I want to ask an open question.
What happen if with correct flap config, trim, cg and engines, you select wrong V1/VR/V2 speeds, with values bellow the real ones?
last winter at orly, a french charter B744 outbound to french west indies close to MTOW, rotated at 132KTS as calculated by crews on their ladtops.
it ended up by large pieces of underfuselage near the tail being torn off on runway.the crews didn't realize the tailstrike, but understood something was wrong and release back pressure on the controls and aircraft smoothly took off and departed
after an in flight visual check performed by a figther 45 minutes later, the company decided to call back the plane that landed back two hours later
each of the crew had more than 10000 hours
PS : the flight has been reported at last minute the evening before due to technical problem and curfew time