March 2019

U.S. Navy/P-V (Piasecki-Venzie) Engineering Forum, Inc. XHRP-X ‘Dogship’

First flight: March 7, 1945; First successful U.S. tandem rotor helicopter

During World War II, the Navy contracted with the P-V Engineering Forum headed by Frank Piasecki for a challenging Coast Guard maritime-rescue requirement: hoisting up to eight survivors (one at a time) from the sea following the sinking of a ship. This constituted a payload of 1,440 lb (650 kg) plus the crew of two and the fuel required, far more capability than provided by any existing helicopters.

P-V Engineering was an audacious choice, since its sole — albeit successful — helicopter was the small (1,000 lb / 450 kg) single-seat PV-2 with a single main rotor and a separate anti-torque tail rotor. However, the two most prominent American helicopter companies, Platt-LePage and Sikorsky, were already fully involved with their existing projects, the XR-1 and XR-4, respectively.

The proposed tandem-rotor configuration of the PV-3 was also audacious. Two lifting rotors were considered necessary in order to avoid scaling up existing transmissions and rotors beyond a reasonable size, but only the side-by-side arrangement had been fully validated at the time. Nevertheless, the likelihood of achieving the mission requirement was significantly improved by eliminating the weight and drag of the side-by-side rotor mounting structure.

The Navy designated it the HRP — “H” for helicopter, “R” for transport (not rescue), and “P” for P-V Forum, subsequently Piasecki Helicopter. Against the odds, Frank Piasecki and his team were successful. A Continental R-975 radial engine powered the full-scale prototype XHRP-X, driving two, non-intermeshing, 41 ft (12.5 m) diameter three-bladed rotors, which turned in opposite directions to counteract torque. It first flew on March 7, 1945.

The production HRP (the official name was “Rescuer,” but it was more familiarly known as the “Flying Banana” or “Harp” after the letters of its designation) was powered by the more powerful 600 hp (450 kW) Pratt & Whitney R-1340 radial engine. The gross weight was 7,225 lb (3,275 kg) — 50% more that the Platt-LePage R-1 and nearly three times heavier than the Sikorsky R-4. The cabin provided space for eight passengers or six litters.

Although the HRP was put into production too late for service in World War II, 19 Rescuers (one crashed before delivery) were used for helicopter-mission demonstrations/evaluations in addition to the Coast Guard assignment, including marine assault, cargo transport externally, carrier-plane guard and antisubmarine warfare utilizing dipping sonar. A commercial helicopter company briefly operated a few military-surplus HRPs for transport of large externally slung loads.

Main photo: Piasecki Aircraft Corp.

Text: Tommy H. Thomason

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