Piasecki designed and successfully sold a series of tandem rotor helicopters to the United States Navy, starting with the HRP-1 of 1944. The HRP-1 was nicknamed the "flying banana" because of the upward angle of the aft fuselage that ensured the large rotors did not hit each other in flight, and because the Coast Guard painted the aircraft yellow. The name would later be applied to other Piasecki helicopters of similar design.
In 1949, Piasecki provided the H-21 Workhorse to the United States Air Force, an improved, all-metal derivative of the HRP-1. Piasecki's tandem-rotor helicopters flew higher than competing single rotor designs, and offered a smoother ride.
In 1946, to fund expansion, Piasecki sold a 51% interest in the company to Laurance Rockefeller and A. Felix du Pont, Jr. for $500,000. Don R. Berlin was brought in as president and director of Piasecki Helicopters in 1953, while Frank Piasecki was chairman of the board. The majority owners eventually lost faith in Frank Piasecki's leadership and by May 1956 he was out of the company. He had formed a new company, Piasecki Aircraft Corporation to pursue the development of compound helicopters and other rotorcraft. In two successive special stockholders' meetings the board then changed the name of Piasecki Helicopter to Vertol (for vertical take-off and landing) Aircraft Corporation and amended the bylaws to bar Piasecki's re-election as a director, on the grounds that he was running a rival company.