HOVER PERFORMANCE METHODOLOGY AT BELL HELICOPTER TEXTRON

Bell Helicopter Textron's Hover Performance Methodology is described in detail. First, the key elements of the analytical approach necessary for consistent and accurate performance prediction are presented. Emphasis is placed on the requirement for lifting surface theory, the complexity required in the rotor wake geometry, and the necessity of a fuller treatment of three-dimensional compressibility. Throughout this presentation, analogies and contrasts to fixed wing aerodynamics are used to highlight fundamental concepts. For instance, these comparisons show how to correctly calculate induced power for the rotor using lifting surface theory. Second, the build-up process from isolated rotor calculations to helicopter power required in hover is described and guidelines for estimating airframe vertical drag, fin losses, power train efficiencies, and accessory loads are presented. Finally, confidence in the methodology is established through correlation of predicted performance to both isolated rotor and helicopter measurements. Examples of the correlation are included as an appendix to the paper. Based on this correlation base, the BHT Hover Performance Methodology is shown to predict the gross weight that can be hovered at a specified altitude to an accuracy of ± 3 percent.