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•This causes a buildup of air pressure below the helicopter, which acts as a cushion to support the machine in the hover.•This effect is effective to approximately ½ the diameter of the main rotor.•When the helicopter moves at 3-5 knots the ground cushion is left.
Ground effect (continued)•First and most important is the reduction of the velocity of the induced airflow.•Since the ground interrupts the airflow under the helicopter, the entire flow is altered.•This reduces downward velocity of the induced flow. The result is less induced drag and a more vertical lift vector. •The lift needed to sustain a hover can be produced with a reduced angle of attack and less power because of the more vertical lift vector:
Translational Lift•Helicopter requires a large portion of its power to maintain a hover.•The power is used to give momentum to the mass of air moving through the rotor.•If the chopper is moving at more than 15 kns the performance of the main rotor improves.•Because of the increased volume of air passing through the rotor.•Called Translational lift.> less engine power is required to maintain flight when flying horizontal. The leading edge of the downwash pattern is being overrun and is well back under the helicopter nose.At about 16 to 24 knots (depending upon the size, blade area, and RPM of the rotor system) the rotor completely outruns the recirculation of old vortexes, and begins to work in
Tail Rotor•Torque forces applied to the rotor shaft will cause the helicopter to turn in the opposite direction.•The tail rotorprevents this action.•Also called the antitorque rotor.•Main rotor turns to left (counterclockwise) as viewed for the top and the helicopter will want to turn to the right.•Tail – rotor force must therefore be applied to the right to keep heading.•tail rotors consume up to 30% of the engine power.•size and weight constraints, tail rotors are fairly delicate compared to main rotors.•they cannot survive an encounter with very large obstacles. Because they are mounted at the rear of the helicopter, out of the pilot's sight, a fairly common cause of helicopter accidents is hitting an obstacle with the tail rotor, losing all anti-torque capability, and crashing due to the rotation of the entire helicopter.
Tail rotor•During hovering flight, a single main rotor helicopter tends to drift in the same direction as antitorque rotor thrust. This drifting tendency is called translating tendency or lateral drift tendency.•counteract this drift, one or more of the following features may be used:The main transmission is mounted so that the rotor mast is rigged for the tip-path plane to have a built-in tilt opposite tail thrust, thus producing a small sideward thrust.Flight control rigging is designed so that the rotor disc is tilted slightly opposite tail rotor thrust when the cyclic is centered.