207WF Posted August 15, 2014 Report Share Posted August 15, 2014 My Ctsw has recently started behaving with intermittent, small, uncommanded pitch excursions; always nose down. These are easily corrected, and of course, not even noticed on autopilot. I have checked all the cables and pushrods that I can see, and nothing is obviously loose. Any ideas? WF Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 15, 2014 Report Share Posted August 15, 2014 Is the trim moving? Do you have to trim again for level flight? Link to comment Share on other sites More sharing options...
207WF Posted August 15, 2014 Author Report Share Posted August 15, 2014 No trim change. It piches down, I catch it, then its back to normal. WF Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 15, 2014 Report Share Posted August 15, 2014 weight shifts trim tab moves stabilator moves flaperons droop flaps move Link to comment Share on other sites More sharing options...
FastEddieB Posted August 15, 2014 Report Share Posted August 15, 2014 A mystery. But take it very seriously - something is amiss and slack in a control cable run can lead to flutter, with serious consequences. One other thought: With some of the issues others have had, could a control surface or other skin be popping in and out - perhaps with the skin delaminating from the foam core? In a metal plane I think it's called "oil canning". Most likely culprits would be the horizontal stabilizer, elevator or trim tab. Link to comment Share on other sites More sharing options...
coppercity Posted August 15, 2014 Report Share Posted August 15, 2014 Might double check the swivel bearing area the flexible pushrod runs thru in the center console near the brake master cylinder. There is a nut on each side that could have a little slop in it. Check they are snug. Link to comment Share on other sites More sharing options...
FastEddieB Posted August 15, 2014 Report Share Posted August 15, 2014 BTW, my suggestion about "oil canning" goes back to a situation I had with my Tiger. I would adjust lateral trim to be near perfect, then suddenly the plane would be wing heavy - not related to fuel balance or anything else I could determine. The problem was traced back to one of my flaps. Grummans use a honeycomb core, I think, with the aluminum skin bonded to it. Not sure if that's the case with the flaps, but when mine would "pop" and change shape it caused a lateral imbalance. It takes very little change in shape to noticeably affect aerodynamics. Again, I would go to the back of your plane and firmly squeeze the horizontal stabilizer and elevator and see if there's any give. I may be way off base, but it's easy enough to check, and if the cables and pulleys are fine, it's hard to imagine what else it could be. Link to comment Share on other sites More sharing options...
Grateful Posted August 15, 2014 Report Share Posted August 15, 2014 It could be a section of the speed tape on the stabilator is causing a small airflow separation/attachment. Link to comment Share on other sites More sharing options...
Jim Posted August 15, 2014 Report Share Posted August 15, 2014 It could be a section of the speed tape on the stabilator is causing a small airflow separation/attachment. This. Check the gap seal tape between the stabilator and the anti-servo tab. I've had something like this happen when there's a loose or binding piece of tape. Link to comment Share on other sites More sharing options...
Runtoeat Posted August 15, 2014 Report Share Posted August 15, 2014 Removal of the stabilator doesn't take long and this allows good visual inspection of the pivot and mechanisms that control the stabilator. Wondering if you have a CTSW that was required to have reinforcing done to the control rods attachment bracket where this is attached to the trim tab and if this was done? Insure the attachement bracket is solidy attached to the trim tab. Ref: SB-ASTM-CTSW-03 "Servo Tab'. Quick check: Have two persons each hold one of the sticks stationary while a third moves the stabilator and trim tab to check for looseness. Reverse this and hold the stabilator and trim tab stationary while each person, in succession, attempts to move their stick for/aft. Link to comment Share on other sites More sharing options...
207WF Posted August 19, 2014 Author Report Share Posted August 19, 2014 Some great advice, Guys! Here is what I have found so far. The tape is in good shape. The stab. itself shows no signs of delamination that would cause "oil canning,", based on squeezing it hard all over. Both sides feel symmetric. My bird did have the mod to beef up the stabilator attachment area. When I fix the control stick by using the seat belt to hold it back hard aft, the stab does have some play in it. The question now becomes: How much play is normal? I can't find anything in the maintenance manual that addresses the amount of play. So, I wonder if someone else does this, how much play do you find in the stabilator? (E.g., how many inches of travel at either the front or the back of the stab?) WF Link to comment Share on other sites More sharing options...
WmInce Posted August 19, 2014 Report Share Posted August 19, 2014 . . . "the stab does have some play in it." . . .What kind of play are you observing? Lateral, axial, vertical? Link to comment Share on other sites More sharing options...
207WF Posted August 26, 2014 Author Report Share Posted August 26, 2014 I took some measurements today. There is no lateral play in the stabilator. All the play is nose up, nose down. I measured with the stick held back and with the stick held fully forward. I measured both sides of the stab. and got the same numbers on the left and right sides. Its hard to be very accurate about this, but: Max up-down play in the stab. with the stick fully back: Measured at the leading edge of the stab, against the empennage, is 1/4" Measured at the trailing edge of the stab, not including the trim tab, is 1/2" Max up-down play with the stick full forward: Measured at the leading edge = 1/4" Measured at the trailing edge = 3/4" Can some of you please check the play on your birds, so we can see what is "normal"? Many thanks, WF Link to comment Share on other sites More sharing options...
