View source for Allison T56

{{short description|American-built military turboprop (1954–)}}
{{Use dmy dates|date=May 2022}}
{{Use American English|date=May 2022}}
<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{|{{Infobox aircraft begin
 |name= T56 / Model 501
 |image= File:Allison T56 turboprop for C-130 2007.JPEG
 |caption= A T56 mounted on a U.S. Air Force C-130 Hercules receives maintenance. 
}}{{Infobox aircraft engine
 |type= [[Turboprop]]
 |national origin = [[United States]]
 |manufacturer= [[Allison Engine Company]] <br /> [[Rolls-Royce plc]]
 |first run=
 |major applications= [[Convair 580]] <br /> [[Grumman C-2 Greyhound]] <br /> [[Lockheed C-130 Hercules]] <br /> [[Lockheed L-188 Electra]] <br /> [[Lockheed P-3 Orion]]  <br /> [[Northrop Grumman E-2 Hawkeye]] <br /> [[Lockheed CP-140 Aurora]]<ref name="Aurora"/>
 |number built =>18,000<ref name="NumberBuilt201811"/>
 |developed from = [[Allison T38]]
 |developed into = [[Rolls-Royce T406]]
 |variants with their own articles =
}}
|}

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<ref name="gs"/> entering production in 1954. It has been a [[Rolls-Royce plc|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.<ref name="rr"/>

==Design and development==
[[File:Allison T56-A1 Turboprop Engine Cutaway.jpg|thumb|Allison T56-A1 turboprop engine cutaway, at the Smithsonian National Air and Space Museum]]

The T56 turboprop, evolved from Allison's previous [[Allison T38|T38]] series,<ref name="gs"/> was first flown in the nose of a B-17 test-bed aircraft in 1954.<ref name="gs" /> 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.<ref name="Flight19540430"/> Originally fitted to the [[Lockheed C-130 Hercules]] [[military transport aircraft]], the T56 was also installed on the [[Lockheed P-3 Orion]] [[maritime patrol aircraft]] (MPA), [[Grumman E-2 Hawkeye]] [[airborne early warning]] (AEW) aircraft, and [[Grumman C-2 Greyhound]] [[carrier onboard delivery]] (COD) aircraft, as well as civilian airliners such as the [[Lockheed L-188 Electra|Lockheed Electra]] and the [[Convair 580]].<ref name="gs" />

The T56-A-1 delivered to Lockheed in May, 1953, produced only {{cvt|3000|shp|0}}, compared to the required {{cvt|3750|shp|0}} 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 {{cvt|4591|shp|0}} rating with a pressure ratio of 9.25:1 while the T56-A-427 fitted to the E-2 Hawkeye has a {{cvt|5250|shp|0}} rating and a 12:1 pressure ratio. In addition, the T56 produces approximately {{cvt|750|lbf|2}} residual thrust from its exhaust.<ref name="T56IsFifty"/>

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 {{cvt|3,460|shp|kW|adj=pre|propeller}} at a {{cvt|59|F|C R K}} ambient temperature. Successive engine follow-ups included the Series II, which was introduced in 1958 and had an increased power rating of {{cvt|3,755|shp|kW|adj=pre|prop}}, and the Series III, which came out in 1964 and had another power increase to {{cvt|4,591|shp|kW|adj=pre|prop}}. The Series II and III derivatives were developed under military component improvement programs (CIP).<ref name="LaughlinToth1985"/> By 1965, Allison was proposing the development of Series IV derivatives,<ref name="AllisoNews19650115"/> but in 1968, the [[United States Congress]] restricted CIP work to reliability and maintainability improvements instead of performance improvements.<ref name="LaughlinToth1985"/> The Series IV derivatives were finally 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 {{cvt|5,912|shp|kW|adj=pre|prop}}, but it was [[torque]]-limited to {{cvt|5,250|shp|kW|adj=pre|prop}}.<ref name="McIntireSeriesIV"/>

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.<ref name="rr21"/> It drives six-bladed [[scimitar propellers]] from [[Dowty Rotol]].<ref name="DowtyR391"/>

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.<ref name="HurricaneHunters"/> 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 III engines.<ref name="FG20150910"/> As part of the T56 Series 3.5 upgrade, parts from the T56 Series IV engine (such as the compressor seals) and the uncooled turbine blades from the [[AE 1107C]] turboshaft would be retrofit into existing T56 Series III casing installations.<ref name="AFT20140709">{{cite news |work=Airforce Technology |title=US approves Rolls-Royce's T56 Series 3.5 engine upgrade for C-130H fleet |url=https://www.airforce-technology.com/news/newsus-approves-rolls-royces-t56-series-35-engine-upgrade-for-c-130h-fleet-4315040/ |date=9 July 2014 |access-date=16 February 2023}}</ref> 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,<ref name="Warzone20180108"/> and will be adopted on the P-3 Orion.<ref name="AIN20180717"/>

