Recommended Practices for Exposing Pilot-Induced Oscillations or Tendencies in the Development Process

Abstract

It has now been more than a century since the first powered flight took place on the dunes of Kill Devil Hills. An often overlooked element of those remarkable first four flights was the occurrence of longitudinal axis pilot-induced oscillations (PIO). Looking back it is now easy to see how the inherent instability of the 1903 Wright Flyer design resulted in PIO with either Orville or Wilbur at the controls. Since that time, aircraft have grown in capability and complexity. For example, the systems designed to control the aircraft have evolved from reversible cables and pulleys where the force of the pilot's inputs directly manipulates the control surfaces to modern fly-by-wire designs where software interpretations of the pilot's inputs manipulate the control surfaces. There has been, however, one constant through this evolution - the ongoing occurrence of pilot-induced oscillations, sometimes with catastrophic results. In the last 30 years almost every military or commercial aircraft designed has experienced PIO, either in the development process or in operational flight. If recent history is any indication, PIO will certainly continue to occur in the future. In this paper, status of relevant PIO criteria will be given, on-board detection and alleviation schemes will be described, and flight test methods will be reviewed. Finally, recommended practices will be outlined to expose PIO tendencies, if they exist, so that the catastrophic events can be minimized or eliminated.