Aircraft classified by lift

Aircraft can be categorised into two main categories according to the lifting method used to fly: aerostats and aerodynes.

Aerostats are lighter-than-air aircraft (such as balloons or blimps) (Merriam-Webster Online Dictionary, 20091) that use aerostatic lift. They use large bags to contain gases (such as helium, hydrogen or hot air) which are lighter than the surrounding air outside those bags. As the combined weight of the bag, the gas it containes, and any accessories and people attached to the bag is lighter than the surrounding air, the aircraft lifts (or "floats"). Aerostasts lift up to a height where air is as heavy as the weight of the aircraft. Because aerostasts lift due to an uneven balance between the gas in the bag and the surrounding air, they may use some "powered method" for propulsion or navigation, but not for lifting purposes.
Aerostat Description Videos embedded from Youtube on 18 March 2009
Balloon Balloons are unpowered aircraft consisting of a bag filled with a lighter-than-air gas, such as helium or hydrogen, or, simply, heated air. A typical balloon also has a gondola for carrying passengers.
Airship Airships are lighter-than-air aircraft that are powered for propulsion and steerable for navigation purposes. Dirigibles, dirigible balloons, zeppelins and blimps are all airships.
Aerodynes are heavier-than-air aircraft (such as airplanes, helicopters, or gliders)" (Merriam-Webster Online Dictionary, 20092) that use aerodynamic lift. Because of being heavier than air, aerodynes need a a way of generating lift in order to fly. Properly speaking, aerodynes use aerodynamic lift for flying. But some may also use powered lift before switching to aerodynamic flight. Aerodynamic lift is achieved with the help of wings (be this fixed wings such as those of airplanes or rotary wings such as those of helicopters). Wings are horizontal surfaces that "cut" through the air but are designed in a shape that allows air to circulate at different speeds above and below the wing: the air moving above the wing moves faster and, thus, creates like a "vacuum" that lifts the aircraft. Although a winged aircraft can "fly" (actually, "glide") without any source of power, the typical aerodyne is powered for the purpose of generating lift from stationary as well as for sustaining flight for long times. Powered lift is achieved with the help of engine thrust. Powered lift seems to be restricted to aircraft that use engine thrust for vertical take-off and landing but otherwise transition to or from aerodynamic lift for flying1.
Aerodyne Description Videos embedded from Youtube on 18 March, 2009
Fixed-wing aircraft These aircraft have wings attached to the main body of the aircraft in a relatively fixed position. These wings generate lift because of their design but are otherwise passive accessories2. Because the wings are fixed, lift can only be achieved if the aircraft is moving in a forward direction. Attachments to the wings, such as engines, ailerons and flaps, allow the aircraft to move forward and be steered. The video shows a fixed-winged aircraft (a Boeing 747) lifting off.
Rotorcraft Unlike fixed-wing aircraft, rotorcraft have rotor(s) spinning in the air for generating lift. The rotors are "wings" and, thus, generate lift in a similar fashion than fixed-wings. However, because the rotors spin in a circular motion, the lift is achieved vertically3 Rotorcraft wings are, thus, mobile and active in producing lift4. To compensate the rotor forces and prevent the rotorcraft from spinning around itself horizontally, an opposite horizontal force needs to be applied, normally at the tail of the aircraft. The video shows a helicopter lifting off.
Powered-lift aircraft Also called vertical take-off aircraft, these aircraft are typical fixed-wing aircraft that use engine thrust for taking-off and landing vertically. They push exhaust gas downwards resulting in a upward force. They will use typical fixed-wing aerodynamic flight for other phases of flight. The video shows a Harrier II landing vertically.
Lifting-body aircraft Lifting-body aircraft generate lift from their fuselage rather than from mounted wings. Still, the design of the aircraft uses a lifting method similar to that of fixed-wing aircraft5. The video shows an experimental lifting-body aircraft.
1. MERRIAM-WEBSTER ONLINE DICTIONARY (2009). Aerostat. Retrieved from The Merriam-Webster Online Dictionary on 15 May 2009.
2. MERRIAM-WEBSTER ONLINE DICTIONARY (2009). Aerodyne. Retrieved from The Merriam-Webster Online Dictionary on 15 May 2009.
3. WIKIPEDIA (2009). Aircraft. Retrieved from Wikipedia on 14 March 2009.

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