Radioplane RP-77

The Radioplane RP-77 was a small target drone missile built mostly from plastic materials by Northrop Corporation’s Radioplane division. The U.S. Army tested the RP-77D successfully but chose not to buy it.

Design and development

Development of the RP-77 started in 1955. Its shape resembled Radioplane’s earlier OQ-19. Four prototypes were built: two RP-77s with a four-cylinder McCulloch piston engine and two RP-77As with a six-cylinder Lycoming engine. Flight tests did not interest the Army enough, but in 1957 a proposal for an improved RP-77D, powered by a Boeing 502 turboprop, led to a contract for 20 aircraft.

The RP-77D used a lot of glass-polyester plastic. It launched with a rocket-assisted take-off system using four Loki rockets. Radio control, aided by radar tracking, let operators fly the drone far from its launch point. Besides standard target drone equipment, it could carry reconnaissance or meteorological sensors, or air sampling gear.

The drone used Radioplane’s RPTA tracking system, which controlled it with audio frequency tones. Tip tanks held extra fuel to extend range, and a parachute recovered the drone after flight. A planned improved version would have launched RP-76 target missiles.

Operational history

The RP-77D first flew in March 1958. The Army evaluated it through the rest of that year, conducting nearly 40 test flights. Results were generally satisfactory, but the Army decided the drone’s performance was not enough of an improvement over existing types to order production. The project was canceled, along with the improved RP-86, a dedicated reconnaissance variant.

After the Army’s evaluation ended, Radioplane privately improved the RP-77D by fitting a larger wing and other modifications that boosted performance. These changes did not rekindle Army interest.

Variants included the RP-77 (two prototypes with McCulloch engine), RP-77A (two prototypes with Lycoming IMO-360 engine), RP-77B (proposed with turbo-supercharged McCulloch, none built), RP-77C (proposed with turbo-supercharged Lycoming SO-360M, none built), RP-77D (20 production prototypes with Boeing 502 turboprop), and RP-86 (proposed reconnaissance version, none built).