Turboprop

Source: Wikipedia, the free encyclopedia.
(Redirected from
Turboprops
)
Not to be confused with propfan or turbofan.

GE T64 turboprop, with the propeller on the left, the gearbox with accessories in the middle, and the gas generator (turbine) on the right

A turboprop is a

turbine engine that drives an aircraft propeller.[1]

A turboprop consists of an

fuel-air mixture then combusts. The hot combustion gases expand through the turbine stages, generating power at the point of exhaust. Some of the power generated by the turbine is used to drive the compressor and electric generator. The gases are then exhausted from the turbine. In contrast to a turbojet or turbofan, the engine's exhaust gases do not provide enough power to create significant thrust, since almost all of the engine's power is used to drive the propeller.[3]

Technological aspects

Schematic diagram showing the operation of a turboprop engine
Propulsive efficiency comparison for various gas turbine engine configurations

Exhaust thrust in a turboprop is sacrificed in favor of shaft power, which is obtained by extracting additional power (beyond that necessary to drive the compressor) from turbine expansion. Owing to the additional expansion in the turbine system, the residual energy in the exhaust jet is low.[4][5][6] Consequently, the exhaust jet produces about 10% of the total thrust.[7] A higher proportion of the thrust comes from the propeller at low speeds and less at higher speeds.[8]

Turboprops have bypass ratios of 50–100,[9][10] although the propulsion airflow is less clearly defined for propellers than for fans.[11][12]

The propeller is coupled to the turbine through a

reduction gear that converts the high RPM/low torque output to low RPM/high torque. This can be of two primary designs, free-turbine and fixed. A free-turbine turboshaft found on the Pratt & Whitney Canada PT6, where the gas generator is not connected to the propeller. This allows for propeller strike or similar damage to occur without damaging the gas generator and allowing for only the power section (turbine and gearbox) to be removed and replaced in such an event, and also allows for less stress on the start during engine ground starts. Whereas a fixed shaft has the gearbox and gas generator connected, such as on the Honeywell TPE331
.

The propeller itself is normally a

constant-speed (variable pitch) propeller type similar to that used with larger aircraft reciprocating engines, except that the propeller-control requirements are very different.[13] Due to the turbine engine's slow response to power inputs, particularly at low speeds, the propeller has a greater range of selected travel in order to make rapid thrust changes, notably for taxi, reverse, and other ground operations.[14] The propeller has 2 modes, Alpha and Beta. Alpha is the mode for all flight operations including takeoff. Beta, a mode typically consisting of zero to negative thrust, is used for all ground operations aside from takeoff.[14] The Beta mode is further broken down into 2 additional modes, Beta for taxi and Beta plus power. Beta for taxi as the name implies is used for taxi operations and consists of all pitch ranges from the lowest alpha range pitch, all the way down to zero pitch, producing very little to zero-thrust and is typically accessed by moving the power lever to a beta for taxi range. Beta plus power is a reverse range and produces negative thrust, often used for landing on short runways where the aircraft would need to rapidly slow down, as well as backing operations and is accessed by moving the power lever below the beta for taxi range.[14] Due to the pilot not being able to see out of the rear of the aircraft for backing and the amount of debris reverse stirs up, manufacturers will often limit the speeds beta plus power may be used and restrict its use on unimproved runways.[14] Feathering of these propellers is performed by the propeller control lever.[14]

The constant-speed propeller is distinguished from the reciprocating engine constant-speed propeller by the control system. The turboprop system consists of 3

turbine engine
in that the fuel control unit is connected to the governor to help dictate power.

To make the engine more compact, reverse airflow can be used. On a reverse-flow turboprop engine, the compressor intake is at the aft of the engine, and the exhaust is situated forward, reducing the distance between the turbine and the propeller.[15]

Unlike the small-diameter fans used in

disc loading (thrust per unit disc area) increases the aircraft's energy efficiency, and this reduces the fuel use.[18][19]

Propellers work well until the flight speed of the aircraft is high enough that the airflow past the blade tips reaches the speed of sound. Beyond that speed, the proportion of the power that drives the propeller that is converted to propeller thrust falls dramatically. For this reason turboprop engines are not commonly used on aircraft

feathered, thus minimizing the drag of the non-functioning propeller.[20]

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.[21]

History

Drawings of the Hungarian Varga RMI-1 X/H – the world's first working turboprop-powered aircraft.

