FLIGHT CONDITION ADAPTABLE HORIZONTAL STABLIZER (SMART WING) FOR HELICOPTERS
Background of the Invention
Horizontal stabilizer (HT) functions in a helicopter are to enable pitch stability and to maintain
the desired fuselage attitude during high speeds flights for low drag. In addition, the horizontal' stabilizer has significant impact on the main rotor blade flap loads, on shaft loads and on the longitudinal cyclic control.
Aerodynamics of the helicopter is highly complex due to the presence of main rotor and tail rotor wakes as they interact with each other, with airframe and with other secondary control surfaces (HT, VT and EPs). During design phase, the designers must consider these interactions to achieve the optimum performance of respective individual system as well as the complete helicopter. For example, the effect of horizontal stabilizer is to be considered on the fuselage pitch attitude and probable instabilities of the helicopter in case of HT placed in the vicinity of the rotor wake.
For instance, the helicopters with tail rotor installed on the tail boom, the horizontal stabilizer would be placed underneath main rotor when there is no other go. Horizontal stabilizer produces huge down force even in hover due to the rotor wake impingement and leads to a high nose up attitude during hover and low speed flights. High nose up attitude is always coupled with the helicopter safety and the pilot sitting comfort. Having high nose up is hazardous in view of safety; the tail may touch the ground during take-off and landings and may end up with a tail damage. Therefore the designer must consider the fuselage attitude though the HT placed underneath the rotor wake.
Summary of the Invention
This invention belongs to the helicopter domain; specifically to the helicopters with the horizontal stabilizer placed underneath the main rotor wake when there is no other go. Design of a horizontal stabilizer in order to have good hovering and low speed handling qualities is imperative while ensuring the level flight-requirements though it is challenging for a horizontal

stabilizer placed in the rotor wake. However, the designer should aim in that direction to achieve an ideal design or an adequate trade off in the horizontal stabiliser design.
Current invention provides a horizontal stabilizer design that substantially reduces the forces that lead to helicopter nose high attitude by having very low down force in hover while satisfying the desired functions in forward speeds.
Flight Condition Adaptable Horizontal Stabilizer reported in this report includes a main wing (1), extendable traditional flap (2), a sliding channel (3) and a gurney flap (4) to vary the chord, camber and the angle of attack simultaneously. Chord, camber and the angle of attack are function of the helicopter flight speed. The extendable flap is identical to the deployable high lift devices (flaps) in the fixed wing aircraft. However, the control mechanism entirely varies where as the aircraft uses an artificial energy means like hydraulic or pneumatic actuation. In the current design; the energy means would be obtained from the helicopter speed that is a drag component.
The operating mechanism includes a spring (5) that connects a rigid pillar (6) inside the wing to the extendable flap. In the level flights enormous amount of airflow exerts the drag force when it interacts with various components of the helicopter; similarly the drag force (7) on the gurney flap mounted on to the extendable flap. The drag force (7) on the gurney flap pulls out the

extendable flap thus the flap slides out through the sliding channel {3). The amount of the flap displacement, camber and the angle of attack depends on the flight speed; higher the flight speed larger the chord, camber and the angle of attack. Change in the chord, camber and angles of attack with the speed are illustrated in Figure 2 (2D airfoil) and Figure 3 (Finite Wing) for typical understanding.