The main purposes of an airspeed indicator in an aircraft?

Answer 1

The primary purpose of an airspeed indicator in an aircraft is to give the pilot some sense of how fast the aircraft is moving. A pitot tube, which is a forward pointing hollow tube that is mounted on the plane, is pressurized by the force of the air the plane encounters as it flies. This air pressure is compared to a static reference, and the difference is proportional to the airspeed. The faster the plane moves, the higher the pressure in the pitot tube, and the greater the difference between that and the reference. All that will result in higher indicated air speed. There are some issues associated with the accuracy of the system (like when the plane is flying into a headwind), and information on that and more detail in general can be found by using the link to Wikipedia. The pictures are informative, and a reader can pick up a handful of specialized terms relating to the device and the principles upon which it operates.

Answer

The airspeed indicator provides the pilot with an indication of relative airspeed -- or how fast the aircraft is moving relative to the air in which it is flying. This is important to a pilot because it is relative airspeed that affects the performance of the airplane. If airspeed gets too low, the plane will stall; if airspeed gets too high, the plane will suffer structural damage/failure. By monitoring airspeed, and making necessary control adjustments, a pilot ensures that the airplane performs as designed. Fortunately, aircraft are designed -- and pilots are trained -- such that these extreme cases are routinely avoidable.