The Radioplane RP-77 was a small target drone missile, constructed largely of plastic materials, produced by the Radioplane division of the Northrop Corporation. Although the RP-77D was successfully tested by the United States Army, the decision was made not to procure the aircraft. Design and development The development of the RP-77 began in 1955. Similar in outline to Radioplane's earlier OQ-19, four prototypes of the RP-77 were constructed, two each of the RP-77, powered by a four-cylinder McCulloch piston engine, and of the RP-77A, powered by a six-cylinder Lycoming engine. Results of flight-testing were insufficient to interest the U.S. Army, however in 1957 a proposal for an improved RP-77D, powered by a Boeing 502 turboprop, resulted in a contract for the construction of 20 aircraft. The design of the RP-77D made extensive use of glass-polyester plastic materials. The drone was launched using a rocket-assisted take-off system consisting of four Loki rockets, and was fitted with a radio control apparatus that, with the assistance of radar tracking, allowed the drone to be operated at a considerable distance from its launching point. In addition to equipment typically carried by target drones, the RP-77D could be equipped with reconnaissance or meteorological sensors, or with air sampling equipment. The RP-77D utilised the RPTA tracking system, developed by Radioplane, using audio frequency tones for control. Tip tanks allowed for carriage of additional fuel to extend the aircraft's range, and recovery at the end of the flight was by parachute. An improved version of the RP-77D was projected, with provision for launching RP-76 target missiles. Operational history Following its maiden flight in March 1958, evaluation of the RP-77D by the U.S. Army took place throughout the remainder of that year, nearly 40 test flights being conducted. Although the test results were generally satisfactory, it was determined that the performance of the aircraft was an insufficient improvement over existing types in service to have the aircraft ordered into production, and the project was cancelled, along with the improved RP-86, a dedicated reconnaissance variant. Following the termination of the Army's evaluation, Radioplane, as a private venture, conducted an improvement program for the RP-77D, fitting the aircraft with a larger wing, along with other modifications that improved the performance of the drone. However these improvements were insufficient to produce a renewed interest from the Army. Variants RP-77 Prototype model powered by McCulloch piston engine; two built. RP-77A Prototype model