While the aircraft's undercarriage retained the basic tailwheel undercarriage layout of the SM-8, the split-axle mainwheels of the earlier aircraft were replaced by a semi-cantilever design, in which the mainwheels and shock-absorber units were enclosed in streamlined fairings attached to a short stub wing, which was also used to carry wing bracing struts.

[5] The prototype made its maiden flight, piloted by Edward Stinson, in autumn 1931 and was certified as airworthy on 25 January 1932.

Stinson immediately set off on a sales tour with the prototype, and that same evening was carrying out a demonstration flight from Chicago when fuel shortage forced him down.

[6] Production continued, but the Great Depression caused sales to be slow, and only 39 aircraft were built, including five Model R-3s fitted with retractable undercarriage.

[7] It was succeeded in production by the Stinson Reliant, which managed similar performance at much lower cost ($3995 compared with $5595 for the Model R and $6495 for the R-3).