The Allison T56turboprop engine has been developed extensively throughout its production run, the many variants are described by the manufacturer as belonging to four main series groups.
Initial civil variants (Series I) were designed and produced by the Allison Engine Company as the 501-D and powered the Lockheed C-130 Hercules. Later variants (Series II,III, 3,5 and IV) gave increased performance through design refinements.
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/kWh), 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.
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. Used on the 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.
Offered in 1979 as the initial engine for Lockheed's proposed L-100-60 (a stretched derivative of the Lockheed 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 IV) Offered for the Lockheed L-100 civil aircraft, starting in 1979 for the proposed L-100-60 as the successor engine to the 501-D22E, producing 5,575 shp (4,157 kW) with 14 ft diameter (4.3 m) propellers; was the commercial version of the 501-M71.
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 started in 1964 that was 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).
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.
A 5,175 shp (3,859 kW) turboshaft engine targeted for a 60-70 seat commuter helicopter proposal from Lockheed-California in 1966.
Engine candidate for the turboprop version of the Air Force A-Xclose air support aircraft, requiring 4,400 shp (3,300 kW) of engine power.
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 when the HTTB became airborne during a ground test on February 3, 1993.
A 6,000 shp (4,500 kW) demonstrator engine for NASA's Propfan Test Assessment (PTA) program. It had a modified reduction gearbox that reversed the direction of rotation and increased the output speed from 1,020 rpm to 1,698 rpm. The engine was attached to an eight-bladed, 9 ft diameter (2.7 m), single-rotation Hamilton Standard SR-7L propeller. The 501-M78 was flight-tested on a Gulfstream II aircraft beginning in May 1987.
A turboprop engine offered as an equal partnership between Allison and Pratt & Whitney to power Lockheed's proposed successor to the P-3 Orion, which was developed for the U.S. Navy's long-range air antisubmarine warfare (ASW) capable aircraft (LRAACA) program.
A propfan engine studied for the MPC 75 that was based on the T406 core and rated at 11,000 lbf thrust (5,000 kgf; 49 kN).
(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 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.
(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) Used on the P-3A, EP-3A, and RP-3A.
(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 3.5) Upgrade of the T56-A-15 on the Air Force LC-130H.
Maintenance of a T56-A-16, 2009
(Series III) Used on the KC-130F, KC-130R, LC-130F, and LC-130R.: 3
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); used an eight-bladed Hamilton Standard variable-camber propeller.
^Stone, Irving (January 24, 1955). "T56 boosts U.S. turboprop airliner bid". Air transport. Aviation Week. Vol. 62 no. 4. pp. 80, 83. ISSN 0005-2175.
^Hazen, R.M.; Gerdan, D.; LaMotte, R.R. (April 9–12, 1956). The Allison power package for the Lockheed Electra. SAE National Aeronautic Meeting. SAE Technical Papers. New York City, New York, U.S.A.: SAE International. doi:10.4271/560273. ISSN 0148-7191. OCLC 5817960717.
^Pigott, Peter (July 2003). Taming the skies: A celebration of Canadian flight. p. 157. ISBN 9781550024692. OCLC 52286158.
^ abcMcIntire, W.L. (June 4–7, 1984). A new generation T56 turboprop engine(PDF). Turbo Expo: Power for Land, Sea, and Air. 2: Aircraft engine, marine, microturbines and small turbomachinery. Amsterdam, Netherlands. doi:10.1115/84-GT-210. ISBN 978-0-7918-7947-4. OCLC 4434363138.
^Woodley, David R.; Castle, William S. (October 16–18, 1973). Heavy lift helicopter main engines. National Aerospace Engineering and Manufacturing Meeting. SAE Technical Papers. Los Angeles, California, U.S.A.: Society of Automotive Engineers (SAE) (published February 1973). doi:10.4271/730920. ISSN 0148-7191.
^ abAllison Division - General Motors (July 1965). Powerplant studies for shaft-driven helicopter (Report). OCLC 872723329.
^Ulsamer, Edgar E. (January 1970). "AX: Lethal, accurate, agile, and cheap". Air Force and Space Digest. pp. 33–36, 39. ISSN 0002-2349.
^Stinger, D.H.; Redmond, W.A. (1978). "Advanced gas turbine for marine propulsion model 570-K". SAE Technical Paper Series. SAE Technical Papers. 1. Society of Automotive Engineers (SAE) (published February 1978). doi:10.4271/780702. ISSN 0148-7191.
