Unpowered flight

Unpowered flight is flight through an atmosphere or space without using any active propulsion. Unpowered flight can be achieved via numerous mechanisms, including lifting gas (buoyancy), updraft, aerodynamic lift and ballistics, and some of these physical principles have been exploited by nature and by humankind.

In aerospace engineering, the term unpowered flight typically concerns unpowered aircraft, which are aerial vehicles (both lighter-than-air and heavier-than-air) that can stay airborne in a predictable manner without involving any propulsive output. It is also of interest in aviation safety regarding deadstick landing during incidences of fuel starvation and turbine engine failure.

In nature, many organisms, particularly terrestrial animals, are capable of sustained flight by aerodynamic interaction between air currents and appendages with large wetted area typically known as wings or patagia. The ability of flying and gliding animals to stay airborne short or long distances has evolved many times, and active flight is common among winged insects, birds and bats, while unpowered gliding flight and kiting can be seen in insects (e.g. gliding ant), arachnids (some spiders and spider mites), molluscs (e.g. flying squid), fish (e.g. flying fish, freshwater hatchetfish), amphibians (flying frogs), reptiles (flying lizards and flying snakes) and mammals (e.g. flying squirrels, gliders, flying lemurs).