Maximum speed limit Helicopter

the main limitation of helicopter low speed. there several reasons helicopter cannot fly fast fixed-wing aircraft. when helicopter hovering, outer tips of rotor travel @ speed determined length of blade , rotational speed. in moving helicopter, however, speed of blades relative air depends on speed of helicopter on rotational speed. airspeed of advancing rotor blade higher of helicopter itself. possible blade exceed speed of sound, , produce vastly increased drag , vibration.

at same time, advancing blade creates more lift traveling forward, retreating blade produces less lift. if aircraft accelerate air speed blade tips spinning, retreating blade passes through air moving @ same speed of blade , produces no lift @ all, resulting in high torque stresses on central shaft can tip down retreating-blade side of vehicle, , cause loss of control. dual counter-rotating blades prevent situation due having 2 advancing , 2 retreating blades balanced forces.

because advancing blade has higher airspeed retreating blade , generates dissymmetry of lift, rotor blades designed flap  – lift , twist in such way advancing blade flaps , develops smaller angle of attack. conversely, retreating blade flaps down, develops higher angle of attack, , generates more lift. @ high speeds, force on rotors such flap excessively, , retreating blade can reach high angle , stall. reason, maximum safe forward airspeed of helicopter given design rating called vne, velocity, never exceed. in addition, possible helicopter fly @ airspeed excessive amount of retreating blade stalls, results in high vibration, pitch-up, , roll retreating blade.