 A new aircraft, known as the Aeroscraft, is under construction. In considering the Aeroscraft, one needs to keep in mind that it is not a Blimp. Rather, it is best to think of it as a sort of flying Queen Mary 2. When completed, the Aeroscraft will ferry passengers in style across continents and oceans as they stroll about the one-acre cabin or relax in luxurious staterooms. Unlike dirigibles, the craft is not lighter than air. Its helium hoist carries only two thirds of the weight of the ship. Huge rearward propellers generate enough additional lift to keep the craft aloft and cruising. During takeoff and during landing, jet engines push the ship upward or downward as is necessary.
Aircraft – machine for carrying out flights in atmosphere or in space.
On November 13, 1907, French bicycle inventor Paul Cornu designed and built a helicopter. The helicopter took-off with its inventor as pilot to 1 foot (0.3 mtrs) and remained aloft for 20 seconds. Even this helicopter proved to be unstable and was abandoned.
In Russia, Igor Sikorsky built two helicopters - in 1908 and 1909. Helicopter took-off into air but was not strong enough to carry a pilot. Hence, Sikorsky lost interest in helicopters and started designing of an aero plane. Sikorsky returned back to designing of helicopters only in 1938 so as to keep his company aloft. The first more or less perfect flying sample of Sikorsky’s helicopter VS-300(S-46) appeared in 1939.
Till the invention of swash plate in 1911, it was impossible to even discuss about a manned flight in a helicopter. In 1922, Professor George Botezat, who migrated to USA from Russia after the revolution, built the first steady manned helicopter as per the order of US Army. Helicopter can lift into skies with load upto 5 meters and was aloft in air for several minutes.
Aircraft is capable of flying due to special cambered shape of wing, which rotates in air flow approach. Lifting force is created since the distance, traveled by airflow above the wing is more than the distance of airflow below the wing and accordingly, speed of the airflow above the wing is more. According to Bernoulli’s law, force, directed towards the airflow with high speed, acts upon the wing. Helicopter also uses the same principle but the role of wings is played by the blades of rotor.
Torque develops as the engine turns the rotor, creating a torque effect which causes the body of helicopter to turn in the opposite direction of the rotor. Usually additional small vertical tail rotor (anti torque control) is used to eliminate this effect. If this rotor (ducted fan) is built-in in tail boom, then it is called “Fenestron”.
Ка-52 "Alligator": Two large main rotors, rotating in opposite direction on a single axis is another variant. The second rotor is called aerodynamically symmetric coaxial main rotor. This variant is used, for example, in Russian Ка-50. Helicopters of such variants have more thrust to weight ratio, however, in case of insufficient design reasoning, can possess the increased probability rotor blade whipping during sharp lateral maneuvering.
Other helicopters also exist, which use Coanda effect (surface attachment of air jet) (adhesion of liquid or gas jet to solid surface) so as to eliminate the anti torque effect without additional rotors. Maximum speed of the helicopter is restricted since it is not always possible to attain sonic speed regularly on extreme sections of the blades (general maximum speed on edge of the blade equals to diameter of rotor rotating hub multiplied by its revolutions per second + speed of the helicopter) which lead to the failures of design.
When the helicopter flies forward, blades, rotating in front, have high velocity with respect to air, rotating at the back. As a result, one of the rotors creates large lifting force than the other and the helicopter turns sideways. To eliminate the sideways turn, compensation mechanism, built-in in the swash plate, is used so that the angle of slope of blades in left and right halve of rotors is different. Besides, rotor creates vibration, threatening with the destruction of design. Therefore, in most cases, active damping system for occurring oscillations is used. |
