Ceiling fan be used to reduce the stratification of warm air in a room by forcing it down to affect both occupants' sensations and thermostat readings, thereby improving climate control energy efficiency. Punkah-type ceiling fans date back to 500 BC, and are native to India. Unlike modern rotary fans, these punkah fans move air by moving to and fro, and were operated manually by cord. The first rotary ceiling fans appeared in the early 1860s and 1870s in the United States. At that time, they were not powered by any form of electric motor. Instead, a stream of running water was used,
Blown flap up room on the outside of the wing, which makes them unsuitable for use on a fighter. The principle of the jet flap, a type of internally blown flap, was proposed and patented in 1952 by the British National Gas Turbine Establishment (NGTE) and thereafter investigated by the NGTE and the Royal Aircraft Establishment. The concept was first tested at full-scale on the experimental Hunting H.126. It reduced the stall speed to only , a number most light aircraft cannot match. The jet flap used a large percentage of the engine exhaust, rather than compressor bleed air, for blowing. One