Pratt & Whitney J58

Pratt & Whitney J58, engine intake

Pratt & Whitney J58, engine exhaust

The Pratt & Whitney J58 (civil name Pratt & Whitney JT11 ) is a turbojet engine from the US manufacturer Pratt & Whitney . It was specially developed for the drive of the Lockheed A-12 and its successor Lockheed SR-71 for a speed of up to Mach 3.2. In addition to turbojet operation, it also works as a ramjet engine at high speeds, as air is guided around the turbojet stage via six pipes, which are a unique distinguishing feature, and reaches the afterburner directly.

construction

The J58 is an afterburner equipped with an axial jet engine. Instead of the original 8 compressor stages , 9 were used in the series engines. At high flight speeds, bleed air could be withdrawn from the compressor after the 4th stage and fed directly to the afterburner via 6 pipes. This prevented the flow in the compressor from stalling and reduced fuel consumption by up to 15%. At the same time, the afterburner was supplied with fresh, unburned air and was able to deliver a lot of thrust. At top speed, the afterburner stage generated 80% of the thrust this way. This type of engine was called a bypass turbojet. The high-boiling JP-7 was intended as fuel for military use , while the prototypes and pre-production engines were operated with JP-4 and JP-5 . The combustion took place in a tubular ring combustion chamber with 8 flame tubes. The turbine inlet temperature was around 1100 ° C. The turbine itself had a 2-stage design. It was started with the help of an AG330 starter car, whose 440 kW (600 PS) V8 engine accelerated the turbine to the starting speed of 3200 revolutions per minute. Pyrophoric triethylborane was used for ignition . Each engine had a 600 cm³ storage tank for this chemical ignition aid, which was pressurized with nitrogen . The tank capacity was sufficient for 16 starts.

Development and use

J58 on the test bench with full afterburner performance , the afterburner is glowing, clearly recognizable Mach knots .

The first preliminary investigations began in 1956, when the US Navy became interested in aircraft with a maximum speed of Mach 2.5, with the option of temporarily increasing this to Mach 3 in an emergency. The development contract was awarded to Pratt & Whitney, which designed an engine with a thrust (with afterburner) of 115.7 kN , which was first run on a test bench in 1957. In August 1958, a 50-hour acceptance run was successfully completed, and a year later the Navy ordered 30 engines for US $ 11.2 million. In January 1963 the first pre-series engine was installed in an A-12 and the first flight tests were carried out. A total of 11 prototypes (XD-1 to XD-11) and 10 development engines (FX-111 to X-120) as well as 51 prototypes that were delivered in 1963 for the A-12 and YF-12 (P648201YJ to P648251YJ). In 1964, 99 series copies followed for the SR-71 (P648301K to P648399K)

The main feature of the military version is the hydraulically movable inlet cone in the turbine inlet and the adjustable air caps in the inlet area. It was initially controlled by an analog computer, which, however, did not work reliably and quickly enough at low airspeeds. It was replaced by a digital computer in the engines for the SR-71.

The J58 with a fan stage was proposed by Pratt & Whitney for use on the Civil Project SST (JT-11-F4) and the Convair B-58C .

SNECMA wanted to manufacture a civilian variant (JT-11B3) for the Concorde under license under the designation M-35 , but a version of the Rolls-Royce Olympus was used there.

On September 12, 2002, a J58 engine was fired in a ground run at Edwards AFB for the last time to use up the last fuel supplies on JP-7.

Flap system

Flap system of the J58 in the SR-71

The J58 was used in a turbine cell that was equipped with an extensive system to control the air flow to the engine. This included the adjustable inlet cone , an air flap on the central body that was connected to the outside of the turbine cell, as well as additional air openings both at the front and rear, plus a suction air opening and a tertiary additional air opening directly in front of the nozzle. In addition, the outlet nozzle was adjustable and in the area of ​​the cone there was a bleed air opening with which cooling air for the engine could be conveyed from the shock wave in the inlet cone.

At takeoff and at low speed, the cone was pushed all the way forward. All air flaps, except for the rear additional air opening, were open. Air also flowed to the turbine inlet via the air flap on the central body. The suction air opening let air flow around the turbine to the nozzle, the nozzle itself was set to the smallest diameter.

From Mach 0.5, the suction flap and the front and rear additional air openings closed. Air from the intake system now exited from the air flap of the central body, while air was taken from the bleed air opening in the cone area to cool the turbine. Air that was not drawn in by the compressor now flowed around the engine. At this point in time it was already partially working as a ramjet, even if its share of the total thrust was still small.

At Mach 1.5, the front additional air openings were opened again depending on the speed in order to control the position of the shock wave in the inlet. The tertiary auxiliary air flaps were closed. The outlet cross-section of the nozzle has been enlarged slightly.

At Mach 2.5, the cone was partially retracted and the rear additional air openings opened. The outlet cross-section of the nozzle has been enlarged further.

At Mach 3.2, the cone was fully retracted and the front auxiliary air openings were open depending on the position of the intake shock wave. The outlet cross-section of the nozzle has been enlarged to the maximum. At this speed, 80% of the total thrust was provided by the ramjet. The turbojet engine worked as a combustion chamber for the ramjet component.

Technical specifications

• Thrust:
  • 151.3 kN with afterburner
  • 106.3 kN without afterburner
• Mass: 2835 kg
• Length: 5485 mm
• Max diameter: 1411 mm
• Air flow: 147.8 kg / s
• Compression: 8.5: 1

Web links

Commons : Pratt & Whitney J58  - Collection of Images, Videos and Audio Files

• http://aerostories.free.fr/technique/J58/
• http://www.enginehistory.org/p&w_j58.htm
• http://www.hill.af.mil/library/factsheets/factsheet.asp?id=5786
• Pratt & Whitney Data Sheet