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Ed,

Check your gear doors.  Outback gear doors have a slight bulge, creating a
negative pressure area.  Normal doors might vibrate under certain
circumstances.

To identify where it possibly occurs you should jack up the plane, crawl
underneath using a creeper, with hydraulic pressure off, raise one gear,
prop it up in the retracted position with a wooden stick.  Test the gear
door by playing piano keys or typewriter pecking with your index fingers
tap, tap tapping on my front door.  Listen for reflected or bouncing sounds
where the door may not be fully seated onto the 4 bid ledge.  If you find
the door is not properly seated see if adjusting the attachment link solves
the problem. Sometimes it is to short thus squeezing the center of the gear
door into the wheel well and the lower edge of the gear door stands away
from the wing seat area. If after adjustment you have not solved the
problem; use tongue depressors, heat gun and carefully heat the door edge to
conform the door to the seated ledge.  Take your time working one small area
at a time. After that is done and you are satisfied then prop the door and
gear up and then do likewise with the inner door the same way.  Test with
full hydraulic pressure to see if it is cured.  Do the same with the other
wheel well.

I had the same problem with a seat of your pants vibration at cruise
throttle descending at the fast speeds.  The onset was sudden, prop pitch
and/or rpm or power settings did not diminish the problem.  The problem
dissipated gradually as I slowed down.  Changing prop pitch, power and rpm
settings eliminates motor mount, harmonic problems. I finally took Don the
Geotz with me and it happened that  the noise dissappeared. I was excited
because we were still flying and the circumstance changed. Upon inspection
the aft bid ledge broke on the right outside gear door aft ledge.  I
repaired it and did the above reshaping technique and have eliminated the
noise.  I can now go to VNE no vibration.  I cannot advise you to go to VNE
unless and until you are absolutely sure the gear doors are the problem and
that problem is solved. It gets pretty nervy pushing the envelope,
especially with present vibrations.  Good luck and let us know what you find
out.

Also you mentioned the canopy seal.  Sometimes canopy seals vibrate although
I don't know how you would feel that in the seat of your pants.

Bob Smiley
N94RJ

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