|T56 / Model 501|
|National origin||United States|
|Manufacturer||Allison Engine Company |
|Major applications||Convair 580 |
Grumman C-2 Greyhound
Lockheed C-130 Hercules
Lockheed L-188 Electra
Lockheed P-3 Orion
Northrop Grumman E-2 Hawkeye
Lockheed CP-140 Aurora
|Developed from||Allison T38|
|Developed into||Rolls-Royce T406|
The Allison T56 is an American single-shaft, modular design military turboprop with a 14-stage axial flow compressor driven by a four-stage turbine. It was originally developed by the Allison Engine Company for the Lockheed C-130 Hercules transport entering production in 1954. It has been a Rolls-Royce product since 1995 when Allison was acquired by Rolls-Royce. The commercial version is designated 501-D. Over 18,000 engines have been produced since 1954, logging over 200 million flying hours.
Design and development
The T56 turboprop, evolved from Allison's previous T38 series, was first flown in the nose of a B-17 test-bed aircraft in 1954. One of the first flight-cleared YT-56 engines was installed in a C-130 nacelle on Lockheed's Super Constellation test aircraft in early 1954. Originally fitted to the Lockheed C-130 Hercules quad-turboprop military transport aircraft, the T56 was also installed on the Lockheed P-3 Orion quad-turboprop maritime patrol aircraft (MPA), Grumman E-2 Hawkeye twin-turboprop airborne early warning (AEW) aircraft, and Grumman C-2 Greyhound twin-turboprop carrier onboard delivery (COD) aircraft, as well as civilian airliners such as the quad-turboprop Lockheed Electra and the Convair 580.
The T56-A-1 delivered to Lockheed in May, 1953, produced only 3,000 shp (2,237 kW), compared to the required 3,750 shp (2,796 kW) for the YC-130A. Evolution of the T56 has been achieved through increases in pressure ratio and turbine temperature. The T56-A-14 installed on the P-3 Orion has a 4,591 shp (3,424 kW) rating with a pressure ratio of 9.25:1 while the T56-A-427 fitted to the E-2 Hawkeye has a 5,250 shp (3,915 kW) rating and a 12:1 pressure ratio. In addition, the T56 produces approximately 750 lbf (3,336.17 N) residual thrust from its exhaust.
Over the years, there have been a number of engine development versions, which are grouped by series numbers. The Series I collection of derivatives came out in 1954, producing a sea-level static power rating of 3,460 propeller shp (2,580 kW) at a 59 °F (15 °C; 519 °R; 288 K) ambient temperature. Successive engine follow-ups included the Series II, which was introduced in 1958 and had an increased power rating of 3,755 prop shp (2,800 kW), and the Series III, which came out in 1964 and had another power increase to 4,591 prop shp (3,424 kW). The Series IV derivatives were developed in the 1980s after being approved for a U.S. Air Force engine model derivative program (EMDP) in the 1979 fiscal year budget. Series IV engines include the Air Force EMDP T56-A-100 demonstrator, model T56-A-101 for the Air Force's C-130 aircraft, T56-A-427 for NAVAIR's E-2C and C-2A aircraft, 501-D39 for the Lockheed L-100 aircraft, and the 501-K34 marine turboshaft for NAVSEA. The T56-A-427 was capable of 5,912 prop shp (4,409 kW), but it was torque-limited to 5,250 prop shp (3,910 kW).
The Lockheed Martin C-130J Super Hercules which first flew in 1996, has the T56 replaced by the Rolls-Royce AE 2100, which uses dual FADECs (Full Authority Digital Engine Control) to control the engines and propellers. It drives six-bladed scimitar propellers from Dowty Rotol.
The T56 Series 3.5, an engine enhancement program to reduce fuel consumption and decrease temperatures, was approved in 2013 for the National Oceanic and Atmospheric Administration (NOAA) WP-3D "Hurricane Hunter" aircraft. After eight years of development and marketing efforts by Rolls-Royce, the T56 Series 3.5 was also approved in 2015 for engine retrofits on the U.S. Air Force's legacy C-130 aircraft that were currently in service with T56 Series 3 engines. Propeller upgrades to eight-bladed NP2000 propellers from UTC Aerospace Systems have been applied to the E-2 Hawkeye, C-2 Greyhound, and older-model C-130 Hercules aircraft, and will be adopted on the P-3 Orion.
Production of the T56 engine is expected to continue to at least 2026, with the U.S. Naval Air Systems Command (NAVAIR) order in 2019 of 24 additional E-2D Advanced Hawkeyes (AHEs) powered by the T56-A-427A engine variant.