^O'Neil, William D. (November 14, 1977). Land-based aircraft options for naval missions. SAE Transactions. 86 (4). Los Angeles, California, U.S.A.: Society of Automotive Engineers (SAE). pp. 3316–3330. doi:10.4271/770965. ISSN 0096-736X. JSTOR 44644625. OCLC 5817964451.
^ abcdCote, S.M. (June 17, 1983). Survey of P-3C mission profiles for development of the T56-A-14 duty cycle (Report). Naval Air Systems Command (NAVAIR). OCLC 38850276.
^Lockheed Aeronautical Systems (May 19, 1989). "Lockheed HTTB sets STOL records for time-to-climb, payload lift" (Press release). Palmdale, California, U.S.A.: PR Newswire – via Gale Research.
^Darden, Stan (February 4, 1993). "Plane that crashed was simulating engine failure". Marietta, Georgia, U.S.A. United Press International (UPI).
^Poland, Dyckman T. (December 1986). "PTA—Research at full scale". Lockheed Horizons. No. 22. pp. 2–11. ISSN 0459-6773.
^Moxon, Julian (May 9, 1987). "Propfanned G2 takes to the air" (PDF). World News. Flight International. Vol. 131 no. 4061. Marietta, Georgia, USA. p. 2. ISSN 0015-3710. Archived from the original (PDF) on December 7, 2019.
^Competition Advocate General, Department of the Navy. Long range acquisition estimates (FY 88 base year projections) (Report). p. 154. hdl:2027/uiug.30112104099186. Retrieved August 1, 2020.
^"Navy surprise on V-22 power" (PDF). Propulsion. Flight International. Vol. 129 no. 3995. Detroit, Michigan, USA. January 25, 1986. p. 16. ISSN 0015-3710. Archived from the original (PDF) on April 19, 2014.
^MBB CATIC Association (July 1987). MPC 75 feasibility study - Summary report: B1 - Project definition (PDF) (Report). pp. B1–23 to B1–25, B1–30, B1–31.
^Greff, E. (September 9–14, 1990). Aerodynamic design for a new regional aircraft(PDF). Congress of the International Council of the Aeronautical Sciences (17th ed.). Stockholm, Sweden. pp. 1251–1265. OCLC 1109530657.
^Wheatley, John B.; Zimmerman, D.G.; Hicks, R.W. (April 18–21, 1955). The Allison T56 turbo-prop aircraft engine. SAE Golden Anniversary Aeronautical Meeting. SAE Technical Papers. New York City, New York, U.S.A.: SAE International. doi:10.4271/550075. ISSN 0148-7191. OCLC 1109574510.
^The 1961 aerospace year book(PDF) (42nd ed.). American Aviation Publications. 1961. p. 400.
^Allen, Brooke E. (March 1957). "What we've learned about turboprops". Air Force Magazine. Vol. 40 no. 3. pp. 82, 85–86. ISSN 0730-6784.
^DeFrank, Thomas (July 2008). "The things it carried: How an unremarkable Convair C-131H transported cops, patients, prisoners, and Gerald Ford". Air & Space Magazine. ISSN 0886-2257.
^ abWade, Mark D. (October 2002). Aircraft/auxiliary power units/aerospace ground support equipment emission factors (Report). United States Air Force IERA. p. 6. OCLC 834246721.
^ abLaughlin, T.P.; Toth, Joseph (March 18–21, 1985). T56 derivative engine in the improved E-2C(PDF). ASME 1985 International Gas Turbine Conference and Exhibit. Houston, Texas, U.S.A. doi:10.1115/85-GT-176. ISBN 978-0-7918-7938-2. OCLC 7344649118.
^"Enhanced T56 engine could save billions in C-130H operating costs". Defense Update. September 19, 2012. Retrieved September 8, 2020.
^Meister, Jake (March 16, 2016). "Raytheon given $573M contract for continued missile production". Design World (published March 21, 2016). ISSN 1941-7217.
^The 1969 aerospace year book(PDF). Aerospace Industries Association of America (AIA). 1969. p. 52.
^McIntire, W.L.; Wagner, D.A. (April 18–22, 1982). Next generation turboprop gearboxes(PDF). Turbo Expo: Power for Land, Sea, and Air. 2: Aircraft engine, marine, microturbines and small turbomachinery. London, England, U.K. doi:10.1115/82-GT-236. ISBN 978-0-7918-7957-3. OCLC 8518954720.