Experimental plenum-chamber type; yellow, red, blue naugahyde covered; 1957
Crowley Hydro-Air Vehicle
Sir Christopher Cockerell usually receives credit for inventing the hovercraft, also known as the Air-Cushion Vehicle (ACV) or Ground-Effect Machine (GEM). The scale and success of this Briton's efforts were undoubtedly the primary reason why the ACV developed into a practical mode of transport. Nonetheless, several American inventors, more than a year before the demonstration of Cockerell's machine, worked individually and with their own finances, to develop successful, albeit small, machines that operated effectively over land and water while carrying their operator. One of these amateur engineers, Walter A. Crowley, constructed a simple, yet functional, machine out of readily available materials and created the first American ACV.
The concept of using an air cushion to travel with minimal friction over water and other level surfaces first appeared in the eighteenth century. In 1716, Emmanual Swadenborg, a Swede, sketched out a theoretical design for an ACV. In 1865 Britain, John Scott Russell, expounded on the theory by using air pump to "lubricate" the passage of a ship through water. The technology took a significant step in the 1870s when Sir John Thornycroft, a British engineer, experiment with pumping air into pockets on the bottom of boat hulls to reduce friction. In 1906, a F.W. Schroeder filed a patent in Britain for plenum chamber air cushion boat. A plenum chamber is a large cavity on the underside of the craft into which an air pump increases the air pressure to the point at which it begins to escape around the edges of the vehicles, thus eliminating much of the drag caused by the contact of the vessels structure with the water.
In 1909, one of Thornycroft's descendents demonstrated a punt boat equipped with an air pump and a plenum chamber. This watercraft demonstrated speeds far greater than were possible with a standard punt, but was not amphibious. Between 1927 and 1940, Vladimir Levkov in the Soviet Union made significant strides in ACV research. He tested a number of plenum chamber air cushion watercraft that demonstrated the ability to move at speeds of up to 130 kph (81 mph) and could operate in marshy areas and float over ice. These early designs often foundered in sea conditions that were anything other than calm and could not cross solid terrain except for relatively smooth surfaces. In the mid 1930s, Toivio Kaairo, a Finnish engineer, successfully demonstrated an even more refined plenum chamber ACV. He also flew the first example of another type of ACV, the ram-wing, in which a propeller pushed the vehicle along the snow or ice and specially shaped airfoil intake in the front of the vehicle forced air into a modified plenum chamber. World War 2 delayed further ACV experimentation until the early 1950s.
In 1957, Crowley completed his Hydro-Air Vehicle, originally known as the "Gadget," in his home basement. He used the simplest approach to hovercraft design - the plenum chamber. This configuration employs an engine driven fan or pump to pressurize the chamber. As air escapes around the bottom edge of the chamber, it lifts the vehicle off the ground. Crowley constructed the plenum chamber for his ACV by stitching red, blue, and yellow Naugahyde (vinyl fabric) around a frame of welded electrical piping.
A 12-horsepower McCulloch target drone engine drove a fan that pressurized the plenum chamber, providing up to 88 kilograms per square meter (18 lb/sq ft) of lift, while a 6-horsepower KieKhafer drone engine powered a mast-mounted tractor propeller that sat in front of the single-seat open cockpit. A steering wheel, taken from a Pontiac, swiveled the tractor propeller a full 360 degrees to provide directional control, while twin rudders, controlled with foot pedals provided a means for yaw correction. It was stable enough for the operator to climb out of the craft without upsetting it. A boat-shaped bow allowed the craft to negotiate small waves safely. During tests over open water, the Hydro-Air Vehicle carried two small pontoons strapped to each side to prevent sinking in the event of engine failure. Crowley's initial tests proved promising, but ruined his wife's flower garden. In June 1957, he then tested the vehicle at a nearby golf course in Royal Oak, Michigan, sustaining heights of up to 15 cm (6 in) off the ground and reaching speeds of 56 kph (35 mph).
By 1958, with the Cold War approaching its zenith, there was considerable interest in the potential of ACVs as high-speed landing craft that could reduce the exposure of a landing force to atomic attack. One company eager to enter into the ground floor of the new field was Washington, DC-based Spacetronics, Inc. In the fall of 1958, the company bought the Hydro-Air Vehicle and all rights to its development. It saw the craft as an effective demonstration tool to encourage investment in much larger military or commercial models.
In November 1958, with Crowley at the controls, Spacetronics demonstrated the Hydro-Air Vehicle on the Anacostia River to the Office of Naval Research at the Anacostia Naval Air Station. Despite problems with the lift engine, it successfully demonstrated the potential of ACVs to officials of the Navy, Marine Corps, Army, and Air Force who attended the tests. Spacetronics shipped the craft to the Army's Detroit Ordnance Depot for demonstrations.
Spacetronics did succeed in obtaining a development contract from the Marine Corps, and constructed a cumbersome 9.14 m x 7.32 m (30 ft x 24 ft) ACV, also called the Hydeo-Air, in association with the Aluminum Corporation of America (ALCOA). Demonstrations took place in April 1960 at Daytona Beach, Florida, but its performance was mediocre. The plenum chamber configuration was already obsolescent compared to the peripheral jet approach, already applied to ACVs by Dr. William Bertelsen in the US on his Aeromobile (see NASM collection) and by Christopher Cockerell on the Saunders-Roe SR.N1.
On July 25, 1959, Cockerell and two crewmembers traversed the English Channel in the SR.N1, which the British government financed as a secret research project. This comparatively lavish craft was much larger in scale than Crowley's design and demonstrated far superior performance. Cockerell's design, when combined with air cushion "skirts" patented by C.H. Latimer-Needham, became the basis of the practical ACV. Crowley and his American peers quickly faded into anonymity as Britain became the center of hovercraft development - a position it held for several decades.
Some American inventors tried to claim patent rights to the hovercraft, but Cockerell, with the full weight and resources of the British government behind him, prevailed. During the 1960s, the U.S. military lost much of its initial enthusiasm for the hovercraft and maintained only a passing interest in the technology. Within a few years, the early American efforts faded into distant memory.
Although Cockerell quickly outshone the efforts of Crowley and his peers, their efforts remain as a remarkable testament to the determination of the individual inventor with nothing to go on except an idea. In the United States, the hovercraft remains a largely unrecognized mode of transport, but this unique vehicle type is essential to U.S. Marine Corps amphibious operations by providing the primary means of moving heavy equipment ashore in combat assaults. The National Air and Space Museum acquired the historic Hydro-Air Vehicle in 1960.
Length:4.88 m (16 ft)
Width:2.74 m (9 ft)
Height:1.22 m (4 ft)
Weight:Empty, 249 kg (550 lb)
Gross, 340 kg (750 lb)
Engines:1 x KieKhafer, 2 cylinder, 6 hp; 1 x McCulloch 4318A, 4 cylinder, 12 hp
References and Further Reading:
Crowley Hydro-Air Vehicle curatorial file, Aeronautics Division, National Air and Space Museum