A helicopter utilizes lift provided by a rotor (rotating wing). Gliders and planes use wings to provide lift, but a minimum forward speed is essential to maintain height. A plane is pulled forward by a propeller, or is pushed by the reaction forces of hot expanding gases from one or more jet engines or rocket engines. The increased speeds of modern aircraft to supersonic (speeds in excess of that of sound, approximately 1,225 km/h or 760 mph) and the accompanying shock waves this produces has brought about changes in wing and fuselage designs to improve streamlining. While with hypersonic speeds (in excess of five times the speed of sound or Mach 5), the forces involved again change fundamentally requiring further design changes.
Related category• AERODYNAMICS AND AERONAUTICS
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