While cleaning the elevator this weekend, I noticed a noise in the tailcone region when lifting the elevator up. The noise doesn't occur when the elevator is moved with the control column, and I can't feel any play in the bellcrank just forward of the aft bulkhead, nor in the pushrod just aft of the aft bulkhead. Pushing gently against a locked control column also reproduces the noise. See the video below:



or the youtube URL:

https://www.youtube.com/watch?v=GNJq-ox ... e=youtu.be

Any ideas what that might be?

It sounds to me like the sheet-metal might be oil canning not sure where though


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Did you look on the underside and see if the rear of the horizonal stab. is binding with the elevator. It is a close fit and if there is a ding, they might be hitting. Also, pull the tail cone and check the rod that goes forward to the bellcrank the elevator cables attach to. Something must be making contact in there.

Horiz stab binding vs elev; don't think so - noise comes with elev in trail with stab with control lock in place vs considerable up elev without control lock in place. I looked closely at the tunnel the pushrod goes thru, but no binding seen. And why would it occur at dfferent elev angle depending on control lock?

I would look at elevator torque tube( look inside from the inboard side of the elevator).

I would consider disconnecting the push pull tube from the elevator bell crank. Block the bell crank so it doesn't move and try to move the elevator see if the noise is there.. at least get everything forward of the elevators either eliminated or not, as being the cause.


Check the elevator down spring brackets. Check the bolts at the bell crank.
Check the elevator hinge bearings and hardware.

Mike


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No down spring on mine; apparently that happened on SN 50662 and later.

Tailcone off, extended baggage out. No noise in the elevator itself when it is disconnected. Pushing forward on the pushrod with the elevator disconnected recreates the sound, but hard to figure out where it's coming from. The aft elev bellcrank doesn't seem loose with no cracks in the support bracket and a tight center bolt. I'll crawl back there when I can get my wife to work the elevator later tonight and see if I can localize it.

I crawled way back in the fuselage with my wife toggling the elevator, and felt the various components, trying to figure out where the noise was coming from. It appeared that the vibration/report/noise was coming from the bottom of the rear elevator bellcrank. Since the noise only occurred when force was directed through the pushrod, I made a calculated guess and thought it might be the pushrod bearing at the bottom of the bellcrank. Unfortunately, the Cessna PM's don't list that bearing or the central pivot bearing part numbers. You can read the central pivot bearing part number right on the bearing itself; it's a Torrington 4NCC910P which now goes by the name of MS24472-4 and is available from McFarlane and others for $64 or so at this time. The other bearing doesn't have a legible PN, but the pushrod ends are interchangeable and the actual elevator bellcrank, called an elevator pylon assembly by Cessna, calls out an AN200KP4 bearing, which now is called a MS27640-4. These are available from AC Spruce for about $20. Measuring the existing rear elevator bellcrank pushrod bearing and the elevator pylon assembly bearing, leads one to the conclusion that they have the same dimensions, and coincidently, they match the dimensions described by AC Spruce. Oddly enough, I have a spare one of those for the next time I feel brave enough to pull the elevator to mess with the jackscrews. So, sockets in hand, I headed to the Harbor Fright 12 ton press:



after cooling the hermetically sealed bearing pouch on ice:



I then pressed in the new bearing:



While I was back there, I decided to swap out the cable barrels and eye to the newer, pinned-style hardware, since my McFarlane cables are already pin-capable. Unfortunately, the pinned-style eye used on the rear elevator bellcrank is kind of an odd duck in that it is a NAS648-22RS, and apparently is unavailable in the more common MS21254 series (it would be a MS21254-4RS, but I couldn't find that any have ever been made). Nevertheless, the NAS648 is equivalent to the MS21254 series, so in they went:



[Drum roll now please] After retensioning the elevator and autopilot pitch cables, and pinning the turnbuckles, the noise is completely gone! Although I couldn't detect any play or roughness in the replaced bearing, it apparently had bad ju-ju and is now gone. Hopefully this will help someone down the road.

Thanks for posting your findings. I squirted ACF-50 in most of mine when I first got it 20 some years ago and think it helped with stuff like this as well as corrosion. Little messy but......

Unfortunately, I'd already tried LPS-2'ing the the bejabers out of the bellcrank, so I don't think more ACF or Corrosion-X would have helped (the aircraft was treated with Corrosion-X about a year ago).