Pratt & Whitney JT8D

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The Pratt & Whitney JT8D is a low-bypass (0.96 to 1) turbofan jet engine, introduced by Pratt & Whitney in February 1964 with the inaugural flight of Boeing's 727. It was a modification of the Pratt & Whitney J52 turbojet engine, which powered the US Navy A-6 Intruder attack aircraft. Generally, it is an axial-flow front turbofan engine which drives a dual-spool (i.e. it drives two independent rotating assemblies - one for the low pressure compressor (LPC) which consists of the first six stages (including the two stages for the fan) i.e. pairs of rotors and stators, and one for high pressure compressor (HPC) which has seven stages).

Generally, there are four turbine stages. The first extracts some of the energy to shaft horsepower to drive the HPC and the 2nd, 3rd and 4th drive the LPC. The fan has two stages. The annular discharge duct runs along the full length so that the fan air and exhaust gases can both exit through the same nozzle.

Eight models comprise the JT8D standard engine family cover the thrust range from 14,000 to 17,400 pounds-force (62 to 77 kN) and power 727, 737-100/200, and DC-9 aircraft. More than 14,000 JT8D engines have been produced, totaling more than one-half billion hours of service with more than 350 operators making it the most popular of all low-bypass turbofan engines ever produced.

Within the fan inlet case, there are anti-icing air bosses and probes to sense the inlet pressure and temperature. Similar ones exist throughout the engine to check temperatures and pressures. At the 13th stage, air is bled out and used for anti-icing. The amount is controlled by the Pressure Ratio Bleed Control sense signal (PRBC). The diffuser case at the end, houses the 13th stage. It causes the compressed air to expand, thereby slowing it down and diffusing (hence "diffuser case") the air to allow for proper fuel/air mixing for combustion. Again, there are two bosses to extract 13th stage air for anti-icing, de-icing of fuel and airframe use. The air is also used to cool the first turbine stage and combustion chamber liners.

There are nine combustion chambers positioned in a can-annular arrangement. Each chamber has three hole sizes: the smallest is for cooling, the medium is for burning and the large for forming an air blanket.

Two types of bearings are used, roller and ball. They are usually made of forged steel. A small amount of air is allowed to leak into the bearing compartment to prevent lubricating oil from escaping into the engine areas. This is known as the "breather pressure".

In response to environmental concerns that began in the 1970s, the company began developing a new version of the engine, the JT8D-200 series. Designed to be quieter, cleaner, more efficient, yet more powerful than earlier models, the -200 Series power-plant was re-engineered with a significantly higher bypass ratio (1.74 to 1) covering the 18,500 to 21,700 pound-force (82 to 97 kN) thrust range and powering the McDonnell Douglas MD-80 series. Since entering service in 1980, more than 2,900 of the -200 series engines have been produced.

The JT8D-217 and -219 engine(s) underwent tests in 2001 and found to be suitable replacements for the old TF33 engines on military and commercial aircraft as part of the Super 27 re-engining program. The updated engines offer reduced (Stage-3) noise compliance standards without the need for hush kits, enhanced short field performance, steeper and faster climb rates with roughly a 10% reduction in fuel burn for extended range.

An afterburning JT8D variant powers the Swedish Saab Viggen fighter aircraft.

Another variant is slated to power the Aerion SBJ.

[edit] Military Usage

Northrop Grumman has selected Pratt & Whitney to reengine the United States Air Force’s fleet of 19 Joint Surveillance Target Attack Radar System (Joint STARS) aircraft. Pratt & Whitney, in a joint venture with Seven Q Seven (SQS), will produce and deliver the complete JT8D-219 propulsion system. This will allow the JSTARS more time on station due to the jets fuel effeciency. JSTARS is programmed to be used til 2025

There have been on and off again discussions of using the engine for B-52H's. B-52Hs are programmed to be used til 2040

[edit] Variants

• JT8D-7, operating on the Boeing 727-100 and some 727-200 aircraft
• JT8D-9, operating on the Boeing 737-100, 737-200 and McDonnell Douglas DC-9-30 aircraft
• JT8D-9A, which is another version of the JTD8-9, operating on the Boeing 737-100, 737-200 and McDonnell Douglas DC-9-30 aircraft
• JT8D-11, operating on the Boeing 727-200 and McDonnell Douglas DC-9-40 aircraft
• JT8D-15, operating on the Boeing 727-200 aircraft, Dassault Mercure and McDonnell Douglas DC-9-30, DC-9-40 and McDonnell Douglas DC-9-50 aircraft
• JT8D-17, operating on the McDonnell Douglas YC-15
• JT8D-17R & S, operating on the Boeing 727-200 Advanced aircraft and McDonnell Douglas DC-9-50 aircraft
• JT8D-209, used on McDonnell Douglas MD-81
• JT8D-217A/C, used to power the McDonnell Douglas MD-82/MD-88 and MD-87
• JT8D-219, used to power the McDonnell Douglas MD-83
• Variant of the JT8D-219 is to be used on the proposed Aerion SBJ.