Mathematical modelling of a helicopter rotor track and balance: Theory

Non-uniformity of helicopter blades results in vibrations at low frequencies. These vibrations result in increased fatigue of the crew, discomfort to passengers and maintenance and reliability problems. Non-uniformities include geometric, mass, structural and aerodynamic aspects. Typical blades have special devices by which intentional non-uniformities can be introduced, in order to cancel the influence of ''natural'' non-uniformities of the blades. Non-uniformities also result in out-of-track behavior of the blades. In many cases the corrections are aimed at decreasing the out-of-track behavior of the blades, based on the assumption that this effort will also decrease the vibrations that are transferred from the rotor to the hub. Unfortunately, tracking does not necessarily result in optimal reduction of the vibrations. The present paper presents a general mathematical definition of track and balance, and the relation between them. This mathematical model opens the way for a thorough investigation on optimal rotor tuning. (C) 1997 Academic Press Limited.