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                                                      JET

Air breathing jet engines provide thrust by taking in air, burning it with fuel in a combustion chamber, and accelerating the exhaust rearwards so that it ejects at high speed. The reaction against this acceleration provides the engine thrust.

Jet engines can provide much higher thrust than propellers, and are naturally efficient at higher altitudes, being able to operate above 40,000 ft (12,000 m). They are also much more fuel-efficient at normal flight speeds than rockets. Consequently, nearly all high-speed and high-altitude aircraft use jet engines.

The early turbojet and modern turbofan use a spinning turbine to create airflow for takeoff and to provide thrust. Many, mostly in military aviation, use afterburners which inject extra fuel into the exhaust.

Use of a turbine is not absolutely necessary: other designs include the crude pulse jet, high-speed ramjet and the still-experimental supersonic-combustion ramjet or scramjet. These designs require an existing airflow to work and cannot work when stationary, so they must be launched by a catapult or rocket booster, or dropped from a mother ship.

The bypass turbofan engines of the Lockheed SR-71 were a hybrid design – the aircraft took off and landed in jet turbine configuration, and for high-speed flight the afterburner was lit and the turbine bypassed, to create a ramjet.

The motorjet was a very early design which used a piston engine in place of the combustion chamber, similar to a turbocharged piston engine except that the thrust is derived from the turbine instead of the crankshaft. It was soon superseded by the turbojet and remained a curiosity.

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                              SKYWAY

In an urban setting, a skyway, catwalk, sky bridge, or skywalk is a type of pedway consisting of an enclosed or covered bridge between two buildings. This protects pedestrians from the weather. These skyways are usually owned by businesses, and are therefore not public spaces(compare with sidewalk). Skyways usually connect on the first few floors above the ground-level floor, though they are sometimes much higher, as in Petronas Towers, SWFC and Kingdom Centre (though this skyway is often referred to as a sky bridge). The space in the buildings connected by skyways is often devoted to retail business, so areas around the skyway may operate as a shopping mall. Non-commercial areas with closely associated buildings, such as university campuses, can often have skyways and/or tunnels connecting buildings.

The world's largest skyway network – Calgary, Alberta's "+15 Walkway" system – has a total length of 16 km (10 miles). However, the system is discontinuous, and it does not connect every downtown building. The largest continuous network of skyways – the Minneapolis Skyway System – spans 8 miles (13 km) connecting 69 blocks in downtown Minneapolis.

Other cities in the Midwest, such as Des Moines, Cedar Rapids, Rochester, and Paul also have significant skyway systems. On a smaller scale, terminals of large airports are often connected by skywalk systems, as at Manchester Airport, United Kingdom.

The Mumbai Skywalks system is a discontinuous system of 50 skywalks planned in the Mumbai, each 1 to 2 km in length. When completed, the system will be the largest skyway system in the world. The first of these is a 1.3km (0.8mi) long skywalk connecting the suburban regions of Bandra and Kurla.

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                                                      JET

Air breathing jet engines provide thrust by taking in air, burning it with fuel in a combustion chamber, and accelerating the exhaust rearwards so that it ejects at high speed. The reaction against this acceleration provides the engine thrust.

Jet engines can provide much higher thrust than propellers, and are naturally efficient at higher altitudes, being able to operate above 40,000 ft (12,000 m). They are also much more fuel-efficient at normal flight speeds than rockets. Consequently, nearly all high-speed and high-altitude aircraft use jet engines.

The early turbojet and modern turbofan use a spinning turbine to create airflow for takeoff and to provide thrust. Many, mostly in military aviation, use afterburners which inject extra fuel into the exhaust.

Use of a turbine is not absolutely necessary: other designs include the crude pulse jet, high-speed ramjet and the still-experimental supersonic-combustion ramjet or scramjet. These designs require an existing airflow to work and cannot work when stationary, so they must be launched by a catapult or rocket booster, or dropped from a mother ship.

The bypass turbofan engines of the Lockheed SR-71 were a hybrid design – the aircraft took off and landed in jet turbine configuration, and for high-speed flight the afterburner was lit and the turbine bypassed, to create a ramjet.

The motorjet was a very early design which used a piston engine in place of the combustion chamber, similar to a turbocharged piston engine except that the thrust is derived from the turbine instead of the crankshaft. It was soon superseded by the turbojet and remained a curiosity.

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                                                      FIXED-WINGS

Airplanes or aero planes are technically called fixed-wing aircraft.

The forerunner of the fixed-wing aircraft is the kite. Whereas a fixed-wing aircraft relies on its forward speed to create airflow over the wings, a kite is tethered to the ground and relies on the wind blowing over its wings to provide lift. Kites were the first kind of aircraft to fly, and were invented in China around 500 BC. Much aerodynamic research was done with kites before test aircraft, wind tunnels and computer modeling programs became available.

