Helicopter roll-pitch coupling feedback model and comparisons with handling qualities flight test data

This paper presents results which help explain a helicopter phenomena which significantly impacted pilot opinion during a high gain slalom task recently flight tested by DLR. This is characterized by a sequence in which a roll response creates a pitch response and the pitch response feeds back to alter the original roll response. This rate or pilot induced phenomena is termed coupling in this paper. Due to the impact of double on pilot handling qualities ratings, an effort was made to model it mathematically and to validate the model with flight test data. The model was applied to both an unaugmented BO 105 helicopter and the BO 105 in-flight simulator ATTHeS (Advanced Technology Testing Helicopter System). The ATTHeS aircraft was programmed to fly a wide variety of inter-axis configurations for the slalom task. The double model was found to predict well the overall slope of a cross plot of longitudinal and lateral cyclic activity measured during the slalom task. Samples of the flight test data correlations are included. A plot format is presented on which the characteristics of the double model are conveniently displayed. NOMENCLATURE L~~ roll moment due to coupled roll rate, 11s ~p roll moment due to roll rate, 11s Lq roll moment due to pitch rate, 11s