Delta Wing Phoenix Mariah M-9

Early in 1977, Bennett asked his chief designer, Richard Boone, to develop for experienced pilots a new high-performance version of the Phoenix series of hang gliders. They named it the Mariah. The biggest change was to increase aspect ratio (ratio of wingspan to wing chord) as the leading-edge convergence angle grew to 120 degrees. Boone kept the ‘deflexor’ cables – wires supported by short posts along the wing leading edges – seen on previous designs. By applying tension to the wires, the pilot could deflect the wing to improve flying and stall characteristics. The wing was more responsive to pilot control inputs but was not as stable as previous gliders in the Phoenix line. Bennett and Boone believed that competent, experienced pilots could handle the high-performance wing with.

Australian Bill Bennett helped promote hang gliding in the late 1960s and early 1970s. Bennett's first gliders were kites for water skiers, such as the Model 162. He based these designs on a flexible wing that Francis Rogallo evaluated while working for the National Aeronautics and Space Administration (NASA). The space agency wanted to develop a recovery system for Gemini and Apollo capsules (see NASM collection) that allowed astronauts to steer the capsule to a landing as an alternative to unguided parachutes. The difficulties the agency experienced trying to recover the Mercury capsules (see NASM collection), and the near tragedy that followed Gus Grissom's splashdown in July 1961, no doubt encouraged NASA to develop alternative capsule recovery systems that gave astronauts more control over where they landed.

NASA and several aerospace companies experimented with Rogallo wings from 1961 to 1965. NASA built and tested the Parasev (or Paraglider Research Vehicle, see NASM collection) research vehicle from 1962 to 1964. The concept used a Rogallo wing but was eventually discarded in favor of recovering spacecraft with simpler, more reliable and more economical parachutes. Publicity from NASA’s experimental work sparked interest among enthusiasts such as Australian Bill Bennett to evaluate the Rogallo flexible wing.

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 wing with Dickenson control appealed to the freewheeling sport leisure culture of the late 1960s, and across America, Bennett's kites grew in popularity.

By the late 1970s, modified Rogallo wings began to replace the standard Rogallo designs. The new generation of hang gliders allowed pilots to fly farther and faster with better control. The new gliders were even capable of performing loops and wingovers. The Phoenix Mariah represents an interim step in this transition from standard to modified Rogallo wing aircraft.

The fabric covering, or 'sail,' that formed the airfoil on the standard Rogallo limited the glider’s performance because it attached only at the leading edges of the wing and along the central keel tube. This was satisfactory in stable flight when the air flowing beneath the sail kept it taut. In turbulence or slow-speed flight, the sail could sag and 'luff,' lose lift and cause loss of control. This was particularly dangerous when foot-launching the glider from high and rugged terrain. Bennett and other designers worked to reduce the angle of the leading edges and shorten the length of the keel to increase aspect ratio, boosting lift while minimizing drag. Performance increased while maintaining stability and control.

In 1973 and 1974, Bennett and his designers experimented with numerous variations of the standard Rogallo wing. Bennett then incorporated the results into a new line of hang gliders he named the Phoenix series. On these gliders, Bennett increased the leading edge convergence angle from 80 to more than 95 degrees. The first Phoenix hang gliders flew with a long fantail, a device thought to improve stability. Total wing surface area was slightly less than standard Rogallo models, but the aspect ratio (wingspan to wing chord ratio) increased substantially. As Bennett continued to develop the Phoenix series, he increased the leading edge convergence angle even further, and removed the fantail after flight experience showed no increase in stability.

By January 1975, Bennett, and his chief designer, Richard Boone, had completed the Phoenix IV. This variant used truncated wing tips to provide stability to the glider by enhancing the wing's tip vortices. This modification also moved the center of lift point nearer to the wingtips but away from the center of gravity, making the glider more difficult to turn and reducing stability in turbulent air. Bennett and Boone solved this problem when they introduced the Phoenix VI (see NASM collection).

Early in 1977, Bennett asked Boone to design a new high performance Phoenix variant intended for experienced pilots. They named it the Mariah and it introduced several radical features. Aspect ratio increased by lengthening wingspan and reducing wing chord as the leading edge convergence angle grew to 120 degrees. Boone also incorporated wires supported by short posts along the wing leading edges. He and Bennett had first tested these devices, called ‘deflexors,’ on the Phoenix VI.B (see NASM collection). Pilots could adjust the wires to alter wing shape and flying characteristics according to flying conditions. The Mariah wing was more responsive to pilot inputs but not as stable as previous gliders in the Phoenix line.

Bennett and Boone made another significant change when they added a lower fabric sail that covered 45 percent of the top surface area. The wing now had two surfaces and was beginning to resemble the thicker wings of conventional aircraft.

The lower fabric extended from the leading edge back to cover the crossbar tube and reduce drag. No longer was the crossbar tube bolted to the keel tube, but only attached to the wing leading edges, allowing it to 'float' relative to the keel tube. Now the wing could flex and adjust more efficiently to changes in load, speed, and angle of attack. Boone used truncated, or rounded, wing tips which he also drooped to give pilots more control during stalls. By early 1978, the United States Hang Gliding Manufacturers Association had tested and certified the Mariah, and Delta Wing Kites and Gliders began selling them for $1,395. They were available in three sizes, 150, 170, and 190. The number referred to the wing area and heavier pilots flew the larger gliders.

The Mariah was not popular. Pilots thought the handling was stiff. The droop tips appeared to be the culprit and they were dropped from the Mariah line. Other manufactures introduced higher performance gliders similar to the Mariah at about the same time, and when pilots began to fly these advanced designs near the limits of their performance envelopes, a serious problem emerged. Pilots reported that their gliders (including several Mariahs) had tumbled end-over-end under low-G conditions, fortunately with few injuries. This problem limited the popularity and success of the Mariah and similar hang gliders. Designers started to focus on improving longitudinal stability. By the end of 1978, Bennett had ceased marketing the Mariah in favor of new designs with more stable pitch characteristics, however, Mariah pilots did set several records including an altitude gain of 3,109 m (10,200 ft).

The Mariah's stability problems led to a short commercial life but most of the technical innovations introduced on this aircraft continued to influence hang glider design. Bill Bennett donated a Mariah and several other Delta Wing models to the National Air and Space Museum in 1984. The operational flight history of the Mariah on display is unknown.