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24-519: The T40 concept originated at Allison in 1944, where design studies were carried out on a 4,000 shp (2,983 kW) turboprop engine. Taking advantage of this effort, the US Navy awarded Allison a contract for the design and development of a 4,100 shp (3,057 kW) turboprop engine. The resulting T40 combined two Allison T38-A-1 power sections side-by-side with a common reduction gearbox powering contra-rotating propellers . Similar in layout to

48-524: A fixed wing aircraft, in November 1954. Continuing concerns over propellers and the poor payload and performance precluded further development. Some flying was carried out with the Hiller X-18 but most research was carried out with the aircraft attached firmly to a force measuring platform, that could be raised hydraulically, to gather data on ground cushion effects. Limited flying was carried out by

72-437: A power section in the event of failure worked successfully. During a run in a test cell one power section developed a major oil leak and an attempt to shut it down failed because the engine carried on running on the leaking oil. After many attempts to shut it down the offending power section could only be shut down by destroying the compressor with debris thrown down the intake, proving the de-coupling system. First flight test of

96-613: The Armstrong Siddeley Double Mamba , the T40 differed in that each engine drove both the forward and the rear propellers, unlike the Double Mamba, where each Mamba power section drove either the front or the rear propeller separately. The T38-A-1 power sections each contained 17-stage compressors giving a pressure ratio of 6.3:1, eight combustion chambers, and four-stage turbines. A combining reduction gearbox

120-761: The Convair CV-240-21 Turboliner were rated to 2,750 shp (2,050 kW) equivalent. In 1951, the United States Air Force decided that the production version of the Beechcraft XT-36 trainer—then in the mockup stage and designed for the Pratt & Whitney R-2800 —would be retrofitted with the T38 when the engine entered full-scale production, which was anticipated to occur in 1955–1960. This decision ultimately doomed

144-681: The Douglas A3D Skywarrior . The most notable successes of the T40 were in the field of vertical take-off aircraft, being used to power three different types, the Convair XFY-1 Pogo , Lockheed XFV-1 and the Hiller X-18 tilt-wing research aircraft. Fitted with the more powerful 7,100shp YT40-A-6 the XFY-1 flew the first full flight from vertical take-off to horizontal flight and back to vertical flight for landing, of

168-573: The T40 was in the Convair XP5Y flying boat on 18 April 1950 fitted with four T40-A-4 developing 5,250 shp (3,915 kW). Service use of the T40 revealed problems with integrity of the propellers and gearboxes with at least one instance each of a propeller breaking free and a gearbox separation. One unusual problem was discovered during ground running of the Republic XF-84H Thunderscreech turboprop powered fighter;

192-684: The T40 was the Convair XP5Y-1 patrol aircraft prototype. As flying boat patrol aircraft became redundant, the US Navy changed the role of the aircraft from Anti-Submarine Warfare to Transport. Modifications to the XP5Y-1 (such as provision of air conditioning and pressurisation) produced the Convair R3Y Tradewind , which was to become the only aircraft using the T40 to actually enter service. These large four-engined flying boats served primarily between NAS Alameda and Hawaii during

216-534: The aircraft, as the design changes required to accommodate the T38 delayed the project and rendered the aircraft overweight and over budget. Although the only other aircraft slated to receive the T38 as a production engine, the Convair T-29E , was cancelled, the T38 did power a converted Convair CV-240 (the CV-240-21 Turboliner, a project that would be abandoned due to engine problems), and

240-497: The compressor and the extension shaft to the reduction gearbox. Initially rated at 2,000 shp (1,500 kW) the T38 first ran in 1947 and flew in the nose of a Boeing B-17 Flying Fortress test-bed on 19 April 1949, rated at 2,250 shp (1,680 kW). Problems with gearbox vibration and combustion were dealt with during the test program and were mirrored by problems in the Allison T40 programme. The engines fitted to

264-477: The engine nacelles to ease storage aboard ship. It had a crew of three: pilot, co-pilot/bombardier, and gunner who sat in a pressurised cabin in the nose of the aircraft. Up to 10,500 lb (4,800 kg) of bombs could be carried in a large enclosed bomb-bay in the center fuselage, while the planned defensive armament was a remotely controlled tail turret with two 20 mm cannon. Construction of two prototypes started 1 October 1948, but due to delays developing

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288-505: The engine was stopped. Anti-icing for the air intakes was supplied by compressor bleed air. The contra-rotating propeller consisted of two 14 ft (4.3 m) three-bladed Aeroproducts propellers fitted to concentric shafts. Testing of the XT40 began on 4 June 1948. There was a vibration problem in the reduction gearbox due to the coincidence of tooth-meshing frequencies which required a redesign. The de-coupling system, designed to disconnect

