Unpowered flight

Unpowered flight is the ability to stay airborne for a period of time without using any power source.

Many creatures capable of sustained wing-powered flight also soar unpowered for much of the time they are airborne.

A balloon is a bag filled with a gas with a lower density than the surrounding air to provide buoyancy.

The pilot can control the altitude of a free-flying balloon, either by heating the gas or by releasing ballast weight.

A sufficiently light object can make use of updrafts and drift on the wind in this way for long periods of time.

Many mould and bacterial spores, even live bacteria, are small enough to drift for long distances and to great heights on the wind.

The high ratio of surface area to weight reduces the rate of descent of the parachute, allowing it to stay airborne for longer periods.

Although mostly done by small spiderlings, adults weighing over 100 mg and with a body size of up to 14 mm have been observed casting parachutes a meter across into a strong updraft.

In this way a gliding object can gain additional potential energy from sources such as thermals and ridge lift.

Soaring is where the object/animal obtains additional energy from rising air without exerting any power to remain airborne.

An example is the albatross, which is a large seabird renowned for its ability to stay aloft by soaring above the waves for days at a time.