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                                                                                                                                                                    Date:  03 December 2008                                                                                                                                                                                                                                               

                                                                                                                                

Swept back Wing

 Swept Back Wing

A sweptback wing is one in which the leading edge slopes backward. When a disturbance causes an airplane with sweepback to slip or drop a wing, the low wing presents its leading edge at an angle that is perpendicular to the relative airflow. As a result, the low wing acquires more lift, rises and the airplane is restored to its original flight attitude.

Sweepback also contributes to directional stability. When turbulence or rudder application causes the airplane to yaw to one side, the right wing presents a longer leading edge perpendicular to the relative airflow. The airspeed of the right wing increases and it acquires more drag than the left wing. The additional drag on the right wing pulls it back, yawing the airplane back to its original path.

Wingtip vortices

Wingtip vortices are regions of high vorticity which develop at the tip of a wing as it flies through the air (or potentially another fluid). Wingtip vortices are a form of induced drag, an essentially unavoidable side-effect of the wing generating lift. Designing a wing with a vortex of preferable shape is critically important in aerospace engineering. Wingtip vortices also form the major component of wake turbulence.

As a wing flies through the air, it generates aerodynamic lift by creating a region of higher air pressure beneath the wing than above it, among other factors like air deflection for instance. It must be kept in mind that lift is a sum of forces not a single force. Fluids are forced to flow from high to low pressure and the relatively high pressure air below the wing tends to escape to the top of the wing. The air does not escape around the leading or trailing edge of the wing due to airspeed, but it can flow around the tip. Consequently, air flows from below the wing and out around the tip to the top of the wing in a circular fashion. This leakage will raise the pressure on top of the wing and lower the overall lift that the wing can produce. It also produces an emergent flow pattern with low pressure in the center surrounded by fast moving air with curved streamlines.

Wingtip vortices only affect the portion of the wing closest to the end. Thus, the longer a wing is, the smaller the affected fraction of it will be. As well, the shorter the chord of the wing, the less opportunity air will have to form vortices. This means that for an aircraft to be most efficient, it should have a very high aspect ratio. This is evident in the design of long-range airliners and gliders, where fuel efficiency is of critical importance. However, increasing the wingspan reduces the maneuverability of the aircraft, which is why combat and aerobatic planes usually feature short, stubby wings despite the efficiency losses.

Another method of reducing fuel consumption is use of winglets, as seen on a number of modern airliners such as the Airbus A340.

Swept Wing

A swept-wing is a wing planform common on high-speed aircraft. A swept-wing is typically swept back, instead of being set at right angles to the fuselage. Forward sweep is also used on some aircraft. They were initially used only on fighter aircraft, but have since become almost universal on jets, including airliners and business jets.

This applies to the wing as well, which suggests that wings should have very low aspect ratios, long chord, and be very thin. Examples of this sort of wing can be found on the F-104 Starfighter for instance, which is highly optimized for high-speed performance. However, these same characteristics make a wing have much higher drag at low speeds, and generally have poor performance. The Starfighter is somewhat infamous as a "widowmaker" due to the large number of landing accidents caused by its very fast landing speeds.

Swept wings essentially "fool" the airflow at high speeds into thinking the wing has a longer and flatter profile than it has as measured "head on" to the wing. At high speeds, airflow over the wing travels almost directly front to back, so a wing swept at 45 degrees would see an effective chord 1.4 times the actual chord. This reduces the effects of wave drag, making transonic flight much more economical.

What Is Mach Number?

Mach number, a useful quantity in aerodynamics, is the ratio of air speed to the local speed of sound. At altitude, for reasons explained, Mach number is a function of temperature. Aircraft flight instruments, however, operate using pressure differential to compute Mach number, not temperature. The assumption is that a particular pressure represents a particular altitude and, therefore, a standard temperature. Aircraft flight instruments need to operate this way because the stagnation pressure sensed by a Pitot tube is dependent on altitude as well as speed.
                                     
