The HelicopterThe Helicopter

How do Helicopters FlyHow do Helicopters Fly

Helicopters generate Helicopters generate lift by rotating its lift by rotating its wings!!wings!!

A cross-section of a A cross-section of a rotor blade has an rotor blade has an aerofoil shape, similar aerofoil shape, similar to that of a to that of a conventional aircraft conventional aircraft wing.wing.

When a rotor blade When a rotor blade moves through the air it moves through the air it can be made to generate can be made to generate lift.lift.The engine makes the The engine makes the blades rotate and this can blades rotate and this can be done even when the be done even when the aircraft is stationary.aircraft is stationary.The rotor blades must The rotor blades must rotate fast enough to rotate fast enough to generate enough lift to generate enough lift to make the helicopter rise make the helicopter rise off the ground.off the ground.

The blades must also The blades must also have an angle of attack to have an angle of attack to the airflow.the airflow.The blades are fitted into The blades are fitted into the hub or rotor head.the hub or rotor head.The angle between the The angle between the chord line of the blade’s chord line of the blade’s aerofoil section and its aerofoil section and its plane of rotation can be plane of rotation can be varied, which alters the varied, which alters the angle of attack and allows angle of attack and allows the pilot to vary the the pilot to vary the amount of lift.amount of lift.

If a pilot is airborne If a pilot is airborne and slightly reduces and slightly reduces the angle of attack of the angle of attack of the blades so that the the blades so that the lift from the rotor now lift from the rotor now balances the weight balances the weight of the helicopter, it will of the helicopter, it will hover.hover.

The collective pitch The collective pitch control ‘collectively’ control ‘collectively’ alters the pitch angle alters the pitch angle and hence the angles and hence the angles of attack of all the of attack of all the main rotor blades by main rotor blades by the same amount and the same amount and at the same time.at the same time.

Moving HorizontallyMoving Horizontally

To make an aircraft To make an aircraft fly forward, horizontal fly forward, horizontal thrust must be thrust must be available. available. In a helicopter this is In a helicopter this is done by tilting the lift done by tilting the lift in the direction of the in the direction of the required movement.required movement.It is It is not achievednot achieved by by tilting the whole rotor tilting the whole rotor head!!head!!

Each blade is hinged, Each blade is hinged, and can be made to and can be made to rise and fall as it goes rise and fall as it goes round the plane of round the plane of rotation (or disc).rotation (or disc).To go forward the To go forward the blades are made to blades are made to rise as it reaches the rise as it reaches the rear of the disc, and rear of the disc, and descend as it reaches descend as it reaches the front .the front .

Thus, the disc is tilted Thus, the disc is tilted forwards, and there is forwards, and there is a horizontal a horizontal component of thrust component of thrust to propel the to propel the helicopter forwards.helicopter forwards.

Torque reactionTorque reaction

When the engine of a When the engine of a helicopter drives the helicopter drives the rotor in its circular rotor in its circular motion, there is a motion, there is a tendency for an tendency for an opposing force called opposing force called ‘torque reaction’ to ‘torque reaction’ to spin the fuselage of spin the fuselage of the helicopter the the helicopter the opposite way.opposite way.

The solution is to fit a The solution is to fit a small rotor far back small rotor far back on the tail for on the tail for leverage, with its leverage, with its rotational disc rotational disc vertical.vertical.Its horizontal thrust Its horizontal thrust force opposes the force opposes the fuselage torque fuselage torque reaction and permits reaction and permits balanced flightbalanced flight

The pilot can vary the The pilot can vary the thrust force provided thrust force provided by the tail rotor, to by the tail rotor, to maintain balanced maintain balanced flight or to yaw the flight or to yaw the aircraft at will. (very aircraft at will. (very useful when useful when hovering.)hovering.)

Flying ControlsFlying Controls

There are four main flying controls:There are four main flying controls:

A) Collective Pitch ControlA) Collective Pitch Control

B) The Hand ThrottleB) The Hand Throttle

C) Cyclic Pitch ControlC) Cyclic Pitch Control

D) Tail Rotor ControlD) Tail Rotor Control

Collective Pitch ControlCollective Pitch Control

The collective pitch The collective pitch control or lever which control or lever which changes the pitch changes the pitch angle of all the blades angle of all the blades of the rotor by the of the rotor by the same amount at the same amount at the same time, controls same time, controls the vertical movement the vertical movement of the helicopterof the helicopterIt is found on the It is found on the pilots leftpilots left

It is moved up to increase It is moved up to increase the pitch angle of the the pitch angle of the blades (more lift)and down blades (more lift)and down to decrease the angle.to decrease the angle.(less lift)(less lift)With increased angle of With increased angle of attack comes more drag attack comes more drag therefore more power is therefore more power is required to keep them required to keep them rotating at the correct rotating at the correct speed!speed!Therefore,the lever is also Therefore,the lever is also connected to the cam connected to the cam which slightly opens the which slightly opens the throttle .throttle .

Hand ThrottleHand Throttle

The hand throttle is The hand throttle is situated on the end of the situated on the end of the collective lever; it is a collective lever; it is a twist grip control similar to twist grip control similar to a motor cycle throttlea motor cycle throttle

The pilot holds the The pilot holds the collective pitch by the collective pitch by the twist-grip hand throttle twist-grip hand throttle and so can operate both and so can operate both at the same time.at the same time.

Cyclic Pitch ControlCyclic Pitch Control

Tail Rotor ControlTail Rotor Control

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