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The Wright brothers made their first successful attempts at flight in a fixed-wing aircraft on December 17, 1903. Since then, mankind has been involved in a steady pursuit of ever-increasing airspeeds. The speed at which any given plane travels is subject to many different variables and can be measured in different ways.

Identification
The "speed" of a plane is actually a complex concept. A plane's air speed is probably the measurement that most closely approximates its "speed," as that word is commonly used. The air speed of a plane is the rate at which it is traveling through the air, not over the ground. The ground speed, then, is the rate at which it is traveling over the ground. While it may seem counterintuitive, these two speeds can differ greatly. A small plane that has an air speed of 100 mph, for instance, may actually be going backwards over the ground while flying into winds that exceed 100 mph. In this article, the term "speed" will be used to describe air speed and will be given in mph (miles per hour).

History
The earliest planes were extremely slow by contemporary standards. They were, in fact, much slower than early automobiles. The first successful flight by the Wright brothers, for example, took place in an airplane that was capable of reaching speeds of about 30 mph. Today, jet planes are able to travel at speeds measured in thousands of miles per hour.

Types
The type of aircraft that is involved in any given flight determines the speed at which that flight takes place. Jet aircraft, for example, fly at much higher speeds than propeller aircraft. A typical single-engine propeller aircraft, for example, might cruise at speeds around 135 mph. A single-engine jet airplane, however, may cruise at speeds around 550 mph. And when top speed is considered, the difference would be even more striking.

Considerations
There are many different variables involved in determining how fast a given plane can fly. The weight, aerodynamics, design and engine characteristics of the airplane are all of extreme importance. For instance, a small fighter jet with two engines may be able to achieve speeds exceeding 1,000 mph, while a jumbo jet with two engines cannot fly nearly as fast. In fact, despite their extraordinarily powerful engines, large passenger jets usually cruise at speeds around 450-550 mph due to relatively poor aerodynamics and their great weight.

Potential
The world record speed for a manned, fixed-wing aircraft reached Mach 9.6 (roughly 7,000 mph) on November 16, 2004, by NASA's X-43A. The X-43A is the latest demonstration of the outer limits of speed that can be achieved by airplanes, but it in no way demonstrates a boundary. The ultimate limit of what can be achieved by planes is, unknown. What is certain, however, is that people will continue striving for ever-faster speeds.

NASA's X-43A