The floor of the assembly line at the pratt & whitney facility in middletown, connecticut, is adorned with pieces of brown paper of various shapes and sizes. The cutouts represent fixtures, jigs, platforms, machinery, and other new equipment associated with the expansion of the production line of the F119-PW-F100—the engine that powers the Lockheed Martin F/A-22 Raptor.
As Pratt & Whitney employees and customers celebrate the 100th F119 to roll off the assembly line this October, the company’s engineers are busy optimizing the assembly process that will generate the next several hundred Raptor engines.
“More than 650 engine deliveries are currently planned for the F/A-22 program,” notes Cliff Stone, integration manager for the F119 engine program at Pratt & Whitney. “The F119 is a program in transition,” he continues. “The development phase of the program is nearly finished, and now we’re into production. While we are still supporting flight test, we are also gearing up for operational support. Like Lockheed Martin, we instituted support operations at Nellis AFB, Nevada. We are also supporting a new operational location at Tyndall AFB, Florida, and we’ll be up and running at Langley AFB, Virginia, next year.”
Gearing Up For Production
The transition from development to production requires a transformation of the assembly line for military engines at Middletown as the production rate for F119s doubles from three engines per month in 2003 to six engines per month in 2008. Production peaks at seventy-four engines in 2009 and is scheduled to wind down in 2012 unless more F/A-22s are ordered. At its peak, F119 production is expected to account for almost one-third of the total Pratt & Whitney commercial and military engine workload at Middletown.
“We are doubling the space of our military product assembly area,” notes Mike Shea, the product line manager for the F119. “We have been working F119s into the flow line for the F100-PW-229 engine, which powers the F-16. We have been building -229s at a rate of twelve to fourteen per month. But the increased volume of the F119 won’t allow us to mix engines on the same line any longer.”
The Middletown facility has 250,000 square feet of space for production assembly and another 300,000 square feet devoted to engine development. Once the F119 line is established, the assembly area will support five distinct production lines—two military engines and three commercial. The three commercial lines produce the PW4000 for Boeing’s 747, 767, 777, and the Airbus A330; the V2500 for the Airbus A319, A320, and A321; and the PW2000 for Boeing’s 757 and as the F117 military derivative engine for the C-17.
Pratt & Whitney’s Middletown facility houses several critical organizations, including the Engine Center, which includes engine assembly and test areas, and the Compression Systems Module Center, which produces fans and compressors for both military and commercial Pratt & Whitney engines. Approximately 2,500 people work in the facility. About fifty of the 130 employees working directly on the military production lines are engaged in F119 production.
Pratt & Whitney engine assembly formerly took place at facilities in East Hartford, Connecticut, and West Palm Beach, Florida, as well as in Middletown. The company consolidated its engine production equipment and skills resources in Middletown in 1999 to improve quality and affordability. Similarly, other Pratt & Whitney facilities are now focused on other centralized engineering and production functions, such as component manufacturing, module assembly, and specialized developmental testing. The East Hartford plant, for example, not only produces specific parts and components for the F119, it also manufactures the F/A-22’s aircraft-mounted nozzle sidewall and coats the fairing for the arresting gear system. Both of these assemblies protect vital parts of the Raptor from high temperatures and detection by enemy defense systems.
The F119, like other engines, is assembled at a series of workstations. The assembly of the F119 engine begins with the delivery of parts from four main module centers: The compression system module center provides the fan and high-pressure compressor. The combustor, augmentor, and nozzle center provides combustors, augmentors (afterburners), and nozzles. The turbine module center delivers the high-pressure and low-pressure (fan drive) turbines. Hamilton Sundstrand, like Pratt & Whitney, a division of United Technologies Corporation, supplies the engine controls and external components.
Parts from the module centers are delivered to a part-kitting area, where they are unpackaged, sorted, placed on carts, and moved to the various workstations to feed engine assembly.
The assembly begins with the engine core, consisting of the high-pressure compressor, combustor, and high-pressure turbine. The assembled core module is then moved to successive workstations where it is mated with the low-pressure (fan drive) turbine and fan, the augmentor and, finally, the thrust-vectoring nozzle that helps give the F/A-22 its exceptional maneuverability and survivability. The nearly complete engine is then moved to the final assembly workstations where various controls and external components, such as plumbing and wiring harnesses, are installed and connected. Once all the parts are available, it takes only thirteen days to assemble an entire F119 engine.
