Erik,
Your speed related vibration sounds like a similar situation
we encountered a few years ago. After much head scratching, and the
resulting slivers, it turned out that the leading edges of the nose gear
doors were acting like the reeds on a woodwind instrument, albeit not as
tuneful. To fix it we bonded some scrap 'glass pieces to the inside of the
lower cowl where it crosses the front of the gear opening, lowering that area
below the level of the door leading edges. No more vibration. This
isn't necessarily your problem but it's easy to shim the cowl and find
out. For those still building, it's a good idea to assure the lower cowl
is below the level of the nose gear doors. Can't hurt.
Leighton Mangels
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