Torque ReactionTorque ReactionTorque ReactionTorque Reaction

The fuselage’s reaction to the turning of the main rotor systemThe fuselage’s reaction to the turning of the main rotor systemis is Torque ReactionTorque ReactionThe fuselage’s reaction to the turning of the main rotor systemThe fuselage’s reaction to the turning of the main rotor systemis is Torque ReactionTorque Reaction

Newton's third law of motion states that for every action, thereNewton's third law of motion states that for every action, there

is an equal and opposite reaction. The engine power on mostis an equal and opposite reaction. The engine power on most

American built single engine helicopters causes the rotor systemAmerican built single engine helicopters causes the rotor system

to rotate in a counterclockwise directionto rotate in a counterclockwise direction. The reaction is that . The reaction is that

the fuselage will rotate clockwisethe fuselage will rotate clockwise. The degree of right yaw is. The degree of right yaw is

directly proportional to the amount of power applied.directly proportional to the amount of power applied.

Newton's third law of motion states that for every action, thereNewton's third law of motion states that for every action, there

is an equal and opposite reaction. The engine power on mostis an equal and opposite reaction. The engine power on most

American built single engine helicopters causes the rotor systemAmerican built single engine helicopters causes the rotor system

to rotate in a counterclockwise directionto rotate in a counterclockwise direction. The reaction is that . The reaction is that

the fuselage will rotate clockwisethe fuselage will rotate clockwise. The degree of right yaw is. The degree of right yaw is

directly proportional to the amount of power applied.directly proportional to the amount of power applied.

As viewed from the topAs viewed from the top As viewed from the topAs viewed from the top

Translating TendencyTranslating Tendency is the movement of a is the movement of a helicopter in the direction of helicopter in the direction of Tail Rotor thrust. Tail Rotor thrust. This This is caused by trying to cancel a turning moment is caused by trying to cancel a turning moment about the mast with a thrust force and moment about the mast with a thrust force and moment from the tail rotor.from the tail rotor.The potential for movement is proportional to the The potential for movement is proportional to the amount of power applied and the amount of tail amount of power applied and the amount of tail rotor thrust needed to overcome torque reaction. rotor thrust needed to overcome torque reaction.

Translating TendencyTranslating Tendency is the movement of a is the movement of a helicopter in the direction of helicopter in the direction of Tail Rotor thrust. Tail Rotor thrust. This This is caused by trying to cancel a turning moment is caused by trying to cancel a turning moment about the mast with a thrust force and moment about the mast with a thrust force and moment from the tail rotor.from the tail rotor.The potential for movement is proportional to the The potential for movement is proportional to the amount of power applied and the amount of tail amount of power applied and the amount of tail rotor thrust needed to overcome torque reaction. rotor thrust needed to overcome torque reaction.

Direction of RotationDirection of RotationDirection of RotationDirection of Rotation

Torque EffectTorque EffectTorque EffectTorque Effect

OverallOveralleffect is foreffect is forhelicopterhelicopterto drift toto drift tothe rightthe right

OverallOveralleffect is foreffect is forhelicopterhelicopterto drift toto drift tothe rightthe right

Torque EffectTorque EffectTorque EffectTorque Effect

Tail Rotor ThrustTail Rotor ThrustTail Rotor ThrustTail Rotor Thrust

Corrections for translating tendency:Corrections for translating tendency:Corrections for translating tendency:Corrections for translating tendency:

•Rigging of the cyclic systemRigging of the cyclic system

•Application of some left cyclic, the method used in most Application of some left cyclic, the method used in most

American-built helicoptersAmerican-built helicopters

•Tilting the rotor mast to the leftTilting the rotor mast to the left

•Programmed mechanical inputs from Automatic Flight Control Programmed mechanical inputs from Automatic Flight Control

System (AFCS), Stabilization Augmentation System (SAS), System (AFCS), Stabilization Augmentation System (SAS),

Mechanical Mixing Unit (MMU), or any combination of the threeMechanical Mixing Unit (MMU), or any combination of the three

•Rigging of the cyclic systemRigging of the cyclic system

•Application of some left cyclic, the method used in most Application of some left cyclic, the method used in most