Runtoeat Posted August 29, 2014 Report Share Posted August 29, 2014 WF, did a check on my friend's 2008 CTLS. With stick held back, there was very little up/down noted on trailing edge of stabilator. Maybe 1/4" at most. Link to comment Share on other sites More sharing options...
207WF Posted September 26, 2014 Author Report Share Posted September 26, 2014 With my chute repacked, I could go over and see my mechanic about the pitch excursions. We went over everything in the control system and none of the bolts were loose and we found no cracks in anything using a borescope. The hypothesis now is that the telescopic cable, FD part #C9997092, might be wearing inside its sheathing. This is a sheathed cable covered in Teflon that runs from the controls under the center consol to the back of the tail cone, where it actuates the stabilator. Maybe after a thousand hours of "stick bumping," the thing is wearing out. Does anyone have any experience with this? WF Link to comment Share on other sites More sharing options...
Anticept Posted September 26, 2014 Report Share Posted September 26, 2014 That sheath is called a fairlead. I have two CTs with over 2200 hours each, and original cabling and fairleads. I doubt the fairleada are going to cause an issue for you as they are very small degree changes. If anything, wearing through the fairleads will cause the controls to drag. Is your trim slipping? Link to comment Share on other sites More sharing options...
Roger Lee Posted September 27, 2014 Report Share Posted September 27, 2014 Hi Wayne, Have you removed the stab and torqued the stab pivot pin nuts to 200 in/lbs? Have you looked at those two bearings that the pivot pin rotates in? Have you checked each hinge on the trim tab for looseness? Have you checked the trim tab rod end attachment bracket? These at least should all be ruled out as a factor. Link to comment Share on other sites More sharing options...
sandpiper Posted September 27, 2014 Report Share Posted September 27, 2014 Might double check the swivel bearing area the flexible pushrod runs thru in the center console near the brake master cylinder. There is a nut on each side that could have a little slop in it. Check they are snug. I was having the same problem with pitch excursion. I did as Eric recommended and the problem went away. It wasn't loose by much, but it needed to be snugged up. Link to comment Share on other sites More sharing options...
207WF Posted January 8, 2015 Author Report Share Posted January 8, 2015 I think we might have solved this one. Replaced the green stabilator push-pull cable that runs from the center consol back to the tail. The part was $714 from FD and it took two days to do, but I have not had a recurrence of the pitch bobbing sense. It seems that after about 1,000 hours of stick bumping, the cable had worn internally so that it had play in it. They use similar cables on some ultralights, where the part is time limited. Something to watch out for, I guess. WF Link to comment Share on other sites More sharing options...
Anticept Posted January 8, 2015 Report Share Posted January 8, 2015 Do you still have the cable? One of the things you want to do before you remove a cable is to mark where it goes into fairleads and around pulleys. When you remove it, you can easily see the wear characteristics. I would be very interested in seeing the cable. Link to comment Share on other sites More sharing options...
Tom Baker Posted January 8, 2015 Report Share Posted January 8, 2015 Do you still have the cable? One of the things you want to do before you remove a cable is to mark where it goes into fairleads and around pulleys. When you remove it, you can easily see the wear characteristics. I would be very interested in seeing the cable. Corey, you might want to take a look at how the stabilator control system is done. There are no fairleads or pulleys. Link to comment Share on other sites More sharing options...
Anticept Posted January 8, 2015 Report Share Posted January 8, 2015 Corey, you might want to take a look at how the stabilator control system is done. There are no fairleads or pulleys. I know there aren't any pulleys, but there are fairleads. I double checked the MM, and it shows a picture on page 4-75. Link to comment Share on other sites More sharing options...
Roger Lee Posted January 8, 2015 Report Share Posted January 8, 2015 I guess it depends on your individual definition. It's basically just a guide and comes in all sizes and shapes. http://en.wikipedia.org/wiki/Fairlead Link to comment Share on other sites More sharing options...
FredG Posted January 8, 2015 Report Share Posted January 8, 2015 Did you replace the rod-end bearings on the push-pull cable? Wear of the bearing might introduce some control slop. Corey, I do not think that the push-pull cable goes around any pulleys. Rather, on my plane, it is a mostly straight run but is held captive in two pivot blocks to allow for a small amount of flexing motion (in the 2008 CTsw Parts and Assembly Manual, Release 5, the blocks are called the "forward connection" and the "rear connection", see pages 255 through 259). Fred 2006 CTsw E-LSA Link to comment Share on other sites More sharing options...
Tom Baker Posted January 8, 2015 Report Share Posted January 8, 2015 I know there aren't any pulleys, but there are fairleads. I double checked the MM, and it shows a picture on page 4-75. You must be looking at a different picture than I am. There is a rear mounting block for the cable housing, but it isn't a fairlead. Link to comment Share on other sites More sharing options...
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