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Schematic diagram showing the operation of a turboprop engine An ATR-72, a typical turboprop aircraft.

A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.[1]

The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller. The engine's exhaust gases contain little energy compared to a jet engine and play only a minor role in the propulsion of the aircraft.

The propeller is coupled to the turbine through a reduction gear that converts the high RPM, low torque output to low RPM, high torque. The propeller itself is normally a constant speed (variable pitch) type similar to that used with larger reciprocating aircraft engines.

Turboprop engines are generally used on small subsonic aircraft, but some aircraft outfitted with turboprops have cruising speeds in excess of 500 kt (926 km/h, 575 mph). Large military and civil aircraft, such as the Lockheed L-188 Electra and the Tupolev Tu-95, have also used turboprop power. The Airbus A400M is powered by four Europrop TP400 engines, which are the third most powerful turboprop engines ever produced, after the Kuznetsov NK-12 and Progress D-27.

In its simplest form a turboprop consists of an intake, compressor, combustor, turbine, and a propelling nozzle. Air is drawn into the intake and compressed by the compressor. Fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts. The hot combustion gases expand through the turbine. Some of the power generated by the turbine is used to drive the compressor. The rest is transmitted through the reduction gearing to the propeller. Further expansion of the gases occurs in the propelling nozzle, where the gases exhaust to atmospheric pressure. The propelling nozzle provides a relatively small proportion of the thrust generated by a turboprop.

Turboprops are very efficient at flight speeds below 450 mph (390 knots; 725 km/hr) because the jet velocity of the propeller (and exhaust) is relatively low. Due to the high price of turboprop engines, they are mostly used where high-performance short-takeoff and landing (STOL) capability and efficiency at modest flight speeds are required. The most common application of turboprop engines in civilian aviation is in small commuter aircraft, where their greater reliability than reciprocating engines offsets their higher initial cost. Turboprop airliners now operate at near the same speed as small turbofan-powered aircraft but burn two-thirds of the fuel per passenger.[2] However, compared to a turbojet (which can fly at high altitude for enhanced speed and fuel consumption) a propeller aircraft has a much lower ceiling. Turboprop-powered aircraft have become popular for bush airplanes such as the Cessna Caravan and Quest Kodiak as jet fuel is easier to obtain in remote areas than is aviation-grade gasoline (avgas).


Technological aspects

Flow past a turboprop engine in operation

Thrust in a turboprop is sacrificed in favor of shaft power, which is obtained by extracting additional power (up to that necessary to drive the compressor) from turbine expansion. While the power turbine may be integral with the gas generator section, many turboprops today feature a free power turbine on a separate coaxial shaft. This enables the propeller to rotate freely, independent of compressor speed. Owing to the additional expansion in the turbine system, the residual energy in the exhaust jet is low. Consequently, the exhaust jet produces (typically) less than 10% of the total thrust.

Propellers are not efficient when the tips reach or exceed supersonic speeds. For this reason, a reduction gearbox is placed in the drive line between the power turbine and the propeller to allow the turbine to operate at its most efficient speed while the propeller operates at its most efficient speed. The gearbox is part of the engine and contains the parts necessary to operate a constant speed propeller. This differs from the turboshaft engines used in helicopters, where the gearbox is remote from the engine.

Residual thrust on a turboshaft is avoided by further expansion in the turbine system and/or truncating and turning the exhaust 180 degrees, to produce two opposing jets. Apart from the above, there is very little difference between a turboprop and a turboshaft.

While most modern turbojet and turbofan engines use axial-flow compressors, turboprop engines usually contain at least one stage of centrifugal compression. Centrifugal compressors have the advantage of being simple and lightweight, at the expense of a streamlined shape.

Propellers lose efficiency as aircraft speed increases, so turboprops are normally not used on high-speed aircraft. However, propfan engines, which are very similar to turboprop engines, can cruise at flight speeds approaching Mach 0.75. To increase the efficiency of the propellers, a mechanism can be used to alter the pitch, thus adjusting the pitch to the airspeed. A variable pitch propeller, also called a controllable pitch propeller, can also be used to generate negative thrust while decelerating on the runway. Additionally, in the event of an engine outage, the pitch can be adjusted to a vaning pitch (called feathering), thus minimizing the drag of the non-functioning propeller.