American-built helicoptersAmerican-built helicopters

•Tilting the rotor mast to the leftTilting the rotor mast to the left

•Programmed mechanical inputs from Automatic Flight Control Programmed mechanical inputs from Automatic Flight Control

System (AFCS), Stabilization Augmentation System (SAS), System (AFCS), Stabilization Augmentation System (SAS),

Mechanical Mixing Unit (MMU), or any combination of the threeMechanical Mixing Unit (MMU), or any combination of the three

When left cyclic is applied to prevent the right When left cyclic is applied to prevent the right translating tendency, the force of the main rotor is translating tendency, the force of the main rotor is applied to the left. If the left force created by the applied to the left. If the left force created by the main rotor is a greater distance from the center of main rotor is a greater distance from the center of gravity then the right force of the tail rotor, the a left gravity then the right force of the tail rotor, the a left rolling moment will occur. rolling moment will occur. This will cause the helicopter to hover left skid low This will cause the helicopter to hover left skid low and will be more pronounced in a tail low hover (aft and will be more pronounced in a tail low hover (aft CG)CG)

When left cyclic is applied to prevent the right When left cyclic is applied to prevent the right translating tendency, the force of the main rotor is translating tendency, the force of the main rotor is applied to the left. If the left force created by the applied to the left. If the left force created by the main rotor is a greater distance from the center of main rotor is a greater distance from the center of gravity then the right force of the tail rotor, the a left gravity then the right force of the tail rotor, the a left rolling moment will occur. rolling moment will occur. This will cause the helicopter to hover left skid low This will cause the helicopter to hover left skid low and will be more pronounced in a tail low hover (aft and will be more pronounced in a tail low hover (aft CG)CG)

Translational LiftTranslational LiftTranslational LiftTranslational Lift

The additional lift obtained through the increased efficiencyThe additional lift obtained through the increased efficiencyof the rotor system with airspeed obtained either by horizontalof the rotor system with airspeed obtained either by horizontalflight or by hovering into windflight or by hovering into wind

The additional lift obtained through the increased efficiencyThe additional lift obtained through the increased efficiencyof the rotor system with airspeed obtained either by horizontalof the rotor system with airspeed obtained either by horizontalflight or by hovering into windflight or by hovering into wind

HoverHoverHoverHover 6-10 knots6-10 knots6-10 knots6-10 knots

As airspeed increases, the helicopter starts out runningAs airspeed increases, the helicopter starts out runningmajor downwash, causing the relative wind to become moremajor downwash, causing the relative wind to become morehorizontalhorizontal

As airspeed increases, the helicopter starts out runningAs airspeed increases, the helicopter starts out runningmajor downwash, causing the relative wind to become moremajor downwash, causing the relative wind to become morehorizontalhorizontal

At 16-24 knots the rotor system At 16-24 knots the rotor system has outrun the effects of has outrun the effects of downwash. The airflow is nearly downwash. The airflow is nearly horizontal through the rotor with horizontal through the rotor with little recirculation back into the little recirculation back into the rotor. This horizontal flowrotor. This horizontal flowsignificantly reduces inducedsignificantly reduces inducedflow which increases angle of flow which increases angle of attack. attack.

At 16-24 knots the rotor system At 16-24 knots the rotor system has outrun the effects of has outrun the effects of downwash. The airflow is nearly downwash. The airflow is nearly horizontal through the rotor with horizontal through the rotor with little recirculation back into the little recirculation back into the rotor. This horizontal flowrotor. This horizontal flowsignificantly reduces inducedsignificantly reduces inducedflow which increases angle of flow which increases angle of attack. attack.

Just as the main rotor gains efficiency with horizontal airflow,Just as the main rotor gains efficiency with horizontal airflow,the tail rotor too becomes more efficient during this transitionthe tail rotor too becomes more efficient during this transitionto forward flight. As the tail rotor gains efficiency, it producesto forward flight. As the tail rotor gains efficiency, it producesmore thrust and causes the nose of the helicopter to yaw left.more thrust and causes the nose of the helicopter to yaw left.During a takeoff where power is constant, the aviator mustDuring a takeoff where power is constant, the aviator mustapply right pedal as speed increases to correct for the left yaw.apply right pedal as speed increases to correct for the left yaw.

