Cowl Vibration

[davidfreedman]

I finally completed my BRF yesterday after being grounded for 3 months due to a long string of maintenance and repairs.  I was flying at max gross with my CFII in the right seat and one of his CFII students in the rear right.  I followed advice from a separate threat climbing to altitude with WOT and prop full forward.  On my right crosswind, I noticed more cowl vibration than I had ever noticed before when I looked out over the nose.  I backed off to 25 squared (my previous technique) to see if that made any difference and it did not.  Figuring my cowl must be loose, I called tower and landed immediately for inspection.  I did not pay attention to vibration on descent.  On the ground, I found the cowling to be fully fastened. 

I bounced ideas around with my CFII and he suggested that the vibration may have been a result of max gross + a different loading situation than I normally fly (a 190 pound man in the back rather than just luggage).  He thought this may have increased the angle of attack for same climb performance.  I should mention that he's also my IA an usually pretty good at diagnosing these sorts of things if they are mechanical problems.

Have any of you experienced this?  Any thoughts?

[KSMooniac]

I don't think cowl vibration would have anything to do with loading or climb power.  You might remove the top piece and check for cracks...it could be that you now have one and the resulting loss of stiffness is leading to more deflection than you remember.  You also might check the condition/engagement of the baffle seals on the cowl before you remove it, too.

[Magnum]

I would get a prop balance done. Not very expensive and you will exactly know how much your engine shakes. If it is well within the limits you can continue your search, but maybe it will be gone after the balance.