A critical examination of PIO prediction criteria

Abstract

Five criteria for the prediction of linear (Category I) pitch PIO susceptibility have been subjected to a critical examination, including the application of a consistent flight research data base, and analysis of the strengths and weaknesses of each. The criteria chosen for analysis were the Bandwidth/Pitch Rate Overshoot, Neal-Smith (original definition), Neal-Smith (revised by the Moscow Aviation Institute), Smith-Geddes, and Gibson Phase Rate/Gain criteria. The data base consisted of 207 separate configurations from seven references, covering fighter up-and-away maneuvering and precision landing of both fighters and transports. The best criteria in terms of correlation were Bandwidth/Pitch Rate Overshoot, with a success rate (correctly predicting both the absence and occurrence of PIOs) of 91%, and correctly predicting the existence of PIO for 78 of 91 cases. Gibson's criteria were second overall, at 80%, but predicted only 66 of the 91 PIOs. The other criteria were noticeably less effective, with the original Neal-Smith criteria under-predicting and both the revised Neal-Smith and Smith-Geddes criteria over-predicting the occurrence of PIO.