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A hummingbird in flight
A Barn Swallow in flight




Types of flight[edit]

Buoyant flight[edit]

A blimp flies because the upward force is equal or greater than the force of gravity.


An aerostat is a system that remains aloft primarily through the use of buoyancy to give an aircraft the same overall density as air. Aerostats include free balloons, airships, and moored balloons. An aerostat's main structural component is its envelope, a lightweight skin containing a lifting gas[1][2] to provide buoyancy, to which other components are attached.

Aerostats are so named because they use "aerostatic" lift, a buoyant force that does not require lateral movement through the surrounding air mass. By contrast, aerodynes primarily use aerodynamic lift, which requires the lateral movement of at least some part of the aircraft through the surrounding air mass.

Aerodynamic flight[edit]

Unpowered flight versus powered flight[edit]



Female Mallard Duck
Tau Emerald dragonfly




Most birds fly (see bird flight), with some exceptions. The largest birds, the Ostrich and the Emu, are earthbound, as were the now-extinct Dodos and the Phorusrhacids, which were the dominant predators of South America in the Cenozoic era. The non-flying penguins have wings adapted for use under water and use the same wing movements for swimming that most other birds use for flight.[citation needed] Most small flightless birds are native to small islands, and lead a lifestyle where flight would offer little advantage.

Among living animals that fly, the Wandering Albatross has the greatest wingspan, up to 3.5 meters (11 feet); the Great Bustard has the greatest weight, topping at 21 kilograms (46 pounds).[6]

Many species of insects also fly (See insect flight).


Mechanical flight: A Robinson R22 Beta helicopter



Supersonic flight is flight faster than the speed of sound. Supersonic flight is associated with the formation of shock waves that form a sonic boom that can be heard from the ground,[7] and is frequently startling. This shockwave takes quite a lot of energy to create and this makes supersonic flight generally less efficient than subsonic flight at about 85% of the speed of sound.











Many human cultures have built devices that fly, from the earliest projectiles such as stones and spears,[8][9] the boomerang in Australia, the hot air Kongming lantern, and kites.


George Cayley studied flight scientifically in the first half of the 19th century,[10][11][12] and in the second half of the 19th century Otto Lillienthal made over 200 gliding flights and was also one of the first to understand flight scientifically. His work was replicated and extended by the Wright brothers who made gliding flights and finally the first controlled and extended, manned powered flights.[13]


Spaceflight, particularly human spaceflight became a reality in the 20th Century following theoretical and practical breakthroughs by Konstantin Tsiolkovsky and Robert H. Goddard. The first orbital spaceflight was in 1957[14] and Yuri Gagarin was carried aboard the first manned orbital spaceflight in 1961.[15]





Finally, momentum dominates the flight of ballistic flying objects.


Main forces on a heavier-than-air aircraft

Forces relevant to flight are[16]

These forces must be balanced for stable flight to occur.


In the context of an air flow relative to a flying body, the lift force is the component of the aerodynamic force that is perpendicular to the flow direction.[17] It contrasts with the drag force, which is the parallel component of the aerodynamic force. In all cases, aerodynamic lift is associated with pressures on the wing that sum over the area of the flight surfaces to create the lift force, and there is a net movement of air in the opposite direction from the force which is indirectly created by these pressures, in accordance with Newton's third law of motion.

Lift is commonly associated with the wing of an aircraft, although lift is also generated by rotors on rotorcraft. While common meanings of the word "lift" suggest that lift opposes gravity, aerodynamic lift can be in any direction. When an aircraft is in cruise for example, lift does oppose gravity, but occurs at an angle when climbing, descending or banking.



For a solid object moving through a fluid, the drag is the component of the net aerodynamic or hydrodynamic force acting opposite to the direction of the movement.[18][19][20][21] The component perpendicular to this direction is considered lift. Therefore drag opposes the motion of the object, and in a powered vehicle it is overcome by thrust.




Lift-to-drag ratio[edit]

Speed and drag relationships for a typical flight article

When lift is created by the motion of an object through the air, this deflects the air, and this is the source of lift. For sustained level flight lift must be equal to weight.

However, this lift inevitably causes some drag also, and it turns out that the efficiency of lift creation can be associated with a lift-to-drag ratio for a vehicle; the lift-to-drag ratios are approximately constant over a wide range of speeds.

Lift-to-drag ratios can be determined by flight test, by calculation or by testing in a wind tunnel.[citation needed] Lift-to-drag ratios for practical aircraft vary from about 4:1 up to 60:1 or more. The lower ratios are generally for vehicles and birds with relatively short wings, and the higher ratios are for vehicles with very long wings, such as gliders. In general, long wings permit a large amount of air to be deflected and accelerated by a small amount, rather than a small amount of air by a large amount. Since energy is a square law on deflection speed, whereas lift is a linear relation, it takes less energy, and less lift-induced drag is created, with longer wings.

Thrust to weight ratio[edit]

Thrust-to-weight ratio is, as its name suggests, the ratio of instantaneous thrust to weight (where weight means weight at the Earth’s standard acceleration g_0).[22] It is a dimensionless parameter characteristic of rockets and other jet engines and of vehicles propelled by such engines (typically space launch vehicles and jet aircraft).



Flight dynamics[edit]




Energy efficiency[edit]


Propulsive efficiency determines how much energy vehicles generate from a unit of fuel.[23][24]




Power-to-weight ratio[edit]


Takeoff and landing[edit]

Vehicles that can fly can have different ways to takeoff and land. Conventional aircraft accelerate along the ground until sufficient lift is generated for takeoff, and reverse the process for landing. Some aircraft can takeoff at low speed, this is called a short takeoff. Some aircraft such as helicopters and Harrier jump jets can takeoff and land vertically. Rockets also usually takeoff and land vertically, but some designs can land horizontally.

Guidance, Navigation and Control[edit]











Flight safety[edit]


See also[edit]


  6. ^ "Swan Identification." The Trumpeter Swan Society. Retrieved: January 3, 2012.
  9. ^ "Ancient history." Automata. Retrieved:May 6, 2012.
  10. ^ "Sir George Cayley". Flyingmachines.org. Retrieved 26 July 2009. "Sir George Cayley is one of the most important people in the history of aeronautics. Many consider him the first true scientific aerial investigator and the first person to understand the underlying principles and forces of flight." 
  14. ^ http://history.nasa.gov/sputnik/sputorig.html
  15. ^ "Gagarin anniversary." NASA. Retrieved: May 6, 2012.
  17. ^ "Definition of lift." NASA. Retrieved: May 6, 2012.
  18. ^ French 1970, p. 210.
  20. ^ "What is Drag?" NASA. Retrieved: May 6, 2012.
  21. ^ "Motions of particles through fluids." lorien.ncl.ac. Retrieved: May 6, 2012.
  24. ^ Honicke et al. 1968[page needed]

External links[edit]