[Tarig Elsheikh]

GENERAL

Helicopter, Lift is obtained by means of one or more power driven horizontal propellers which called Rotors. When the rotors of helicopter turns it produces lift and reaction torque, reaction torque which tends to make helicopter spin. on most helicopters a small rotor near the tail which called tail rotor compensates for this torque. On twin rotor helicopter the rotors rotate in opposite directions, their reactions cancel each other. The direction of helicopter is controlled by inclining the axis of the main rotor path in that direction.

Function of Controls

There are three major controls in the helicopter that the pilot must use during flight. They are : ( 1 ) Collective pitch control. ( 2 ) Anti Torque Pedals or Tail Rotor Control. ( 3 ) Cyclic Stick Control.

Collective Control

The collective pitch lever or stick is located by the left side of the pilot's seat and is operated with the left hand. The collective is used to increase main rotor pitch at all points of the rotor blade rotation. It increases or decreases total rotor thrust. The collective lever is connected to the swash plate by a series of bush pull tubes. Raising the collective lever increases the pitch on the main rotor blade, lowering the collective lever decreases the main rotor blade pitch. The amount of movement of th elever determines the amount of blade pitch change. As the angle of attack increase, drag increases and Rotor RPM and Engine RPM tend to decrease . As the angle of attack decreases, drag decreases and the RPM tend to increase.Since it is essential that the RPM remain constant, there must be some means of making a proportionate change in power to compensate for the change in drag. This coordination of power change with blade pitch angle change is controlled through a collective pitch lever- trottle control cam linkage which automatically increases power when the collective pitch lever is raised and decreases power when the lever is lowered.

The picture above is the typical collective lever but the detail of control may varies depend on each munufacturer .The main functions are still the same for all helicopters.

Collective Lever is connected to the rotor system via push pull tubes. It also has droop com pensation devics which sense change in the collective pitch lever and increases or decreases fuel to the engine automatically somewhat in anticipated of a change in power required. This helps to minimize the RPM fluctuations during collective pitch change.


Engine Control (Emergency) is the throttle twist grip. During emergency condition, between flight and flight idle positions. This is useful during any event which would cause engine or rotor RPM to go too high or while landing after a tail rotor failure.

Idle Release Button, when the throttle is rolled from " off " to " idle " the idle release button snaps into a detent which prevents the throttle from being rolled back to " off "

Starter Button : Pushing this button will cause the starter / generator to act as a starter motor ( Starter / Generator is a component that funtion in either mode as a starter or generator ) , turning over the engine.

Landing Light Switch has a three position which are " off " , " forward " and "both " . In forward , only the forward light is activated. In both, the forward and downward lights are activated .


Power Trim Switch ,by holding it in " increase " or " decrease " the pilot can set the RPM that the pilot attempt to maintain


Function of Controls
Anti-Torque Pedals or Tail Rotor Control

In accordance with Newton's law of action and reaction, the helicopter fuselage tends to rotate in the direction opposite to the rotor blades . This effect is called torque . Torque must be counteracted and controlled to make flight is possible . Compensation for torque in a single main rotor helicopter is accomplished by means of a variable pitch antitorque rotor (tail rotor) located on the end of the tail boom extension at the rear of fuselage.

Heading Control : In addition to counteracted torque, the tail rotor and its control linkage also permit control of the helicopter heading during flight . Application of more control than is necessary to counteract torque will cause the nose of helicopter to turn in the direction of pedal movement.

In forward flight , the pedals are not used to control the heading of the helicopter (except during portions of crosswind takeoff and approach). They are used to compensate for torque to put the helicopter in longitudinal trim so that coordinated flight can be maintained.

The thrust of the tail rotor is depend upon the pitch angle of the tail rotor blades. The tail rotor may have a positive pitch angle or it may have a negative pitch angle which to push the tail to the right or pull the tail to the left.

With the right pedal pressed or moved forward of the neutral position will cause the tail rotor blades to change the pitch angle and the nose of helicopter will yaw to the right . With the left pedal pressed or moved forward of the neutral position will cause the tail rotor blades to change the pitch angle opposite to the right pedal and the nose of helicopter will yaw to the left.

Function of Controls

Cyclic Control

As mention earier , the total lift force is always perpendicular to the tip-path plane of the main rotor. When the tip path plane is tilt away from the horizontal, the lift -thrust force is divide into two components of forces that are, the horizontal acting force, thrust and the upward acting force, lift.

The purpose of the cyclic pitch control is to tilt the tip path plane in the direction that horizontal movement is desired. The thrust component of force then pulls the helicopter in the direction of rotor tilt. The cyclic control changes the direction of this force,thus controlling the attitude and air speed of helicopter.

The rotor disc tilts in the same direction of the cyclic stick was moved. If the cyclic stick is moved forward, the rotor disc tilt forward: if the cyclic is moved aft, the rotor disc tilt aft, and so on. The rotor disc will always tilt in the same direction that the cyclic stick is moved.

The above picture is only typical for cyclic control stick which different manufacturer will have some detail different but the main fuction is the same.

The radio switch is used for pilot to transmit radio by clicking the switch.


The trim switch , pilot use this switch to neutralize stick force . Pilot can use the trim switch to put the stick to the right , left , forward or backward . This runs electric motor which will tension the spring which will tend to hold the stick. The cyclic will stay where it is even the pilot were let it go . This also release tension from pilot.

The cargo release switch is the option switch, some manufacturer may have other function switch.

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