Explain How Helicopters Fly - Essay Example

?Running Head: EXPLAIN HOW HELICOPTERS FLY Inserts His/Her Inserts Grade Inserts Helicopters Helicopters are the most flexible vehicle for transport these days. No other transport vehicle or system can give an equivalent level of freedom of maneuverability to its operator. During the 1840s, Leonardo Da Vinci gave the first design that may be called an ‘aerial screw’ and was the foundation on which future helicopters developed. Focke-Wulf Fw 61 was the first operational helicopter in 1936. A Russian engineer, Igor Sikorsky (1889-1972), designed the first helicopter in 1942 that went into full-scale production phase. Helicopters have found a large number of applications in modern day transportation including military, medical services, tourism, surveillance, fire fighting, search and rescue, etc. Its flight features allow movement in all direction: upwards, downwards, sideways, forward as well as in reverse direction. This flexibility allows the helicopter to be flown in small and congested areas where it is not possible to land the airplanes. Since it can fly in any direction, it has a lot of parameters to take care of while flying. Therefore, the pilot needs to be very skilled and capable and must give full attention while flying. Helicopters not only move in all three dimensions but can also rotate and hover at one point in air. These features, although, make it a unique mode of transport, also make it a very complex machine to understand as well as to pilot. The main parts of helicopter are: Main Rotor – The vertically mounted rotor in center Fuselage – The main body of helicopter Transmission system – Speed control mechanism of rotors Tail boom – Rear portion on which the tail rotor is mounted Tail rotor – Small horizontal axis rotor at the rear Engine – Main engine used to spin the shaft To understand the flight of a helicopter, we can begin from the simple vertically up and down motion. For a helicopter to move upwards, it needs wings that have air moving on its surface in one direction. In case of an airplane, the wings are fixed and the whole plane moves forward for the air to move on the surface of wings and generate lift. However, in case of helicopter we keep it on the same spot. Instead, the wings are rotated to generate the desired lift effect. Wings are shaped in such a manner that they deflect the air downwards and as a reaction, the helicopter is lifted. This shape of the wings is called airfoil. Two or more wings are mounted on a shaft and the shaft is made to rotate thereby, giving a continuous motion to the wings. This rotating wings and shaft are collectively called the main rotor. The main rotor is the most important part of any helicopter. It not only generates the lift force required for the helicopter to fly but also provides for the lateral movement, spinning and changing the altitude. The rotor has to be very strong as it supports all the forces on the helicopter and its weight. The wings have a swivel mechanism at the point where they connect to the rotor. This swivel functionality allows for changing the angle of blades, which changes the path of air. To affect lift, the angle of blades needs to be altered with respect to the oncoming wind. This is known as the angle of attack. The angle alteration mechanism for all wings is collectively called the hub. A device known as the swash plate assembly makes the adjustment of the angles of the rotor blades. The swash plate assembly has two plates, fixed swash plate and a rotating swash plate. The swash plate assembly has two main functions: Firstly, it changes the angle of all the blades simultaneously. It increases the overall lift, thereby gaining or losing altitude. Secondly, the swash plate can change the angle of individual blades while revolving. This gives the flexibility to a helicopter to move in any direction. This alteration of angle, called pitch, is carried out by means of the pitch control rods, which control the function of rotating swash plate. The fixed swash plate has another set of control rods to alter its angle. The pilot has a system of controls available in the cockpit for the control of swash plates. These consist of two main controls – the cyclic controls and the collective controls. The collective controls allow the angle of attack to be changed on all wings at the same time, while, the cyclic controls are there to tilt the whole swash plate assembly. This makes the angle of attack to alter on any one side of the helicopter. When the pilot desires to hover the helicopter, the cyclic controls are adjusted to keep helicopter from moving forward, backwards or sideways, while the collective controls are used to keep the vehicle at a fixed altitude. An engine is required to rotate the main rotor in order to generate enough lift. Gas turbines or gasoline piston engines are most commonly used for this purpose. The engine driveshaft is connected to the rotor through a gear transmission system. This system works perfectly until the time helicopter stays on the ground. As the helicopter lifts, it loses contact with the ground. According to the laws of motion, any force produces an equal force in opposite direction. In absence of anything to hold, the body of the helicopter starts rotating in the direction opposite to the rotor spin. A system of opposing force is developed to cater for this problem. To prevent the body of helicopter from rotating, helicopters are fixed with an additional small rotor called the tail rotor. An opposing force is produced by means of rotating wings attached to a long boom at the end of the body. These tail rotors produce a sideways thrust similar to the propeller of an airplane, opposing the spin of the body. In order to spin the helicopter on its main shaft axis, the angle of attack on the tail rotor is altered. A system of two foot pedals is available in the cockpit for the pilot to alter the angle of attack of tail rotors. The tail rotors help the helicopter to spin on main rotor axis without moving in any other direction. Tail rotors are a weak part of the helicopter as they are vulnerable to colliding with passing birds. This is very dangerous because without a tail rotor, the helicopter becomes uncontrollable and results in a crash. Some helicopters are designed with twin rotor mechanism. Twin rotor is a relatively simpler design in which two rotors rotate a pair of wings each in directions opposite to each other. Both rotors are mounted on the same shaft. The opposing rotation cancels their reaction. Therefore, there is no spin effect on the body once it is in air. The helicopter can be piloted in a particular direction by tilting the axis of the main rotor in that direction. Helicopters have a few limitations that become a disadvantage in certain situations. The main disadvantage is its low speed. This happens because the wind coming towards the rotors has too high speed to be properly deflected downwards by the rotating wings. A situation may occur at higher speed that the wing instantaneously on the front generate too much lift while the wing retreating to the rear side develop too much stall, unbalancing the whole helicopter. This also results in compression of air that produces drag and vibrations. If the vibrations become resonant, the helicopter may even break apart. References Day, Dwayne A., 2003, ‘Igor Sikorsky – VS 300’, Centennial of Flight Commission, Retrieved April 18, 2012 Hirschberg, Michael J. and David K. Dailey, 2000, ‘Sikorsky’, US and Russian Helicopter Development in the 20th Century, American Helicopter Society, International. Retrieved April 18, 2012 Rumerman, Judy, 2003, ‘Early Helicopter Technology’, Centennial of Flight Commission, Retrieved April 18, 2012 Read More