Validation of helicopter mathematical models

The validation of theoretical flight-mechanics models for helicopters is of considerable practical importance for the design of new rotorcraft. Conventional validation methods have involved comparisons of the responses of simulated and real helicopters to a simple input, such as a step or a pulse. The use of sufficiently small inputs allows the development and validation of linear models which can be used by the control system designer to endow the helicopter with acceptable stability characteristics and handling qualities over a limited operating envelope. For non-linear models, more suited to the investigation of large and rapid manoeuvres, one approach to model validation is to' use linearisation about a range of trim conditions and apply system identification and parameter identification techniques. Additionally, it is possible to transform the problem to the frequency domain in order to eliminate subsystems from the validation process. The large amplitudes of typical nap-of-the-earth manoeuvres demand a new approach to validation. Inverse simulation has demonstrated its value in this context.