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De Lackner HZ-1 Aerocycle

During the 1950s and 1960s the United States Army spent considerable energy developing one- and two-man flying machines to carry its soldiers into battle. These vehicles were intended to offer a powerful advantage in scouting and observation, and to give infantrymen unprecedented freedom of movement on the battlefield. Ultimately the US Army hoped to give the common foot soldier a set of wings.

The US National Advisory Committee on Aeronautics (NACA) began to conduct feasibility research on such technology in the early 1950s. After some encouraging results in the laboratory using compressed air, several companies went on to build experimental vehicles. This brief fad of military aviation gave rise to a number of unique contraptions, including such unlikely inventions as backpack helicopters, hovering platforms, and flying jeeps.

The research was first spawned by NACA engineer Charles H. Zimmerman, who determined that a helicopter-style vehicle would be significantly more stable if the rotors were mounted on the bottom rather than on top. Furthermore, he suggested that a human’s innate balancing mechanisms could be used to keep such a machine upright. He referred this as “kinesthetic control,” a set of reflexes similar to those which allow humans to ride bicycles and surfboards.

Among the first flying platforms was the HZ-1 Aerocycle from De Lackner. It used a forty horsepower outboard motor to turn two counter-rotating helicopter blades. The two opposing rotors cancelled one another’s torque, allowing the mounted platform to maintain orientation rather than spinning. Secured by safety belts, the soldier-pilot stood on a platform just above the churning blades, using motorcycle-like handlebars to turn the vehicle and to change altitude. Directional control was achieved by leaning in the desired direction of travel, with a maximum velocity of 65-70mph.

Hiller VZ-1 Pawnee

Captain Selmer Sundby, an experienced pilot with over 1,500 hours of flying experience, was the test operator for the Aerocycle. He made many flights, with times varying from a few seconds to over forty minutes. The HZ-1 was designed to be used by soldiers after twenty minutes of instruction. Captain Sundby said, “. . . it only took me one flight to realize that a non-flyer would have considerable difficulty operating it.” Twice during testing the contra-rotating blades flexed and collided, causing the apparatus to fall out of the sky. Sundby was lucky to survive both incidents, one of them from forty feet in the air. The project was cancelled after the second accident, and Sundby was awarded the Distinguished Flying Cross for his efforts.

A similar prototype was the VZ-1 Pawnee developed by Hiller Aviation. As with the Aerocycle it was hoped that soldiers could operate the Pawnee with only an hour or two of instruction. Using two 44 horsepower engines, the platform was lifted by two counter-rotating five-foot-wide rotors in a round enclosure, a configuration known as a ducted fan.

In horizontal flight, the VZ-1 demonstrated an automatic self-righting tendency. This occurred because the leading edge lip of the duct generated more lift than the trailing edge, causing an upward pitch. This force worked to balance the pilot’s weight as he shifted the platform in the direction he wanted to fly. Consequently, the platform was almost impossible to topple.

The Army saw some promise in the design, and two larger prototypes were built which also worked quite well, but ultimately the project was abandoned as too impractical. The idea that a soldier could use the Pawnee to snipe at the enemy turned out to be a fantasy, as it was very noisy and made the soldier a highly vulnerable target. Another shortcoming was that the Pawnee had a top speed of only 16 mph.

A few companies applied the hovering concept to larger vehicles. The best attempt at making a flying jeep was the VZ-8 Airgeep built by Piasecki. The VZ-8 was built around two ducted fans driven by a pair of 180 horsepower engines. Both power plants were connected to a single central gearbox so that both rotors would continue to turn even if one engine failed. Controls for the Airgeep were very much like conventional helicopter controls.

Piasecki VZ-8 Airgeep

Although the Airgeep was intended to operate within a few feet of the ground it was also capable of flying at altitudes of several thousand feet. The Airgeep was a very stable weapons platform and could hover or fly around most any obstacle. A larger, more powerful version called the Airgeep II was developed in 1962, and it proved even more capable. Further evaluation of the concept, however, led the Army to conclude that the design lacked the ruggedness and flexibility of conventional helicopters, and that its maintenance demands were too high. The Airgeep was abandoned in the early 1960s.

At around the same time, Bell Aerosystems was developing a series of rocket and jet packs for military use. The army lost interest when it found that maximum practical flight time was less than thirty seconds, but the small kerosene jets used in these jet packs were later employed in other configurations. This engine would become the basis for Williams Research Corporation’s WASP (Williams Aerial Survey Platform). Test pilots would come to give it the nickname “Flying Pulpit”.

The WASP, later named the X-Jet, was the result of fifteen years of development. It looked a bit like a flying garbage can, with the pilot standing on the fuel tank and a 600-pound turbofan engine mounted in front of him. Performance of the WASP was impressive, with a speed of 60 mph and a service ceiling of 10,000 feet. Maximum flight time was just over 30 minutes. The craft was listed in Jane’s All the World’s Aircraft as late as the 1985 edition but once again the army, which had financed its development, lost interest. Today the Williams Corporation makes compact jet engines for cruise missiles and jets.

Williams WASP

The United States Army also tested a series of one-soldier assault helicopters, including a device named the Hiller Rotorcycle which could collapse into the volume of a large trunk. Several attempts were also made to develop backpack helicopters, but the idea never got off the ground because the machines were much too large and heavy to be practical. Moreover, the constant vibrations during short test flights left operators extremely disoriented and unable to properly control the craft.

By the 1970s the US military largely abandoned such flights of fancy. Although a one- or two-man light aircraft was an intriguing concept, all of the vehicles shared common weaknesses in regards to maintenance, noise level, vulnerability, and the lack of practical applications. There were also very valid concerns about the stability of the small aircraft in windy conditions. Examples of these unique military aircraft can currently be found at aviation museums all over the country.