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.
Design
It is an axial-flow front turbofan engine incorporating dual-spool design. There are two coaxially-mounted independent rotating assemblies: one rotating assembly for the low pressure compressor (LPC) which consists of the first six stages (i.e. six pairs of rotating and stator blades, including the first two stages which are for the bypass turbofan), driven by the second (downstream) turbine (which consists of three stages); and a second rotating assembly for the high-pressure compressor (HPC) section, which has seven stages. The high-pressure compressor is driven by the first (upstream) turbine, which has a single stage.
The front-mounted bypass fan has two stages. The annular discharge duct for the bypass fan runs along the full length of the engine, so that both the fan air and exhaust gases can exit through the same nozzle. This arrangement allows some noise attenuation, in that the still-hot fast-moving turbine exhaust is shrouded in much-cooler and slower-moving air (from the bypass fan) before interacting with ambient air. Thus the JT8D noise levels were significantly reduced from previous non-turbofan engines, although the low bypass ratio meant that high noise levels were still produced.
Eight models comprise the JT8D standard engine family, covering the thrust range from 12,250 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 units exist throughout the engine to check temperatures and pressures.
At the 13th (i.e. the final) compressor 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 aft end of the compressor houses the 13th stage. Its increasing cross-sectional area allows the compressed air to slow down before entering one of the engine's nine burner cans. Again, there are two bosses to extract 13th stage air for anti-icing, de-icing of fuel, and airframe (cabin pressurization) use. Not all the compressed air enters the burner cans at the fuel-ignition point; some bypasses the can completely and cools the first turbine stage, and some is gradually introduced into the burner can's perimeter in such a way that the burning fuel is held near the can's centerline.
There are nine combustion chambers positioned in a can-annular arrangement. Each chamber has three air inlet 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 to mount the rotating assemblies: 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. This increase was achieved by increasing bypass fan diameter (from 39.9 to 49.2 inches) and fan pressure ratio (from 1.92 to 2.21). Overall engine pressure ratio was also increased from 15.4 to 21.0[1].
Since entering service in 1980, more than 2,900 of the -200 series engines have been produced.
Military Usage
In 1962, the basic JT8D-22 engine was chosen to power the Swedish Saab Viggen fighter aircraft in absence of a suitable and available engine designed for military use. An afterburner was fitted by Volvo Aero well as uprated internal components designed for military use.
Another variant is slated to power the Aerion SBJ.
Update programs
The JT8D-217 and -219 engine(s) were tested in 2001 and were deemed 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.
Pratt & Whitney, in a joint venture with Seven Q Seven (SQS) and Omega Air, has developed the JT8D-219 as a re-engine powerplant for Boeing 707-based aircraft.[2] Northrop Grumman has the -219 to re-engine the United States Air Force’s fleet of 19 Joint Surveillance Target Attack Radar System (E-8 Joint STARS) aircraft, which will allow the JSTARS more time on station due to the engine's greater fuel efficiency. NATO also plans to re-engine their fleet of E-3 Sentry AWACS aircraft. The -219 is publicized as being half the cost of the competeing 707 re-engine powerplant, the CFM-56.[2]
There have been on and off again discussions of using the engine for B-52Hs, which are programmed for use until 2040.
Variants
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- JT8D-5, operating on the McDonnell Douglas DC-9-10 Aircraft
- 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 and 737-200 aircraft, Dassault Mercure and McDonnell Douglas DC-9-30, -40 and -50 aircraft
- JT8D-17, operating on the McDonnell Douglas YC-15, Boeing 727-200 aircraft and 737-200 aircraft
- 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 and MD-87
- RM 8A/B, used in Saab 37 Viggen fighter (JT8D-22 derivative with afterburner)
- Variant of the JT8D-219 is to be used on the proposed Aerion SBJ.