Some commercial aircraft with turboprop engines include the Bombardier Dash 8, ATR 42, ATR 72, BAe Jetstream 31, Embraer EMB 120 Brasilia, Fairchild Swearingen Metroliner, Saab 340 and 2000, Xian MA60, Xian MA600, and Xian MA700, Fokker 27, 50 and 60.


A Rolls-Royce RB.50 Trent on a test rig at Hucknall, in March 1945
A Rolls-Royce RB.50 Trent on a test rig at Hucknall, in March 1945
Kuznetsov NK-12M Turboprop, on a Tu-95 Rolls-Royce Dart turboprop engine Alan Arnold Griffith had published a paper on turbine design in 1926. Subsequent work at the Royal Aircraft Establishment investigated axial turbine designs that could be used to supply power to a shaft and thence a propeller. From 1929, Frank Whittle began work on centrifugal turbine designs that would deliver pure jet thrust.[3]

Gy rgy Jendrassik published a turboprop idea in 1928, on March 12, 1929 he patented his turboprop invention. In 1938, he built a small-scale (100 Hp) prototype of his patent.[4] The world's first turboprop was the Jendrassik Cs-1, designed by the Hungarian mechanical engineer Gy rgy Jendrassik.[5] It was produced and tested in the Ganz Works in Budapest between 1939 and 1942. It was planned to fit to the Varga RMI-1 X/H twin-engined reconnaissance bomber in 1940, but the program was cancelled.

The first public mention of turboprop engine in a general public press, was in the British aviation publication, Flight International, in February 1944 issue, which included a detailed cutaway drawing of what a possible future turboprop engine would possible look like. The drawing was very close to what the future Rolls-Royce Trent would look like.[6] The first British turboprop engine was the Rolls-Royce RB.50 Trent, a converted Derwent II fitted with reduction gear and a Rotol 7-ft, 11-in five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 — the sole "Trent-Meteor" — which thus became the world's first turboprop-powered aircraft, albeit a test-bed not intended for production.[7][8] It first flew on 20 September 1945. From their experience with the Trent, Rolls-Royce developed the Dart, which became one of the most reliable turboprop engines ever built. Dart production continued for more than fifty years. The Dart-powered Vickers Viscount was the first turboprop aircraft of any kind to go into production and sold in large numbers.[9] It was also the first four-engined turboprop. Its first flight was on 16 July 1948. The world's first single engined turboprop aircraft was the Armstrong Siddeley Mamba-powered Boulton Paul Balliol, which first flew on 24 March 1948.[10]

The Soviet Union built on German World War II development by Junkers (BMW and Hirth/Daimler-Benz also developed and partially tested designs). While the Soviet Union had the technology to create a jet-powered strategic bomber comparable to Boeing's B-52 Stratofortress, they instead produced the Tupolev Tu-95 Bear, powered with four Kuznetsov NK-12 turboprops, mated to eight contra-rotating propellers (two per nacelle) with supersonic tip speeds to achieve maximum cruise speeds in excess of 575 mph, faster than many of the first jet aircraft and comparable to jet cruising speeds for most missions. The Bear would serve as their most successful long-range combat and surveillance aircraft and symbol of Soviet power projection throughout the end of the 20th century. The USA would incorporate contra-rotating turboprop engines, such as the ill-fated Allison T40, into a series of experimental aircraft during the 1950s, but none would be adopted into service.

The first American turboprop engine was the General Electric XT31, first used in the experimental Consolidated Vultee XP-81.[11] The XP-81 first flew in December 1945, the first aircraft to use a combination of turboprop and turbojet power. The technology of the Lockheed Electra airliner was also used in military aircraft, such as the P-3 Orion and the C-130 Hercules, using the Allison T56. One of the most produced turboprop engines is the Pratt & Whitney Canada PT6 engine.

