In the last years of World War II, Stout, in co-operation with Owen-Corning, began what was called "Project Y" to build a one-off car for evaluation of ideas like a frame-less fiberglass body, belt drive rear wheel drive, a suspension which kept the vehicle from leaning into turns by adjusting the suspension using compressed air, and push button electric doors. When the vehicle was made public in 1946, Stout picked the name "Forty-Six" for that year. Some firms considered producing the Forty-Six, but as Stout stated he doubted there would be much of a market for a $10,000 dollar car, the estimated price if it had been mass-produced. Stout's aviation career began as a result of his success in his automotive efforts. He began to build a number of all-metal aircraft designs, which, like the earliest aircraft designs of Andrei Tupolev in the Soviet Union, was based on the pioneering work of Hugo Junkers. In February 1923, newspapers carried stories of the test flights of the "Stout Air Sedan" with Walter Lees as the pilot. In 1924 his company, the Stout Metal Airplane Company, was bought by the Ford Motor Company. Stout developed a thick-wing monoplane, and his design of an internally braced cantilevered wing improved the efficiency of aircraft. This led to the development of the famous "Batwing Plane" and the all-metal "Torpedo Plane". After his career at Packard Motors, he left for Washington to serve as the advisor to the United States Aircraft Board. Stout developed an all-metal transport aircraft for mail use, the Stout 2-AT. His three engine follow-on, the Stout 3-AT, was underpowered, and did not perform as well, leaving Stout out of the engineering role in his company newly acquired by Ford. The redesigned 3-AT did form the basis for the popular Ford Trimotor aircraft. In August 1925, Stout inaugurated Stout Air Services, which operated the first regularly scheduled airline in the United States. Stout also built the Liberty-powered all-metal monoplanes to initiate this service. Later, between 1928 and 1932, the airline flew passengers and Ford cargo between Dearborn, Chicago and Cleveland. In 1929, Stout sold Stout Air Services to United Airlines. After the Great Depression in 1929 reduced sales of the Trimotor aircraft, Stout left Ford in 1930. Although no longer with Ford, he continued to operate his Stout Engineering Laboratory.