Extendable Chord Rotors for Helicopter Envelope Expansion and Performance Improvement

Abstract

This study explores the benefits of rotor chord extension in stall-dominant conditions. Simulations are based on a UH-60A Blackhawk helicopter with an effective chord increase of 20% realized by extending a trailing-edge plate (TEP) through a slit in the trailing edge between 63% and 83% blade span. Since TEP extension changes the baseline SC-1094R8 airfoil profile, two-dimensional aerodynamic coefficients of the modified profile from Navier–Stokes computational fluid dynamics calculations are used, coupled with 12 × 12 dynamic inflow and the Leishman–Beddoes dynamic stall model in the Rotorcraft Comprehensive Analysis System. While a fixed 20% larger chord produces comparable advantages to TEP extension in stall-dominant conditions, the rotor power requirements increase by up to nearly 4% for low gross weight, low-altitude operations, a penalty easily avoided with TEP retracted. From the simulations in the study, reductions of up to nearly 18% in rotor power requirements were observed with TEP for operation at high gross weight and altitude. Furthermore, increases of around 18 kt in maximum speed, 1500 lb in maximum gross weight capability, and 1800 ftin maximum altitude were observed. TEP extension generally reduces maximum angles of attack on the retreating side and weakens stall. Lift generally increases over the annulus where the TEP is present but reduces over the outer rim because the nose-down pitching moments produce larger nose-down elastic tip twist. With TEP extension, the offloading of the outer rim reduces drag, rotor torque, and power.