Loose Stabilator

[Roger Lee]

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• Posted from another site:
• scrapman1959
  
  Its all a little fussy, because it was a year ago or so, but at about 400 hrs we had for and aft movement of the stabilator if you gripped it at the outer tip and moved it front to back. This was the stabilator pivot point bushing getting wore, and if I recall it caused the stick to vibrate. The only way to stop it was to put a lot of out of trim pressure on the elevator and then fly it by hand so as not to overwork the autopilot. A new brass bushing was installed to fix the problem.

  
  

  
  

  
  

  
  

  Tip Ruffner
  Senior Member

• Hello Scrapman,
  
  
  Could you come up with the part number for the replacement bushing? And, how did the shutter radiator front work out for you? Do you have one on your new LS and are they still available?
  
  
  Thanks
  
  

[Roger Lee]

Hi All,

 

This post was discussed here a while back.

I have now inspected 17 CT's and 14 have had the stabilator pivot pin nut torque too loose. The nuts don't move, but due to wear and the carbon fiber back at the stabilator mount relaxing from it's sprung tension the torque changes. I have found these any where from 80 in/lbs to 140 in/lbs. The proper torque is 200 in/lbs. I have included in all my inspections the removal and torque check of each plane's stabilator pivot pin nuts. It seems that after a few hundred hours this happens and once re-torqued they seem to stay at the proper torque. I would advise each person to have their mechanic check this during the next inspection. If the stab gets to the point that it moves for and aft then the torque is really loose. I have never seen one that ever needed any thing other than re-torquing. I wrote this up and sent it to FD months ago, but have never heard any thing from it. I was hoping this would come out as an SB to check, butttt?

[Runtoeat]

Roger, when I removed my stabilator to do the SB on it, I found that the torque was extremely low on the pivot bolt just as you indicate. The bolt removal was started before we realized that the torque was low so the torque wasn't measured but the nuts turned extremely easy. Torque was probably around 80 in. lb. Also, I would highly recommend that anyone who doesn't have torque check paint on the two bolts and nuts that hold the stabilator to the bracket do so. This gives a quick visual inspection aid when getting ready to go flying. These two bolts are critical and any back-off of the torque must be monitored.

[Roger Lee]

Hi Dick,

 

In all the cases where I have found the pivot pin nuts below torque, not a one of them had moved from the torque seal mark. The nuts never moved. The looseness all came from wear and the relaxing of the carbon fiber where the pivot pin bolt is. It can only relax so far so once it gets re-torqued it stays put. I think a good place to check this is around 300-400 hrs. It has to have time to wear a little and for the relaxation of the carbon fiber to take place. The relaxation is normal due to the constant inward pressure from the torquing of these nuts and it can only go so far so I believe once it has been done your good to go for a long time. I have not confirmed this on a plane with 1000 hrs. or so though.

[Jacques]

Just found mine loose also.

for everyone info,here is a picture of what it is

red arrow on bottom right of picture

one nut each side

[Runtoeat]

Excellent picture Jacques. Roger, good to know that re-torquing lasts better than original. Still, it is best to check this every couple hundred hours as you have indicated. The two 6mm stabilator bolts shown in Jacques picture are the bolts I was referring to in my previous note. These two 6mm bolts are the only attachments for our stabilator (aside from the two trim tab control rods). I check these before each flight and the torque check paint gives me a visual aid to make sure the nuts have not moved since torqued.

[Roger Lee]

Hi Dick,

 

Torque seal is a good idea for the two control rod nuts The good thing here is I have never found these loose.

[Runtoeat]

Roger, have you found that tightening the stabilator pivot bolt has resulted in the stabilator moving a little "sluggishly" on any CT's that were re-torqued?

[Roger Lee]

Hi Dick,

 

Because of the way the stab is set up the torquing won't affect it's movement from the cockpit.

[ozairangel]

Hi Dick,

 

Because of the way the stab is set up the torquing won't affect it's movement from the cockpit.

If my memory is orrect, I believe there is an aluminium spacer tube on that pivot shaft. I suspect that shaft is collapsing a little with the torque applied to the nuts, and maybe continuing to relax a bit after tightening.Mine showed signs of distortion.