Experimental and non-turboprop uses
The T56/Model 501 engine has been used in a number of experimental efforts, and as something other than a turboprop powerplant. In early 1960, two Allison YT56-A-6 experimental turbine engines without propellers were added next to existing propulsion engines on flight tests of a Lockheed NC-130B 58-0712 aircraft. The YT56-A-6 produced pressurized air for blowing over control surfaces to demonstrate boundary layer control (BLC), which helped to enable short takeoff and landing (STOL) performance.:42–44 In 1963, Lockheed and Allison designed another STOL demonstrator, this time for a U.S. Army requirement. Lockheed internal designation GL298-7 involved a C-130E Hercules that was re-engined with 4,591 shp (3,424 kW) 501-M7B turboprops. The 501-M7B produced more power than the normally installed, 3,755 shp (2,800 kW) T56-A-7 engines by about 20% (though the 501-M7B was limited to 4,200 shp (3,100 kW) to avoid additional structural changes), because the introduction of air cooling in the turbine's first-stage blade and the first and second-stage vanes allowed for an increase in the turbine inlet temperature.
In 1963, an aeroderivative line of industrial gas turbines based on the T56 was introduced in under the 501-K name. The 501-K is offered as a single-shaft version for constant speed applications and as a two-shaft version for variable-speed, high-torque applications. Series II standard turbines included the natural gas-fueled 501-K5 and the liquid-fueled 501-K14. The air-cooled Series III turbines included the natural gas-fueled 501-K13 and the liquid-fueled 501-K15. A marinized turboshaft version of the 501-K is used to generate electrical power onboard all the U.S. Navy's cruisers (Ticonderoga class) and almost all of its destroyers (Arleigh Burke class).
During the late 1960s, the U.S. Navy funded the development of the T56-A-18 engine, which introduced a new gearbox compared with the early gearbox on the T56-A-7. The 50-hour preliminary flight rating test (PFRT) was completed for the T56-A-18 in 1968. In the early 1970s, Boeing Vertol selected Allison (at that time known as the Detroit Diesel Allison Division (DDAD) of General Motors) to power a dynamic-system test rig (DSTR) supporting the development of its Model XCH-62 heavy-lift helicopter (HLH) program for the U.S. Army, using the Allison 501-M62B turboshaft engine. The 501-M62B had a 13-stage compressor based on the 501-M24 demonstrator engine, which was a fixed single-shaft engine with an increased overall pressure ratio and a variable-geometry compressor, and it had an annular combustor based on the T56-A-18 and other development programs. The turbine was derived from the fixed single-shaft T56, which had a four-stage section in which the first two stages provided enough power to drive the compressor, and the other two stages offered enough power to drive the propeller shaft. For the double-shaft 501-62B engine, it was split into a two-stage turbine driving the compressor, where the turbine stages had air-cooled blades and vanes, and a two-stage free power turbine driving the propeller through a gearbox. The 501-62B also incorporated improvements proven by Allison's GMA 300 demonstrator program, which allowed for an airflow of 42 lb/s (1,100 kg/min). After DSTR testing was successful, the 501-62B engine was further developed into the XT701-AD-700 engine for use on the HLH. The 8,079 shp (6,025 kW) XT701 passed the tests required to enter ground and flight testing on the HLH, but funding of the HLH program was canceled in August 1975, when the triple-turbine, tandem-rotor helicopter prototype had reached 95% completion.:3
Following the HLH program cancellation, Allison decided in early 1976 to apply the XT701 engine technology into a new industrial gas turbine product, the 570-K. The industrial engine, which entered production in the late 1970s, was derated to 7,170 shp (5,350 kW) and adapted for marine, gas compressor, and electrical power generation variants. The only major changes made for the 570-K were the elimination of compressor bleed air and replacing the XT701's titanium compressor case with a steel case. The 570-K was then adapted to the 6,000 shp (4,500 kW) 501-M78B demonstration engine, which Lockheed flew on a Grumman Gulfstream II as part of the NASA Propfan Test Assessment Program in the late 1980s. The 501-M78B had the same 13-stage compressor, combustor, 2-stage gas producer turbine, and 2-stage free power turbine used on the XT701 and 570-K, but it was connected through a 6.797 reduction ratio gearbox to a 9 ft diameter (2.7 m) Hamilton Standard single-rotation propfan, containing propfan blades that were swept back 45 degrees at the tips.
