Design and Analysis of Trailing-Edge Flaps and Servotabs for Primary Control

Two swashplateless primary control systems are studied: one with a trailing edge flap (TEF), and another with a tab actuated trailing edge flap. A swashplateless rotor has the potential to reduce aircraft drag and control power requirement, increase payload, and provide individual blade control capability for simultaneous primary and vibration control. The focus of the present paper is on primary control. First, a systematic study is performed to design a TEF system and a tab actuated TEF system for efficient primary control in hover and forward flight. Second, the predicted power of the swashplateless system is compared with a conventional rotor using measured estimates of TEF drag. Finally, the aeroelastic stability of a tab actuated TEF system is studied in hover. A TEF configuration with 15% chord (c) flap achieved coupled trim with flap deflections within ±10°, and flap hinge moment within ±3 ft-lb. A flap-tab configuration with 22% c flap and 13% c tab, achieved coupled trim with tab deflections within ±5°, and tab hinge moment within ±4 ft-lb. A 15% c TEF with 40% radius span is shown to incur an equivalent flat plate drag of 5ft2 at high speed (155 knots). There is no substantial change in the power requirement for hover. The hover stability analysis shows that the blade flapping and torsion modes are sufficiently damped. The TEF and tab modes are sensitive to the TEF hinge stiffness. Depending on the TEF hinge stiffness, the TEF mode can exhibit significantly reduced damping (5%), while the tab mode can become unstable.