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 [[Northrop Grumman E-2 Hawkeye#E-2D Advanced Hawkeye|E-2D Advanced Hawkeyes]] (AHEs) powered by the T56-A-427A engine variant.<ref name="AIN20190411"/>

===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.{{R|"STOL-BLC"|pp=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 {{cvt|4,591|shp|kW}} 501-M7B turboprops. The 501-M7B produced more power than the normally installed, {{cvt|3,755|shp|kW}} T56-A-7 engines by about 20% (though the 501-M7B was limited to {{cvt|4,200|shp|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.<ref name="AWST19630107"/>

In 1963, an [[aeroderivative]] line of industrial gas turbines based on the T56 was introduced in under the 501-K name.{{sfn|Zigmunt|1997|p=[{{GBurl|7wI8SAq6l1cC|p=127}} 127]}} 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.{{sfn|Allison Industrial Gas Turbines|1983}} 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.<ref name="BixlerClifford1967"/> A marinized turboshaft version of the 501-K is used to generate electrical power onboard all the U.S. Navy's cruisers ({{sclass|Ticonderoga|cruiser|4}}) and almost all of its destroyers ({{sclass|Arleigh Burke|destroyer|4}}).

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.<ref name="NextGenGearboxes"/> The 50-hour preliminary flight rating test (PFRT) was completed for the T56-A-18 in 1968.<ref name="1969yearbook"/> 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 [[Boeing Vertol XCH-62|XCH-62]] heavy-lift helicopter (HLH) program for the U.S. Army, using the Allison 501-M62B turboshaft engine.<ref name="ARD197401"/> 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-M62B 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-M62B also incorporated improvements proven by Allison's GMA 300 demonstrator program, which allowed for an airflow of {{cvt|42|lb/s}}.<ref name="HLH_Main_Engines"/> After DSTR testing was successful, the 501-M62B engine was further developed into the [[XT701]]-AD-700 engine for use on the HLH. The {{cvt|8,079|shp}} XT701 passed the tests required to enter ground and flight testing on the HLH,<ref name="1978StingerRedmond"/> but funding of the HLH program was canceled in August 1975, when the triple-turbine, tandem-rotor helicopter prototype had reached 95% completion.{{R|"BVFinalReport1980"|p=[https://archive.org/details/DTIC_ADA085290/page/n4 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 {{cvt|7,170|shp}} and adapted for marine, gas compressor, and electrical power generation variants.<ref name="1978StingerRedmond"/> 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 {{cvt|6,000|shp}} 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 {{cvt|9|ft|m|diameter|adj=mid}} [[Hamilton Standard]] single-rotation [[propfan]], containing propfan blades that were swept back 45 degrees at the tips.<ref name="PTAFinalReport1989"/>

==Variants==
{{Main|Allison T56 variants}}

The T56 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, and IV) and the Series 3.5 engine enhancement kit gave increased performance through design refinements.

Further derivatives of the 501-D/T56 were produced as [[turboshaft]]s for [[helicopter]]s including a variant designated T701 that was developed for the canceled [[Boeing Vertol XCH-62]] project.

==Applications==
{{collist|
* [[Aero Spacelines Super Guppy]]
* [[Boeing Vertol XCH-62]] 
* [[Boeing 929]]
* [[Convair 580|Convair 580 and Convair 5800]]
* [[Grumman C-2 Greyhound]]
* [[Lockheed C-130 Hercules]]
* [[Lockheed CP-140 Aurora]]
* [[Lockheed L-100 Hercules]]
* [[Lockheed L-188 Electra]]
* [[Lockheed P-3 Orion]]
* [[Northrop Grumman E-2 Hawkeye]]
* [[Piasecki H-16 Transporter|Piasecki YH-16B Transporter]]
}}

