The Consolidated PT-11/ BT-6 was an improved version of the PT-3 trainer, but was only produced in small numbers.
Towards the end of 1930 the US Army ran a design contest for a trainer to replace the Consolidated PT-3, which had entered service in 1927, but was based on the PT-1 of 1923, itself developed from an earlier design.
The Model 21-A was based on the PT-3, but it's designer, Joe Gwinn, cleaned up the aerodynamics, and gave it a new tail with much more modern looking curved surfaces, replacing the angular, almost rectangular, surfaces of the PT-1 and PT-3. The Model 21 was a biplane with un-swept staggered wings. The upper wing was level and the lower wing had slight dihedral. The horizontal tail surfaces had a straight tapered leading edge, and curved training edge on the control surfaces. The vertical surface had a large curved rudder .
The prototype made its maiden flight in February 1931, only eight weeks after the design work started. It was powered by a 170hp Kinner engine, but it was designed to take a range of alternative engines, up to 400hp in power. Extra fittings were produced for the wings to allow the balance to be altered to cope with alternative engines.
The USAAC ordered four evaluation aircraft, to be powered by a 165hp Continental R-545-1 engine, and with the designation Y1PT-11. These were delivered in May 1931. They were followed by five PT-11Bs and twenty-one PT-11Ds for a total of 30 aircraft. Another ten similar aircraft were completed as the PT-12 and later become the BT-7.
The Mexican Air Force ordered ten of an armed version of the Model 21, powered by a 420hp Wasp JrSB and armed with one fixed forward firing and one flexibly mounted 0.3in machine gun. At least one saw combat during the Cedillista Rebellion of 1938. Some remained in use in late 1943 when they were transferred to the Naval Aviation School at Veracruz.
In all 66 Model 21s were built in the United States - 30 PT-11s, 10 PT-12s, 4 N4Ys, 10 for Mexico and the rest as civil models.
This was the designation for the first four aircraft, powered by the 165hp Continental R-545-1. Later two were converted to PT-11D standard, the third to the BT-6 standard and the fourth became the only Y1PT-11A.
This was the designation one of the original Y1PT-11 aircraft after it was given a 175hp Curtiss Challenger R-600-1 engine. It was originally the Y1PT-11A but this was later changed to just the PT-11A. It was then altered again, given a Lycoming engine and became the Y1PT-11C.
This was the designation given to one of the original four aircraft when it was given a 210hp Kinner YR-720-1 engine.
These aircraft were also powered by the Kinner engine. Five were built originally as more Y1PT-11Bs, but then just as the PT-11B. They were later converted to the PT-11D standard. Deliveries began in July 1932.
The Y1PT-11C was the designation given to the Y1PT-11A when it was given a 180hp Lycoming YR-680-1 engine
The PT-11D was the main version of the aircraft. They were powered by a 220hp Lycoming R-680-3 nine-cylinder radial engine, and were delivered as the Y1PT-11D, but soon became the PT-11D. Twenty one were built from new, and they were delivered between May and July 1932. Two of the Y1PT-11s and the five PT-11Bs were also converted to this type, for a total of twenty eight.
The third Y1BT-11 was given a 300hp Wright J-6 engine and re-designated as the Y1BT-6. This was later re-designated again as the BT-6, before finally being converted to PT-11D standard.
The final version of the aircraft was the export PT-11C. This was powered by a Wright 760-E7 and had interchangeable wheels or float undercarriage. Eighteen of these aircraft were exported to Columbia in July-August 1934, where they remained in service for some time, with the last being withdrawn in 1952.
The Model 21 was also used by the US Navy, where it was designated as the Consolidated N4Y.
Engine: Lycoming R-680-3 nine-cylinder radial engine
Span: 31ft 7in
Length: 26ft 11in
Height: 9ft 8in
Empty Weight: 1,918lb
Gross Weight: 2,585lb
Maximum Speed: 118mph at sea level
Climb rate: 7.4min to 5,000ft