Alan Arnold Griffith had published a paper on compressor design in 1926. Subsequent work at the Royal Aircraft Establishment investigated axial compressor-based designs that would drive a propeller. From 1929, Frank Whittle began work on centrifugal compressor-based designs that would use all the gas power produced by the engine for jet thrust.[22]

The world's first turboprop was designed by the Hungarian mechanical engineer György Jendrassik.[23] Jendrassik published a turboprop idea in 1928, and on 12 March 1929 he patented his invention. In 1938, he built a small-scale (100 Hp; 74.6 kW) experimental gas turbine.[24] The larger Jendrassik Cs-1, with a predicted output of 1,000 bhp, was produced and tested at the Ganz Works in Budapest between 1937 and 1941. It was of axial-flow design with 15 compressor and 7 turbine stages, annular combustion chamber. First run in 1940, combustion problems limited its output to 400 bhp. Two Jendrassik Cs-1s were the engines for the world's first turboprop aircraft – the Varga RMI-1 X/H. This was a Hungarian fighter-bomber of WWII which had one model completed, but before its first flight it was destroyed in a bombing raid.[25][26] In 1941, the engine was abandoned due to war, and the factory converted to conventional engine production.

A Rolls-Royce RB.50 Trent on a test rig at Hucknall, in March 1945

The first mention of turboprop engines in the general public press was in the February 1944 issue of the British aviation publication

Rotol 7 ft 11 in (2.41 m) 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 to fly, albeit as a test-bed not intended for production.[28][29] It first flew on 20 September 1945. From their experience with the Trent, Rolls-Royce developed the Rolls-Royce Clyde, the first turboprop engine to receive a type certificate for military and civil use,[30] and 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.[31] 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.[32]

The Kuznetsov NK-12 is the most powerful turboprop to enter service

The Soviet Union built on German World War II turboprop preliminary design work by Junkers Motorenwerke, while BMW,

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 used turboprop engines with contra-rotating propellers, such as the Allison T40, on some experimental aircraft during the 1950s. The T40-powered Convair R3Y Tradewind
flying-boat was operated by the U.S. Navy for a short time.

The first American turboprop engine was the

C-130 Hercules
military transport aircraft.

The first turbine-powered, shaft-driven helicopter was the

synchropter, which used a Boeing T50 turboshaft engine to power it on 11 December 1951.[35]

December 1963 saw the first delivery of

Pt6 turboprop engine for the then Beechcraft 87, soon to become Beechcraft King Air.[36]

1964 saw the first deliveries of the

Honeywell Aerospace) on the Mitsubishi MU-2, making it the fastest turboprop aircraft for that year.[37]

Usage

A military transport aircraft, over 2,500 Lockheed C-130 Hercules have been built

In contrast to turbofans, turboprops are most efficient at flight speeds below 725 km/h (450 mph; 390 knots) because the jet velocity of the propeller (and exhaust) is relatively low.[citation needed] Modern turboprop airliners operate at nearly the same speed as small regional jet airliners but burn two-thirds of the fuel per passenger.[38]

Super King Air are the most-delivered turboprop business aircraft, with a combined 7,300 examples as of May 2018[39]

Compared to piston engines, their greater

bush airplanes
.

Turboprop engines are generally used on small subsonic aircraft, but the

Airbus A400M is powered by four Europrop TP400 engines, which are the second most powerful turboprop engines ever produced, after the 11 MW (15,000 hp) Kuznetsov NK-12
.

In 2017, the most widespread turboprop

Fokker 27 and 50
.

Turboprop

Super King Air. In April 2017, there were 14,311 business turboprops in the worldwide fleet.[41]

Reliability

Between 2012 and 2016, the ATSB observed 417 events with turboprop aircraft, 83 per year, over 1.4 million flight hours: 2.2 per 10,000 hours. Three were "high risk" involving engine malfunction and unplanned landing in single‑engine Cessna 208 Caravans, four "medium risk" and 96% "low risk". Two occurrences resulted in minor injuries due to engine malfunction and terrain collision in

air ambulance.[42]

Current engines

Jane's All the World's Aircraft
. 2005–2006.