- The initial civil variant, which was proposed in 1955 with 3,750 equivalent shp (2,800 kW) of power at a brake specific fuel consumption (BSFC) of 0.54 lb/hp/h (0.24 kg/hp/h; 0.33 kg/kW/h), a two-stage gearbox with a reduction ratio of 12.5:1, a 14-stage axial flow compressor with a compression ratio over 9:1, a four-stage turbine, and a 13 1⁄2 ft diameter (4.11 m), three-blade Aeroproducts A6341FN-215 propeller
- (Series I) Commercial version of the T56-A-1 used on the Lockheed L-188 Electra, but using kerosene as the primary fuel and JP4 as the alternate (instead of JP4 as primary and gasoline as secondary), and with the gearbox reduction ratio increased to 13.54 from 12.5, which lowers the propeller blade tip speed by 8 percent to 721 ft/s (220 m/s; 427 kn; 492 mph; 791 km/h) for the 13 ft 6 in (4.11 m) Aeroproducts 606 propeller; 3,750 equivalent shp (2,800 kW) power rating at sea level takeoff, 14-stage axial compressor, 6 cannular combustion chambers, and 4-stage turbine; 13,820 rpm shaft and 1,780 °F (970 °C; 2,240 °R; 1,240 K) turbine inlet temperature; certified on September 12, 1957
- (Series I) Similar to the 501-D13 but using a Hamilton Standard propeller; certified on April 15, 1958
- (Series I) Similar to the 501-D13 except for the location of the rear mount and using D.C. generator drive; certified on December 18, 1959; used on the Convair CV-580 passenger aircraft
- (Series I) Similar to the 501-D13 except for the location of the rear mount; certified on December 18, 1959
- (Series I) Similar to the 501-D13D but with water-methanol injection; certified on February 20, 1964; used on the USAF's General Dynamics NC-131H Samaritan and the Convair CV-580
- A 4,050 shp (3,020 kW) engine under development for the Lockheed Electra
- (Series II) Similar to the 501-D13A but with 4,050 equivalent shp (3,020 kW) power rating at sea level takeoff, a shroud turbine, gearbox offset up, and no auto-feathering; certified on October 28, 1964; Lockheed L-100 Hercules
- (Series III); Similar to the 501-D22 but with 4,680 equivalent shp (3,490 kW) power rating at sea level takeoff and air-cooled first-stage turbine blades, vanes, and stalk blades in all four turbine stages; certified on January 23, 1968
- (Series III) Similar to the 501-D22A but with gearbox offset down, integral mount pads, and water-methanol injection; certified on December 27, 1968; powered the Aero Spacelines Super Guppy
- A 4,591 shp (3,424 kW) derivative to power the proposed Lockheed L-400, a twin-engine version of the L-100
- (Series III) Similar to the 501-D22C but with 4,815 equivalent shp (3,591 kW) power rating at sea level takeoff, a three-mount system, auto-feathering, and no water-methanol injection; certified on March 23, 1984; used on the Convair CV-580
- (Series II) Re-engined powerplant for the Royal Canadian Air Force (RCAF) CC-109 Cosmopolitan in 1966
- (Series IV) Offered for the Lockheed L-100 civil aircraft
- Engine for the proposed Vanguard Model 30 lift fan aircraft that was entered in a 1961 vertical takeoff and landing (VTOL) transport competition; powered two 8 ft diameter (2.4 m) fans within the wings and two 14 ft 6 in diameter (4.42 m) propellers
- Replaces the T56-A-7 on an experimental short takeoff and landing (STOL) version of the Lockheed C-130E (internally designated as the GL298-7) targeted in 1963 for the U.S. Army; power increased by 20% over the T56-A-7 due to lowering of the gear reduction ratio from 13.54 to 12.49, propeller blade changes to take advantage of the higher resulting propeller rotational speed, and a new turbine with air-cooled first and second-stage vanes and first-stage blades, so the turbine inlet temperature can be increased from 1,780 °F (970 °C; 2,240 °R; 1,240 K) for the T56-A-7 to 1,970 °F (1,080 °C; 2,430 °R; 1,350 K); a 4,591 shp (3,424 kW) rate engine that is restricted to 4,200 shp (3,100 kW) and about 10,600 lbf (4,800 kgf; 47 kN) of static thrust on the STOL C-130E, but is capable of 13,000 lbf (5,900 kgf; 58 kN) thrust at full power and with a larger, 15 ft (4.6 m) propeller
