Bill Bennett's Phoenix series of hang gliders is part of the second generation of late twentieth century hang glider designs. Bennett founded Delta Wing Kites and Gliders in 1969. He played a key role in making hang gliding popular in the United States when he developed Rogallo wing ski kites such as the Model 162 (see NASM collection) into gliders that pilots could launch on foot from the ground. Bennett continuously refined his designs to make them safer and to improve their performance. His work helped to grow the sport during the 1970s.
Australian John Dickenson gets too little credit for his monumental breakthrough to invent the technology that allowed pilots to precisely control a hang glider. Early in 1963, the Grafton Water Ski Club in New South Wales, Australia, asked Dickenson to build a kite for an upcoming water ski festival. Dickenson studied the classic flat pentagonal-shaped ski kite and noted its dangerous lack of control and stability. After exploring several ideas, he probably saw drawings of NASA’s Rogallo wings published widely in the popular press. NASA had found no reliable way to deploy the Rogallo wing from a spacecraft, but the wing’s simplicity, low cost, and flight stability may have encouraged Dickenson to choose it for his new ski kite. He made and tested models of a Rogallo-type wing and they showed improved stability, but control was little better than the classic ski kite.
Since Lilienthal’s first flights in 1891, pilots had clung to their hang gliders framework and tried to influence the direction of flight by swinging their legs and body to shift their weight in the direction they wanted to go. The pilots were positioned at the center of the wing and their range of movement was limited by the airframe enclosing them. Control was feeble at best.
While swinging his daughter sideways on a swing set in 1963, Dickenson had the flash of insight that gave pilots precise control and transformed the hang glider. Dickenson’s idea was brilliant and simple, and added little weight. It consisted of a control bar and a seat or harness suspended from the keel tube by a strap. He bolted the control bar directly to the overhead keel tube of the glider and just behind the control bar, and braced it with wires attached to the wing tips. From the hanging strap, he suspended the pilot’s seat. The strap supported the pilot like a pendulum and allowed him or her to shift their weight with ease, pushing and pulling the control bar to make the glider climb, dive, or turn.
Dickenson tested the controls on a half-size flexible Rogallo-type wing too small to fly. The tests were promising so Dickenson built a kite large enough to lift a person. On September 8, 1963, as John Dickenson looked on, a ski boat towed his friend Rod Fuller aloft for the first flight of a Rogallo-type wing ski kite with the improved Dickenson control system. By 1966, Dickenson was selling his adaptation of the Rogallo-type wing ski kite fitted with his new control system, and in 1967, he introduced fellow Australian Bill Bennett to the booming sport of flying ski-kites. Bennett quickly set altitude records in hang gliders equipped with Dickenson's control system. By 1969, Bennett had moved to California to sell commercial models under the Delta Wing Kites and Gliders brand name. The excitement of flying and the ease of access to flight provided by the Rogallo-type wing with Dickenson control appealed to the freewheeling sport leisure culture of the late 1960s, and across America, Bennett's kites grew in popularity.
In 1973 and 1974, Bennett and his designers experimented with variations on the standard Rogallo wing, and then used what they learned to design a new line of hang gliders called the Phoenix series. Bennett increased the leading-edge convergence angle from 80 to more than 95 degrees. This change reduced the sweep angle of the wing and increased the span. This reduced the wing surface area but increased the aspect ratio (wingspan to wing chord). Bennett also added a longer keel tube called a fantail, a feature thought to improve stability. As Bennett continued to develop the Phoenix gliders, he increased the leading-edge convergence angle even further and removed the fantail after flight experience showed that it did not increase stability.
By January 1975, Bennett and chief designer Richard Boone had completed the Phoenix IV. This variant used more rounded wing tips to improve the glider’s stability, but the modification made the glider more difficult to turn and reduced stability in turbulent air. Bennett and Boone solved this problem when they introduced the Phoenix VI. They made pockets in the sail to hold metal tubes called battens. The battens curved up slightly at the wing trailing edge to progressively reduce the wing angle of attack at the wing tips. This design feature reduced stall speed and helped prevent one wing tip from stalling before the other, a condition that could result in loss of control. Batten tips also kept the center of lift point closer to the center of gravity, improving overall control of the glider.
The Phoenix VI on display is equipped with 'deflexor' cables mounted on the wing leading edges to stiffen and carefully curve the wing for better flying performance and increased stability. During assembly at the factory, technicians adjusted the tension on these wires to rig and tune the glider to fly with a tendency to pitch up in high-speed flight. This built-in auto-recovery mode was aimed at helping pilots recover safely from high-speed dives.
The docile handling characteristics and good stability of the Phoenix VI made it a popular trainer at hang glider flying schools. More experienced pilots also favored this model’s higher speeds and improved handling in rough air. The glider flew better in ridge lift and in thermals than earlier standard Rogallo designs.
Towing ski kites behind powerboats was initially the most common launch method. The strong airframe of the Phoenix VI met the rigors of flight behind a powerboat and only a few modifications were required for water operations. Changes included floats added to the ends of the stainless-steel control bar and at the aft end of the keel tube, and a towline hookup.
Delta Wing Kites and Gliders ceased producing gliders in 1989. Bill Bennett donated a Phoenix VI and a VI.B Jr., along with four other hang gliders, to the National Air and Space Museum in 1984. The flight history of the Phoenix VI in the Museum’s collection is unknown. NASM staff removed this aircraft in 2012 from display at the Steven F. Udvar-Hazy Center and stored it at the Paul Garber Facility to make space to display another hang glider.