The Stinson trimotor — General Aviation News

By Frederick Johnsen · November 13, 2022 · 1 Comment

In the 1920s and early 1930s, the engineering and economic formulas for aircraft development favored three-engine aircraft as transports.

The requirements for safety that could be met with redundancy, the limits on available horsepower, and the drive to create larger aircraft for commerce were accommodated with trimotors built by many makers, large and small.

If Ford reached iconic status with its corrugated metal trimotors, other manufacturers like Fokker and Boeing made forays into triple-engine transports.

Small makers came and went, but one builder of trimotor airliners earned a niche by offering economical prices for its trimotors.

The Stinson Aircraft Company had 60% of its stock bought by E.L. Cord, an automotive executive, in September 1929, just before the stock market crash plunged the nation into the Great Depression.

Not dissuaded by the financial situation, Cord pumped capital into Stinson, which allowed the company to offer aircraft at low prices, garnering large enough sales numbers to cover those low prices.

Cord was also part of an effort to create a trimotor transport, the Corman 3000, which was turned over to Stinson engineers who refined it to become the Stinson SM-6000.

The Stinson SM-6000 of 1930, which carried 10 passengers, was powered by three Lycoming R-680 radial engines. The price tag was merely $23,000, and Stinson briefly offered a sale price of only $18,000.

It has been said Stinson's goal was to entice airlines to place orders for the SM-6000 instead of buying aircraft from other makers, but initial sales of the SM-6000 were to new start-up airlines, eager to cash in on the low acquisition costs of the Stinson trimotors.

The SM-6000, prosaic in appearance, was a simple and sturdy fabric-covered taildragger based on welded steel tube construction. The cockpit area was skinned in aluminum. Length was 42 feet, 10 inches; span was an even 60 feet.

It cruised at about 115 miles an hour and landed at 60. SM-6000 variants boosted cruise speed to 122 mph when all three engines were cowled and wheel pants were added. Cruising range was said to be 345 miles.

Inertia starters came standard with the SM-6000. Later models could be equipped with electric starters.

The Stinson SM-6000-A offered interior options that accommodated mail as well as eight or nine passengers. It was alternately called the Stinson Model T, followed in production by the SM-6000-B.

While some SM-6000s had been flown by single pilots, newer SM-6000-A could be fitted with two sets of flight controls in the side-by-side cockpit, to allow one pilot to spell the other on longer flights.

The 6000 could take off in about 700 feet and land in 400. If these performance numbers were not particularly vital to regular airline users in the lower 48 states, the sprightly performance was valued by barnstormers and other non-traditional operators.

The trimotored Stinson Model U of 1932 was pitched to American Airlines. Carrying 10 passengers and a crew of two, the Model U was distinguished by its use of stub wings from the fuselage to the engine nacelles and landing gear, while the main lifting surface was a high-mounted wing, now spanning 66 feet, 2 inches. The stub wing spanned 14 feet, 3 inches. The stub wing included cargo compartments.

The U-bird cruised at 123 mph. Loss of one of the three engines in flight still left the Stinson Model U with enough power from the remaining two Lycomings to maintain flight with a ceiling of 7,000 feet.

About two dozen Stinson Model U trimotors were delivered to customers, including a plush business plane lettered for the Hearst San Francisco Examiner newspaper operation.

A year after certification of the Stinson U, Boeing introduced its revolutionary all-metal twin-engine Model 247 airliner, and the emphasis on fabric-covered trimotors diminished.

Stinson made one more trimotor in the 1930s. The low-wing, strut-braced Model A first flew in 1934. Its survival and production run of 31 aircraft may be attributed at least in part to a waiting list for newer metal Boeing and Douglas twin-engine airliners.

The last Stinson trimotor design retained the older fabric-covered steel-tube fuselage construction, but did so with a modern flair. It featured retractable landing gear and a lavatory. With a sporty cruise speed of 163 miles per hour, the Stinson Model A reframed the notion of trimotors in America.

Model A trimotors served American Airlines, Pennsylvania Central Airlines, Delta Airlines, and Marquette Airlines in the U.S., as well as serving in Australia, where two aging Model As were eventually rebuilt as twin-engine aircraft with R-1340 Wasp engines. Five second-hand Model A airliners went to India. One Model A, rescued from a crash site in Alaska, has been rebuilt to flying status. It is at the Mid-America Flight Museum in Urbana, Ohio.