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Dr. Inderjit Chopra
Alfred Gessow Professor
Director Alfred Gessow
Rotorcraft Center
Aerospace Engineering
University of Maryland
College Park, MD 20742
Ph:  301.405.1122
Fax: 301.314.9001


Rotorcraft Aeromechanics


Figure 1: Schematic with flap and tab


A swashplateless rotor has the potential to reduce the aircraft empty weight, rotor drag, and control power requirement in forward flight, in addition to providing individual blade control capability for vibration reduction and noise mitigation. The focus of the present research is on primary control. A servotab actuated trailing edge flap system is proposed to control blade pitch.

First, concept feasibility is established through wind tunnel testing of a non-rotating, full-scale wing section.

Second, a rigid blade aeroelastic trim analysis is carried out in forward flight using a tab actuated trailing edge flap. A parametric study is conducted with this model to determine an optimized design space for the flap-tab configuration by simultaneously reducing both tab deflection and hinge moment. The baseline model is based on a conceptual rotor with very low blade torsional stiffness.


Figure 2: Trim angles and hinge moment for optimized tab/flap system.

In the third step the flap and tab dynamics are included in the comprehensive analysis UMARC. The rotor used in the comprehensive analysis is based on the UH-60A, and is trimmed at a high-speed flight condition corresponding to 155 knots (advance ratio 0.368), 17300 lbs thrust (cT/σ = 0.084), using tab-actuated trailing edge flaps.

The analysis includes both the inertial and the aerodynamic contributions of the flap and the tab, flexible blades, Theodorsen-Garrick 2D unsteady aerodynamic model, and free wake. A flap-tab configuration with 22% flap and 13% tab, achieved coupled trim with tab deflections within ±5˚, mean tab hinge moment less than 3 ft-lb.


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