REFLECTOR: Elevator torque tube center bearings (Was: Front Vibration 90% resolved)

[KeithHallsten]

I never thought the aluminum bracket (that the center ends of the elevator torque tubes slip into) was a good design.  I didn't use it, but instead got some spherical bearings that slip inside the torque tubes.  I didn't cut off the doubled hinge arm in the center of the canard, but bolted the bearings on either side of it.  This arrangement provides more than twice as much overlap between the support bearing and the torque tube.  It also provides a real bearing, rather than a steel-on-aluminum faying surface.  Several others on the reflector have made a similar design change. 

Obviously there has not been a rash of torque tubes pulling out of the aluminum sleeve, but I think more margin for movement is still a valuable improvement.

Keith Hallsten
 
  ----- Original Message ----- 
  From: Rene Dugas 
  To: reflector at tvbf.org 
  Sent: Monday, October 04, 2004 3:16 PM
  Subject: REFLECTOR: Front Vibration 90% resolved


  Removed my "doghouse" to recheck the flange bolts.  Tightened each less than 1/8th turn.  Already tight.  Bulkhead bolts likewise.  Tight.  It occurred to me that in flight the canard is lifted slightly at the tips, Sooooo.   I propped the tips up slightly then rattled the elevators.  There was a vibration and slack not present in the hinges when at rest on the ground.  I tightened each of l the screws at each hinge to snug and reflew the plane.  Slight vibration at 188 knots.  Much better.

  The slight sag in the canard was compressing the hinges enough to cover the slack.  In flying configuration the slack was significant only at speed.  This may be why my vibration did not cease with pull ups.

  Thanks for all the help and suggestions.  My plane is a better ship for your thoughtful suggestions.



  It occurred to me that in a dramatic pull up the canard could flex enough to distract at the central hinge and COULD even pop the elevator torque tube out of the aluminum "L" bracket in the center of the canard.  The circumference of the circle formed by the line through the elevator is larger than the canard.  The 8 hinges will exert pressure to neutralize this tendency. The sum of these pressures is unknown to me.   Possibly a second bolt holding the two elevators together is in order not just the one through the stick connecting rod.

  Thoughts?

  Rene' Dugas

  N129RD



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