No. 2711. Convair 117 XP5Y-1 (121455) US Navy
Photograph from Convair

Convair 117 XP5Y-1

08/31/2017. Remarks by Johan Visschedijk: "During the latter part of WW II, Consolidated Vultee, operating under the trade name Convair, undertook considerable work at its Hydrodynamic Research Laboratory, led by Ernest G. Stout, into advanced flying-boat hulls with high length-to-beam ratios that promised many improvements over existing designs. Confirmation of these bright prospects came with the examination of captured German research and spurred the USN to go ahead with plans for a long-range patrol flying-boat capable of operating from forward bases and also able to act in the air-sea rescue and anti-submarine warfare (ASW) roles. Manufacturers were invited to submit proposals on December 27, 1945, with the designs to include the latest hydrodynamic research and to be powered by propeller-turbines.

Convair's Model 117 was chosen and two prototype XP5Y-1s (BuNo. 121455, 121456) were ordered on June 19, 1946, with flight tests scheduled to begin in mid-1948. Originally, Convair's team, headed by Herbert Sharp, designed the sleek new flying-boat, with a length-to-beam ratio of 10:1 (double that of the PBY), around the projected Westinghouse 25D (T30) propeller-turbine. However, industrial disputes at Westinghouse caused this engine to fall far behind in schedule and instead, the USN chose the 5,100 shp Allison XT40-A-4. A complex engine, the T40 consisted of two T38s coupled to a reduction gear via dual extension shafts and driving six-blade 15 ft (4.57 m) diameter contra-rotating propellers. Inevitably, development delays occurred which caused further engine delays and the two prototypes were rolled out engineless at San Diego in mid-1949.

Apart from its massive size, the XP5Y-1 was a conventional aircraft with a cantilever high-wing, fixed floats on the wings, and a single tail unit adapted from that used on the XB-46. Convair also foresaw a possible transport application and accordingly, in order to alleviate the need for watertight bulkheads, incorporated a multi-cellular construction technique for the hull. For its originally intended role, the proposed armament was ten 0.787 in (20 mm) cannon in five remotely-controlled barbettes (one one each side of the nose, one each side of the aft fuselage, and one in the tail).

With a gross weight of 123,500 lb (56,019 kg), a bomb load of 8,000 lb (3,629 kg) could be carried and extensive armor for the crew included. However, by early 1949, the primary mission of the P5Y-1 had been changed to ASW and, still later, to mine-laying without any defensive armament. Thus, the turrets of the prototypes were faired over.

Engines were finally ready for installation in the first prototype by the end of 1949, but none had yet achieved a satisfactory 50-hour test. Nevertheless, extensive taxiing tests were conducted from January and the first flight, lasting just 29 minutes, was made with airframe and engine on April 18, 1950, by Sam Shannon. Despite endless troubles with the T40, the XP5Y-1 (world’s first turboprop powered flying boat) managed to establish an endurance record in early August for propeller-turbine-powered aircraft with a flight of 8 hr 6 min.

However, the same month, the Navy announced it would discontinue further development of an ASW version in favor of the aircraft as a pure transport. The XP5Y-1 continued flight tests of the XT40-A-4 until July 15, 1953, when it suffered loss of elevator control during a high speed test dive. Longitudinal trim was used to recover, but the aircraft entered an uncontrollable divergent phugoid (porpoise or longitudinal oscillation) forcing abandonment by project pilot Don Germeraad and his 10-man crew just before its plunging into the ocean off Point Loma, San Diego. The unflown second XP5Y-1, used only for beaching tests and other ground trials, was broken up in 1957.

On August 16, 1950, a contract was placed for six (BuNo. 128445 to 128450) Convair Model 3s, designated R3Y-1 Tradewind, with short-shaft 5,332 shp T40-A-10s in more forward-mounted nacelles. There were other substantial changes in this transport version. The hull was lengthened by 14 ft 7 in (4.45 m) with a 10 ft (3.05 m) cargo hatch in the port side aft of the wing, a pressurized 9 ft (2.74 m) wide cabin accommodated eighty passengers or seventy-two stretchers with eight medical attendants, the barbettes were discarded and round windows installed, and a taller tail introduced. The first flight was made on February 25, 1954, almost a year behind schedule. A year later, one (BuNo. 128448) flew from San Diego to Patuxent River, Maryland, in the record time of six hours at an average speed of 403 mph (649 kmh), a world record for seaplanes that has never been broken.

By this time, an assault transport version of the Tradewind, the R3Y-2, had already flown. This variant featured a raised flightdeck with a shorter bow incorporating power-operated ramps and an upward-opening loading door. Up to four 6.1 in (155 mm) howitzers, six jeeps, three 2.5 ton (2,540 kg) trucks, or two half-track vehicles could be discharged onto landing beach. The first aircraft (BuNo. 128450) was taken from the R3Y-1 order and first flew on October 22, 1954. Five others (BuNo 131720 to 131724) were completed.

Three R3Y-2s and one R3Y-1 were converted for the tanker role with a probe and drogue system developed by the British company Flight Refuelling. Tests with Grumman F9F Cougars from VF-111 in September 1956 were the first simultaneous refueling of four receiver aircraft by any air tanker. The Cougars were refueled with fuel taken from the R2Y-2s wing tanks with a flow of 250 gal (946 l)/min in less than five minutes. A severe problem with turbulence was resolved by extending the inboard hoses further than the outer two, but use of the aircraft was in any case limited.

Seven R3Ys were delivered to VR-2 at NAS Alameda, Califomia, between March and November 1956, to replace the Martin Mars on trans-Pacific services. On October 18, a new seaplane record of 6 hr 45 min was established between Honolulu and NAS Alameda (at 360 mph, 579 kmh) but the new type continued to suffer from engine problems and only a dozen or so flights were made to NAS Honolulu. On May 10, 1957, the Coral Sea Tradewind (all VR-2's aircraft were named), the aircraft that had made the record-breaking run two years earlier, was written off in San Francisco Bay in a heavy alighting following loss of control after a propeller ran away. Then, on January 24, 1958, the Indian Ocean Tradewind lost a complete gearbox while on a return flight to Alameda from Hawaii. A successful alighting was made, but asymmetric power problems caused the R3Y-2 to hit a seawall.

There were no fatalities in either incident, but the USN prudently grounded all Tradewinds immediately. Although it was proposed that the Tradewind participate in the atomic-powered aircraft development program, and be re-engined with Rolls-Royce engines, no further flying took place and the remaining aircraft were scrapped."

Created June 17, 2003