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THE WORKING PRINCIPLES OF HELICOPTERS

The hobby helicopters presnted above are operated by the same mechanical and aerodynamilcal prinsiples as a full scale helicopter.

Helicopter lift is obtained by means of one or more power driven horizontal propellers which called Main Rotor. When the main rotor of helicopter turns it produces lift and reaction torque. Reaction torque 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 same is through about the four-rotor hobby helicopters depicted above.


Main rotor

The main rotor produces the lifting force. Each blade produces an equal share of the lifting force so that the weight of a helicopter is divided evenly between the rotor blades. If the helicopter also accelerates up, the rotor also has to provide for the force needed for acceleration. Furthermore it has to provide the force to overcome air resistence towards the helicopter due to upward motion.


Tail rotor

The spin of the main rotor will make a force on the rest of the helicopter that brings it to spinning in the opposite direction if something does not counteract this spinning. This is called torque reaction. The tail rotor compensates for this torque thus holding the helicopter straight. On twin-rotors helicopter or the four rotor hobby helicopters, the rotors spin in opposite directions, canceling out this reaction. The tail rotor in normally linked to the main rotor via a system of driveshafts and gearboxes , that means if the main rotor makes one turn , the tail rotor is also turn a definite number of times. Most helicopter have the tail rotor turn 3 or 6 times for each turn of the main rotor.


Lifting dissymmetry

All rotor is allways experiencing Dissymmetry of Lift in forward flight . As the helicopter gain air speed , the advanceing blade develops greater lift because of the increased airspeed and the retreating blade will produce less lift , causing the helicopter to roll. This has to be compensated for in some way . The compensation is mostly effectuated passively by blade flapping. Increased airspeed and lift on the advancing blade will cause the blade to flap up and decreasing the angle of attack . The decreased lift on the retreating blade will cause the blade to flap down and increasing the angle of attack . This combination equalizes the lift over the two halves of the rotor disc.


Regulating the force of the main or tail rotor.

This is usually done on a real helicopter by regulating the angle of the rotor blades without changing the speed of the rotors, thus giving the rotors more or less power. At the same time the force of the motor must be regulated up or down by adding or decreasing the gas given. In a hobby helicopter the force may be regulated by changeng the speed of the rotors because the mechanical system used here is simpler.


Regulating the flying direction for the helicopter

A helicopter can hover still in the air, fly forewords, backwords or sidewords. This is done by tilting the helicopter main rotor so that a component of the force from the rotor points in the wanted flying direction. The vertical force component of course still is used to make the helicopter hover. The force used by the motor must also be regulated so that it deliveres enough force both for the horisontal component and the vertical component.


The mechanical regulation of the rotor blade angles and tilting.

This is done by the folowing mechanism in a real helicopter.

Swash Plate Assembly

The swash plate assembly consists of two primary elements through which the rotor mast passes, one of which is a disc, linked to the cyclic pitch control. This disc can of tilt in any direction but does not rotate as the rotor rotates. This non-rotating disc is attached by a bearing surface to a second disc, often refered to as the which turns with rotor and linked to the rotor blade pitch horns.

The Collective Control

When the pilot raises the collective control or pull collective control up , the collective control will raises the entire swash plate assembly as a unit . This has effect to the blades by changing the angle of all blades simultaneously.This causes to increase angle of attack and give more lift.

The Cyclic Control

The pilot has a so-called cyclic control stick at his disposal. The cyclic control will push one side of the swashplate assembly up or down, so that the rotor will be angled in the desired direction. This causes the helicopter to move left or right, forward or backward.

In a hobby helicopter, the remote control system is usually more authomatic, freeing the pilot from thinking about blade angles or tilting. He only has to decide if he will move up or down, in what direction and at what speed.


How it all works together and the pilot stears the helicopter

The lifting forse and speed, and the horisontal forse and speed is regulated by using the pich controle of the main rotor together with the gas. More angulated pich together with more gas gives stronger force and less angulate pich with less gass gives less force for lift and horisontal motion.

The flying direction forewards, backward and to the sides are regulated with the cyclic controle.

The swinging of the helicopter and thus the direction at which it points, is regulated by the pich of the tail rotor.

All these regulatory maneures must be followed by more or less gas, not only the pich of the main rotor, but that is mostly done automatically, even though the pilot can do it manually also.