The first turbine-powered, shaft-driven helicopter was the Bell XH-13F, a version of the Bell 47 powered by Continental XT-51-T-3 (Turbomeca Artouste) engine.[12]

Current engines

manufacturer Country designation dry weight (kg) takeoff rating (kW) Application
DEMC WJ5E 720 2130 Harbin SH-5, Xian Y-7
Europrop International TP400-D6 1800 8203 Airbus A400M
General Electric CT7-5A 365 1294
General Electric CT7-9 365 1447 CASA/IPTN CN-235, Let L-610, Saab 340, Sukhoi Su-80
General Electric T64-P4D 538 2535 Aeritalia G.222, de Havilland Canada DHC-5 Buffalo, Kawasaki P-2J
Honeywell TPE331-3 161 626 Handley Page Jetstream, BAe Jetstream 41, Beechcraft King Air, CASA C-212 Aviocar, Dornier Do 228, Mitsubishi MU-2, Pilatus PC-6, Short Tucano, Swearingen Merlin
Honeywell TPE331-12 181 834
Honeywell TPE331-14GR 281 1462
Honeywell LTP 101-700 147 522 Air Tractor AT-302, Piaggio P.166
Innodyn 165TE 85.3 123
Innodyn 255TE 85.3 190
KKBM NK-12MV 1900 11033 Antonov An-22, Tupolev Tu-95, Tupolev Tu-114
Klimov TV3-117VMA-SB2 560 1864 Antonov An-140
Klimov TV7-117S 520 1839 Ilyushin Il-112, Ilyushin Il-114
Klimov TV7-117S Series 2 430 2610
LHTEC CTP800-4T Twin 517 2013 Ayres LM200 Loadmaster
OMKB TVD-20 240 1081 Antonov An-3, Antonov An-38
Pratt & Whitney Canada PT6A-27 149 507 Beechcraft Model 99, de Havilland Canada DHC-6 Twin Otter, Harbin Y-12, Embraer EMB 110 Bandeirante, Let L-410 Turbolet, Pilatus PC-6 Turbo Porter
Pratt & Whitney Canada PT6A-41 183 634 Beechcraft Super King Air, Piper PA-42 Cheyenne
Pratt & Whitney Canada PT6A-65R 218 1026 Shorts 360
Pratt & Whitney Canada PT6A-68 259.5 1193 Beechcraft T-6 Texan II
Pratt & Whitney Canada PW120 418 1491 ATR 42-300/320
Pratt & Whitney Canada PW121 425 1603 ATR 42-300/320, Bombardier Dash 8 Q100
Pratt & Whitney Canada PW123 C/D 450 1603 Bombardier Dash 8 Q300
Pratt & Whitney Canada PW127 481 2051 ATR 72-200
Pratt & Whitney Canada PW150A 690 3781 Bombardier Dash 8 Q400
Progress AI20M 1040 2940 Antonov An-12, Antonov An-32, Ilyushin Il-18
Progress AI24T 600 1880 Antonov An-24, Antonov An-26, Antonov An-30
PZL TWD-10B 230 254 PZL M28
RKBM TVD-1500S 240 1044 Sukhoi Su-80
Rolls-Royce Dart Mk 536 569 1700 Avro 748, Fokker F27, Vickers Viscount
Rolls-Royce Tyne 21 569 1700 Aeritalia G.222, Breguet Atlantic, Transall C-160
Rolls-Royce 250-B17 88.4 313 Fuji T-7, Britten-Norman Turbine Islander, O&N Cessna 210, Soloy Cessna 206, Propjet Bonanza
Rolls-Royce T56-15 828 3424 C-130 Hercules
Rolls-Royce T56-27 880 3910 E-2 Hawkeye
Rolls-Royce AE2100A 715.8 3095 Saab 2000
Rolls-Royce AE2100C 715.8 2685
Rolls-Royce AE2100D2, D3 702 3424 Alenia C-27J Spartan, Lockheed Martin C-130J Super Hercules
Rybinsk TVD-1500V 220 1156
Saturn TAL-34-1 178 809
Turbomeca Arrius 1D 111 313 Socata TB 31 Omega
Turbomeca Arrius 2F 103 376
Walter M601E 200 560 Let L-410 Turbolet UVP-E
Walter M601F 202 580 L420-UVP
Walter M602A 570 1360 Let L-610
Walter M602B 480 1500

See also




  • Green, W. and Cross, R.The Jet Aircraft of the World (1955). London: MacDonald
  • James, D.N. Gloster Aircraft since 1917 (1971). London: Putnam & Co. ISBN 0-370-00084-6

Further reading

External links

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