how does a helicopter work?

Question

science homework: how does a helicopter work, please help

Answer 1

A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter derives its source of lift from the rotor blades rotating around a mast. The word 'helicopter' is adapted from the French hélicoptère, coined by Gustave de Ponton d'Amecourt in 1861. It is linked to the Greek words helix/helik = "spiral" or "turning" and pteron = "wing".

Most helicopters have a single main rotor but require a separate rotor to overcome torque. This is accomplished through a variable pitch, antitorque rotor or tail rotor. This is the design that Igor Sikorsky settled on for his VS-300 helicopter and it has become the recognized convention for helicopter design, although designs do vary. When viewed from above, designs from Germany, United Kingdom and the United States are said to rotate counter-clockwise, all others are said to rotate clockwise. This can make it difficult when discussing aerodynamic effects on the main rotor between different designs, since the effects may manifest on opposite sides of each aircraft.

Antitorque:
For a helicopter with a single main rotor, torque develops as the engine turns the rotor, creating a torque effect which causes the body of the helicopter to turn in the opposite direction of the rotor. To eliminate this effect, some sort of antitorque control must be used, with a sufficient margin of power available to allow the helicopter to maintain its heading and provide yaw control. The three most common controls used today are the traditional tail rotor, Eurocopter's Fenestron (also called a fantail), and MD Helicopters' NOTAR.

Tail rotor:
The tail rotor is a smaller rotor mounted vertically or near-vertical on the tail of a traditional single-rotor helicopter. The tail rotor either pushes or pulls against the tail to counter the torque. The tail rotor drive system consists of a drive shaft powered from the main transmission and a gearbox mounted at the end of the tail boom. The drive shaft may consist of one long shaft or a series of shorter shafts connected at both ends with flexible couplings. The flexible couplings allow the drive shaft to flex with the tail boom. The gearbox at the end of the tailboom provides an angled drive for the tail rotor and may also include gearing to adjust the output to the optimum RPM for the tail rotor. On some larger helicopters, intermediate gearboxes are used to transition the tail rotor drive shaft from along the tailboom or tailcone to the top of the tail rotor pylon which also serves as a vertical stabilizing airfoil to alleviate the power requirement for the tail rotor in forward flight. It may also serve to provide limited antitorque within certain airspeed ranges in the event that the tail rotor or the tail rotor flight controls fail.

Fenestron:
A Fenestron (or Fantail) is a ducted fan mounted on the tail boom of the helicopter and used in place of a tail rotor. Its housing is integral with the tail skin, and while conventional tail rotors typically possess a maximum of 5 rotor blades, Fenestrons have between 8 and 18 blades. These are arranged in varying distance, so that the noise is distributed over different frequencies and thus appears quieter. The housing allows a higher rotational speed than a conventional rotor and therefore it can have a smaller size than a conventional rotor.


NOTAR:
An acronym for NO Tail Rotor, NOTAR is a relatively new helicopter anti-torque system originally developed by Hughes Helicopters and currently produced by MD Helicopters which eliminates the use of the tail rotor on a helicopter.

Although the concept, which uses the Coandă effect, took some time to refine, the NOTAR system is simple in theory and works to provide antitorque the same way a wing develops lift.[14] A variable pitch fan is enclosed in the aft fuselage section immediately forward of the tail boom and driven by the main rotor transmission. This fan forces low pressure air through two slots on the left side of the tailboom, causing the downwash from the main rotor to hug the tailboom, producing lift, and thus a measure of antitorque proportional to the amount of airflow from the rotorwash. This is augmented by a direct jet thruster (which also provides directional yaw control) and vertical stabilizers.


Helicopter rotor system:
The rotor system, or more simply rotor, is the rotating part of a helicopter which generates lift. A rotor system may be mounted horizontally as main rotors are, providing lift vertically, or it may be mounted vertically, such as a tail rotor, to provide lift horizontally as thrust to counteract torque effect. In the case of tiltrotors, the rotor is mounted on a nacelle that rotates at the edge of the wing to transition the rotor from a horizontal mounted position, providing lift horizontally as thrust, to a vertical mounted position providing lift exactly as a helicopter.

The rotor consists of a mast, hub and rotorblades. The mast is a cylindrical metal shaft which extends upwards from and is driven by the transmission. At the top of the mast is the attachment point for the rotor blades called the hub. The rotor blades are then attached to the hub by a number of different methods. Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: semirigid, rigid, or fully articulated, although some modern rotor systems use an engineered combination of these types.


Controlling flight
Useful flight requires that an aircraft be controlled in all three dimensions. In a fixed-wing aircraft this is easy: small movable surfaces are adjusted to change the aircraft's shape so that the air rushing past pushes it in the desired direction. In a helicopter, however, there is often not enough speed for this method to be practical.

For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the main rotor blades is altered—cycled—during the rotation creating different amount of lifts at different points in the cycle. This is also how the helicopter is propelled: pitching forward causes forward flight.

For rotation about the vertical axis (yaw) the anti-torque system is used. Varying the pitch of the tail rotor alters the sideways thrust produced. Yaw controls are usually operated with anti-torque pedals corresponding to a fixed-wing aircraft's rudder pedals.

Helicopters maneuver with three flight controls besides the pedals. The collective pitch control lever controls the collective pitch, or angle of attack, of the helicopter blades all together, i.e. equally throughout the 360 degree rotation of the rotor. When the angle of attack is increased, the blade produces more lift. The collective control is usually a lever at the pilot's left side. Simultaneously increasing the collective and adding power with the throttle causes the helicopter to rise.

Answer 2

I think this helicopter is one of the best travel media in the world. This helicopter is made of different machine through which it works. There are a lots of things to know about it. Very high technology systems are used in it.

Answer 3

it works by spingin blades that push air downword as they spin and this lifts up the craft.. just like a wing on an airplane, the rotors create lift as they spin thru the air just like when air moves over an airplanes wing while fliying..