Convair R3Y Tradewind The Convair R3Y Tradewind was an American 1950s turboprop - powered flying boat designed and built by Convair . Design and development . Convair received a request from the United States Navy in 1945 for the design of a large flying boat using new technology developed during the war , especially the laminar flow wing and the still developing turboprop technology . Their response was the Model 117 . It was a large high - wing flying boat with Allison T - 40 engines driving six - bladed contra - rotating propellers . It had a sleek body with a single - step hull and a slender high - lift wing with fixed floats . The Navy ordered two prototypes on 27 May 1946 . Designated XP5Y - 1 , the first aircraft first flew on 18 April 1950 at San Diego . In August the aircraft set a turboprop endurance record of 8 hours 6 minutes . The Navy decided not to proceed with the patrol boat version , instead directing that the design should be developed into a passenger and cargo aircraft . One of the XP5Y - 1 prototypes was lost in a non - fatal accident on 15 July 1953 , while design and development continued on the passenger and cargo version of the craft . The transport and cargo version was designated the R3Y - 1 Tradewind and first flew on 25 February 1954 . Major changes were the removal of all armament and of the tailplane dihederal , the addition of a 10 ft ( 3 . 05m ) port - side access hatch , and redesigned engine nacelles to accept improved T40 - A - 10 engines . Cabin sound proofing and airconditioning were added for pressurised accommodation for 103 passengers or 24 tons of cargo . As a medevac aircraft 92 stretcher cases could be carried . A total of eleven aircraft were built . The first two prototypes built were in P5Y configuration , armed with 8 , 000 lb ( 3 , 600 kg ) of munitions ( bombs , mines , depth charges , torpedoes ) and 5 pairs of 20 mm cannon in fore and aft side emplacements and a tail turret . The next five were built as R3Y - 1 aircraft , intended for troop transport and inflight refuelling tanker service . The final six were built as the R3Y - 2 variant with a lifting nose and high cockpit ( similar in concept to the C - 5 Galaxy ' s nose and cockpit ) for heavier transport and landing - ship duties . The front - loading R3Y - 2 aircraft with a hinged nose and high cockpit were intended to be a " Flying LST " ( landing craft ) . In practice , it was discovered that it was almost impossible for the pilots to hold the aircraft steady and nose on to the beach while the aircraft was loaded or unloaded . The aircraft were converted into tankers for the inflight refuelling role . They had a short service life because of the insoluble unreliability of their Allison T40 turboprop engines , a fate common to most T40 - powered aircraft , such as the Douglas A2D Skyshark attack aircraft . Operational service . The R3Y set a transcontinental seaplane record of 403 mph in 1954 by utilising the speed of high - altitude jetstream winds . This record still stands . After service trials the aircraft were delivered to US Navy transport squadron VR - 2 on 31 March 1956 . Problems with the engine / propeller combination led to the ending of Tradewind operations and the unit was disbanded on 16 April 1958 . The six R3Y - 2s were converted into four - point in - flight tankers using the probe - and - drogue method . In September 1956 one example was the first aircraft to successfully refuel four others simultaneously in flight in 1956 , refuelling four F9F Cougar s . The program was halted after thirteen aircraft were built , the reason being the unreliability of the Allison T - 40 turboprops . The crash of one of the two XP5Y - 1 aircraft was judged due to catastrophic engine failure ; when little progress was being made with the engine problems , the Navy halted the program . Subsequently three more aircraft were lost through engine failures , and the Navy gave up on the T - 40 and aircraft powered by it . All the P5Y and R3Y aircraft were grounded in 1958 and subsequently broken up .