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How can helicopter fly
This is just the basic informations for the beginners which did not know any things about the helicopter or airplane before and wants to know some principles that why the helicopter can fly but not in deep details. For the people that want to know more than what I have in here, please go to the text book which have many professors wrote them or go to the specific helicopter manuals. The details about the helicopter has so much to put it all in the WEB.
The wings of the airplane create a lift force when they move through the air. As we known,during flight, there are four forces acting on the helicopter or airplane and those are LIFT , DRAG , THRUST ,and WEIGHT .(please go back and see on What makes an airplane fly ? section).In order to make the wings to move through the air , of course, the plane itself has to move. A helicopter works by having its wings move through the air while the body stays still. The helicopter's wings are called Main Rotor Blades. The shape and the angle of the blades move through the air will determine how much Lift force is created. After the helicopter lifted off the ground, the pilot can tilt the blades, causing the helicopter to tip forward or backward or sideward.
Although we will describe certain terms or parts of helicopter more in the next sections as we go along, but we should familier with all of these terms in order to understand the helicopter better.
Bernoulli'principle :This principle states that as the air velocity increases, the pressure decreases; and as the velocity decreases, the pressure increases .
Airfoil : is technically defined as any surface, such as an airplane aileron, elevator, rudder, wing, main rotor blades, or tail rotor blades designed to obtain reaction from the air through which it moves.
Angle of Attack : is the acute angle measured between the chord of an airfoil and the relative wind.
Angle of Incidence : is the acute angle between the wing's chord line and the longitudinal axis of the airplane. (usually manufacturer had built the aircraft with the wing has some degrees to the horizontal plane or airplane longitudinal axis).
Blades : The blades of the helicopter are airfoils with a very high aspect ratio ( length to chord ). The angle of incidence is adjusted by means of the control from pilots.
The main rotor of the helicopter may have two, three,four , five or six blades, depending upon the design. The main rotor blades are hinged to the rotor head in such a manner that they have limited movement up and down and also they can change the pitch ( angle of incidence ). The controls for the main rotor are called Collective and Cyclic Controls.
The tail rotor is small blades may have two or four blades and mounted on the tail of the helicopter,it rotates in the vertical plane. The tail rotor is controlled by the rudder pedals. Its pitch can be changed as required to turn the helicopter in the direction desired.
Blade Root : The inner end of the blades where the rotors connect to the blade gripos.
Blade Grips : Large attaching points where the rotor blade connects to the hub.
Rotor Hub : Sit on top of the mast , and connects the rotor blades to the control tubes.
Main Rotor Mast : Rotating shaft from the transmission which connects the main rotor blades to helicopter fuselage.
Pitch Change Horn : to converts control tube movement to blade pitch. Control tube is a push-pull tubes that change the pitch of the rotor blades through the pitch changing horn.
Swash Plate Assembly : The swash plate assembly consists of two primary elements through which the rotor mast passes. One element is a disc, linked to the cyclic pitch control. This disc is capable of tilting in any direction but does not rotate as the rotor rotates. This non-rotating disc, often refered to as the Stationary Star is attached by a bearing surface to a second disc, often refered to as the Rotating Star which turns with rotor and linked to the rotor blade pitch horns.
Transmission : The transmission system transmits engine power to the main rotor, tail rotor, generator and other accessories. The engine is operated at a relative high speed while the main rotor turns at a much lower speed. This speed reduction is accomplished through reduction gears in the Transmission System
Lift : is produced by a lower pressure created on the upper surface of an airplane's wings compared to the pressure on the wing's lower surfaces,causing the wing to be LIFTED upward. The special shape of the airplane wing (airfoil) is designed so that air flowing over it will have to travel a greater distance and faster resulting in a lower pressure area (see illustration) thus lifting the wing upward. Lift is that force which opposes the force of gravity (or weight).
Lift depends upon (1) shape of the airfoil (2) the angle of attack (3) the area of the surface exposed to the airstream (4) the square of the air speed (5) the air density.
lift equation
Relative Wind : is the direction of the airflow with respect to an airfoil or to the rotor blades.
Pitch Angle : The rotor blade pitch angle is the acute angle between the blade chord line and the rotor plane of rotation.( you may understand as the angle of incidence ) . This pitch angle can be varied by the pilot through the use of cockpit controls ( collective and cyclic pitch control ).

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