Manufacturer Country Designation Dry weight (kg) Takeoff rating (kW) Application
DEMC China
WJ5E
 720 2130 Harbin SH-5, Xi'an Y-7
Europrop International Multinational TP400-D6 1800 8203
Airbus A400M
General Electric United States CT7-5A 365 1294
General Electric United States CT7-9 365 1447 CASA/IPTN CN-235, Let L-610, Saab 340, Sukhoi Su-80
General Electric United States / Czech Republic
H80 Series[43]
 200 550–625
Nextant G90XT
General Electric United States T64-P4D 538 2535 Aeritalia G.222, de Havilland Canada DHC-5 Buffalo, Kawasaki P-2J
Honeywell United States
TPE331
Series		 150–275 478–1650
Ge man, Mitsubishi MU-2, North American Rockwell OV-10 Bronco, Piper PA-42 Cheyenne, RUAG 228NG, Short SC.7 Skyvan, Short Tucano, Swearingen Merlin, Fairchild Swearingen Metroliner, HAL HTT-40
Honeywell United States LTP 101-700 147 522
Air Tractor AT-302, Piaggio P.166
KKBM Russia NK-12MV 1900 11033 Antonov An-22, Tupolev Tu-95, Tupolev Tu-114
Progress Ukraine TV3-117VMA-SB2 560 1864 Antonov An-140
Klimov Russia TV7-117S 530 2100 Ilyushin Il-112, Ilyushin Il-114
Ivchenko-Progress Ukraine AI20M 1040 2940 Antonov An-12, Antonov An-32, Ilyushin Il-18
Ivchenko-Progress Ukraine AI24T 600 1880 Antonov An-24, Antonov An-26, Antonov An-30
LHTEC United States LHTEC T800 517 2013 Ayres LM200 Loadmaster (not built)
OMKB Russia TVD-20 240 1081 Antonov An-3, Antonov An-38
Pratt & Whitney Canada Canada
PT-6
Series		 149–260 430–1500
Shorts 360, Daher TBM 700, Daher TBM 850, Daher TBM 900, Embraer EMB 314 Super Tucano
Pratt & Whitney Canada Canada PW120 418 1491 ATR 42-300/320
Pratt & Whitney Canada Canada PW121 425 1603
Bombardier Dash 8
Q100
Pratt & Whitney Canada Canada PW123 C/D 450 1603
Bombardier Dash 8
Q300
Pratt & Whitney Canada Canada PW126 C/D 450 1950
BAe ATP
Pratt & Whitney Canada Canada PW127 481 2051 ATR 72
Pratt & Whitney Canada Canada PW150A 717 3781
Bombardier Dash 8
Q400
PZL Poland TWD-10B 230 754
PZL M28
RKBM
 Russia TVD-1500S 240 1044 Sukhoi Su-80
Rolls-Royce Limited United Kingdom Dart Mk 536 569 1700
Fokker F27, Vickers Viscount
Rolls-Royce Limited United Kingdom Tyne 21 1085 4500
Breguet Atlantic, Transall C-160
Rolls-Royce plc
 United Kingdom 250-B17 88.4 313
Cessna 210, Soloy Cessna 206, Propjet Bonanza
Rolls-Royce plc United Kingdom Allison T56 828–880 3424–3910
C-130 Hercules
Rolls-Royce plc United Kingdom AE2100A 715.8 3095 Saab 2000
Rolls-Royce plc United Kingdom AE2100J 710 3424 ShinMaywa US-2
Rolls-Royce plc United Kingdom AE2100D2, D3 702 3424 Alenia C-27J Spartan, Lockheed Martin C-130J Super Hercules
Rybinsk
 Russia TVD-1500V 220 1156
Saturn
 Russia TAL-34-1 178 809
Turbomeca
 France Arrius 1D 111 313 Socata TB 31 Omega
Turbomeca France Arrius 2F 103 376
Walter Czech Republic M601 Series[44] 200 560
PAC FU-24 Fletcher, Progress Rysachok, PZL-106 Kruk, PZL-130 Orlik, SM-92T Turbo Finist
Walter Czech Republic M602A 570 1360 Let L-610
Walter Czech Republic M602B 480 1500

