The Allison T56 is an American single-shaft, modular design military
turboprop
A turboprop is a turbine engine that drives an aircraft propeller.
A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. Fuel ...
with a 14-stage axial flow
compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
driven by a four-stage turbine. It was originally developed by the
Allison Engine Company
The Allison Engine Company was an American aircraft engine manufacturer. Shortly after the death of James A. Allison, James Allison in 1929 the company was purchased by the Fisher Body, Fisher brothers. Fisher sold the company to General Motors, ...
for the
Lockheed C-130 Hercules
The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 was originally design ...
transport
entering production in 1954. It has been a
Rolls-Royce
Rolls-Royce (always hyphenated) may refer to:
* Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct
Automobiles
* Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...
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
![Allison T56-A1 Turboprop Engine Cutaway](https://upload.wikimedia.org/wikipedia/commons/2/22/Allison_T56-A1_Turboprop_Engine_Cutaway.jpg)
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
The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 was originally design ...
military transport aircraft
A military transport aircraft, military cargo aircraft or airlifter is a military aircraft, military-owned transport aircraft used to support military operations by airlifting troops and military equipment. Transport aircraft are crucial to ma ...
, the T56 was also installed on the
Lockheed P-3 Orion
The Lockheed P-3 Orion is a four-engined, turboprop anti-submarine and maritime surveillance aircraft developed for the United States Navy and introduced in the 1960s. Lockheed based it on the L-188 Electra commercial airliner. (AEW) aircraft, and
Grumman C-2 Greyhound
The Grumman C-2 Greyhound is a twin-engine, high-wing cargo aircraft designed to carry supplies, mail, and passengers to and from aircraft carriers of the United States Navy. Its primary mission is carrier onboard delivery (COD). The aircraft p ...
carrier onboard delivery
Carrier onboard delivery (COD) is the use of aircraft to ferry personnel, mail, supplies, and high-priority cargo, such as replacement parts, from shore bases to an aircraft carrier at sea. Several types of aircraft, including helicopters, have ...
(COD) aircraft, as well as civilian airliners such as the
Lockheed Electra and the
Convair 580
The Convair CV-240 is an American airliner that Convair manufactured from 1947 to 1954, initially as a possible replacement for the ubiquitous Douglas DC-3. Featuring a more modern design with cabin pressurization, the 240 series made some inroa ...
.
The T56-A-1 delivered to Lockheed in May, 1953, produced only , compared to the required 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 rating with a pressure ratio of 9.25:1 while the T56-A-427 fitted to the E-2 Hawkeye has a rating and a 12:1 pressure ratio. In addition, the T56 produces approximately 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 at a ambient temperature. Successive engine follow-ups included the Series II, which was introduced in 1958 and had an increased power rating of , and the Series III, which came out in 1964 and had another power increase to . The Series II and III derivatives were developed under military component improvement programs (CIP).
By 1965, Allison was proposing the development of Series IV derivatives,
but in 1968, the
United States Congress
The United States Congress is the legislature of the federal government of the United States. It is bicameral, composed of a lower body, the House of Representatives, and an upper body, the Senate. It meets in the U.S. Capitol in Washing ...
restricted CIP work to reliability and maintainability improvements instead of performance improvements.
The Series IV derivatives were finally developed in the 1980s after being approved for a
U.S. Air Force
The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sign ...
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
The Naval Air Systems Command (NAVAIR) provides materiel support for aircraft and airborne weapon systems for the United States Navy. It is one of the Echelon II Navy systems commands (SYSCOM), and was established in 1966 as the successor to the ...
's E-2C and C-2A aircraft, 501-D39 for the
Lockheed L-100
The Lockheed L-100 Hercules is the civilian variant of the prolific C-130 Hercules military transport aircraft made by the Lockheed Corporation. Its first flight occurred in 1964. Longer L-100-20 and L-100-30 versions were developed. L-100 pro ...
aircraft, and the 501-K34 marine
turboshaft
A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...
for
NAVSEA
The Naval Sea Systems Command (NAVSEA) is the largest of the United States Navy's five "systems commands," or materiel (not to be confused with "material") organizations. From a physical perspective, NAVSEA has four shipyards for shipbuilding, c ...
. The T56-A-427 was capable of , but it was
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
-limited to .
The
Lockheed Martin C-130J Super Hercules
The Lockheed Martin C-130J Super Hercules is a four-engine turboprop military transport aircraft. The C-130J is a comprehensive update of the Lockheed C-130 Hercules, with new engines, flight deck, and other systems.
