The C3 was a rugged biplane with simple straight wings, a tough undercarriage with oleo shock absorbers and two open cockpits with the pilot in the rear and two side-by-side passenger seats in the front. In fact, it was a slightly modified version of the earlier model C2 aircraft. Changes included an increased volume oil tank and larger sized baggage compartment.
Introduced in 1928, the C3 was powered by a variety of engines of between 128 hp and 225 hp, each version having its own designation. The last version of the C3 was the C3R which had several external differences including a cutout in the aft portion of the wing center section for improved pilot visibility, a headrest in the aft cockpit, and slightly increased chord of the rudder and vertical stabilizer.
Although there were several versions of the C3, most were either the C3B and the C3R. A few C3s were approved for float operations.
The C3 was built with light commercial applications in mind, including passenger flying and business flights. The C3MB was a special mail-carrying aircraft based on the C3 with the forward cockpit enclosed as a dedicated cargo compartment. This version was operated in 1928 by National Parks Airways on airmail route CAM 26 from Salt Lake City, Utah to Pocatello, Idaho and Great Falls, Montana.
Data from:Airlife's World Aircraft, Aerofiles:Stearman
Variants produced were:
Four aircraft similar to the C1, with the radiator mounted underneath, hydraulic shock absorbers and dual controls. Variously powered by 90 hp (67 kW) Curtiss OX-5, Wright-Hisso A, Wright Whirlwind and Menasco-Salmson radial engine.