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Pratt & Whitney J57

From Wikipedia, the free encyclopedia

J57 / JT3C
PRATT & WHITNEY J57.jpg
YJ57-P-3 cut-away demonstrator at USAF Museum
Type Turbojet
National origin United States
Manufacturer Pratt & Whitney
First run 1950
Major applications Boeing 707
Boeing B-52 Stratofortress
Boeing KC-135 Stratotanker
Douglas DC-8
McDonnell F-101 Voodoo
North American F-100 Super Sabre
Vought F-8 Crusader
Number built 21,170 built
Developed from Pratt & Whitney XT45
Variants JT3D/TF33
Developed into Pratt & Whitney J52/JT8A
Pratt & Whitney J75/JT4A
Pratt & Whitney XT57/PT5

The Pratt & Whitney J57 (company designation: JT3C) is an axial-flow turbojet engine developed by Pratt & Whitney in the early 1950s. The J57 (first run January 1950[1]) was the first 10,000 lbf (45 kN) thrust class engine in the United States. The J57/JT3C was developed into the J75/JT4A turbojet, JT3D/TF33 turbofan, and PT5/T57 turboprop (of which only one was built).[2] The J57 and JT3C saw extensive use on fighter jets, jetliners, and bombers for many decades.

Design and development

The J57 was a development of the Pratt & Whitney XT45 (PT4) turboprop engine that was originally intended for the Boeing XB-52. As the B-52 power requirements grew, the design evolved into a turbojet, the JT3.

Pratt & Whitney designed the J57 to have a relatively high overall pressure ratio to help improve both Thrust-specific fuel consumption and specific thrust, but it was known that throttling a single high pressure ratio compressor would cause stability problems. As Sir Stanley Hooker explains in his autobiography,[3] the outlet area of a compressor is significantly smaller than that of its inlet, which is fine when operating at the design pressure ratio, but during starting and at low throttle settings the compressor pressure ratio is low so ideally the outlet area should be much larger than its design value. Put crudely the air taken in at the front cannot get out the back, which causes the blades at the front of the compressor to stall and vibrate. The compressor surges, which normally means the airflow reverses direction, causing a sharp drop in thrust.

By the late 1940s three potential solutions to the stability problem had been identified:

1) bleeding any excess compressed air at part speed overboard through interstage blow-off valves

2) incorporating variable geometry in the first few stages of the compressor

3) splitting the compressor into two units, one of which supercharges the other, with both units being mounted on separate shafts and driven by their own turbine

GE adopted the second option with their General Electric J79, whilst Pratt & Whitney adopted the two spool arrangement with their J57.

P&W realised that if they could develop a modest pressure ratio (< 4.5:1) axial compressor to handle adequately at any throttle setting including starting and acceleration, why not put two such compressors in series to achieve a higher overall pressure ratio?

In a two-spool arrangement the first compressor, usually called Low Pressure Compressor (LPC), is driven by the Low Pressure Turbine (LPT), and supercharges another unit known as the High Pressure Compressor (HPC) itself driven by the High Pressure Turbine (HPT). During starting the HP spool starts to rotate first, whilst the LP spool is stationary. As the HP spool accelerates and the fuel:air mixture in the combustor lights-up, at some point there is sufficient energy in the turbine gas stream to start to rotate the LP spool, which accelerates, albeit more sluggishly. Eventually, at full throttle, both spools will rotate at their design speeds. Because the exit temperature of the HPC is obviously higher than that of the LPC, a similar blade tip Mach number for both units is achieved by making the design HP shaft speed significantly higher than that of the LP shaft. Any reductions in compressor diameter going towards the combustor exaggerates the difference.

In the same timeframe as the J57, the Bristol Aeroplane Company Engine Division in the UK also adopted the two spool arrangement into their Rolls-Royce Olympus turbojet engine series, which went on to propel the Avro Vulcan bomber and later Concorde. Within a few months both P&W and Bristol had had a first run of their prototypes. Both demonstrated superb handling.[4][5][6]

Today most civil and military turbofans have a two spool configuration, a notable exception being the Rolls-Royce Trent turbofan series which has three spools.

Incidentally, most modern civil turbofans use all three of the above options to handle the extremely high overall pressure ratios employed today (50:1 typically).

As the Applications section below indicates, during the 1950s the J57 was an extremely popular engine, with numerous military applications. Production figures were in the thousands, which led to a very reliable engine. Consequently it was only natural for Boeing to choose the J57 civil variant, the JT3C, for their 707 jetliner. Douglas did likewise with their DC8. Pressure to reduce jet noise and specific fuel consumption later resulted in P&W using an innovative modification to convert the JT3C turbojet into the JT3D two spool turbofan, initially for civil purposes, but also for military applications like the Boeing B-52H. The prestigious Collier Trophy for 1952 was awarded to Leonard S. Hobbs, Chief Engineer of United Aircraft Corporation, for "designing and producing the P&W J57 turbojet engine". The engine was produced from 1951 to 1965 with a total of 21,170 built.

