Flap back

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"Flap back" is a phenomenon experienced flying helicopters. When moving from the hover flight to forward flight, the advancing blade experiences more lift as a result of its increased relative speed. This results in the advancing blade flapping up and decreasing its angle of attack in the process to overcome dissymmetry of lift. If transitioning into forward flight this flapping will result in the front of the rotor disc tilting up, the opposite to achieving forward flight by positioning the front of the rotor disc down. This discrepancy is felt through the pilots cyclic control and know as flap back which has to be compensated for by moving the cyclic control further forward.