articles - downwash, drag (physics) and Fixed-wing aircraft
Downwash
The term downwash has two nearly unrelated meanings within the field of aerodynamics.
One meaning, used most often by non-engineers, refers to the forcing of air downward during the creation of lift. This usage is most common with regard to helicopters where the effect is most dramatic.
The other meaning, used most often by engineers, refers to the flow of air over the tip of a wing and is a critical component in the creation of wing tip vortices.
Drag (physics)
For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. It therefore acts to oppose the motion of the object, and in a powered vehicle it is overcome by thrust. Types of drag are generally divided into two categories: parasiticdrag and lift-induced drag. Parasitic drag includes form drag, skin friction and interference drga. Lift-induced drag is only relevant when wings or a lifting body are present, and is therefore usually discussed only in the aviation perspective of drag. Beyond these two kinds of drag there is a third kind of drag, called wave drag, that occurs when the solid object is moving through the fluid at or near the speed of sound in that fluid. The overall drag of an object is characterized by a dimensionless number called the drag coefficient, and is calculated using the drag equation.
Fixed-wing aircraft
Fixed-wing aircraft is a term used to refer to monoplanes, biplanes and triplanes, in fact all conventional aircraft that are neither balloons, airships, autogyros, helicopters or tilt rotors. The term embraces a minority of aircraft that have folding wings, intended to fold when on the ground, perhaps to ease stowage or facilitate transport on, for example, a vehicle trailer or the powered lift connecting the hangar deck of an aircraft carrier to its flight deck. It also embraces an even smaller number of aircraft, such as the General Dynamics F-111 Aardvark and the Panavia Tornado that can fold their wings during flight. In the early days of their development, these were termed "variable geometry" aircraft. When the wings of these aircraft are fully swept, usually for high speed cruise, the trailing edges of their wings abut the leading edges of their tail planes, giving an impression of a single delta wing if viewed from above or below.
Sir George Cayley, the inventor of the science of aerodynamics, was building and flying models of fixed wing aircraft as early as 1803, and he built a successful passenger-carrying glider in 1853, but it is known the first practical self-powered airplanes were designed and constructed by the Wright brothers. (Indeed, the German Karl Jatho had already constructed such 4 months earlier and made his first flight 1903 August 28 in Hanover.) Their first successful test flights were in 1903 December 17, and by 1904 the Flyer III was capable of fully-controllable stable flight for substantial periods. Strictly, its wings were not completely fixed, as it depended for stability on a flexing mechanism named wing warping. This was soon superseded by the competitive development of ailerons, attached to an otherwise rigid wing.