Wings | Tail | The Engines | Landing Gear | Flight Controls | Helicopters | Vertical Take-off | Specialised Craft | Aerodynamics in Nature
A helicopter can fly backwards.
The entire aircraft can rotate in the air.
A helicopter can hover motionless in the air.
(Above) The above diagram illustrates the range of movement of the helicopter
Helicopters are heavier-than-air craft that create their lift not from fixed wings like those of aeroplanes, but from a power-driven rotor or rotors, which turn on a vertical axis above the fuselage. Helicopters are very useful as they can rise or descend vertically, hover, and move forward, backward, or sideways. The helicopter was the first type of heavier-than-air craft capable of vertical flight.
(Above) You will notice that the cockpit of the helicopter is considerably simpler and smaller than that of an aeroplane. In the centre you can see the control stick which replaces the yoke as found on the aeroplane. It controls the main rotor blades. The pedals can be seen on the right on the floor. These pedals control the tail rotor blades. |
(Above) The main rotor hub where the rotor's drive
shaft and blades connect has to be extremely strong as well as highly adjustable. The swash plate assembly is the component that provides the adjustability. |
(Above) This is a side view of the tail rotor. It is much smaller than the main rotor blades and its main function is to stabalise the helicopter fuselage. It also changes the direction of the helicopter. |
(Above) The tail rotor's hub allows the pilot to change the angle of attack of the rotor's wings |
When a helicopter is rising vertically from the ground or descending vertically, the lift on all the rotor blades is the same, because they are all moving through the air at the same speed. When the craft is moving forward, the lift on some blades is greater than that on others. This means that the speed of the blades changes with each cycle. If the blades were fixed in a horizontal position, the amount of lift would vary (because the airspeed varies). The helicopter would then tilt to one side. To avoid this, helicopters have flapping blades. These are attached in such a way so that drops or rises to reduce the instability.
Click here to download a movie of the tail rotor at its different angles - (750 KB) - Thanks to HowStuffWorks.com
The helicopter has a great advantage, as it is able to hover and fly in any direction that it chooses. It main uses have been for search and rescue and to lift injured people. They can also spray crops and lift heavy equipment.
V e r t i c a l T a k e - o f f
(Above) A number of craft that achieve vertical take-off. From left to right : A squadron of Hawkers, a vertical-craft (VTOL), a sketch showing how "jump jets" work.
Their are other aircraft besides the helicopter that achieve vertical take-off. They are known as VTOL craft (Vertical Take-off and Landing) Examples of these are : The Harrier, Hawker and a number of prototype vessels. Although not very well armed, the fighters are more useful as utility craft than as combat planes. The Harrier, for instance, can lift off on a shorter strip than conventional planes, making it invaluable in situations were space is limited.
Vertical take-off is created by intaking air through valves found on the top of the fuselage and pushed out again through output valves on the undercarriage.
Another group of aircraft designed for space constraints are the STOL (Short Take-off and Landing) craft. They need less than 150 m (500 ft) to take-off and land making them invaluable at small / rural airports.
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