Implications of Recent Rotary Rig Results for Flight Prediction

Abstract

Analysis of rotary balance data on a generic aircraft model revealed the nature of the flow mechanisms present in subscale experiments, which included the existence of support interference. Recent results on the F/A-18 confirmed the existence of a threshold rotation rate in the rotary data and revealed that in the nonlinear domain at elevated angles of attack, alternatively deterministic or chaotic behavior will prevail, depending on whether or not the magnitude of the initial rotation rate exceeds the threshold value. This has important implications for flight mechanics predictions and control system design as the poststall maneuvering envelope often will include the hysteresis loop. Moreover, dynamic data generated to date in the nonlinear domain have often been restricted to this inner region, limited by the threshold rates, and do not provide any information about the basic hysteretic behavior. Only a comprehensive investigation of steady-state hysteresis and support interference, as in the case of the F/A-18, can provide the basis needed for flight predictions in this domain