Flight test evaluation of techniques to predict longitudinal pilot induced oscillations

Abstract

Abstract : The purpose of this study was to determine if pilot induced oscillations (PIOs) can be predicted prior to flight using existing PIO prediction techniques. Two techniques to predict longitudinal PIO tendencies (Ralph Smith's theory and Roger Hoh's bandwidth method) were studied analytically using an existing PIO data base. Suggestions were made for both techniques to allow prediction of PIO rating. The two techniques were then applied to 18 aircraft/flight control system landing configuration. The 18 configurations were flight tested using a flared landing task with the USAF/ calspan variable stability NT-33A. Smith's theory correctly prediction the PIO tendencies and frequencies provided the configuration was not sensitive to the pilot model used. A suggested modification to Smith's theory correctly predicted PIO ratings within an average of 0.6 rating. A suggested modification to Hoh's bandwidth method predicted PIO ratings within an average of 0.5 rating. The limited data base was too small to draw any definite conclusions. Recommendations for further study included collecting more PIO data and using existing data bases and simulator studies to better define the two techniques and to gain physical insights into PIO mechanization.