Effect of Helicopter Main Rotor Blade Damage on the Rotor Disk (Whole Rotor) Motion

摘要

When a helicopter main rotor blade is ballistically damaged, an imbalance is created in the rotor, causing the rotor disk to execute unwanted motions, which are detrimental to performance. The normally smooth-flying helicopter develops new vibrations that can be physiologically annoying or debilitating to the pilot, can exceed structural fatigue endurance limits, can cause aeromechanical instabilities, and can reduce helicopter performance ability. This report examines the effect of the loss of the outboard section of one rotating blade of a rotor set of four blades on the fixed-system (nonrotating) rotor disk motion. The report shows, beginning with the rotor blade forcing, how a damaged blades response changes, and how this change feeds into the rotor's fixed-system disk motion (the disk referring to the blades acting in concert as a whole entity). With a normally undamaged rotor (referring to all the blades), there exists within the rotor itself the capability of motion canceling of certain frequencies depending on the number of rotor blades in the rotor. This study tracks each individual harmonic (integer multiples of the rotor speed) frequency, one at a time, in order to obtain a first-principles understanding of the phenomena involved with rotor imbalance.