N99AF, the trigear prototype, won the Best New Design Award at Oshkosh in 1983.
The Model A's fuselage had wood stringers along the fuselage sides and bottom. The fuel tank was behind the instrument panel. It used cable-operated brakes with narrow "wheelbarrow" wheels. The engine mount was welded to the fuselage.
Model B (serial numbers below about 250) Edit
The Model B had a separate engine mount bolted to the fuselage. A radiator was mounted outside on the passenger's side. Aluminum wheels were used. There was one diagonal piece of tubing across the cockpit ceiling.
The Heavy Hauler wing was first offered on late Model Bs. Although the spar tubes were thicker aluminum (.083 inches rather than .063) and the lift struts were heavier (7/8 inch rather than 3/4) the rib spacing was still 18 inches.
Model C (serial numbers about 250 to about 900) Edit
The Model C's fuel tanks moved to the wings. Matco wheels and hydraulic brakes were used, and a castoring Matco tailwheel with 1-1/4 inch tailspring. The radiator was mounted inside the cowling on the passenger's side. Tubing replaced the wood stringers along the fuselage sides, but a wood stringer was still used on the bottom.
The single diagonal piece of tubing across the cockpit ceiling was changed to a stronger triangular structure.
The Heavy Hauler wing rib spacing was changed to 12 inches. The Aerobat wing had the same features as the Heavy Hauler but was 6 feet shorter (24 feet vs 30 ft). The Commuter wing was a short STOL wing.
Model D / Mark IV (serial numbers about 900 to about 1550 with D suffix) Edit
The cowling was redesigned to accomodate two radiators at the front. The cowling was split horizontally, rather than vertically as on earlier models. In order to accomodate different engine choices, the vertical stabilizer was straightened and different engine mounts were built for left or right turning engines or gearboxes.
The tailwheel spring was increased to 1-1/2 inches. All fuselage stringers were now tubing. A luggage compartment was added behind the seats with a door to the outside.
From 1995 only the heavier .083 inch spars were supplied.