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. The most significant change was yet another increase in aspect ratio. Wingspan increased and wing chord fell as the leading edge convergence angle grew to 120 degrees. Boone also incorporated wires supported by short posts along the wing leading edges. 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 it 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 no trouble.
Gift of Bill Bennett
Bill Bennett was a trendsetter in hang glider design throughout the 1970's. He founded Delta Wing Kites and Gliders in 1969 to build and market boat-towed kites, such as the Delta Wing Model 162 (see NASM collection) piloted by water skiers. These kites used a wing design invented by Francis Rogallo. They contributed to the rapid growth of hang gliding around the world because they performed reasonably well, cost little to build, and they were easy to transport. By the late 1970s, Bennett's standard Rogallo designs became obsolete and modified Rogallo wings began to appear. These hang gliders were relatively safe, high-performance aircraft capable of performing loops and wingovers. The Phoenix Mariah represents an interim step in this transition from standard to modified Rogallo wing aircraft.
The most troublesome flaw in the standard Rogallo was the fabric covering, or 'sail,' that formed the airfoil. Designers only attached the sail at the leading edges and along the central keel. In stable flight, air passing beneath the sail generated vortices that kept the sail taut. In turbulence or slow-speed flight, the vortices diminished, loosening the sail and causing it to 'luff.' Without correction, this condition often led to an uncontrollable dive. This was particularly dangerous when foot-launching the glider from high terrain. Bennett and other designers soon discovered that by reducing the angle of the leading edges, and shortening the length of the keel, they could create a safer glider with better stability and higher performance.
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 that it did not increase 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). They incorporated metal tubes called battens into the tips to add rigidity without reducing stability. The battens curved up slightly near the tips, adding washout and reducing the wings Angle of Attack. This reduced stall speed and helped reduce the chance that one wing tip would stall completely, a condition known to result in a flat spin. Batten tips also kept the center of lift point closer to the center of gravity, making the glider easier to control.
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. The most significant change was yet another increase in aspect ratio. Wingspan increased and wing chord fell as the leading edge convergence angle grew to 120 degrees. Boone also incorporated wires supported by short posts along the wing leading edges. 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 it 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 no trouble. They made another revolutionary change to the wing's lower surface when they covered 45 percent of it with Dacron. The wing now had two surfaces and it was beginning to strongly resemble the wing of more conventional powered aircraft. A wing spar nestled between the two surfaces, reducing the drag generated in previous designs by the exposed aluminum cross tube. The spar was not connected directly to the keel but 'floated,' allowing the wing to flex and be more efficient with various changes in load, speed, and angle of attack. Boone returned to truncated wing tips, but avoided the earlier problems by using drooped tips. By early 1978, the Mariah was certified and selling for $1,395. Bennett built the Mariah in three sizes, the 150, 170, and 190. The number refers to the square footage of the upper wing surface. The pilot's weight dictated which version he flew. Heavier pilots used the 190.
Boone's Mariah was not popular. Pilot's disliked the stiff handling characteristics but the droop tips seemed to be the primary culprit, and this feature was dropped in later models. Other manufactures introduced high-performance gliders similar to the Mariah at about the same time. As soon as pilots began to fly these advanced designs near the limits of their performance envelope, a serious problem emerged. Experienced pilots began reporting that their gliders (including several Mariahs) had tumbled end-over-end under low-G conditions, fortunately with few injuries. This problem also limited the popularity and success of the Mariah and similar high-performance hang-gliders. In later models, designers focused more 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 in low-G situations. Before if disappeared from the hang gliding community, 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 for many years. 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 this specific Mariah is unknown.