The speed of sound in an ideal gas is independent of frequency, but does vary slightly with frequency in a real gas. It is proportional to the square root of the absolute temperature, but is independent of pressure or density for a given ideal gas. Sound speed in air varies slightly with pressure only because air is not quite an ideal gas. Although (in the case of gases only) the speed of sound is expressed in terms of a ratio of both density and pressure, these quantities cancel in ideal gases at any given temperature, composition, and heat capacity. This leads to a velocity formula for ideal gases which includes only the latter independent variables.

Hypersonic speed

In aerodynamics, a hypersonic speed is one that is highly supersonic (even though the origin of the words is the same: "super" is the Latin cognate of the Greek "hyper"). Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above.

The precise Mach number at which a craft can be said to be flying at hypersonic speed varies, since individual physical changes in the airflow (like molecular dissociation and ionization) occur at different speeds; these effects collectively become important around Mach 5. The hypersonic regime is often alternatively defined as speeds where ramjets do not produce net thrust.Although "subsonic" and "supersonic" usually refer to speeds below and above the local speed of sound respectively, aerodynamicists often use these terms to refer to particular ranges of Mach values. This occurs because a "transonic regime" exists around M=1 where approximations of the Navier-Stokes equations used for subsonic design no longer apply, partly because the flow locally exceeds M=1 even when the freestream Mach number is below this value.

The "supersonic regime" usually refers to the set of Mach numbers for which linearised theory may be used; for example, where the (air) flow is not chemically reacting and where heat-transfer between air and vehicle may be reasonably neglected in calculations.

Generally, NASA defines "high" hypersonic as any Mach number from 10 to 25, and re-entry speeds as anything greater than Mach 25. Among the aircraft operating in this regime are the Space Shuttle and (theoretically) various developing space planes.

                                                       

A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion. The crack of a supersonicbullet passing overhead is an example of a sonic boom in miniature.When an aircraft passes through the air it creates a series of pressure waves in front of it and behind it, similar to the bow and stern waves created by a boat. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of the way of each other. Eventually they merge into a single shock wave, which travels at the speed of sound, a critical speed known as Mach 1, and is approximately 1,225 km/h (761 mph) at sea level and 20 °C (68 °F).

In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail. Because the different radial directions around the aircraft's direction of travel are equivalent (given the "smooth flight" condition), the shock wave forms a Mach cone, similar to a vapor cone, with the aircraft at its tip. The half-angle between direction of flight and the shock wave  is given by:

,

where  is the plane's Mach number. Thus the faster the plane travels, the finer and more pointed the cone is.

There is a rise in pressure at the nose, decreasing steadily to a negative pressure at the tail, followed by a sudden return to normal pressure after the object passes. This "overpressure profile" is known as an N-wave because of its shape. The "boom" is experienced when there is a sudden change in pressure, therefore an N-wave causes two booms - one when the initial pressure rise from the nose hits, and another when the tail passes and the pressure suddenly returns to normal. This leads to a distinctive "double boom" from a supersonic aircraft. When maneuvering, the pressure distribution changes into different forms, with a characteristic U-wave shape.

Since the boom is being generated continually as long as the aircraft is supersonic, it fills out a narrow path on the ground following the aircraft's flight path, a bit like an unrolling a red carpet, and hence known as the boom carpet. Its width depends on the altitude of the aircraft. The distance from the point on the ground where the boom is heard to the aircraft depends on its altitude and the angle .

                                                  

Scramjet

A scramjet (supersonic combusting ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to forcefully compress the incoming air before combustion (hence ramjet), but a ramjet decelerates the air to subsonic velocities before combustion, while airflow in a scramjet is supersonic throughout the entire engine. This allows the scramjet to operate efficiently at extremely high speeds: theoretical projections place the top speed of a scramjet between Mach 12 (8,400 mph; 14,000 km/h) and Mach 24 (16,000 mph; 25,000 km/h).^{[not verified in body]}

The scramjet is composed of three basic components: a converging inlet, where incoming air is compressed; a combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat; and a diverging nozzle, where the heated air is accelerated to produce thrust. Unlike a typical jet engine, such as a turbojet or turbofan engine, a scramjet does not use rotating, fan-like components to compress the air; rather, the achievable speed of the aircraft moving through the atmosphere causes the air to compress within the inlet. As such, no moving parts are needed in a scramjet. In comparison, typical turbojet engines require inlet fans, multiple stages of rotating compressor fans, and multiple rotating turbine stages, all of which add weight, complexity, and a greater number of failure points to the engine.

