21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-4.1.3

SIMULATION OF HELICOPTER FLIGHT DYNAMICS AFTER TAIL ROTOR LOSS OR MAIN ROTOR BLADE FAILURE

Mello O. A. F.
C.T.A., Brazil

Keywords: simulation, helicopter flight dynamics, tail rotor loss, main rotor blade failure

Two applications of flight simulation to the investigation of helicopter accidents are presented. In the first, an accident with typical tail rotor loss characteristics is considered. The investigation board worked on two hypotheses, namely tail rotor shaft failure and pilot's loss of pedal control after he suddenly increased the collective pitch near the ground and delayed applying pedals as needed. A simulation was conducted using simple models of yaw dynamics and tail rotor aerodynamics, and results indicated that pedal control would still be available even with a three second pilot delay in applying the pedals, therefore the hypothesis of loss of pedal control was discarded. In the second application, a helicopter accident at sea in which the aircraft wreck had not been recovered is considered. In that case, the investigation board had to rely on information from the Cockpit Voice/Flight Data Recorder (CVFDR) and a video recorded by an undersea robot. The most significant information obtained from the FDR were extremely high vibrations in all three axes, at a frequency associated with the first harmonic of main rotor rotational speed. The investigation was directed towards several hypotheses associated with main rotor blade and assemblies that might explain the vibrations. A simulation program based on an existing general helicopter flight simulation code was developed and simulations were conducted for the assumed blade failure hypotheses. Results indicated that the excessive accelerations were consistent with the loss of a large rotating mass, due to blade fracture near the root. In both applications, simulation provided substantial grounds for the investigation boards to establish the most probable causes for the accidents.

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