Many J57 models shipped since 1954 contained 7-15% of Titanium, by dry weight. Commercially Pure Titanium was used in the inlet case and low pressure compressor case, whereas the low pressure rotor assembly was made up of 6A1-4V Titanium alloy blades, discs and disc spacers.[7]

Titanium alloys used in the J57 in the mid-50s suffered hydrogen embrittlement[8]:412 until the problem was understood.

On May 25, 1953, a J57-powered YF-100A exceeded Mach 1 on its first flight.

Variants

Data from:Aircraft Engines of the World 1964/65,[9] Aircraft engines of the World 1957[10]

Derivatives

Applications

J57s on a B-52D
J57s on a B-52D
JT3Cs installed on a Boeing 707-123
JT3Cs installed on a Boeing 707-123
Pratt & Whitney JT3 (1/4th scale)
Pratt & Whitney JT3 (1/4th scale)
J57 (Military)
JT3C (Civilian)

Engines on display

Specifications (J57-P-23)

Pratt & Whitney J57 turbojet
Pratt & Whitney J57 turbojet

Data from[citation needed]

General characteristics

  • Type: Afterburning turbojet
  • Length: 244 in (6197.6mm)
  • Diameter: 39 in (990.6mm)
  • Dry weight: 5,175 lb (2,347 kg)

Components

  • Compressor: all-axial, 9-stage LP compressor, 7-stage HP compressor
  • Combustors: cannular, 8 flame tubes
  • Turbine: all-axial, single stage HP turbine, 2-stage LP turbine

Performance

Specifications (JT3C-7)

Data from Flight [15]

General characteristics

  • Type: civil turbojet
  • Length: 155in (3937mm)
  • Diameter: 39in (990.6mm)
  • Dry weight: 4200lb (1905kg)

Components

  • Compressor: all-axial, 9-stage LP compressor, 7-stage HP compressor
  • Combustors: cannular, 8 flame tubes
  • Turbine: all-axial, single stage HP turbine, 2-stage LP turbine

Performance

See also

Related development

Comparable engines

Related lists

References

Notes

  1. ^ The Engines of Pratt & Whitney: A Technical History" Jack Connors, AIAA Inc. 2010, ISBN 978-1-60086-711-8, p. 225
  2. ^ Gunston, p.167
  3. ^ "Not much of an Engineer:an autobiography" Sir Stanley Hooker, Airlife Publishing Ltd. 1984, ISBN 0 906393 35 3, p.103
  4. ^ "Not much of an Engineer:an autobiography" Sir Stanley Hooker, Airlife Publishing Ltd. 1984, ISBN 0 906393 35 3, p.142
  5. ^ "American Airlines Experience with Turbojet/Turbofan Engines" K. F. Whatley , The American Society of Mechanical Engineers. 1962, ASME 62-GTP-16, p.5
  6. ^ "Collier Trophy". www.aerofiles.com. Retrieved 16 April 2018.
  7. ^ "Titanium in Aerospace Applications" RI.Jaffee, W.H Sharp and RS Nycum , Defence Metals Information Society. October 24, 1961, DMIC Memorandum 133, p.44
  8. ^ "Iroquois" a 1957 Flight article
  9. ^ Wilkinson, Paul H. (1964). Aircraft engines of the World 1964/65 (19th ed.). London: Sir Isaac Pitman & Sons Ltd.
  10. ^ Wilkinson, Paul H. (1957). Aircraft engines of the World 1957 (15th ed.). London: Sir Isaac Pitman & Sons Ltd. pp. 82–83.
  11. ^ a b c d e f g h Taylor, John W.R. FRHistS. ARAeS (1962). Jane's All the World's Aircraft 1962-63. London: Sampson, Low, Marston & Co Ltd.
  12. ^ Jane's All the World's Aircraft 1958. Sampson Low, Marston & Company. p. 444. OCLC 852161925.
  13. ^ "First Douglas C-132 Details". Aviation Week. Vol. 65 no. 17. October 22, 1956. p. 35. ISSN 0005-2175.
  14. ^ http://neam.org/index.php?option=com_content&view=article&layout=edit&id=1059 "Pratt & Whitney J57 (JTC3) Cutaway"
  15. ^ Flightglobal archive - Flight International, 27 November 1953 Retrieved: 04 March 2017

Bibliography

External links

This page was last edited on 20 November 2020, at 20:51
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