Due to the nature of their design, scramjet operation is limited to near-hypersonic velocities. As they lack mechanical compressors, scramjets require the high kinetic energy of a hypersonic flow to compress the incoming air to operational conditions. Thus, a scramjet-powered vehicle must be accelerated to the required velocity (usually about Mach 4) by some other means of propulsion, such as turbojet, railgun, or rocket engines.^[1] In the flight of the experimental scramjet-powered Boeing X-51A, the test craft was lifted to flight altitude by a Boeing B-52 Stratofortressbefore being released and accelerated by a detachable rocket to near Mach 4.5.^[2] In May 2013, another flight achieved an increased speed of Mach 5.1.^[3]

While scramjets are conceptually simple, actual implementation is limited by extreme technical challenges. Hypersonic flight within the atmosphere generates immense drag, and temperatures found on the aircraft and within the engine can be much greater than that of the surrounding air. Maintaining combustion in the supersonic flow presents additional challenges, as the fuel must be injected, mixed, ignited, and burned within milliseconds. While scramjet technology has been under development since the 1950s, only very recently have scramjets successfully achieved powered flight

                                          

Scramjets are designed to operate in the hypersonic flight engine, beyond the reach of turbojet engines, and, along with ramjets, fill the gap between the high efficiency of turbojets and the high speed of rocket engines. Turbomachinery-based engines, while highly efficient at subsonic speeds, become increasingly inefficient at transonic speeds, as the compressor fans found in turbojet engines require subsonic speeds to operate. While the flow from transonic to low supersonic speeds can be decelerated to these conditions, doing so at supersonic speeds results in a tremendous increase in temperature and a loss in the total pressure of the flow.

Missle

 A missile, or guided missile, is a self-propelled guided weapon system, as opposed to an unguided self-propelled munition, referred to as just a rocket. Missiles have four system components: targeting and/or guidance, flight system, engine, and warhead. Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles(ballistic, cruise, anti-ship, anti-tank, etc.), surface-to-air missiles (anti-aircraft and anti-ballistic), air-to-air missiles, and anti-satellite missiles. All known existing missiles are designed to be propelled during powered flight by chemical reactions inside a rocket engine, jet engine, or other type of engine.^{[citation needed]} Non-self-propelled airborne explosive devices are generally referred to asshells and usually have a shorter range than missiles.

An ordinary English-language usage predating guided weapons, a missile is "any thrown object", such as objects thrown at players by rowdy spectators at a sporting event.

• A powered, guided munition that travels through the air or space is known as a missile (or guided missile.)
• A powered, unguided munition is known as a rocket.
• Unpowered munitions not fired from a gun are called bombs whether guided or not; unpowered, guided munitions are known as guided bombs or "smart bombs".
• Munitions that are fired from a gun are known as projectiles whether guided or not. If explosive they are known more specifically as shells or mortar bombs.
• A Powered munitions that travel through water are called torpedoes (an older usage includes fixed torpedoes, which might today be called mines).
• Hand grenades are not usually classed as missile
• Guided missiles have a number of different system components:
  
  • Targeting and/or guidance
  • Flight system
  • Engine
  • Warhead

Rockets

A rocket is a missile, spacecraft, aircraft or other vehicle that obtains thrust from a rocket engine. Rocket engine exhaust is formed entirely from propellants carried within the rocket before use.^[1] Rocket engines work by action and reaction. Rocket engines push rockets forward by expelling their exhaust in the opposite direction at high speed. Rockets rely on momentum, airfoils, auxiliary reaction engines, gimballed thrust, momentum wheels, deflection of the exhaust stream, propellant flow, spin, and/or gravity to help control flight.

Rockets are relatively lightweight and powerful, capable of generating large accelerations and of attaining extremely high speeds with reasonable efficiency. Rockets are not reliant on the atmosphere and work very well in space.

Rockets for military and recreational uses date back to at least 13th century China.^[2] Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology for the Space Age, includingsetting foot on the moon. Rockets are now used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites,human spaceflight, and space exploration.

