Flight
Flight or flying is the motion of an object through an atmosphere, or through the vacuum of outer space, without contacting any planetary surface.
This can be achieved by generating aerodynamic lift associated with gliding or propulsive thrust, aerostatically using buoyancy, or by ballistic movement.
Humans have managed to construct lighter-than-air vehicles that raise off the ground and fly, due to their buoyancy in the air.
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.
"Flying" snakes also use mobile ribs to flatten their body into an aerodynamic shape, with a back and forth motion much the same as they use on the ground.
Flying fish can glide using enlarged wing-like fins, and have been observed soaring for hundreds of meters.
It is thought that this ability was chosen by natural selection because it was an effective means of escape from underwater predators.
These machines include aircraft such as airplanes, gliders, helicopters, autogyros, airships, balloons, ornithopters as well as spacecraft.
Supersonic flight is associated with the formation of shock waves that form a sonic boom that can be heard from the ground,[10] and is frequently startling.
Some things generate little or no lift and move only or mostly under the action of momentum, gravity, air drag and in some cases thrust.
A spaceflight typically begins with a rocket launch, which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of the Earth.
Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry, and others reach a planetary or lunar surface for landing or impact.
In 2018, researchers at Massachusetts Institute of Technology (MIT) managed to fly an aeroplane with no moving parts, powered by an "ionic wind" also known as electroaerodynamic thrust.
[12][13] Many human cultures have built devices that fly, from the earliest projectiles such as stones and spears,[14][15] the boomerang in Australia, the hot air Kongming lantern, and kites.
A heavier than air craft, known as an aerodyne, includes flighted animals and insects, fixed-wing aircraft and rotorcraft.
The wind resistance caused by the craft moving through the air is called drag and is overcome by propulsive thrust except in the case of gliding.
A fixed-wing aircraft generates forward thrust when air is pushed in the direction opposite to flight.
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.
[Cl = L / (A * .5 * r * V^2)] The lift coefficient is also affected by the compressibility of the air, which is much greater at higher speeds, so velocity V is not a linear function.
A greater angle of attack relative to the forward movement also increases the extent of deflection, and thus generates extra lift.
The buoyancy, in both cases, is equal to the weight of fluid displaced - Archimedes' principle holds for air just as it does for water.
A cubic meter of air at ordinary atmospheric pressure and room temperature has a mass of about 1.2 kilograms, so its weight is about 12 newtons.
If the thrust-to-weight ratio is greater than the local gravity strength (expressed in gs), then flight can occur without any forward motion or any aerodynamic lift being required.
To create thrust so as to be able to gain height, and to push through the air to overcome the drag associated with lift all takes energy.
Different objects and creatures capable of flight vary in the efficiency of their muscles, motors and how well this translates into forward thrust.
All animals and devices capable of sustained flight need relatively high power-to-weight ratios to be able to generate enough lift and/or thrust to achieve take off.
Conventional aircraft accelerate along the ground until sufficient lift is generated for takeoff, and reverse the process for landing.
Navigation is the systems necessary to calculate current position (e.g. compass, GPS, LORAN, star tracker, inertial measurement unit, and altimeter).
In the VFR case, a pilot will largely navigate using dead reckoning combined with visual observations (known as pilotage), with reference to appropriate maps.
