Pratt & Whitney J57


Pratt & Whitney J57


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) was the first 10,000 lbf (45 kN) thrust class engine in the United States. It was also the first two-spool turbojet to run, a few months before the similar Bristol Olympus in the UK.

The J57/JT3C was developed into the J52 turbojet, the J75/JT4A turbojet, the JT3D/TF33 turbofan, and the XT57 turboprop (of which only one was built). 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, 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, while Pratt & Whitney adopted the two-spool arrangement with their J57.

P&W realized 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, they could 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, while 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 Olympus turbojet engine series, which went on to propel the Avro Vulcan bomber and later the Concorde. Within a few months, both P&W and Bristol had had a first run of their prototypes. Both demonstrated superb handling.

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).

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 DC-8. 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 6Al-4V titanium alloy blades, discs and disc spacers.

Titanium alloys used in the J57 in the mid-50s suffered hydrogen embrittlement: 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, Aircraft engines of the World 1957

Derivatives

  • JT3D/TF33:A turbofan derivative of the J57.
  • XT57/PT5: A 20 ft diameter (6.1 m), 15,000 hp (11,185 kW) turboprop intended for the Douglas C-132

Applications

J57 (Military)
  • Boeing B-52 Stratofortress (A-G)
  • Boeing C-135 Stratolifter and KC-135 Stratotanker
  • Convair F-102 Delta Dagger
  • Convair YB-60
  • Douglas A-3 Skywarrior
  • Douglas F4D Skyray
  • Douglas F5D Skylancer
  • Lockheed U-2
  • Martin B-57 Canberra
  • McDonnell F-101 Voodoo
  • North American F-100 Super Sabre
  • Northrop SM-62 Snark
  • Vought F-8 Crusader
JT3P
  • Boeing 367-80
JT3C (Civilian)
  • Boeing 707
  • Boeing 720
  • Douglas DC-8

Engines on display

  • A J57 is on display at the Texas Air Museum - Stinson Chapter, San Antonio, Texas
  • A J57 cutaway is on display at the New England Air Museum, Bradley International Airport, Windsor Locks, CT.
  • A J57 cutaway is on public display at the Aerospace Museum of California. It is s/n 35 used on the XB-52 program.
  • A J57 is on display at the Loring AFB museum, former Loring AFB Limestone Maine.

Specifications (J57-P-23)

Data from

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

  • Maximum thrust: 11,700 lbf (52.0 kN) dry, 17,200 lbf (76.5 kN) with afterburner
  • Overall pressure ratio: 11.5:1
  • Air mass flow: 165 lb/s (75 kg/s) at maximum power
  • Turbine inlet temperature: 1,600 °F (870 °C)
  • Specific fuel consumption: 2.10 lb/(lbf⋅h) (59 g/(kN⋅s)) with afterburner
  • Thrust-to-weight ratio: 3.32

Specifications (JT3C-7)

Data from Flight

General characteristics

  • Type: civil turbojet
  • Length: 155in (3937mm)
  • Diameter: 39in (990.6mm)
  • Dry weight: 4,200lb (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

  • Maximum thrust: 12,030 lbf (53.5 kN) @ take-off, SLS, ISA
  • Overall pressure ratio: 12.5:1
  • Air mass flow: 180 lb/s (81.65 kg/s)
  • Specific fuel consumption: 0.785 lb/(lbf⋅h) (22.2 g/(kN⋅s)) @ take-off, SLS, ISA; and 0.909 lb/(lbf⋅h) (25.7 g/(kN⋅s)) @ max cruise 3,550 pounds-force (15.8 kN), M0.85, 35,000 ft (11,000 m), ISA
  • Thrust-to-weight ratio: 2.86

See also

Related development

  • Pratt & Whitney JT8A/J52
  • Pratt & Whitney JT4A/J75
  • Pratt & Whitney JT3D/TF33
  • Pratt & Whitney XT57/PT5

Comparable engines

  • Rolls-Royce Avon
  • Bristol Olympus

Related lists

  • List of aircraft engines

References

Notes

Bibliography

External links

  • Pratt & Whitney History page on the J57/JT3
  • Pratt & Whitney J57 Turbojet – National Museum of the United States Air Force
  • Bill Gunston (November 27, 1953). "Two-Spool Turbo-Wasp". Flight Magazine. pp. 697–699. ISSN 0015-3710.
  • Pratt, Whitney Aircraft (April 15, 1957). "Aircraft Power - in Whatever Form It Takes". Aviation Week. Vol. 66, no. 15. pp. 60–61. ISSN 0005-2175.

Text submitted to CC-BY-SA license. Source: Pratt & Whitney J57 by Wikipedia (Historical)



 


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