Aviation glossary
Mast bumping
A hazardous condition on helicopters with a two-bladed semi-rigid rotor: the rotor hub strikes the mast — usually at low or negative G. Almost always catastrophic.
Mast bumping is a phenomenon typical of two-bladed semi-rigid rotors (Robinson R22, R44, Bell 206). If the pilot pushes the cyclic forward abruptly in cruise and generates low or negative G, the rotor stops producing thrust and no longer keeps the fuselage "hanging" beneath it. A corrective cyclic input is then transmitted as a rolling moment on the fuselage (from tail-rotor thrust); the rotor has nothing to tilt against and the hub strikes the mast. The mast is permanently damaged and the rotor separates in flight. Prevention: never generate negative G, correct only with a gentle aft cyclic input, never with lateral cyclic. Fully articulated three-bladed rotors (Cabri G2) and hingeless rotors are not affected.
Related terms
- Cyclic controlThe primary helicopter control operated by the right hand. Tilts the rotor disc and sets the direction of flight — forward, back or sideways.
- Vortex Ring StateA dangerous helicopter aerodynamic condition (VRS). The rotor recirculates its own downwash and loses thrust — adding collective makes it worse.