The first heavier-than-air craft capable of controlled free flight were gliders. A glider designed byCayley carried out the first true manned, controlled flight in 1853.

Besides the method of propulsion, fixed-wing aircraft are generally characterized by their wing configuration. The most important wing characteristics are:

§                     Number of wings – Monoplane, biplane, etc.

§                     Wing support – Braced or cantilever, rigid or flexible.

§                     Wing platform – including aspect ratio, angle of sweep and any variations along the span (including the important class of delta wings).

§                     Location of the horizontal stabilizer, if any.

§                     Dihedral angle – positive, zero or negative (anhedral).

A variable geometry aircraft can change its wing configuration during flight.

A flying wing has no fuselage, though it may have small blisters or pods. The opposite of this is a lifting which has no wings, though it may have small stabilizing and control surfaces.

Most fixed-wing aircraft feature a tail unit or empennage incorporating vertical, and often horizontal, stabilizing surfaces.

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                                               MILITARY

A military aircraft is any fixed-wing or rotary-wing aircraft that is operated by a legal or insurrectionary armed service of any type.Military aircraft can be either combat or non-combat:

§                     Combat aircraft are aircraft designed to destroy enemy equipment using its own armament.

§                     Non-Combat aircraft are aircraft not designed for combat as their primary function, but may carry weapons for self-defense. Mainly operating in support roles.

Combat aircraft divide broadly into fighters and bombers, with several in-between types such as fighter and ground-attack aircraft (including attack helicopters).

Other supporting roles are carried out by specialist patrol, search and rescue, reconnaissance, observation, transport, training and Tanker aircraft among others.

Many civil aircraft, both fixed-wing and rotary, have been produced in separate models for military use, such as the civil Douglas DC-3 airliner, which became the military C-47/C-53/R4D transport in the U.S. military and the "Dakota" in the UK and the Commonwealth. Even the small fabric-covered two-seater Piper J3 Cub had a military version, the L-4 liaison, and observation and trainer aircraft. Gliders and balloons have also been used as military aircraft; for example, balloons were used for observation during the American Civil War and World War I, and military gliders were used during World War II to land troops.

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                                  HELICOPTER

The rotor of a helicopter, may, like a propeller, be powered by a variety of methods such as an internal-combustion engine or jet turbine. Tip jets, fed by gases passing along hollow rotor blades from a centrally mounted engine, have been experimented with. Attempts have even been made to mount engines directly on the rotor tips.

Helicopters obtain forward propulsion by angling the rotor disc so that a proportion of its lift is directed forwards to provide thrust.

Other methods of propulsion

§                     Rocket-powered aircraft have occasionally been experimented with, and the MesserschmittKomet fighter even saw action in the Second World War. Since then they have been restricted to rather specialised niches, such as the Bell X-1 which broke the sound barrier or the North American X-15 which traveled up into space where no oxygen is available for combustion (rockets carry their own oxidant). Rockets have more often been used as a supplement to the main power plant, typically to assist takeoff of heavily loaded aircraft, but also in a few experimental designs such as the Saunders-Roe SR.53 to provide a high-speed dash capability.

§                     The flapping-wing ornithopter is a category of its own. These designs may have potential, but no practical device has been created beyond research prototypes, simple toys, and a model hawk used to freeze prey into stilln

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                                              SKYVECHILE

The Moller Sky car is a prototype personal VTOL (vertical take-off and landing)aircraft — a "flying car" — called a "Volantor" by its inventor Paul Moller, who has been attempting to develop such vehicles for forty years. The design calls for four ducted fans encasing the propellers, which prevents bystanders from being exposed to moving blades as well as improving aerodynamic efficiency at low speeds.

The craft said to be currently under development, the M400, is purported to ultimately transport four people; single-seat up to six-seat variations are also planned. It is described as a car since it is aimed at being a popular means of transport for anyone who can drive, incorporating automated flight controls. It is proposed that in a model for the general public, the driver may only input direction and speed. Piloting knowledge would be unnecessary; however, training will be required.

Further, developers claim that by using eight inexpensive Wankel rotary engines - compared to jet engines, the vehicle's price may eventually fall close to that of a luxury car ($100,000). The fuel consumption is claimed to be 20 miles per gallon— similar to that of a big car— but this has been calculated as unrealistic. According to the developers, operation of a Sky car will produce as much noise as traffic on a nearby freeway when taking off, and this will only last for a few seconds, because it climbs so quickly.

