The Consolidated Model 21 was an American two-seat training aircraft built by the Consolidated Aircraft Company. It was used by the United States Army Air Corps with the designation PT-11 and the United States Coast Guard under the designation N4Y. Design and development The Model 21 was an aerodynamic cleaned up version of the Model 12/PT-3, one of the distinguishing features being curved instead of angular tail surfaces. The aircraft was a single-engined biplane with fixed tailwheel landing gear and accommodation for two in open cockpits. Operational history Designated the PT-11 by the United States Army Air Corps it progressed through a number of trial variants but was not built in large numbers. 11 Examples of the model 21-C were built in Canada as the 21-M for Mexico but none were built for local use. Variants XPT-933 (Model 21A). Prototype powered by Kinner engine, first flew February 1931. YPT-11 Evaluation aircraft for US Army based on the Model 21A with a Continental R-545-1 engine, four built. PT-11A One YPT-11 was re-engined with a Curtiss R-600-1 Challenger engine, originally as Y1PT-11A, later converted to PT-11C standard. Y1PT-11B One YPT-11 was re-engined with a Kinner YR-720-1 engine and designated Y1PT-11B. 5 production aircraft for US Army with another for the United States Coast Guard and designated N4Y-1. PT-11C PT-11A re-engined with a Lycoming YR-680-1 engine. One or two converted for US Army, with 18 new-build aircraft for Colombia. PT-11D Production version with R-680-3 engine, originally designated Y1PT-11D. 21 new-built, plus five conversions from Y1PT11-Bs and two from Y1PT-11s. PT-12 A version of the PT-11 with a 300hp R-985-1 engine and detailed changes, ten built later redesignated BT-7. Y1BT-6 One YPT-11 was re-engined with a 300hp R-985-1 BT-6 Redesignation of Y1BT-6. BT-7 PT-12 aircraft redesignated. XN4Y-1 Evaluation aircraft for the United States Coast Guard, three built. N4Y-1 One YPT-11B for the USCG, later modified to the same standard as the XN4Y-1 Operators United States Army Air Corps United States Coast Guard Colombian Air Force (PT-11C). Paraguayan Air Arm (Model 21-C). Mexican Air Force (Model 21-M). Specifications (PT-11D) See also Consolidated PT-3 References PT-11 Consolidated PT-11 Single-engined tractor aircraft Biplanes