking that you hear and feel are two spring loaded buttons pressing against the side of the trim wheel.  These can and do wear to where they don't apply suffient friction again the side of the wheel.  These buttons can be changed out fairly easily.  If your 79 is basically like my 65, the friction buttons look like those use in kitchen cabinets to hold a door closed. 
Next, the chain drive from the trim wheel mechanism to the cable system could be too loose.  You can pull the center floor plastic cover up and check all this stuff.  It is also recommended that you pull this anyway to clean and inspect the chain. Sometimes, "stuff" falls thru the floor and lodges in the chain drive and can lock up the trim; not your problem in this case.  I have found pieces of electrical wiring, rivets and other junk in the chain and it collects dirt and sand too.
Next, you may have wore and loose jack screws in the rear.
Just a few suggestions where to look. . . .
The S-tek should not have been a factor.  Even if AP misbehaved, I don't believe the trim wheel would have followed the pitch up action.  You mentioned that the trim wheel is "easy" to use.  Now, that is unusual at cruise speeds.  Mine is quite stiff at speeds.  In fact, when I want to change pitch, I use the yoke to find the new pitch angle and then roll in trim to hold it there.  If I used the trim wheel alone, it lets me know that it is under a strain.
Keep us tuned in on what you discover and fixes. . . .D



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First thing I would check is trim cable tension.

 

Mike

 

-----Original Message-----
From: "Steve Osseck (sjosseck@aol.com)" <mailer@mail2.clubexpress.com>
Sent: Monday, November 2, 2015 05:53
To: "Operation Tips" <OperationTips@skywagons.club>
Subject: re: Free wheeling trim wheel <<$137100334514$>>

Thanks David. I'll let you know what I find.

Sent from my iPad

> On Nov 2, 2015, at 12:21 AM, David Lloyd (skywagon@charter.net) <mailer@mail2.clubexpress.com> wrote:
>
>
>
>
> Hi Steve,
>
> Some thoughts on your run-away pitch trim.
>
> These are based on the floor mounted pitch trim system. I forget what it is in a '79.
>
> That whole trim system relies on system frictions and gear ratios mainly in the jack screws in the back.
>
> A run-away sounds like it lost some of its friction required to hold a pitch angle.
>
> The worst is when the shear pin in the axle of the hand trim wheel shears. But it sounds like it flew Ok after the incident.
>
> Next, the clicking that you hear and feel are two spring loaded buttons pressing against the side of the trim wheel. These can and do wear to where they don't apply suffient friction again the side of the wheel. These buttons can be changed out fairly easily. If your 79 is basically like my 65, the friction buttons look like those use in kitchen cabinets to hold a door closed.
>
> Next, the chain drive from the trim wheel mechanism to the cable system could be too loose. You can pull the center floor plastic cover up and check all this stuff. It is also recommended that you pull this anyway to clean and inspect the chain. Sometimes, "stuff" falls thru the floor and lodges in the chain drive and can lock up the trim; not your problem in this case. I have found pieces of electrical wiring, rivets and other junk in the chain and it collects dirt and sand too.
>
> Next, you may have wore and loose jack screws in the rear.
>
> Just a few suggestions where to look. . . .
>
> The S-tek should not have been a factor. Even if AP misbehaved, I don't believe the trim wheel would have followed the pitch up action. You mentioned that the trim wheel is "easy" to use. Now, that is unusual at cruise speeds. Mine is quite still at speeds. In fact, when I want to change pitch, I use the yoke to find the new pitch angle and then roll in trim to hold it there. If I used the trim wheel alone, it lets me know that it is under a strain.
>
> Keep us tuned in on what you discover and fixes. . . .D
>
>
>>> --------------------------------------------------------------------------------------<<
> You have received this message as a member of: International 180/185 Club, Inc
> Change preferences (including opt-out): https://SkywagonsClub.clubexpress.com/content.aspx?page_id=13&club_id=669928
>
>
 
Thanks David. I'll let you know what I find.

