Aviation.

High Speed Flight Subsonic Versus Supersonic Flow In subsonic aerodynamics, the theory of lift is based upon the forces generated on a body and a moving gas (air) in which it is immersed. At speeds of approximately 260 knots or less, air can be considered incompressible in that, at a fixed altitude, its density remains nearly constant while its pressure varies. Under this assumption, air acts the same as water and is classified as a fluid. Subsonic aerodynamic theory also assumes the effects of viscosity (the property of a fluid that tends to prevent motion of one part of the fluid with respect to another) are negligible and classifies air as an ideal fluid conforming to the principles of ideal-fluid aerodynamics such as continuity,  Bernoulli’s principle , and circulation.

Traffic Alert & Collision Avoidance System (TCAS) TCAS, short for Traffic Alert and Collision Avoidance System, is a system equipped on an aircraft that identifies the location and tracks the progress of aircraft equipped with transponders or transmitter-responder device. The goal of TCAS is to prevent mid-air collisions between aircraft operating within the same airspace by warning pilots of transponder-equipped aircraft that may present a collision threat. TCAS operates independently of Air Traffic Control (ATC) by communicating with other transponder-equipped aircraft to build a 3-dimensional map of aircraft in the same airspace. By extrapolating the current range and altitude difference to anticipated future values, TCAS determines the potential of a collision threat. The existence of a collision threat results in subsequent communication of avoidance man oeuvres to flight crew by cockpit display or voice instructions, depending on the TCAS version installed....

How Helicopters Work Ever since Daedalus fashioned wings of feathers and wax for himself and his son Icarus, humans have yearned to master powered, heavier-than-air flight. In the early 20th century, a few daring inventors turned the dream into reality by designing and building flying machines that actually lived up to their names. Everyone knows the story of the Wright brothers and their famed flight across the dunes of Kitty Hawk, N.C., so we won't dwell here on their accomplishments or how airplanes work. Instead, we want to focus on a lesser-known personality -- Igor Sikorsky -- and his vision of the modern  helicopter : an aircraft without wings that achieves vertical flight from the rotation of overhead blades. One thing that has characterized the helicopter since its invention in the 1930s has been the absurdity of the machine. The contraption simply looks unable to deliver on its promise, which is to fly up and down, backward and forward, right and lef...