See also

References

  1. ISBN 978-1-60239-780-4
    .
  2. ^ "Aviation Glossary – Turboprop". dictionary.dauntless-soft.com. Retrieved 7 July 2019.
  3. ^ Rathore, Mahesh. Thermal Engineering. Tata McGraw-Hill Education. p. 968.
  4. ^ a b Hall, Nancy (2021). "Turboprop Engine". Glenn Research Center. NASA. Retrieved 14 March 2023.
  5. ^ a b Hall, Nancy (2021). "Turboprop Thrust". Glenn Research Center. NASA. Retrieved 14 March 2023.
  6. ^ a b "Variations of Jet Engines". smu.edu. Retrieved 31 August 2016.
  7. ^ a b ""The turbofan engine Archived 18 April 2015 at the Wayback Machine", page 7. SRM Institute of Science and Technology, Department of aerospace engineering.
  8. ISBN 0080538649
    .
  9. ^ Ilan Kroo and Juan Alonso. "Aircraft Design: Synthesis and Analysis, Propulsion Systems: Basic Concepts Archived 18 April 2015 at the Wayback Machine" Stanford University School of Engineering, Department of Aeronautics and Astronautics Main page Archived 23 February 2001 at the Wayback Machine
  10. MIT turbines, 2002. Thermodynamics and Propulsion
  11. ^ Hall, Nancy (2021). "Propeller Thrust". Glenn Research Center. NASA. Retrieved 14 March 2023.
  12. ISBN 9781405151030
    .
  13. ^ Airscrews For Turbines, Fairhurst, Flight magazine, 10 November 1949, p.609
  14. ^
    ISBN 0884873382
    .
  15. ^ Martin, Swayne (16 May 2019). "How A Turboprop Engine Works". Boldmethod. Archived from the original on 6 November 2021. Retrieved 6 November 2021.
  16. ^ Paul Bevilaqua. The shaft driven Lift Fan propulsion system for the Joint Strike Fighter Archived 5 June 2011 at the Wayback Machine page 3. Presented 1 May 1997. DTIC.MIL Word document, 5.5 MB. Retrieved 25 February 2012.
  17. ^ Bensen, Igor B. "How They Fly". Archived from the original on 20 April 2001. Retrieved 31 May 2023.{{cite web}}: CS1 maint: unfit URL (link)
  18. ISBN 978-0-486-68230-3
    .
  19. ISBN 978-0-486-64647-3
    .
  20. ^ "Operating Propellers during Landing & Emergencies". experimentalaircraft.info. Retrieved 8 July 2019.
  21. ^ "An Engine Ahead of Its Time". PT6 Nation. Pratt & Whitney Canada.
  22. ^ Gunston Jet, p. 120
  23. ^ Gunston World, p.111
  24. ^ "Magyar feltalálók és találmányok – JENDRASSIK GYÖRGY (1898–1954)". SZTNH. Retrieved 31 May 2012.
  25. ^ "The Jendrassik CS-1: The World's First Turboprop Engine". www.tailsthroughtime.com. Retrieved 4 September 2023.
  26. ^ "RMI / Repülő Muszaki Intézet Varga RMI-1/ X / H". Retrieved 4 September 2023.
  27. ^ "Our Contribution – How Flight Introduced and Made Familiar With Gas Turbines and Jet Propulsion" Flight, 11 May 1951, p. 569.
  28. ^ James p. 251-2
  29. ^ Green p.18-9
  30. ^ "rolls-royce trent – armstrong siddeley – 1950–2035 – Flight Archive". Flightglobal. Retrieved 31 August 2016.
  31. ^ Green p.82
  32. ^ Green p.81
  33. ISBN 978 1 86126 912 6
    , various pages
  34. ^ Green p.57
  35. ^ "Smithsonian National Air and Space Museum – Collections – Kaman K-225 (Long Description)". National Air and Space Museum. Archived from the original on 4 March 2016. Retrieved 4 April 2013.
  36. ^ "PT6 60 YEARS - Pratt & Whitney". www.pwc.ca. Retrieved 27 June 2023.
  37. ^ "Evolution of the Honeywell TPE331". aerospace.honeywell.com. Retrieved 27 June 2023.
  38. ^ "More turboprops coming to the market – maybe". CAPA – Centre for Aviation. 9 July 2010.
  39. ^ "Beechcraft King Air 350i rolls out improved situational awareness, navigation" (Press release). Textron Aviation. 30 May 2018.
  40. ^ "787 stars in annual airliner census". Flightglobal. 14 August 2017.
  41. ^ "Business Aviation Market Update Report" (PDF). AMSTAT, Inc. April 2017.
  42. ^ Gordon Gilbert (25 June 2018). "ATSB Study Finds Turboprop Engines Safe, Reliable".
  43. ^ "The H-Series Engine | Engines | B&GA | GE Aviation". www.geaviation.com. Retrieved 1 June 2016.
  44. ^ [1], PragueBest s.r.o. "History | GE Aviation". www.geaviation.cz. Archived from the original on 29 October 2017. Retrieved 1 June 2016. {{cite web}}: External link in |last= (help)

Bibliography

Further reading

External links
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