- A demonstrator engine later used to derive the 501-M62B engine developed for the XCH-62 helicopter
- A 6,000 shp (4,500 kW) four-stage fixed turbine engine similar to the T56-A-15, but with a 90 °F (32 °C) increase in maximum turbine inlet temperature rating to 1,970 °F (1,080 °C; 2,430 °R; 1,350 K) and a variable geometry compressor for the inlet vane and the first five stator vanes; investigated in 1965 to power helicopters with a 75,000–85,000 lb (34,000–39,000 kg) maximum takeoff weight (MTOW):12,15,213
- A 5,450 shp (4,060 kW) similar to the 501-M25 but with a free turbine instead of a fixed turbine, and a two-stage gas producer turbine:12,15,213
- A 5,175 shp (3,859 kW) turboshaft engine targeted for a 60-70 seat commuter helicopter proposal from Lockheed-California in 1966
- An internal designation for the engine that became the 8,079-shaft-horsepower (6,025-kilowatt) T701-AD-700 turboshaft, which weighed 1,179 lb (535 kg) and was intended to power the Boeing Vertol XCH-62 heavy-lift helicopter; 15 engines built, 700 hours of component testing, and almost 2,500 hours of engine development testing completed before the helicopter project's cancellation
- Engine proposed for transport-type offensive anti-air (TOAA) aircraft versions of the P-3 Orion (stretched derivative) and C-130 Hercules; rated power of 4,678 shp (3,488 kW), equivalent installed thrust-specific fuel consumption at cruise of 0.52 lb/(lbf⋅h) (15 g/(kN⋅s))
- A derivative of the T56-A-14 evaluated by NAVAIR in 1982 to achieve 10% lower fuel consumption, 24% more horsepower, smokeless exhaust, and greater reliability
- (Series IV) A 5,250 hp (3,910 kW) engine using a larger propeller to power the Lockheed L-100-20 (L382E-44K-20) High Technology Test Bed (HTTB) for short takeoff and landing (STOL) starting in 1989, but was destroyed in a fatal crash on February 3, 1993
- A 6,000 shp (4,500 kW), 9-foot diameter (2.7 m) demonstrator engine for NASA's Propfan Test Assessment program; flight-tested on a Gulfstream II aircraft
- Also known as the T406-AD-400, a 6,000 shp class (4,500 kW) turboshaft engine primarily based on the T56-A-427, but with a free-turbine turboshaft added to the single-spool engine; used on the V-22 Osprey tiltrotor assault transport
- PW–Allison 501-M80E
- A 14,800 lbf thrust (6,700 kgf; 66 kN) contra-rotating geared propfan engine derived from the 501-M80C/T406 turboshaft engine and intended for use on a 92-seat version of the proposed MPC 75 regional aircraft; developed jointly with Pratt & Whitney
- A propfan engine studied for the MPC 75:1264 that was based on the T406 core and rated at 11,000 lbf thrust (5,000 kgf; 49 kN):69
- (Series I) A 1,600 lb weight (730 kg) engine delivering 3,460 shp (2,580 kW) and 725 lbf (329 kgf; 3.22 kN) residual jet thrust, which is equal to 3,750 equivalent shp (2,800 kW); single-shaft 14-stage axial flow compressor, cannular combustion chamber with 6-cylindrical through-flow combustion liners, 4-stage axial flow turbine; 13,800-rpm shaft connected to a 2-stage reduction gear with a 12.5-to-1 ratio, consisting of a 3.125-to-1 spur set followed by a 4.0-to-1 planet set
- A 3,750 equivalent shp (2,800 kW) engine used on the Lockheed C-130A Hercules
- Proposed gas generator engines for the McDonnell XHCH-1 helicopter
- A 3,250 equivalent shp (2,420 kW) engine that was paired with an Aeroproducts propeller and test flown by the Military Air Transport Service (MATS) on a pair of Convair YC-131C twin-turboprop aircraft between January and December 1955
- A 2,900 hp (2,200 kW) engine for the C-131D executive transport/VC-131H VIP transport; also the proposed engines for the McDonnell XHRH-1 helicopter, with propeller drive and gas generator bleed for rotor-tip pressure jets
