After World War II, aeronautical engineers in several countries sought to combine a very new aviation technology with a very old one. The former was the turbine (jet) engine; the latter was the seaplane.
In the United States the Navy sought to merge the technologies in jet-propelled flying boats for the maritime patrol and transport roles. Supported by seaplane tenders, such aircraft were envisioned as operating over vast areas without dependence on land bases. In 1945 the Navy invited aircraft manufacturers to propose flying-boat designs that would incorporate emerging technologies. The high speeds provided by jet engines were not vital to the maritime patrol role, thus Convair engineers adopted the turboprop engine for their next generation designs. The engine was essentially a turbine driving a propeller shaft to provide greater fuel economy, hence longer range, than a pure jet.
The Navy selected Convair to develop the next generation maritime patrol flying boat, ordering two prototype XP5Y-1 aircraft on 19 June 1946. Formed in 1943 by the merger of Vultee Aircraft and Consolidated Aircraft firms, Convair had produced a variety of large, multiengine aircraft, among them the PBY Catalina and PB2Y Coronado flying boats. (Consolidated also built the Army Air Forces B-24 and navalized PB4Y-1 Liberator and its maritime patrol derivative, the PB4Y-2 Privateer; more Liberators were produced—more than 18,000—than any other U.S. military aircraft.)
The Convair team, led by Herbert Sharp, developed a radical fuselage design with a length-to-beam ratio of 10:1 or double that of the famed PBY Catalina. A multicellular fuselage construction was used, eliminating internal bulkheads to facilitate the design being used in a transport role.1
The high-mounted wing carried four large engine nacelles enclosing Allison XT40-A-4 turboprops—actually a pair of T38 engines coupled with a reduction gear—driving contrarotating, six-blade propellers. Each T40 was rated at 5,100-shaft horsepower.
The aircraft was attractive, with a tall tail fin and a thin wing with fixed underwing floats. In the combat configuration, a P5Y would carry up to 8,000 pounds of ordnance in nacelle bays and on wing racks. Defensive armament would consist of ten 20-mm cannon in twin remote-control turrets—two on each side of the fuselage and one in the tail position.
The first XP5Y-1 flew at San Diego on 18 April 1950. That summer—despite continued problems with the T40 engines—the aircraft established a turboprop endurance record of 8 hours, 6 minutes. The first prototype flew until it crashed when elevator control was lost during a high-speed dive on 15 July 1953. The second XP5Y-1 never flew.
The Navy decided not to pursue the maritime patrol variant of the Convair design, but gave the go-ahead for the R3Y transport, given the name “Tradewind.” Major differences were that the transport was lengthened; all armament provision was removed; the tail fin was modified; a ten-foot, portside access hatch was added; and the engine nacelles were placed atop the wing, instead of being mounted within the structure, with provision for the T40-A-10 engine. Its payload could be 100-plus passengers or 92 stretchers or 24 tons of cargo in a pressurized cabin. The R3Ys had a maximum takeoff weight, with 103 passengers, of 165,000 pounds.
Five aircraft were built to this R3Y-1 configuration, the first flying on 25 February 1954. The next six aircraft —dubbed “flying LSTs”—had the radical R3Y-2 design with a nose structure that lifted to open the fuselage cargo space for loading/unloading troops, vehicles, and cargo. The -2 could carry four 155-mm towed howitzers or six jeeps or three 6x6 2½-ton trucks. While an attractive concept, in reality there was great difficulty in holding the aircraft steady at the water’s edge or even to a pier to permit loading and unloading.
In a further demonstration of the design’s versatility, one R3Y-1 and three -2 aircraft were modified to the aerial tanker role. Fuel tanks were installed within the fuselage and four probe-and-drogue refueling stations were fitted to the wings, with up to four fighters being refueled at a single time in tests. This marked the first time that four aircraft simultaneously could be refueled by a single tanker.
Beginning in 1956, the Tradewinds operated in transport squadron VR-2, mostly flying between San Diego and Hawaii. They continued to establish performance records. The fourth R3Y-1, later named “Coral Sea Tradewind,” set a speed record flying from San Diego to Patuxent River, Maryland, in six hours at an average speed of 403 miles per hour.2 However, the aircraft were rapidly discarded, primarily because of technical problems with their T40 turboprop engines. (The T40 engine was also being employed in the short-lived North American A2J Savage and Douglas A2D Skyshark attack planes.)
The last of the nine surviving Tradewinds were retired in 1958. (Two aircraft had crashed.)
The P5Y/R3Y was the largest U.S. Navy flying boat except for the Martin JRM Mars transport series and the aborted jet-powered Martin P6M Seamaster seaplane strike aircraft. The P5Y/R3Y project was another fascinating but impractical naval aviation program.
1. See John Wegg, General Dynamics Aircraft and their Predecessors (Annapolis, MD: Naval Institute Press, 1990), pp. 184–86.
2. Seven Tradewinds were named for bodies of water: the South Pacific, Indian Ocean, Coral Sea, China Sea, South Atlantic, Arabian Sea, and Caribbean Sea. See Steve Ginter, Convair XP5Y-1 & R3Y-1/-2 Tradewind (Simi Valley, CA: Naval Fighters, 1996), p. 43.
Mr. Polmar, a columnist for Proceedings and Naval History, is author of the definitive two-volume Aircraft Carriers: A History of Carrier Aviation and Its Influence on World Events (2004, 2008).