What is an airplane

What is the difference between aircraft and airplane? Aircraft is the more general term, and refers to any heavier-than-air craft that is supported by its own buoyancy or by the action of air on its structures. An airplane is a heavier-than-air craft that is propelled by an engine and uses fixed aerodynamic surfaces (i.e. wings) to generate lift. So, every airplane is an aircraft, but not every aircraft is an airplane! Gliders are aircraft that are not airplanes. The Space Shuttle is definitely an aircraft, but it is not an airplane. It does not carry engines for propulsion. Helicopters are also aircraft that are not airplanes because their aerodynamic surfaces are not fixed - they rotate.

Why are there so many different types of airplanes?

The characteristic that most readily identifies the type, performance and purpose of an airplane is the shape of its wings. There are four basic wing types: straight wings, sweep wings (forward-sweep/sweepback), delta wings and the swing-wing (or variable sweep wing). Each shape allows for premium performance at different altitudes and at different speeds.

Another important discriminator between airplanes is speed. Airplanes fly at subsonic, transonic, supersonic and hypersonic speeds. These speed classifications are called the "regimes" of flight. The suffix -sonic refers to the speed of sound, which is dependent on altitude and atmospheric conditions (nominally 340 meters per second). "Mach" is a term used to specify how many times the speed of sound an aircraft is traveling. Mach 1 is one times the speed of sound. Mach 2 is twice the speed of sound, and so on. Mach numbers less than 1 are speeds less than the speed of sound.

Subsonic refers to all speeds less than Mach 1. Transonic refers to all speeds from approximately Mach .9 to Mach 1.5 - that is, the speeds at which an aircraft is going through the speed of sound or "breaking the sound barrier". Supersonic refers to all speeds greater than the speed of sound, which is the same as saying all speeds above Mach 1. Hypersonic refers to all speeds greater than Mach 5. Note that an aircraft flying at hypersonic speeds can also be said to be flying at supersonic speeds.

Every modern aircraft that is built today is built for a specific purpose. Airplanes are designed for different altitudes, different speeds, different weight-carrying capacities, and different performance. Jet fighters are relatively lightweight, highly maneuverable and very fast.

They are designed to carry a relatively small amount of weight, including fuel, which necessitates refueling on long flights. Passenger airplanes are larger, carry more weight, and can fly longer distances. However, they are less maneuverable and slower than jet fighters. Other aircraft like the SR-71, are designed to fly at very high altitudes and high speeds for very long periods of time. Every aircraft fills a particular niche in the gigantic matrix that is modern aviation.

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