Chemical rockets are the most common type of high power rocket, typically creating a high speed exhaust by the combustion of fuel with an oxidizer. The stored propellant can be a simple pressurized gas or a single liquid that disassociates in the presence of a catalyst (monopropellants), two liquids that spontaneously react on contact (hypergolic propellants), two liquids that must be ignited to react, a solid combination of one or more fuels with one or more oxidizers (solid fuel), or solid fuel with liquid oxidant (hybrid propellant system). Chemical rockets store a large amount of energy in an easily released form, and can be very dangerous. 

                                                  

Flight dynamics

Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation around three axes about the vehicle's center of mass, known as pitch, roll, and yaw (quite different from their use as Tait-Bryan angles).

• Roll is a rotation about the longitudinal axis (equivalent to the rolling or heeling of a ship) giving an up-down movement of the wing tips measured by the roll or bank angle.

• Pitch is a rotation about the sideways horizontal axis giving an up-down movement of the aircraft nose measured by the angle of attack.

• Yaw is a rotation about the vertical axis giving a side-to-side movement of the nose known as sideslip.

Flight dynamics is concerned with the stability and control of an aircraft's rotation about each of these axes.

                                        

Jet aircraft

Jet aircraft use airbreathing jet engines, which take in air, burn fuel with it in a combustion chamber, and accelerate the exhaust rearwards to provide thrust.

Turbojet and turbofan engines use a spinning turbine to drive one or more fans, which provide additional thrust. An afterburnermay be used to inject extra fuel into the hot exhaust, especially on military "fast jets". Use of a turbine is not absolutely necessary: other designs include the pulse jet and ramjet. These mechanically simple designs cannot work when stationary, so the aircraft must be launched to flying speed by some other method. Other variants have also been used, including the motorjet and hybrids such as the Pratt & Whitney J58, which can convert between turbojet and ramjet operation.

Compared to propellers, jet engines can provide much higher thrust, higher speeds and, above about 40,000 ft (12,000 m), greater efficiency.^[3] They are also much more fuel-efficient than rockets. As a consequence nearly all large, high-speed or high-altitude aircraft use jet engines.

                                               

Propeller aircraft

Propeller aircraft use one or more propellers (airscrews) to create thrust in a forward direction. The propeller is usually mounted in front of the power source in tractor configuration but can be mounted behind in pusher configuration. Variations of propeller layout include contra-rotating propellers and ducted fans.

Many kinds of power plant have been used to drive propellers. Early airships used man power or steam engines. The more practical internal combustion piston engine was used for virtually all fixed-wing aircraft until World War II and is still used in many smaller aircraft. Some types use turbine engines to drive a propeller in the form of a turboprop or propfan. Human-powered flighthas been achieved, but has not become a practical means of transport. Unmanned aircraft and models have also used power sources such as electric motors and rubber bands.

Rotorcraft

Rotorcraft, or rotary-wing aircraft, use a spinning rotor with aerofoil section blades (a rotary wing) to provide lift. Types includehelicopters, autogyros, and various hybrids such as gyrodynes and compound rotorcraft.

Helicopters have a rotor turned by an engine-driven shaft. The rotor pushes air downward to create lift. By tilting the rotor forward, the downward flow is tilted backward, producing thrust for forward flight. Some helicopters have more than one rotor and a few have rotors turned by gas jets at the tips.

Autogyros have unpowered rotors, with a separate power plant to provide thrust. The rotor is tilted backward. As the autogyro moves forward, air blows upward across the rotor, making it spin. This spinning increases the speed of airflow over the rotor, to provide lift. Rotor kites are unpowered autogyros, which are towed to give them forward speed or tethered to a static anchor in high-wind for kited flight.

Cyclogyros rotate their wings about a horizontal axis.

Compound rotorcraft have wings that provide some or all of the lift in forward flight. They are nowadays classified as powered lifttypes and not as rotorcraft. Tiltrotor aircraft (such as the V-22 Osprey), tiltwing, tailsitter, and coleopter aircraft have their rotors/propellers horizontal for vertical flight and vertical for forward flight.