The Sky car demonstrated limited tethered flight capability in 2003 by hovering only. Scheduled tethered flight tests, which were to occur in mid-2006, were apparently canceled. Moller upgraded the Sky car’s engines in 2007, and the improved prototype is now called the "M400X". According to a 2008 article in the media, a prototype is supposed to be flying in 2012, with certified versions "a few years later".

Moller International's website claims that only $100 Million has been spent in R & D at Moller International,

The company is also developing a more advanced model called M600, with an intended capacity for 6 passengers or a payload of about 2000 lbs (900 kg).

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Heavier than air – aerodynes

Heavier-than-air aircraft must find some way to push air or gas downwards, so that a reaction occurs (by Newton's laws of motion) to push the aircraft upwards. This dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic upthrust:aerodynamic lift, and powered lift in the form of engine thrust.

Aerodynamic lift is the most common, with fixed-wing aircraft being kept in the air by the forward movement of wings, and rotorcraft by spinning wing-shaped rotors sometimes called rotary wings. A wing is a flat, horizontal surface, usually shaped in cross-section as anaerofoil. To fly, air must flow over the wing and generate lift. A flexible wing is a wing made of fabric or thin sheet material, often stretched over a rigid frame. A kite is tethered to the ground and relies on the speed of the wind over its wings, which may be flexible or rigid, fixed or rotary.

With powered lift, the aircraft directs its engine thrust vertically downwards.

The initialism VTOL (vertical take off and landing) is applied to aircraft that can take off and land vertically. Most are rotorcraft. Others, such as the Hawker Siddeley Harrier and F-35B, take off and land vertically using powered lift and transfer to aerodynamic lift in steady flight. Similarly, STOL stands for short take off and landing. Some VTOL aircraft often operate in a short take off/vertical landing mode known asSTOVL.

A pure rocket is not usually regarded as an aerodyne, because it does not depend on the air for its lift (and can even fly into space); however, many aerodynamic lift vehicles have been powered or assisted by rocket motors. Rocket-powered missiles which obtain aerodynamic lift at very high speed due to airflow over their bodies are a marginal case

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 Lighter than air – aerostats

Aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low density gas such as helium, hydrogen or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces.

Small hot air balloons called sky lanterns date back to the 3rd century BC, and were only the second type of aircraft to fly, the first being kites.

Originally, a balloon was any aerostat, while the term airship was used for large, powered aircraft designs – usually fixed-wing– though none had yet been built. The advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelins being the largest and most famous. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these aircraft. Then several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a "balloon" is an unpowered aerostat, whilst an "airship" is a powered one.

A powered, steer able aerostat is called a dirigible. Sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloonis regarded as the definition of an airship (which may then be rigid or non-rigid). Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. These soon became known as blimps. During the Second World War, this shape was widely adopted for tethered balloons; in windy weather, this both reduces the strain on the tether and stabilizes the balloon. The nickname blimp was adopted along with the shape. In modern times any small dirigible or airship is called a blimp, though a blimp may be unpowered as well as powered.

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                                                     GENERAL AVIATION

General aviation is a catch-all covering other kinds of private and commercial use, and involving a wide range of aircraft types such as business jets (bizjets), trainers, homebuilt, types, racers, gliders, war birds, firefighters, medical transports, and cargo transports, to name a few. The vast majority of aircraft today are general aviation types.

Within general aviation, there is a further distinction between private aviation (where the pilot is not paid for time or expenses) and commercial aviation (where the pilot is paid by a client or employer). The aircraft used in private aviation are usually light passenger, business, or recreational types, and are usually owned or rented by the pilot. The same types may also be used for a wide range of commercial tasks, such as flight training, pipeline surveying, passenger and freight transport, policing, crop dusting, and medical evacuations. However the larger, more complex aircraft are more likely to be found in the commercial sector.

For example, piston-powered propeller aircraft (single-engine or twin-engine) are common for both private and commercial general aviation, but for aircraft such as turboprops like the Beech craft King Air and helicopters like the Bell JetRanger, there are fewer private owners than commercial owners. Conventional business jets are most often flown by paid pilots, whereas the new generations of smaller jets are being produced for private pilots.

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                                                 AIRCRAFT

Aircraft are vehicles which are able to fly by being supported by the air, or in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.

Although rockets and missiles also travel through the atmosphere, most are not considered aircraft because they use rocket thrust instead of aerodynamics as the primary means of lift. However, rocket planes and cruise missiles are considered aircraft because they rely on lift from the air. Another type of aircraft is thespaceplane which is an aircraft designed to fly up to extreme altitudes into space and land as a conventional aircraft.

The human activity which surrounds aircraft is called aviation. Manned aircraft are flown by an onboard pilot. Unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Target drones are an example of UAVs. Aircraft may be classified by different criteria, such as lift type, propulsion, usage and others.