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 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 T38 or T-38 may refer to: * T38 (classification), a disability sport classification for disability athletics * T.38, a standard for fax over IP * T-38 tank, a Soviet light tank * Allison T38, a turboprop aircraft engine * Northrop T-38 Talon, a U.S ...

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 military transport aircraft, 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.NAVAIR's E-2C and C-2A aircraft, 501-D39 for the Lockheed L-100 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 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 A scimitar propeller is a type of propeller that has curved blades with increasing sweep along the leading edge. Their name is derived from their visual similarity to the curved blades of scimitars. In the early 1900s, as established by the Fre ...

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 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 (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 Flight testing is a branch of aeronautical engineering that develops specialist equipment required for testing aircraft behaviour and systems. Instrumentation systems are developed using proprietary transducers and data acquisition systems. D ...

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 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 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 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 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 . After DSTR testing was successful, the 501-M62B engine was further developed into the

XT701 The Allison T56 turboprop 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 pr ...

-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 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 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 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 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. Further derivatives of the 501-D/T56 were produced as

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 ...

Design and development

Experimental and non-turboprop uses

Variants

Applications

Specifications (T56 Series IV)

See also

References

Bibliography

External links