Just as the main rotor gains efficiency with horizontal airflow,Just as the main rotor gains efficiency with horizontal airflow,the tail rotor too becomes more efficient during this transitionthe tail rotor too becomes more efficient during this transitionto forward flight. As the tail rotor gains efficiency, it producesto forward flight. As the tail rotor gains efficiency, it producesmore thrust and causes the nose of the helicopter to yaw left.more thrust and causes the nose of the helicopter to yaw left.During a takeoff where power is constant, the aviator mustDuring a takeoff where power is constant, the aviator mustapply right pedal as speed increases to correct for the left yaw.apply right pedal as speed increases to correct for the left yaw.

At a given angle of incidence, At a given angle of incidence, a more vertical airflow increases a more vertical airflow increases induced flow and aerodynamically induced flow and aerodynamically reduces the angle of attack, creating reduces the angle of attack, creating the need for more pitch in the blade to the need for more pitch in the blade to maintain a constant lift vectormaintain a constant lift vector

At a given angle of incidence, At a given angle of incidence, a more vertical airflow increases a more vertical airflow increases induced flow and aerodynamically induced flow and aerodynamically reduces the angle of attack, creating reduces the angle of attack, creating the need for more pitch in the blade to the need for more pitch in the blade to maintain a constant lift vectormaintain a constant lift vector

Reduced inflow velocity causesReduced inflow velocity causesangle of attack to increase withangle of attack to increase withno increase in blade pitch. This no increase in blade pitch. This results in an increase in lift withresults in an increase in lift witha decrease in induced drag. Thea decrease in induced drag. Thereduction in induced drag results reduction in induced drag results in a more vertical lift vector forin a more vertical lift vector foreach rotor bladeeach rotor blade

Reduced inflow velocity causesReduced inflow velocity causesangle of attack to increase withangle of attack to increase withno increase in blade pitch. This no increase in blade pitch. This results in an increase in lift withresults in an increase in lift witha decrease in induced drag. Thea decrease in induced drag. Thereduction in induced drag results reduction in induced drag results in a more vertical lift vector forin a more vertical lift vector foreach rotor bladeeach rotor blade

Transverse Flow EffectTransverse Flow EffectTransverse Flow EffectTransverse Flow Effect

Simply stated, Simply stated, Transverse Flow EffectTransverse Flow Effect is the difference in lift is the difference in liftbetween the forward and aft portions of the rotor disk.between the forward and aft portions of the rotor disk.Simply stated, Simply stated, Transverse Flow EffectTransverse Flow Effect is the difference in lift is the difference in liftbetween the forward and aft portions of the rotor disk.between the forward and aft portions of the rotor disk.

The result is an increase in induced drag in the aft portion The result is an increase in induced drag in the aft portion of the rotor system caused by the air having a greater of the rotor system caused by the air having a greater downwash angle in the aft portion of the rotor disk.downwash angle in the aft portion of the rotor disk.

The result is an increase in induced drag in the aft portion The result is an increase in induced drag in the aft portion of the rotor system caused by the air having a greater of the rotor system caused by the air having a greater downwash angle in the aft portion of the rotor disk.downwash angle in the aft portion of the rotor disk.

Because of coning and forward tilt of the rotor system, airBecause of coning and forward tilt of the rotor system, airmoving over the forward half of the rotor disk is moremoving over the forward half of the rotor disk is morehorizontal then air over the aft portion of the rotor diskhorizontal then air over the aft portion of the rotor disk

Because of coning and forward tilt of the rotor system, airBecause of coning and forward tilt of the rotor system, airmoving over the forward half of the rotor disk is moremoving over the forward half of the rotor disk is morehorizontal then air over the aft portion of the rotor diskhorizontal then air over the aft portion of the rotor disk

Airflow over the aft half ofAirflow over the aft half ofthe rotor with a greaterthe rotor with a greaterinduced flow and a reducedinduced flow and a reducedangle of attackangle of attack

Airflow over the aft half ofAirflow over the aft half ofthe rotor with a greaterthe rotor with a greaterinduced flow and a reducedinduced flow and a reducedangle of attackangle of attack

Airflow over the forward portionAirflow over the forward portionof the rotor with more horizontalof the rotor with more horizontalairflow, reduced induced flowairflow, reduced induced flowand a greater angle of attackand a greater angle of attack