==Specifications (T56 Series IV)==
{{jetspecs
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|ref=''Rolls-Royce.''<ref name="TrainingManual2003"/>
|type=[[Turboprop]] [[Aircraft engine|engine]]
|length={{cvt|146.1|in|mm|lk=on}}
|diameter={{cvt|27|in|mm}}
|weight={{cvt|1,940|lb|kg|lk=on}}
|compressor=14 stage [[Axial compressor|axial flow]]
|combustion=6 [[Can combustor|cylindrical flow-through]]
|turbine= 4 stage shared load
|fueltype=[[Kerosene]], [[jet fuel]] (Jet A, Jet A-1, JP-4, JP-5, or JP-8), or [[aviation gasoline]] (grade 115/145 or lower)<ref name="TCDS"/>
|oil system=1  system (Oil is shared between power section and [[reduction gearbox]].)
|power=''SLS, {{cvt|59|F}}, max power'': {{cvt|5,912|shp}} ([[torque]] limited to {{cvt|5,250|shp}}); ''{{cvt|25,000|ft|m|adj=mid|altitude}}, [[Mach number|Mach]] 0.5, max continuous power'': {{cvt|3,180|shp}}<ref name="McIntireSeriesIV"/>
|thrust=
|eqivshaftpower=
|pressratio=14.5:1
|bypass=
|airmassflow={{cvt|240 - 280|lb|abbr=on}}
|turbinetemp={{cvt|860|°C|°F|lk=on}}
|fuelcon= {{cvt|2,412|lb/h|abbr=on}}
|specfuelcon=''SLS, {{cvt|59|F}}, max power'': {{cvt|285.3|mg/Wh|lb/hph kg/hph kg/kWh|order=out}}; ''{{cvt|25,000|ft|m|adj=mid|altitude}}, [[Mach number|Mach]] 0.5, max continuous power'': {{cvt|255.5|mg/Wh|lb/hph kg/hph kg/kWh|order=out}}<ref name="McIntireSeriesIV"/>
|power/weight={{cvt|2.75|shp/lb|kW/kg|lk=on}}
|thrust/weight=
}}

==See also==
{{Portal|Aviation}}
{{Aircontent
|related=
* [[Allison T38]]
* [[Allison T40]]
* [[Allison T78]]
* [[Rolls-Royce AE 2100]]
* [[Rolls-Royce AE 3007]]
* [[Rolls-Royce T406]]
|similar engines=
* [[Bristol Proteus]]
* [[Ivchenko AI-20]]
* [[Lycoming T55]]
* [[Napier Eland]]
* [[Rolls-Royce Tyne]]
|lists=
* [[List of aircraft engines]]
|see also=
}}