The C-130J is the newest v ...
which first flew in 1996, has the T56 replaced by the
Rolls-Royce AE 2100
The Rolls-Royce AE 2100 is a turboprop developed by Allison Engine Company, now part of Rolls-Royce North America. The engine was originally known as the GMA 2100, when Allison was a division of former corporate parent General Motors.
Developm ...
, which uses dual FADECs (Full Authority Digital Engine Control) to control the engines and propellers.
It drives six-bladed
scimitar propellers from
Dowty Rotol
Dowty Propellers is a British engineering company based in Brockworth, Gloucestershire that specialises in the manufacture, repair and overhaul of propellers and propeller components for customers around the world. It is owned by General Elect ...
.
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
UTC Aerospace Systems (UTAS) was one of the world’s largest suppliers of aerospace and defense products, headquartered in Charlotte, North Carolina, United States. The company was formed in August 2012 when parent United Technologies Corporation ...
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
The Naval Air Systems Command (NAVAIR) provides materiel support for aircraft and airborne weapon systems for the United States Navy. It is one of the Echelon II Navy systems commands (SYSCOM), and was established in 1966 as the successor to the ...
(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
Boundary layer control refers to methods of controlling the behaviour of fluid flow boundary layers.
It may be desirable to reduce flow separation on fast vehicles to reduce the size of the wake (streamlining), which may reduce drag. Boundary l ...
(BLC), which helped to enable
short takeoff and landing
A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh condition ...
(STOL) performance. In 1963, Lockheed and Allison designed another STOL demonstrator, this time for a
U.S. Army
The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cl ...
requirement. Lockheed internal designation GL298-7 involved a C-130E Hercules that was re-engined with 501-M7B turboprops. The 501-M7B produced more power than the normally installed, T56-A-7 engines by about 20% (though the 501-M7B was limited to 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
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...
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
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
-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 () and almost all of its destroyers ().
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
Boeing Rotorcraft Systems (formerly Boeing Helicopters and before that Boeing Vertol) is the former name of an American aircraft manufacturer, now known as Vertical Lift division of Boeing Defense, Space & Security.
The headquarters and main r ...
selected Allison (at that time known as the Detroit Diesel Allison Division (DDAD) of
General Motors
The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
) to power a dynamic-system test rig (DSTR) supporting the development of its
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
In aeronautical engineering, overall pressure ratio, or overall compression ratio, is the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine. The terms ''compression ratio'' and ''pressure ...
and a variable-geometry compressor, and it had an
annular combustor
A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, the ''combustor'' or combustion chamber is fed ...
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 .
After DSTR testing was successful, the 501-M62B engine was further developed into the
XT701-AD-700 engine for use on the HLH. The 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.
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 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
Bleed air is compressed air taken from the compressor stage of a gas turbine upstream of its fuel-burning sections. Automatic air supply and cabin pressure controller (ASCPCs) valves bleed air from high or low stage engine compressor sections. Low ...
and replacing the XT701's titanium compressor case with a steel case. The 570-K was then adapted to the 501-M78B demonstration engine, which Lockheed flew on a
Grumman Gulfstream II
The Gulfstream II (G-II) is an American twin engine business jet designed and built by Grumman and then in succession, Grumman American and finally Gulfstream American. Its Grumman model number is G-1159 and its US military designation is C-11A. ...
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
Hamilton Standard
Hamilton Standard was an American aircraft propeller parts supplier. It was formed in 1929 when United Aircraft and Transport Corporation consolidated Hamilton Aero Manufacturing and Standard Steel Propeller into the Hamilton Standard Propeller C ...
single-rotation
propfan
A propfan, also called an open rotor engine, or unducted fan (as opposed to a ducted fan), is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed an ...
, containing propfan blades that were swept back 45 degrees at the tips.
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
The Allison Engine Company was an American aircraft engine manufacturer. Shortly after the death of James A. Allison, James Allison in 1929 the company was purchased by the Fisher Body, Fisher brothers. Fisher sold the company to General Motors, ...
as the 501-D and powered the
Lockheed C-130 Hercules
The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 was originally design ...
. Later variants (Series II, III, 3,5 and IV) gave increased performance through design refinements.
Further derivatives of the 501-D/T56 were produced as
turboshaft
A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...
s for
helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
s including a variant designated T701 that was developed for the canceled
Boeing Vertol XCH-62
The Boeing Vertol XCH-62 (Model 301) was a triple-turbine, heavy-lift helicopter project designed for the United States Army by Boeing Vertol. Approved in 1971, one prototype reached 95% completion before it was canceled in 1975. The prototype wa ...
project.
Applications
Specifications (T56 Series IV)
See also
References
Bibliography
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External links
T56 page at Rolls-Royce website
{{USAF system codes
1950s turboprop engines
T56