* Presented by: S.H.Hoseini When aircraft enters the transonic speeds just below the speed of sound, an effect known as wave drag starts. * Near the speed of sound oblique shock wave is generated. * Shock waves require energy to form. * The energy reduces airplanes power. * * Anglo-Irish engineer John William Dunne was experimenting along similar lines, obsessed with achieving innate stability in flight. He was able to successfully employ severely swept wings in his tailless aircraft as a means of creating positive longitudinal static stability.[2] For a low- speed aircraft, swept wings are useful to avoid problems with the * 1-center of gravity, to move the wing spar into a more convenient location, * 2- to improve the sideways view from the pilot's position * * * One of the simplest and best explanations of how the swept wing works was offered by Robert T. Jones: "Suppose a cylindrical wing (constant chord, incidence, etc.) is placed in an airstream at an angle of yaw - ie., it is swept back. Now, even if the local speed of the air on the upper surface of the wing becomes supersonic, a shock wave cannot form there because it would have to be a sweptback shock - swept at the same angle as the wing - ie., it would be an oblique shock. Such an oblique shock cannot form until the velocity component normal to it becomes supersonic." * Mcrit : ‘Mcrit’ in aerodynamics, is in fact the ‘critical Mach Number’ of an aircraft. It is the lowest Mach number at which the airflow over some point on the aircraft reaches the speed of sound. A Mach number of 1.0 indicates an airspeed equals to the speed of sound in the air The drag divergence Mach number (not to be confused with critical Mach number) is the Mach number at which the aerodynamic drag on an airfoil or airframe begins to increase rapidly as the Mach number continues to increase.[1] This increase can cause the drag coefficient to rise to more than ten times its low speed value. * 1. Sweep back 2. Sweep forward 3. Variable sweep * forward sweep * * * Allowing more space in generally cramped corporate jet cabins * Relatively expensive. * Highly maneuverable at transonic speeds * Sweptback wing * Swept wing : A wing planform favoured for transonic and supersonic  Extra lateral stability. flying.  Longitudinally stable on its own. * To reduce the wave drag.  Delay the compressibility * first investigated in Germany effect when flying at from 1935 onwards transonic speed. * Disadvantages * When a swept wing travels at high speed, the airflow has little time to react and simply flows over the wing almost straight from front to back. At lower speeds the air does have time to react, and is pushed spanwise by the angled leading edge, towards the wing tip. At the wing root, by the fuselage, this has little noticeable effect, but as one moves towards the wingtip the airflow is pushed spanwise not only by the leading edge, but the spanwise moving air beside it. At the tip the airflow is moving along the wing instead of over it, a problem known as spanwise flow.