Mast Bumping

Mast bumping is when the the rotor hub contacts the rotor mast. The phenomena can occur in two-bladed helicopters during low-g maneuvers. the following videos describe this process. As many people learn to fly in the Robinson series helicopters, specific knowledge and prevention of mast bumping is required for anyone flying a Robinson helicopter, this requirement is in included in SFAR 73.

The following video from the U.S. Army describes this phenomena very well. It also shows that is it not a new issues or specific to just the Robinson helicopters.