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THE WORKING PRINCIPLES OFHELICOPTERSThe advanced hobby helicopters presnted above are operated by the

same mechanical and aerodynamilcal prinsiples as a full scalehelicopter.Helicopter lift is obtained by means of one or more power drivenhorizontal propellers which called Main Rotor. When the main rotorof helicopter is turning it produces lift and reaction torque. Reactiontorque tends to make helicopter spin. On most helicopters, a smallrotor near the tail which is called tail rotor is counteracting thistorque. On twin rotor helicopter the rotors rotate in oppositedirections, their reactions cancel each other, the same is throughabout the four-rotor hobby helicopters depicted above.Main rotor

The main rotor produces the lifting force and force for all movement.The force depends upon the angle of the rotor blades against the axisand the rotating speed of the main rotor.

Each blade produces an equal share of the lifting force so that theweight of a helicopter is divided evenly between the rotor blades. Ifthe helicopter also accelerates up, the rotor also has to provide forthe force needed for acceleration. Furthermore it has to provide theforce to overcome air resistence towards the helicopter due toupward motion.The main rotor also gives force to move foreward, backwards orsidewise by tilting the rotor.Tail rotorThe spin of the main rotor will make a force on the rest of thehelicopter that brings it to spinning in the opposite direction ifsomething does not counteract this spinning. This is called torquereaction. The tail rotor compensates for this torque thus holding thehelicopter straight. On twin-rotors helicopter or the four rotor hobbyhelicopters, the rotors spin in opposite directions, canceling out thisreaction. The tail rotor in normally linked to the main rotor via asystem of driveshafts and gearboxes , that means if the main rotormakes 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 ofthe main rotor.Why does the rotor effect force

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It is commonly said that the blades of a helicopter rotor acts like awing, but it is more like a big propellar actually. When a rotor bladeregulated to an angle against the rotating axis moves aroud, itcompresses the air at the underside making the pressure at that sideincrease. Compressing air downwards mens that air is taken awayfrom the upper side so that the air pressure her decreases. The

difference of air pressure between the under-side and upper sidemakes a force that can be used for lifting and horisontal motion.Techically one uses the Bernoulli equation to calculate the pressureand thereby the lift. This use gives right answars, but the logicalexplanation for using this equation for this application is usuallywrong.Lifting dissymmetryAll rotor is allways experiencing Dissymmetry of Lift in forward flight. As the helicopter gain air speed , the advanceing blade developsgreater lift because of the increased airspeed and the retreating

blade will produce less lift , causing the helicopter to roll. This has tobe compensated for in some way . The compensation is mostlyeffectuated passively by blade flapping. Increased airspeed and lifton the advancing blade will cause the blade to flap up and decreasingthe angle of attack . The decreased lift on the retreating blade willcause the blade to flap down and increasing the angle of attack . Thiscombination 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 ofthe rotor blades without changing the speed of the rotors, thus

giving the rotors more or less power. After start the rotor isaccelerated up to the working speed without the blades twisted.Then the blades are twisted to the angle that gives the force oneneeds at any time.At the same time the force of the motor must be regulated up ordown by adding or decreasing the gas given.

The same principles are used in advanced hobby helicopters.In asimple hobby helicopter the force may be regulated by changeng thespeed of the rotors because the mechanical system used here issimpler.Regulating the flying direction for the helicopterA helicopter can hover still in the air, fly forewords, backwords orsidewords. This is done by tilting the helicopter main rotor so that acomponent of the force from the rotor points in the wanted flyingdirection. The vertical force component of course still is used to makethe helicopter hover. The force used by the motor must also be

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regulated so that it deliveres enough force both for the horisontalcomponent and the vertical component.

The mechanical regulation of the rotor blade angles andtilting.This is done by the folowing mechanism in a real helicopter.Swash Plate Assembly : The swash plate assembly consists of twoprimary elements through which the rotor mast passes, one of whichis a disc, linked to the cyclic pitch control. This disc can of tilt in anydirection but does not rotate as the rotor rotates. This non-rotatingdisc is attached by a bearing surface to a second disc, often referedto as the which turns with rotor and linked to the rotor blade pitchhorns.The Collective Control : When pilot raises the collective control or pullcollective control up , the collective control will raises the entireswash plate assembly as a unit . This has effect to the blades bychanging the angle of all blades simultaneously.This causes toincrease angle of attack and give more lift.The Cyclic Control : The pilot has a so-called cyclic control stick at hisdisposal. The cyclic control will push one side of the swashplateassembly up or down, so that the rotor will be angled in the desireddirection. This causes the helicopter to move left or right, forward orbackward.

In a hobby helicopter, the remote control system is usually moreauthomatic, freeing the pilot from thinking about blade angles or

tilting. He only has to decide if he will move up or down, in whatdirection and at what speed.