[Runtoeat]

Hi David. I wasn't aware that there is the aluminum spacer but looking at the CTSW parts manual shows you to be correct on this. Did you notice any resistance when moving your stabilator after torquing the pivot bolt? If so, does this eventually go away as the spacer "relaxes"?

[ozairangel]

Gidday Dick, Have had my stabilator off three times for various reasons and noticed some collapse of spacer tube on first removal. This would have been the first time every removed. I inserted a mandrel of the precise inside dia of the spacer and corrected the distortion. Upon reassembly, I noticed distortion starting to take place as the required torque was being reached, Have checked torque since, all ok. I guess the danger is that one will preload the pivot bearings if not carefull.I think it would be better if this spacer tube was steel or ss. It may also be to do with the precise length of the tube. At no time did I have any play in the stabilator.

Rgds D

[Runtoeat]

Hi David. Thanks for your reply. I'll check the distortion situation out. I can see how the slight collapse of the spacer would allow a bearing preload. Your thought about a stainless steel spacer is a good idea. How about trimming the spacer to the same width as the stabilator bracket and then shimming the gaps on each side out to the bearings with steel washers?

[Roger Lee]

Hi Dick,

 

You should not have to take anything out. You shouldn't have any big issues with the tubes. Just torque the nuts back up to 200 in/lbs. Once I have done this they seem to stay put. I believe it's just a new aircraft over the first few hundred hours settling and wearing in some. Just normal stuff. It really is nothing to loose sleep over and is simple to do. The reason for the original post was just to make owners and mechanics aware so at some point it might actually get checked because the majority of the mechanics would never pull the stab off and check them. I believe it should be done on all CT's around the 200-300 hour mark. If you do it at the 50 hr. mark it would most likely not be settled in yet. You know a good time to do it would be at the wing inspection time. The first 100 hrs. after the second annual.

[Runtoeat]

Roger, I did find that the torque on the pivot nuts was really low when these were rermoved for the stab mod. My CT had about 400 hrs. hobbs time. Checking stabilator pivot nut torque at wing inspection intervals makes sense.

[Roger Lee]

Hi Dick,

 

I need your serial number from your plane.

 

Anyone else that finds a low torque value on the stab pivot pin nuts please send me your aircraft serial number, not "N" number. I really need these so please send them. I would like to know if it is an LS or SW, too.

[Runtoeat]

Hi Roger. The torque on the stabilator pivot bolt nuts on my CTSW tail number N9922Z was very low and estimated to be less than 100 in. lbs. during teardown prior to performing the stabilator modification. My aircraft records indicate that this area of my CT has not been worked on prior to my purchase of the aircraft.

 

I'll send you an email about this also so you will have it for your records.

[207WF]

I have recently noticed a new stabilator issue at 540 hours. Actually, its the stabilator trim tab. Moving it up and down on preflight it began to "click" like something was working loose. On further inspection, it appears that one of the hinges near the center, holding the trim tab to the stabilator, has worn either the hinge pin or the hinge itself down to the point where there is noticable play in the hinge. I assume this is not a big safety issue, just wonder if anyone else has had this. WF

[Roger Lee]

I haven't seen this yet, I don't know about anyone else?

Worst case would be to have to drill all the rivets out and replace the hinge then the rivets.

[Tad Olmsted]

I'll start a new thread on this one.

 

During a 100 hr inspection of a CTLS I found the horizontal stabilator to be loose and moved front to aft. I grabbed the outboard edge of the horz stab to check for security and found excessive play. I checked the torque and it was right on the money, so I started my investigation.

 

The problem wasnt the stab itself, but rather the steel bracket that holds it on. The 2 bolts fit very snuggly in the stab as designed, but with the stab on the bench I checked the steel bracket with the bolts and came to the conclusion.

 

I happened to have 2 other CT's in my shop. One was a SW and the other was a LS. The SW was fine, but the LS had the same play as well. This meant 2 out of the 3 CT's in my shop for MX had excessive play in the horz stab.

 

As luck would have it, Daniel from Germany was in Sebring and we came up with a mod for the steel pivot bracket that holds the horz stab on the A/C. There is only one other CT that has had this problem ( 3 total worldwide), but I want all CT owners and MX stations to be aware and recommend checking this area. I have the LOA for the mod and can forward any info to anyone who might need it.