312-584: The engines, the first flight was not until 4 January 1952. The competing Douglas XA3D , the prototypes of which were ordered the year after construction had begun on the XA2J prototypes, first flew in October 1952. The A3D had far superior performance, which doomed the XA2J. The root cause for the failure of the XA2J was the protracted development and poor reliability of the Allison T40 engines. The T40 engine

336-506: The gearbox, it was intended in most instances that the aircraft could cruise on one half of the engine and only engage the second power-section when there was need. In practice the system did not work well. Failure to recognize that one of the T38s had failed, and its compressor was devouring power produced by the other section, led to the loss of the first prototype Douglas XA2D-1 and its pilot on 14 December 1950. The first aircraft to fly with

360-561: The mid-1950s (replacing the Martin Mars flying boats). There were numerous problems with the T40s. One resulted in near disaster in 1956, when an R3Y managed to land with a runaway engine, resulting in a collision with a seawall. This event gave the US Navy one more reason to ground the R3Y, which it did soon after. The only other aircraft to be produced in any quantity to be powered by the T40

384-407: The special transonic 3-bladed single propeller set up harmonics that proved to be harmful to humans within a certain distance from the aircraft. The major problems of the T40 included gearbox failures, and the propeller control system (all the engine accessories were powered by a vacuum system which used 25 hoses), and the engine was far from reliable. As the individual power plants were clutched into

408-555: The two Republic XF-84H Thunderscreech turboprop fighter aircraft, but the continuing difficulties with the T40 engine, supersonic propeller, not to mention performance completely overshadowed by contemporary rivals led to cancellation of production plans. Data from: Data from Aircraft engines of the World 1953 Turbojet History and Development 1930–1960 vol.2 Related development Comparable engines Related lists Allison T38 The Allison T38 (company Model 501 )

432-690: Was a prototype carrier-based attack aircraft built in the early 1950s. It was developed by North American Aviation (NAA) from the smaller AJ Savage . The XA2J was intended to be a turboprop -powered derivative of the AJ Savage, with the design as initially proposed in December 1947 a simple modification of the Savage, with extensive use of components of the earlier aircraft. The design gradually evolved, however, to improve performance and increase compatibility with operations from aircraft carriers, as it

456-402: Was an ambitious engine design with two power sections, (the T38 was developed from the T40 to assist in its development, by using a single power section with extension shaft and gearbox), driving two large contra-rotating propellers through a combining gearbox. Both the engines and the gearbox proved to be unreliable. The T40 engine was also used in the developmental of other aircraft . After

480-462: Was an early turboprop engine developed by Allison Engine Company during the late 1940s. The T38 became the basis for the very successful family of Allison T56 turboprop engine. Developed as a stand-alone single section of the T40 (Model 500) twin engine to aid in development of the T40, the T38 started life with a 19-stage axial compressor, eight can type combustion chambers, a 4-stage turbine driving

504-407: Was driven via extension shafts from the power sections. Each transmission shaft incorporated a clutch to allow the power sections to be run independently. Accessories included a Master Control Unit, mounted above the compressors, and an air driven starter on the gearbox. The compound reduction gear had an overall reduction ratio of 15.75:1 and incorporated an airscrew brake to prevent windmilling when

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528-581: Was fitted in the nose of the McDonnell XF-88B to drive experimental supersonic propellers. Further development of the T38 provided the power sections for the Allison T40 as well as forming the basis for the Allison T56 /Model 501 and the projected Allison T39 . Data from Aircraft engines of the World 1953 Related development Related lists North American A2J-1 Super Savage The North American Aviation XA2J "Super Savage"

552-506: Was recognized that the AJ Savage was deficient in performance and was a less-than-satisfactory carrier aircraft. The A2J was essentially an enlarged AJ Savage with the two reciprocating engines replaced with two Allison T40 turboprop engines and removal of the tail-mounted turbojet . Like the AJ, it was a high-winged monoplane with unswept wings. The wings were fitted with leading edge slats and large trailing edge flaps, and folded outside of

576-568: Was the Douglas A2D-1 Skyshark . Of the sixteen examples built, the twelve used for evaluation suffered similar problems to the R3Y. Propeller control problems and gearbox failures were among the more common problems. The T40 was also fitted to the North American A2J-1 Super Savage but the poor performance of the aircraft and continuing difficulties with the engines forced cancellation in favour of

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