Development of a Comprehensive Rotorcraft Model to Study the Susceptibility of Teetering Rotors to Mast Bumping Accidents

Rotorcraft with a teetering rotor design are susceptible to a phenomenon known as "mast bumping" or “excessive flapping” which can lead to severe shaft structural damage followed by total separation of the rotor from the vehicle and a potential incursion of the rotor blade into the fuselage. Mast bumping accidents are nearly always fatal and are generally unavoidable once specific flight conditions are met. Certain teetering rotor vehicles are prohibited from specific maneuvers that may lead to mast bumping events. However, specific incidents indicate that certain causes of mast bumping may have not yet been determined, and the extreme danger of the phenomenon makes studies using flight testing impossible. This research uses the Rotorcraft Comprehensive Analysis System (RCAS) to create a physics-based, parameterized model of a nominal teetering rotor helicopter to simulate and assess the mast bumping risk of various level flight conditions and specific maneuvers. This data is used to develop a metric to quantify the mast bumping risk of any maneuver. This model is also used to study the sensitivity of a vehicles mast bumping tendency to conceptual rotor design parameters. Preliminary analyses show a relationship between mast bumping risk and high airspeed, as well as low g-force. Studies on variations in blade mass properties indicate that increasing the blade mass or placing the blade CG farther towards the tip increases mast bumping risk in low speed flight regimes.