The Boeing-Stearman Model 75 'Kaydet' was the main primary trainer used by the USAAF and US Navy with just over 8,500 complete aircraft built by the time production ended in 1945.
The Stearman Aircraft Company was founded by Lloyd Stearman in 1927. All versions of the aircraft built before 1939 were Stearman aircraft. In 1939 the company became the Wichita Division of Boeing, and after that the Stearman Model 75 officially became the Boeing Model 75 but the Stearman name stuck. The Navy also kept the Stearman designation for all of its later aircraft, which remained the N2S rather than becoming the N2B (Boeing had produced an XN2B in the mid 1920s).
In 1933 Stearman began work on a new biplane trainer, developed from the earlier Stearman Model C. The new aircraft made its maiden flight in December 1933 as the Stearman X-70. It was a two-seat single bay unequal span biplane, with a slightly shorter lower wing. The wings had a wooden framework with a fabric cover. The fabric-covered fuselage was built around a welded steel tube framework.
The undercarriage was fixed. It had a tail wheel and a divided axle main landing gear, with cleanly faired oleo-spring shock absorbers for the main wheels. The main difference between the six main production versions and their many sub-versions came in the engine.
The X-70 was submitted to the Air Corps in 1934 in response to a primary trainer requirement, but it was the Navy that was first to order it into production. The first Naval aircraft were given the designation Stearman NS-1 and the internal designation of Model 73.
The Army took longer to place its first orders. Stearman developed the Model X75 in 1934, giving it a 225hp Wright R-670E Whirlwind engine. The Army tested this aircraft in October 1934. The sole X75 was then given a 220hp Lycoming R-680-3 engine, and became the Model X75L3. This was also tested by the army, and finally, in 1936 the army ordered the Lycoming-powered PT-13. This was the first production version of the Model 75, and all later US versions of the aircraft kept that designation. The 'Kaydet' name was given to the Model 75 in Canadian service. It was unofficially used elsewhere.
Eventually the US military accepted 8,298 aircraft. 4,359 were ordered for the Army, 3,639 for the Navy and 300 for Lend-Lease. The type was also exported, with 17 Model 73s, 48 Model 75s and 78 Model 76s sold. This makes a total of 8,441 aircraft (Boeing Aircraft since 1916 gives 8,584, but its figures include 122 cancelled aircraft from naval orders). Enough spare parts to build almost 2,000 complete aircraft were also built, for an effective production run of 10,346.
The Boeing-Stearman PT-13 was the original army version of the aircraft. It was first ordered in 1936 and was powered by a Lycoming R-680 engine. A total of 1,267 PT-13s were built.
The PT-17 was the second main army type and used the Continental R-670 engine. It was the main Army version, with 3,519 built.
A smaller run of PT-18s was also built, powered by a Jacobs R-755 engine. A total of 150 were built.
Three hundred Model 75s were built for Canada under the lend-lease scheme. The USAAF called them the PT-27, while the Canadians were the first to call the aircraft the Kaydet. They had a Continental engine and were similar to the PT-17.
The Boeing-Stearman NS was the first version to enter production. It was ordered from the independent Stearman Company, where it was called the Model 73. The NS was powered by surplus Wright J-5 (R-790-8) engines. Sixty-one were built.
The Boeing-Stearman N2S was the Naval designation for all of their Model 75 trainers, with various sub-types powered by Continental or Lycoming engines. A total of 3,578 N2Ss were built.
The Philippines bought seven aircraft in two batches in 1936-37. They were all powered by 200hp Lycoming R-680 engines and used the undercarriage from the Model 75. The first batch of three was delivered in March 1936 and was powered by US Navy R-680-4 engines. The second batch of four was delivered in April 1937 and were powered by civil R-580C-1 engines.
Seven A73B1s went to Cuba, four in October 1939 and three in March 1940. They were powered by a 235hp Wright R-760ET (J-6-7) Whirlwind engine.
The Philippines received another three aircraft in July 1938. These were slightly improved versions, also using a Lycoming engine.
The Model A75B4 was produced for Venezuela. It was powered by a 320hp Wright R-760-E2 and carried military equipment. Five were built and were delivered in November 1941.
The Model A75L3 was the export version of the PT-13, and was powered by a civil Lycoming R-680-B4D engine. Forty-three were built. Brazil was the largest customer, with 20, followed by the Philippines with 12, Venezuela with 7 and the Parks Air College with four.
Boeing Model 76
The Model 76 was an armed combat trainer and light attack aircraft. It used 300-400hp engines and could carry two fixed guns, one flexibly mounted gun and up to 120lb of bombs. It was produced in five variants, and a total of 78 were sold.
Engine: Varies (see text)
Span: 32ft 2in
Length: 24ft 1/4in
Height: 9ft 2in
Empty Weight: 1,936lb
Loaded Weight: 2,717lb
Maximum Speed: 124mph
Cruising Speed: 106mph
Climb rate: 840ft/ min
Range: 505 miles