Helicopters are extremely useful pieces of flying equipment, with the ability to both take off and land vertically. This along with being able to hover in a given place and fly in any direction, including backwards and to either side, means that they have a huge amount of uses worldwide and in many different environments, which include but are not limited to rescue operations, observation platforms, firefighting and military purposes.
Helicopters get their power from rotors or blades. They do not look much like a helicopter, but the rotors blades have an aerofoil shape when spinning, much like the wings of an airplane. This means that as the rotors turn, air flows more quickly over the tops of the blades than it does below which creates the lift required for flight.
http://www.boeing.com/companyoffices/aboutus/wonder_of_flight/heli.html Accessed on 25/11/14
The same aerodynamic principles allow helicopters to fly as well as any other aircraft. The force needed to keep any aircraft in the air is ‘Lift’, which is produced by air flowing over the wings.
Wings are shaped so that the air flowing over the top surface has to travel further, therefore travelling quicker than the air under the wing. This in turn causes pressure above the wing to be lower, meaning that the lower part of the wing is sucked up by the lower pressure. This therefore makes any aircraft fly and helicopters are no different.
A helicopter however is a far more complex machine than an aeroplane although the fundamental principles of flight are the same. The rotor blades of a helicopter are identical to the wings of an aeroplane, in where air is blown over them, lift is produced. The major difference between an aeroplane and a helicopter however is that the flow of air is produced by rotating the wings (rotor blades), rather than by moving the entire aircraft. When a helicopters rotor blades start to rotate, the air flowing over them produces lift which causes the helicopter to rise into the air. Thus it is seen that the engine is used to turn the blades which produce the required lift, rather than using an engine to produce thrust to lift an aeroplane into the air.
There is more required from a helicopter however as it is required to lift into the air when wanted, rather than rise up as soon as the engine is started. In a helicopter, for various reasons, the blades need to be turned at the same speed all the time so a different way to control the amount of lift produced is needed.
The magnitude of this lift is actually changed by altering the angle at which the rotor blades meet the air blowing over them. This is known as increasing or decreasing the pitch angle of the rotor blades, which changes the amount of lift produced. This enables helicopters to be able to hover when the pilot decides to, by increasing the pitch on the wings.
However, increasing the lift also causes more drag to appear in the blades. This means the engine needs to produce more power in order to prevent the rotor blades slowing down. In the past this had to be operated by the pilot, however in present day helicopters this is operated automatically. This massively improves the safety aspect and takes more responsibility away from the pilot, allowing him to concentrate on other vital aspects of flying.
As mentioned earlier, helicopters are able to move in all directions. This is done by changing the pitch angle of the rotor blades, which differs between each blade individually and by a different amount. To turn the helicopter left or right however, the pitch angle of the tail rotor only ‘ the small rotor at the end of the helicopter is altered.
This is a basic outline of how helicopters achieve flight and there are various other factors which have not been mentioned here, such as different air to flow over each blade.
http://www.decodedscience.com/how-do-helicopters-fly/20418/2, accessed on 25/11/14
There are a variety of helicopters in the market and the design has changed over the years, however nowadays the most popular type is one with a lift blade and tail blade.
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