Presentation on theme: "Torque Reaction The fuselage’s reaction to the turning of the main rotor system is Torque Reaction Newton's third law of motion states that for every action,"— Presentation transcript:
1 Torque ReactionThe fuselage’s reaction to the turning of the main rotor systemis Torque ReactionNewton's third law of motion states that for every action, thereis an equal and opposite reaction. The engine power on mostAmerican built single engine helicopters causes the rotor systemto rotate in a counterclockwise direction. The reaction is thatthe fuselage will rotate clockwise. The degree of right yaw isdirectly proportional to the amount of power applied. As viewed from the top
2 Translating Tendency is the movement of a helicopter in the direction of Tail Rotor thrust. This is caused by trying to cancel a turning moment about the mast with a thrust force and moment from the tail rotor.The potential for movement is proportional to the amount of power applied and the amount of tail rotor thrust needed to overcome torque reaction.
4 Torque Effect Tail Rotor Thrust Overall effect is for helicopter to drift tothe rightTail Rotor Thrust
5 Corrections for translating tendency: Rigging of the cyclic systemApplication of some left cyclic, the method used in most American-built helicoptersTilting the rotor mast to the leftProgrammed mechanical inputs from Automatic Flight Control System (AFCS), Stabilization Augmentation System (SAS), Mechanical Mixing Unit (MMU), or any combination of the three
6 When left cyclic is applied to prevent the right translating tendency, the force of the main rotor is applied to the left. If the left force created by the main rotor is a greater distance from the center of gravity then the right force of the tail rotor, the a left rolling moment will occur.This will cause the helicopter to hover left skid low and will be more pronounced in a tail low hover (aft CG)
7 Translational LiftThe additional lift obtained through the increased efficiencyof the rotor system with airspeed obtained either by horizontalflight or by hovering into windHover6-10 knotsAs airspeed increases, the helicopter starts out runningmajor downwash, causing the relative wind to become morehorizontal
8 Just as the main rotor gains efficiency with horizontal airflow, At knots the rotor system has outrun the effects ofdownwash. The airflow is nearly horizontal through the rotor with little recirculation back into the rotor. This horizontal flowsignificantly reduces inducedflow which increases angle of attack.Just as the main rotor gains efficiency with horizontal airflow,the tail rotor too becomes more efficient during this transitionto forward flight. As the tail rotor gains efficiency, it producesmore thrust and causes the nose of the helicopter to yaw left.During a takeoff where power is constant, the aviator mustapply right pedal as speed increases to correct for the left yaw.
9 At a given angle of incidence, a more vertical airflow increases induced flow and aerodynamically reduces the angle of attack, creating the need for more pitch in the blade to maintain a constant lift vectorReduced inflow velocity causesangle of attack to increase withno increase in blade pitch. Thisresults in an increase in lift witha decrease in induced drag. Thereduction in induced drag resultsin a more vertical lift vector foreach rotor blade
10 Transverse Flow Effect Simply stated, Transverse Flow Effect is the difference in liftbetween the forward and aft portions of the rotor disk.Because of coning and forward tilt of the rotor system, airmoving over the forward half of the rotor disk is morehorizontal then air over the aft portion of the rotor diskThe result is an increase in induced drag in the aft portionof the rotor system caused by the air having a greaterdownwash angle in the aft portion of the rotor disk.
12 Airflow over the aft half of the rotor with a greaterinduced flow and a reducedangle of attackAirflow over the forward portionof the rotor with more horizontalairflow, reduced induced flowand a greater angle of attack
13 The increased angle of attack in the front half of the rotor increases lift of the blade at that location. This in turn causes the blade to flap up. Due to phase lag, themaximum upflapping displacement occurs over the leftside of the helicopter.The decreases angle of attack in the rear half of the rotorcauses the blade to flap downward. Phase lag causesthe maximum downflapping to occur over the right side.The combined effects result in the rotor disk tilting to theright and changing the direction of the lift vector.
14 +-+-BeforeAfterOversimplified illustrations of Transverse Flow Effect before and after Gyroscopic EffectThe pilot can recognize Transverse Flow Effect because of increased vibrations in the helicopter as airspeeds increase towards ETL on take off and decelerating through ETL during landing. The greatest lift differential occurs at those speeds.
15 At higher airspeeds, lift differential between thefore and aft portions ofthe disk begins todecrease. The cyclicmust be moved back tothe right at higher cruisespeedsAs the pilot senses theright tilt of the rotor, hemust apply left cyclicto prevent a change inthe attitude of the disk.