Sent from my iPad

> On Nov 2, 2015, at 12:21 AM, David Lloyd (skywagon@charter.net) <mailer@mail2.clubexpress.com> wrote:
>
>
>
>
> Hi Steve,
>
> Some thoughts on your run-away pitch trim.
>
> These are based on the floor mounted pitch trim system. I forget what it is in a '79.
>
> That whole trim system relies on system frictions and gear ratios mainly in the jack screws in the back.
>
> A run-away sounds like it lost some of its friction required to hold a pitch angle.
>
> The worst is when the shear pin in the axle of the hand trim wheel shears. But it sounds like it flew Ok after the incident.
>
> Next, the clicking that you hear and feel are two spring loaded buttons pressing against the side of the trim wheel. These can and do wear to where they don't apply suffient friction again the side of the wheel. These buttons can be changed out fairly easily. If your 79 is basically like my 65, the friction buttons look like those use in kitchen cabinets to hold a door closed.
>
> Next, the chain drive from the trim wheel mechanism to the cable system could be too loose. You can pull the center floor plastic cover up and check all this stuff. It is also recommended that you pull this anyway to clean and inspect the chain. Sometimes, "stuff" falls thru the floor and lodges in the chain drive and can lock up the trim; not your problem in this case. I have found pieces of electrical wiring, rivets and other junk in the chain and it collects dirt and sand too.
>
> Next, you may have wore and loose jack screws in the rear.
>
> Just a few suggestions where to look. . . .
>
> The S-tek should not have been a factor. Even if AP misbehaved, I don't believe the trim wheel would have followed the pitch up action. You mentioned that the trim wheel is "easy" to use. Now, that is unusual at cruise speeds. Mine is quite still at speeds. In fact, when I want to change pitch, I use the yoke to find the new pitch angle and then roll in trim to hold it there. If I used the trim wheel alone, it lets me know that it is under a strain.
>
> Keep us tuned in on what you discover and fixes. . . .D
>
>
>>> --------------------------------------------------------------------------------------<<
> You have received this message as a member of: International 180/185 Club, Inc
> Change preferences (including opt-out): https://SkywagonsClub.clubexpress.com/content.aspx?page_id=13&club_id=669928
>
>
 
Hi Steve,
Some thoughts on your run-away pitch trim.
These are based on the floor mounted pitch trim system.  I forget what it is in a '79.
That whole trim system relies on system frictions and gear ratios mainly in the jack screws in the back.
A run-away sounds like it lost some of its friction required to hold a pitch angle. 
 
The worst is when the shear pin in the axle of the hand trim wheel shears.  But it sounds like it flew Ok after the incident. 
Next, the clicking that you hear and feel are two spring loaded buttons pressing against the side of the trim wheel.  These can and do wear to where they don't apply suffient friction again the side of the wheel.  These buttons can be changed out fairly easily.  If your 79 is basically like my 65, the friction buttons look like those use in kitchen cabinets to hold a door closed. 
Next, the chain drive from the trim wheel mechanism to the cable system could be too loose.  You can pull the center floor plastic cover up and check all this stuff.  It is also recommended that you pull this anyway to clean and inspect the chain. Sometimes, "stuff" falls thru the floor and lodges in the chain drive and can lock up the trim; not your problem in this case.  I have found pieces of electrical wiring, rivets and other junk in the chain and it collects dirt and sand too.
Next, you may have wore and loose jack screws in the rear.
Just a few suggestions where to look. . . .
The S-tek should not have been a factor.  Even if AP misbehaved, I don't believe the trim wheel would have followed the pitch up action.  You mentioned that the trim wheel is "easy" to use.  Now, that is unusual at cruise speeds.  Mine is quite still at speeds.  In fact, when I want to change pitch, I use the yoke to find the new pitch angle and then roll in trim to hold it there.  If I used the trim wheel alone, it lets me know that it is under a strain.
Keep us tuned in on what you discover and fixes. . . .D
 
i was 20 minutes hand flying my 1979 185 well trimmed for level flight. S-tech auto pilot on standby. Suddenly plane went into severe nose up attitude. i fought the yoke with forward pressure then noticed trim wheel had moved to a nose up position. I reset trim and returned to airport without issue. A post flight check did not detect anything obvious. 
Has this happened to anyone?
Could the trim wheel change position on its own?
Did the S-tech on standby have anything to do with it?
Trim wheel clicks when rolled but does move fairly easily. 
 
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