==References==
{{Reflist|refs=
  <ref name="DowtyR391">{{cite web |author=Smithsonian National Air and Space Museum |author-link=Smithsonian National Air and Space Museum |title=Propeller, variable-pitch, 6-blade, Dowty R391 |url=https://airandspace.si.edu/collection-objects/propeller-variable-pitch-6-blade-dowty-r391 |access-date=August 4, 2020}}</ref>
  <ref name="Aurora">{{cite book |section-url=http://jproc.ca/rrp/rrp3/cp140.html |section=CP-140 Aurora |access-date=August 25, 2020 |given=Jerry |surname=Proc |title=Radio communications and signals: Intelligence in the Royal Canadian Navy}}</ref>
  <ref name="NumberBuilt201811">{{cite web |url=https://www.rolls-royce.com/products-and-services/defence-aerospace/transport-tanker-patrol-and-tactical/t56.aspx#section-overview |title=The world's number one large turboprop |publisher=[[Rolls-Royce plc]] |access-date=August 25, 2020}}</ref>
  <ref name="AIN20190411">{{cite news |work=[[AINonline]] |title=Advanced Hawkeye marches on |url=https://www.ainonline.com/aviation-news/defense/2019-04-11/advanced-hawkeye-marches |given=David |surname=Donald |date=April 11, 2019 |department=Defense |access-date=September 9, 2020}}</ref>
  <ref name="AIN20180717">{{cite news |work=[[AINonline]] |title=New look for an old warrior |url=https://www.ainonline.com/aviation-news/defense/2018-07-17/new-look-old-warrior |given=David |surname=Donald |date=July 17, 2018 |department=Farnborough Air Show |access-date=August 4, 2020}}</ref>
  <ref name="Warzone20180108">{{cite news |work=The Drive |department=The War Zone |title=USAF eyeing new props and upgraded engines to breathe extra life into old C-130Hs |url=https://www.thedrive.com/the-war-zone/17465/usaf-eyeing-new-props-and-upgraded-engines-to-breathe-extra-life-into-old-c-130hs |date=January 8, 2018 |given=Joseph |surname=Trevithick |access-date=August 4, 2020}}</ref>
  <ref name="HurricaneHunters">{{cite news |url=http://www.aero-news.net/subscribe.cfm?do=main.textpost&id=95b16316-e19c-47eb-8ba7-0048908e816f |title=NOAA 'Hurricane Hunters' first to get T56 series 3.5 engine enhancement |work=Aero News |date=November 14, 2013 |access-date=December 1, 2013}}</ref>
  <ref name="TCDS">{{cite web |title=Type Certificate Data Sheet E-282 |edition=30th |date=July 25, 2013 |url=https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/37851AD3AA37B87486257BB800525FC6 |publisher=[[U.S. Department of Transportation]] (DOT) |website=[[Federal Aviation Administration]] (FAA) |access-date=August 11, 2020}}</ref>
  <ref name="FG20150910">{{cite news |work=[[FlightGlobal]] |title=USAF approves production of Rolls-Royce T56 Series 3.5 upgrade |url=https://www.flightglobal.com/usaf-approves-production-of-rolls-royce-t56-series-35-upgrade/118158.article |date=September 10, 2015 |given=James |surname=Drew |access-date=August 11, 2020 |url-access=limited}}</ref>
  <ref name="rr21">{{cite web |url=http://www.rolls-royce.com/Images/AE2100_tcm92-6712.pdf |title=AE 2100 turboprop: Power for the Hercules, Spartan, US-2 and SAAB 2000 AEW&C |publisher=[[Rolls-Royce plc]] |access-date=November 2, 2012 |archive-url=https://web.archive.org/web/20130217053215/http://www.rolls-royce.com/Images/AE2100_tcm92-6712.pdf |archive-date=2013-02-17 |url-status=dead}}</ref>
  <ref name="rr">{{cite web |url=http://www.rolls-royce.com/Images/t56_tcm92-6711.pdf |title=T56: Power for the Hercules, Orion, Hawkeye and Greyhound |publisher=[[Rolls-Royce plc]] |access-date=August 25, 2020 |archive-url=https://web.archive.org/web/20130207210055/http://www.rolls-royce.com/Images/t56_tcm92-6711.pdf |archive-date=February 7, 2013 |url-status=dead}}</ref>
 <ref name="T56IsFifty">{{cite web |url=http://miravim.org/avimlibrary/Manuals/Powerplant%20Manuals/Aircraft%20Propellers/Other%20Manufacturers/Rolls-Royce%20Allison%20T56%20Turns%2050.pdf |title=The Rolls-Royce Allison T56 is fifty |publisher=New Zealand Aviation News |publication-date=September 2004 |access-date=November 2, 2013 |archive-url=https://web.archive.org/web/20141021001335/http://miravim.org/avimlibrary/Manuals/Powerplant%20Manuals/Aircraft%20Propellers/Other%20Manufacturers/Rolls-Royce%20Allison%20T56%20Turns%2050.pdf |archive-date=October 21, 2014 |url-status=dead |given=Phillip |surname=McKinnon}}</ref>  
  <ref name="TrainingManual2003">{{cite book |publisher=[[Rolls-Royce plc]] |title=Training manual: T56/501D Series III |year=2003 |pages=8-1 to 8-24}}</ref>
  <ref name="STOL-BLC">{{cite book |given=Bill |surname=Norton |title=STOL progenitors: The technology path to a large STOL aircraft and the C-17A |year=2002 |url={{GBurl|8zl09uULN8IC|p=42}} |pages=42–[{{GBurl|8zl09uULN8IC|p=43}} 43] |isbn=978-1-56347-576-4 |oclc=50447726 |publisher=[[American Institute of Aeronautics and Astronautics]] (AIAA) |doi=10.2514/4.868160}}</ref>
  <ref name="gs">{{cite web |url=http://www.globalsecurity.org/military/systems/aircraft/systems/t56.htm |title=Global Security T56 |publisher=www.globalsecurity.org |access-date=1 November 2012}}</ref>
  <ref name="PTAFinalReport1989">{{cite book|title=Propfan test assessment (PTA): Final project report |oclc=891598373 |surname1=Little |given1=B. H. |surname2=Poland |given2=D. T. |surname3=Bartel |given3=H. W. |surname4=Withers |given4=C. C. |surname5=Brown |given5=P. C. |url=https://ntrs.nasa.gov/search.jsp?R=19900002423 |volume=NASA-CR-185138|hdl=2060/19900002423 |hdl-access=free |date=July 1989}} [https://archive.org/details/NASA_NTRS_Archive_19900002423 alternate url]</ref>
