Prediction and Assessment of Aircraft/Rotorcraft-Pilot Coupling Phenomena

The description by the Wright Brothers of their first and subsequent powered flights suggests that they experienced pitch oscillations of a pilot-induced nature. Their aircraft were unstable and there was a need for a relatively high level of anticipatory control by the pilot to hold a desired flight path. The re-construction of the flights of the Wright Brothers' aircraft in piloted simulation in the Liverpool Wright Project has brought these so called PIOs (pilot-induced-oscillations) to life and we have been able to explain the circumstances that lead to them, and the underlying physical mechanisms. The early Wright aircraft had poor handling qualities, compared with any modern standard, but even aircraft with good handling qualities while in normal flight, can be forced into a PIO given the right circumstances and it is this insidious character of the phenomena that has led to its continuing mystery and consequent stimulus for research. The presence of PIO's in the first ever powered flights was a signal that they would be ever present in the development of aviation. The infamous examples of fixed wing aircraft PIOs, such as the roll PIO during the 'first' flight of the YF-16 and the pitch departure of the Saab Grippen in two demonstration flights, tend to be remembered because of the intense public interest and subsequent analysis but equally dramatic instabilities have occurred on rotorcraft and can be seen on 'unofficial' videos, e.g. roll PIO of a V-22 during shipboard landing and collective/heave PIO and subsequent crash of a CH-53 with external load. Results from the analysis of these, or similar, occurrences have not been published in the open literature and the generally poor understanding of the peculiarities of RPC's means that the risk of continuing occurrence is high; especially with the increasing utilisation of new technologies, particularly full authority digital flight control systems, a contributing factor in several fixed-wing aircraft incidents. PIOs are in a class of phenomena called aircraft/rotorcraft-pilot-couplings (A/RPCs) and this topic is the subject of the proposed research. The intention in our research is to develop theory which 'models' and explains the physical mechanisms that contribute to APCs. The theory will be informed by case studies based on actual occurrences and reconstructed pilot simulations. The research will go on to explore options for including A/RPC considerations within design and testing procedures for new aircraft.