Airflow over the forward portionAirflow over the forward portionof the rotor with more horizontalof the rotor with more horizontalairflow, reduced induced flowairflow, reduced induced flowand a greater angle of attackand a greater angle of attack

The increased angle of attack in the front half of the The increased angle of attack in the front half of the rotor increases lift of the blade at that location. This in rotor increases lift of the blade at that location. This in turn causes the blade to flap up. Due to phase lag, theturn causes the blade to flap up. Due to phase lag, themaximum upflapping displacement occurs over the leftmaximum upflapping displacement occurs over the leftside of the helicopter.side of the helicopter.

The increased angle of attack in the front half of the The increased angle of attack in the front half of the rotor increases lift of the blade at that location. This in rotor increases lift of the blade at that location. This in turn causes the blade to flap up. Due to phase lag, theturn causes the blade to flap up. Due to phase lag, themaximum upflapping displacement occurs over the leftmaximum upflapping displacement occurs over the leftside of the helicopter.side of the helicopter.

The decreases angle of attack in the rear half of the rotorThe decreases angle of attack in the rear half of the rotorcauses the blade to flap downward. Phase lag causescauses the blade to flap downward. Phase lag causesthe maximum downflapping to occur over the right side.the maximum downflapping to occur over the right side.The combined effects result in the rotor disk tilting to theThe combined effects result in the rotor disk tilting to theright and changing the direction of the lift vector.right and changing the direction of the lift vector.

The decreases angle of attack in the rear half of the rotorThe decreases angle of attack in the rear half of the rotorcauses the blade to flap downward. Phase lag causescauses the blade to flap downward. Phase lag causesthe maximum downflapping to occur over the right side.the maximum downflapping to occur over the right side.The combined effects result in the rotor disk tilting to theThe combined effects result in the rotor disk tilting to theright and changing the direction of the lift vector.right and changing the direction of the lift vector.

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Oversimplified illustrations of Oversimplified illustrations of Transverse Flow Effect Transverse Flow Effect before before and after and after Gyroscopic EffectGyroscopic EffectOversimplified illustrations of Oversimplified illustrations of Transverse Flow Effect Transverse Flow Effect before before and after and after Gyroscopic EffectGyroscopic Effect

BeforeBeforeBeforeBefore AfterAfterAfterAfter

The pilot can recognize The pilot can recognize Transverse Flow EffectTransverse Flow Effect because of because of increased vibrations in the helicopter as airspeeds increase increased vibrations in the helicopter as airspeeds increase towards ETL on take off and decelerating through ETL during towards ETL on take off and decelerating through ETL during landing. The greatest lift differential occurs at those speeds.landing. The greatest lift differential occurs at those speeds.

The pilot can recognize The pilot can recognize Transverse Flow EffectTransverse Flow Effect because of because of increased vibrations in the helicopter as airspeeds increase increased vibrations in the helicopter as airspeeds increase towards ETL on take off and decelerating through ETL during towards ETL on take off and decelerating through ETL during landing. The greatest lift differential occurs at those speeds.landing. The greatest lift differential occurs at those speeds.

As the pilot senses the As the pilot senses the right tilt of the rotor, heright tilt of the rotor, hemust apply left cyclicmust apply left cyclicto prevent a change into prevent a change inthe attitude of the disk.the attitude of the disk.

As the pilot senses the As the pilot senses the right tilt of the rotor, heright tilt of the rotor, hemust apply left cyclicmust apply left cyclicto prevent a change into prevent a change inthe attitude of the disk.the attitude of the disk.

At higher airspeeds, liftAt higher airspeeds, liftdifferential between thedifferential between thefore and aft portions offore and aft portions ofthe disk begins to the disk begins to decrease. The cyclicdecrease. The cyclicmust be moved back tomust be moved back tothe right at higher cruisethe right at higher cruisespeedsspeeds

At higher airspeeds, liftAt higher airspeeds, liftdifferential between thedifferential between thefore and aft portions offore and aft portions ofthe disk begins to the disk begins to decrease. The cyclicdecrease. The cyclicmust be moved back tomust be moved back tothe right at higher cruisethe right at higher cruisespeedsspeeds

Questions?Questions?Questions?Questions?