- A 2,100 shp (1,600 kW) turboshaft version for the Piasecki YH-16B Transporter helicopter
- Gas generator engines for the NC-130B (58-0712) boundary layer control (BLC) demonstrator
- (Series II) A 4,050 shp (3,020 kW) engine flight-tested on a U.S. Air Force Allison Boeing B-17 flying testbed aircraft, intended for the Lockheed C-130B; also used on the C-130E; produces about 9,500 lbf (4,300 kgf; 42 kN) of static thrust
- (Series II) Lockheed C-130B Hercules Starting May 1959
- (Series II) Used on the U.S. Air Force C/HC/NC-130B, MC-130E, and WC-130F; similar to -A-7A
- (Series II) Entered production in 1959; the original engine on the Grumman E-2C, using the Aeroproducts A6441FN-248 propeller
- (Series I) Used on the U.S. Air Force C/AC/DC/NC/RC-130A and the C-130D
- (Series I) Lockheed C-130A Hercules starting December 1956 and on all Grumman E-2A Hawkeyes from 1960
- (Series I) Similar to -A-9D
- (Series II) Water injection model that entered production in 1960
- (Series II) Used on the P-3A, EP-3A, and RP-3A:3
- (Series 3.5) Enhancements that improve SFC by 7.9%, increase maximum engine torque limit operation from 90 to 118 °F (32 to 48 °C; 549 to 578 °R; 305 to 321 K), and increase turbine life; tested on a C-130H testbed aircraft in 2012
- (Series III) Lockheed P-3/EP-3/WP-3/AP-3/CP-140 Aurora from August 1962; entered production in 1964
- (Series 3.5) Fuel efficiency and reliability upgrade, Lockheed WP-3D Orion from May 2015.
- (Series III) Lockheed C-130H Hercules USAF from June 1974
- (Series 3.5) Upgrade of the T56-A-15 on the Air Force LC-130H
- (Series III) Used on the KC-130F, KC-130R, LC-130F, and LC-130R:3
- (Series 3.5)
- Navy-funded development with air-cooled blades and vanes in the first two stages; 50-hour preliminary flight rating test completed in 1968; introduced major gearbox update after 4,000 hours of back-to-back testing, featuring a double helical first gear stage, a planetary helical gear for the second stage, and fewer parts for the accessory gearing (compared with a first-stage spur gear, second-stage planetary spur gear, and separable clamped components in the accessory gearing for the T56-A-7 gearbox)
- (Series IV) U.S. Air Force EMDP demonstrator
- (Series IV) Offered for the Lockheed C-130 Hercules
- Used on U.S. Navy Northrop Grumman E-2C Hawkeye aircraft
- Used on U.S. Navy Lockheed EC-130G and EC-130Q aircraft
- (Series III) Replaced the T56-A-8 on the Grumman E-2C, using the 13.5 ft diameter (4.1 m) Hamilton 54460-1 propeller; Grumman C-2A Greyhound from June 1974
- Used on the C-2A, E-2B, and TE-2A:3
- (Series IV) Northrop Grumman E-2 Hawkeye upgrades from 1972
- (Series IV) Used on the Northrop Grumman E-2D Advanced Hawkeye (AHE), which first flew in 2007
- An 8,079 shp (6,025 kW) turboshaft powerplant developed from the 501-M62B and intended for use on the canceled three-engine Boeing Vertol XCH-62 heavy-lift helicopter
Specifications (T56 Series IV)
Data from Rolls-Royce.
- Type: Turboprop engine
- Length: 146.1 in (3,710 mm)
- Diameter: 27 in (690 mm)
- Dry weight: 1,940 lb (880 kg)
- Compressor: 14 stage axial flow
- Combustors: 6 cylindrical flow-through
- Turbine: 4 stage shared load
- Fuel type: Kerosene, jet fuel (Jet A, Jet A-1, JP-4, JP-5, or JP-8), or aviation gasoline (grade 115/145 or lower)
- Maximum power output: SLS, 59 °F (15 °C), max power: 5,912 shp (4,409 kW) (torque limited to 5,250 shp (3,910 kW)); 25,000 ft altitude (7,600 m), Mach 0.5, max continuous power: 3,180 shp (2,370 kW)
- Turbine inlet temperature: 860 °C (1,580 °F)
- Fuel consumption: 2,412 lb/h (1,094 kg/h)
- Specific fuel consumption: SLS, 59 °F (15 °C), max power: 0.4690 lb/shp/h (0.2127 kg/shp/h; 0.2853 kg/kW/h); 25,000 ft altitude (7,600 m), Mach 0.5, max continuous power: 0.4200 lb/shp/h (0.1905 kg/shp/h; 0.2555 kg/kW/h)
- Power-to-weight ratio: 2.75 shp/lb (4.52 kW/kg)
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