The Piasecki PD-22 (H-21) was an improved version of the HRP-2 Rescuer. It was the 4th tandem-rotor design from Piasecki. Because of its shape, covering the tail rotor transmision shaft, it was commonly called the Flying Banana. The H-21 had a fully articulated, three bladed, counter-rotating rotor system, with twin vertical fins fitted at the tail. Early versions were powered by a single Curtis-Wright R1820-103 Cyclone 1150 hp supercharged piston engine. It held a side by side crew of 2, in a dual-control cabin. Equipped with a hoist and a dorsal quick-release cargo sling, on a fixed tricycle undercarriage, it offered optional wheels, skis, or floats. The H-21 first flew on 11 Apr 1952. 707 of all versions were built, including two H-21D experimental models with a single and a twin turboshaft, replacing the piston Cyclone.