George Appelbay designed the Zuni in 1975 to compete in 15-Meter Class sport sailplane competitions. A 15-Meter Class sailplane has wings that span 15 meters (49 ft 3 in) and it is equipped with flaps and wing tanks to carry water ballast. European designs made of fiberglass had ruled competitive soaring since the late 1960s and Applebay believed he could challenge their domination in the 15-Meter category with a sailplane designed and built in the United States.

In 1980 Appelbay announced the improved Zuni II. The designer made numerous refinements to the cockpit, landing gear, and wings. He built a special Zuni II from Kevlar, with assistance from the Dupont Company. Applebay completed this airplane on February 6, 1981, and sold it to J. G. Mercer. William G. Hill carried out the first three test flights for Mercer on the 14th, 15th, and the 22nd. Mercer first flew his glider on March 7 for one hour and 11 minutes. During the flight, Mercer reached a speed of 247 kph (153 mph) and he noted in his log book that the sailplane exhibited no tendency to tuck its nose at this speed. After flying a total of fifty-six hours and twenty minutes, Mercer donated his Zuni II to the National Air and Space Museum in November 1983.

George Appelbay designed this sailplane for pilots who wished to compete in the 15-Meter Class sailplane competitions. Aircraft equipped with flaps and water ballast are allowed but wingspan cannot exceed 15 meters (49 ft 3 in). Soaring pilots worldwide recognize two other classes of competition. The Standard Class resembles the 15-Meter grouping except that flaps are prohibited but the Open Class has no restrictions on wingspan or aerodynamic gadgetry. Fiberglass-reinforced plastic (FRP) sailplanes designed and built in Europe had ruled all three classes of competitive soaring since the late 1960s and Applebay believed he could challenge their domination with a sailplane designed and built in the United States.

Applebay first flew the Zuni prototype in 1976 and four year later, William Gaines, spokesman for Appelbay Sailplanes, announced an improved model called the Zuni II in an article by Billy Hill published in the February 1980 issue of "Soaring" magazine. Many improvements distinguished the new glider from the prototype. Applebay had redesigned the cockpit and relocated the original side-stick pitch and roll control to the center of the floor ahead of the seat. To reduce friction and make the stick easier to move, Appelbay switched to ball-bearing races in the control system and he added a new and more comfortable seat to increase pilot comfort on long flights. He improved the canopy, rudder pedals, and the handle used to activate the flaps.

He increased wing dihedral to 2° for better stability when a pilot circled in thermals and the he repositioned the landing gear to reduce ground forces on the tail wheel. Building the gear doors from Kevlar and other manufacturing tweaks reduced the empty weight. The factory also improved their composite finishing techniques and the Zuni II flew with smoother wing surfaces and straighter wing leading edges.

Applebay built the National Air and Space Museum's Zuni II from Kevlar with assistance from the Dupont Company. He completed the airplane on February 6, 1981, and sold it to Jerrry G. Mercer who arranged for William G. Hill to conduct the first three test flights. Mercer first flew his glider on March 7 for one hour and 11 minutes and he reached a speed of 247 kph (153 mph). He noted in his logbook that the Zuni II exhibited no tendency to tuck its nose at this speed. Mercer regularly flew the sailplane every month until July when the aircraft ground-looped during landing and incurred significant damage. George Applebay made the last entry in Mercer's logbook on August 6, 1981. He noted the following: "...Replaced landing gear, stabilator, repaired rudder, dorsal fin and wing fairing area...following ground loop accident. No weight change. Aircraft is ok for flight." These cryptic log entries give no hint that Mercer earned seven distinct soaring badges during a single flight at the controls of this sailplane over Taos, New Mexico, in 1982. According to George Applebay, he acquired all of his Silver (3) and Gold badges (3) and two Diamond badges. Applebay contends that before Mercer's flight, no one had earned more badges during one sailplane flight. Mercer generously donated this Zuni II to the National Air and Space Museum in November 1983.