  <ref name="LaughlinToth1985">{{cite conference |chapter=T56 derivative engine in the improved E-2C |chapter-url=https://micronanomanufacturing.asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1985/79382/V001T01A003/4456523/v001t01a003-85-gt-176.pdf |given1=T.P. |surname1=Laughlin |given2=Joseph |surname2=Toth |title=Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery |conference=ASME 1985 International Gas Turbine Conference and Exhibit |location=Houston, Texas, U.S.A. |date=March 18–21, 1985 |doi=10.1115/85-GT-176 |oclc=7344649118 |isbn=978-0-7918-7938-2|doi-access=free }}</ref>
  <ref name="McIntireSeriesIV">{{cite conference |chapter=A new generation T56 turboprop engine |chapter-url=https://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1984/79474/V002T02A007/2395358/v002t02a007-84-gt-210.pdf |given=W.L. |surname=McIntire |title=Volume 2: Aircraft Engine; Marine; Microturbines and Small Turbomachinery |conference=Turbo Expo: Power for Land, Sea, and Air |location=Amsterdam, Netherlands |volume=2: Aircraft engine; marine; microturbines and small turbomachinery |date=June 4–7, 1984 |doi=10.1115/84-GT-210 |oclc=4434363138 |isbn=978-0-7918-7947-4|doi-access=free }}</ref>
  <ref name="NextGenGearboxes">{{cite conference |chapter=Next generation turboprop gearboxes |chapter-url=https://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1982/79573/V002T02A013/2393964/v002t02a013-82-gt-236.pdf |given1=W.L. |surname1=McIntire |given2=D.A. |surname2=Wagner |title=Volume 2: Aircraft Engine; Marine; Microturbines and Small Turbomachinery |conference=Turbo Expo: Power for Land, Sea, and Air |location=London, England, U.K. |volume=2: Aircraft engine; marine; microturbines and small turbomachinery |date=April 18–22, 1982 |doi=10.1115/82-GT-236 |oclc=8518954720 |isbn=978-0-7918-7957-3|doi-access=free }}</ref>
  <ref name="BVFinalReport1980">{{cite report |author=Boeing Vertol Company |title=Heavy lift helicopter — Prototype technical summary |url=https://archive.org/details/DTIC_ADA085290 |publication-date=April 1980 |oclc=227450087}} [https://apps.dtic.mil/docs/citations/ADA085290 alternate url]</ref>
  <ref name="1978StingerRedmond">{{cite book |issn=0148-7191 |chapter=Advanced gas turbine for marine propulsion model 570-K |publication-date=February 1978 |given1=D.H. |surname1=Stinger |given2=W.A. |surname2=Redmond |title=SAE Technical Paper Series |journal=SAE Technical Papers |year=1978 |volume=1 |publisher=[[Society of Automotive Engineers]] (SAE) |doi=10.4271/780702}}</ref>
  <ref name="ARD197401">{{cite magazine |title=H.L.H. 1975 flight test projected: Component technology program meeting development goal|issn=0004-2560 |magazine=Army Research and Development  |url=https://hdl.handle.net/2027/msu.31293012265199?urlappend=%3Bseq=228 |publication-date=January–February 1974 |pages=10–11 |hdl=2027/msu.31293012265199 |volume=15 |number=1}}</ref>
  <ref name="HLH_Main_Engines">{{cite conference |issn=0148-7191 |title=Heavy lift helicopter main engines |date=October 16–18, 1973 |publication-date=February 1973 |given1=David R. |surname1=Woodley |given2=William S. |surname2=Castle |journal=SAE Technical Papers |series=SAE Technical Paper Series |volume=1 |publisher=[[Society of Automotive Engineers]] (SAE) |location=Los Angeles, California, U.S.A. |conference=National Aerospace Engineering and Manufacturing Meeting |doi=10.4271/730920}}</ref>
  <ref name="1969yearbook">{{cite book |year=1969 |title=The 1969 aerospace year book |url=https://www.aia-aerospace.org/wp-content/uploads/2016/06/THE-1969-AEROSPACE-YEAR-BOOK.pdf#page=61 |page=52 |publisher=Aerospace Industries Association of America (AIA)}}</ref>
  <ref name="BixlerClifford1967">{{cite conference |chapter=Gas turbine electrical power and steam generation at Allison Division of General Motors |chapter-url=https://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1967/79887/V001T01A041/2389841/v001t01a041-67-gt-42.pdf |given1=G.W. |surname1=Bixler |given2=H.J. |surname2=Clifford |title=ASME 1967 Gas Turbine Conference and Products Show  |date=March 5–9, 1967 |location=Houston, Texas, U.S.A. |isbn=978-0-7918-7988-7 |oclc=8518878647 |doi=10.1115/67-GT-42|doi-access=free }}</ref>
  <ref name="AllisoNews19650115">{{cite newsletter |work=AllisoNews |title=Dice sees anniversary as time to look ahead |url=https://indianamemory.contentdm.oclc.org/digital/collection/AT/id/6110 |publication-date=January 15, 1965 |editor-first=Milan C. |editor-last=Olbina |pages=1, [https://indianamemory.contentdm.oclc.org/digital/collection/AT/id/6116 7] |volume=24 |number=15 |oclc=42343144}}</ref>
  <ref name="AWST19630107">{{cite magazine |issn=0005-2175 |magazine=[[Aviation Week and Space Technology]] |title=Power boost planned for STOL C-130 |url=https://archive.org/details/Aviation_Week_1963-01-07/page/n27 |department=Aeronautical engineering |publication-date=January 7, 1963 |given=David A. |surname=Anderton |location=Marietta, Georgia, U.S.A. |pages=54–55, 57}}</ref>
  <ref name="Flight19540430">{{cite magazine |issn=0015-3710 |magazine=[[Flight (magazine)|Flight]] |url=https://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201209.html |url-status=dead |archive-date=December 27, 2014 |archive-url=https://web.archive.org/web/20141227224406/https://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201209.html |title=T56 test-bed: The Allison engine for the C-130 fitted to a Super Constellation |publication-date=April 30, 1954 |page=539}}</ref>
}}

