Discovered by British engineer

Christopher Cockerell Sir Christopher Sydney Cockerell CBE RDI FRS (4 June 1910 – 1 June 1999) was an English engineer, best known as the inventor of the hovercraft. Early life and education Cockerell was born in Cambridge, where his father, Sir Sydney Cocker ...

, the momentum curtain is a unique and efficient way to reduce

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

between a vehicle and its surface of travel, be it water or land, by levitating the vehicle above this surface via a cushion of air. It is this principle of levitation upon which a

hovercraft A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious Craft (vehicle), craft capable of travelling over land, water, mud, ice, and other surfaces. Hovercraft use blowers to produce a large volume of air below the hull ...

is based, and Christopher Cockerell set about applying his momentum curtain theory to hovercraft to increase their abilities in overcoming

in travel. Levitating a vehicle above the ground/water to reduce its drag was not a new concept. John Thornycroft, in 1877, discovered that trapping air beneath a ship's hull, or pumping air beneath it with

bellows A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather sides enclosing an approximately airtigh ...

, decreased the effects of friction upon the hull thereby increasing the ship's top attainable speeds.Discovery Channel: Ultimate Hovercraft However, technology at the time was insufficient for Thornycroft's ideas to be developed further. Cockerell used the idea of pumped air under a hull (this then becoming a

plenum Plenum may refer to: * Plenum chamber, a chamber intended to contain air, gas, or liquid at positive pressure * Plenism, or ''Horror vacui'' (physics) the concept that "nature abhors a vacuum" * Plenum (meeting), a meeting of a deliberative assem ...

, i.e. the opposite of a

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...

) and improved upon it further. Simply pumping air between a hull and the ground wasted a lot of energy in terms of leakage of air around the edges of the hull. Cockerell discovered that by means of generating a wall (curtain) of high-speed downward-directed air around the edges of a hull, that less air leaked out from the sides (due to the momentum of the high-speed air molecules), and thus a greater pressure could be attained beneath the hull. So, with the same input power, a greater amount of lift could be developed, and the hull could be lifted higher above the surface, reducing friction and increasing clearance. This theory was tried, tested and developed throughout the 1950s and 1960s until it was finally realised in full-scale in the

SR-N1 The Saunders-Roe SR.N1 (Saunders-Roe Nautical 1) was the first practical hovercraft. The concept has its origins in the work of British engineer and inventor Christopher Cockerell, who succeeded in convincing figures within the services and in ...

hovercraft.

References

Classical mechanics