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ANOTHER PROP INCIDENT
Ray Johnson from the San Francisco
Bay area, flew his VariEze to Las Vegas, where it was parked in the desert sun for 5 days.
He then took off and headed south at 12,500 ft. About 20 miles north of Apple Valley
airport, a horrendous vibration set in. Ray throttled back, pulled the mixture to idle cut
off and pulled the nose up to slow down. When the engine stopped turning, the vibration
went away. Ray glided in to a landing at Apple Valley. Other than the Cessna that pulled
out in front of Ray on final, causing him to have to land off to one side of the runway,
it was uneventful. Rays prop was still on the airplane. 5 bolts had sheared, one was
bent but still holding and the spinner retained the prop.
This is a classic case of flying from a moist ocean climate to a dry desert climate. The wood prop shrinks just a little bit, the bolts no longer have the correct torque, so the prop starts to move and in literally seconds, the bolt holes and drive lug holes become elongated, and the bolts break off at the drive lug due to fatigue.
Check your prop bolt torque, it should be between 18 ft/lbs (216 inch/lbs) and 20 ft/lbs (240 inch/lbs). With a new prop, you should check the torque after one flight. Then again after 10 hours, then at 25 hours, and thereafter every 25 hours.