==Bibliography==
* {{cite book |title=Allison, the people and the power: A pictorial history |url={{GBurl|7wI8SAq6l1cC}} |given=Joan Everling |surname=Zigmunt |date=June 1997 |publisher=Turner Publishing Company |isbn=1-56311-315-5 |oclc=37537128}}
* {{cite book |given1=Paul |surname1=Sonnenburg |given2=William A |surname2=Schoneberger |title=Allison power of excellence 1915-1990 |url=https://archive.org/details/allisonpowerofex0000sonn |year=1990 |url-access=limited |isbn=0-9627074-0-6 |oclc=22964244}}
* {{cite web |ref={{SfnRef|Allison Industrial Gas Turbines|1983}} |website=International Power Technology |author=Allison Gas Turbine Operations |title=Allison industrial gas turbines 501-K, 570-K |url=http://intpower.com/wp-content/uploads/1986/10/501-brochure.pdf |date=August 1983 |access-date=August 7, 2020}}
* {{cite magazine |issn=0005-2175 |magazine=[[Aviation Week & Space Technology]] |title=New family of Allison engines evolving |url=https://archive.aviationweek.com/issue/19740812/#!&pid=44 |pages=44(4) |publication-date=August 12, 1974 |given=Michael L. |surname=Yaffee |department=Aeronautical engineering |url-access=subscription}}
* {{cite book |ref={{SfnRef|AIA Yearbook|1958}} |author=Aircraft Industries Association, Inc. |title=1957-1958 aircraft year book |url=https://www.aia-aerospace.org/wp-content/uploads/2016/06/THE-1957-AIRCRAFT-YEAR-BOOK.pdf |edition=39th |year=1958 |publisher=American Aviation Publications, Inc. |access-date=12 August 2020 |archive-date=22 January 2022 |archive-url=https://web.archive.org/web/20220122005549/http://www.aia-aerospace.org/wp-content/uploads/2016/06/THE-1957-AIRCRAFT-YEAR-BOOK.pdf |url-status=dead }}
* {{cite magazine |issn=0005-2175 |magazine=[[Aviation Week]] |title=Allison moves to boost its airline sales |url=https://archive.org/details/Aviation_Week_1955-12-12/page/n13 |pages=27, 29–31 |publication-date=December 12, 1955 |given=Robert |surname=Hotz |location=Indianapolis, Indiana, U.S.A. |department=Management |volume=63 |number=24}}

==External links==
{{Commons category}}
* [http://www.rolls-royce.com/defence/products/tactical_aircraft/t56/index.jsp# T56 page at Rolls-Royce website]

{{Allison aeroengines}}
{{Rolls-Royce plc aeroengines}}
{{USAF gas turbine engines}}
{{USAF system codes}}

[[Category:1950s turboprop engines]]
[[Category:Allison aircraft engines|T56]]