Development of the Phase-Aggression Criterion for Rotorcraft—Pilot Coupling Detection

Significant effort has been expended to develop criteria to predict the susceptibility of an air vehicle to so-called pilot-induced oscillations . Much of this work has been carried out for fixed-wing aircraft and it is only recently that their applicability to rotorcraft has started to be assessed. Real time pilot-induced oscillation identification methods provide an alternative means to at least warn the pilot that a pilot-induced oscillation is in progress so that preventative action can be taken. Existing methods, however, have some limitations and have rarely been used for rotary-wing purposes. Specifically, the existing methods assessed in this paper do not provide an indication of the severity of the event and mask the underlying data that are being used to generate the warning. This paper proposes and presents a new method to identify pilot-induced oscillations, either in near real time or as a postprocessing aid for recorded flight-test data, that addresses both of these issues. The new method, entitled “phase-aggression criterion,” is compared with current methods. It is shown, for a specific set of test cases and a limited test pilot population, that not only can it provide more information about the pilot-induced oscillation but it can also provide an earlier warning of its onset