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Whale Tail Strike ... 380

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Vmu = Minimum Unstick Speed. Done during takeoff. Over rotate to drag the tail and note the speed at which the aircraft becomes airborne.
 
I remember watching some footage of a 707 undergoing Vmu tests - when it finally got into the air, it was just over stall speed and wallowing like a, well, whale. I imagine it would be rather high pucker factor for the pilots, being in an aircraft, just off the ground, barely over stall speed.
 
The Vmu test is performed to ensure that the aircraft can still take off if it is rotated too early by the pilot. Some early types (DC-6, I think) would stop accelerating if they were rotated early, so even though you were trying to fly, it was never going to happen.
Certification standards under Part 25 require an aircraft to be able to take off at any speed above that where the elevator physically has the authority to raise the nose off the ground. The high alpha involved in the test means the tail usually scrapes along the runway before liftoff.
 
I think the purpose of this test is to prove the aircraft can become airborne if over-rotated, or rotated too early. I can't remember which plane it was, but an early jet was over-rotated onto its tail and subsequently crashed because it was not able to get airborne after that event. Part of the certification of new jets is to make sure they can power out of that situation.
 

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