Once fully assembled, the engine is moved to an adjacent test facility where it is mounted on an overhead fixture called a strongback. The mount travels on an overhead monorail system into one of several test cells. The engine is connected to control, electrical, and fuel lines; fired up; and run for several hours in a specified series of acceptance tests. During these tests, the nozzle is vectored through its entire range. During each phase of testing, qualified technicians monitor engine performance to ensure that it meets specification requirements as it is put through a variety of throttle transients up to and including maximum afterburning power.
The engine is then dismounted, stripped of all test equipment, inspected thoroughly externally and internally with a fiber optics borescope, and cleaned. US Government personnel perform a final inspection of the engine itself and of its performance as characterized and recorded during the acceptance testing. Once the inspectors are satisfied the engine meets all delivery specifications and criteria, it is formally accepted by the US Government in the signing of DoD Form DD250.
New engines, safely packed in special shock-mounted containers and mounted on standard military logistics trailers, are shipped, usually in pairs, to Lockheed Martin’s Marietta, Georgia, production facility where they are installed in brand new F/A-22 Raptor aircraft.
“We streamlined our production processes when we consolidated engine assembly in Middletown,” notes Shea. “We model our production system on proven lean production methods. The number of workstations and the tasks assigned to each station are set by the delivery rate. We are going through that evaluation for the F119 line now. We have to combine or split workstations in order to match the number of tasks assigned to each station with the required production rate. This match ensures that capacity meets projected requirements.”
“The change paid off,” Shea continues. “We went from struggling to deliver six military engines a month to delivering twelve to fourteen per month on schedule and within cost. We implemented this production concept, which we call flow line assembly, on military engines in 1999 and moved the practice to our commercial lines soon thereafter.”
Pratt & Whitney applied its flow line approach early in the F119 program, building the F/A-22 flight test engines on the assembly line in Middletown after the 1999 assembly line consolidation. “We had never built flight test engines in a production environment before,” notes Shea. “In building twenty-five F/A-22 flight test engines, we used the same mechanics who would eventually build the production F119 on the assembly line. Previously, flight test and production engines were always built in separate environments. Our approach has been amazingly successful. In the process, we developed experience and expertise that are paying off now that we have initiated full production of the F119.”
The company is taking the approach one step further with the engine that will power the Lockheed Martin F-35 Joint Strike Fighter, the F135. “We are using the fundamental production flow line to build F135 developmental engines,” notes Shea. “We started building the first engine-to-test in mid-June 2003. The engine went to test in September; that’s at least six months earlier than we have ever assembled a first engine-to-test before.”
Propelling Innovations
Each F/A-22 Raptor is powered by two F119 35,000-pound thrust class, advanced technology turbofan engines. The high-efficiency, dual-rotor F119 engine produces more than 22,000 pounds of thrust in military power, without afterburning. This thrust level coupled with an aerodynamic design allow the Raptor to supercruise, or fly at supersonic speeds without afterburner, for relatively long periods of time. The engine’s thrust vectoring nozzles provide unprecedented maneuverability, and its designed-in stealth features ensure the highest level of survivability in the modern combat environment.
The F119 is also the first military engine to incorporate hollow fan blades, which reduce weight and improve throttle responsiveness. The engine’s three-stage fan and six-stage compressor are driven, respectively, by single-stage, high-pressure and low-pressure (fan drive) turbines on counter-rotating shafts. The previous generation of military engines required two-stage turbines to drive similar compression systems. This reduction in the number of hot-section components greatly reduces cost and improves safety, reliability, and maintainability.
The F119 has been designed with other special features for improving maintainability. All controls and externals are located on the bottom half of the engine, allowing maintenance crews ground-level access when the F/A-22 engine bay doors are open. Only six tools are needed to remove the controls and externals, and each line-replaceable unit can be removed and replaced in twenty minutes or less. Modular construction, color-coded harnesses, and quick plumbing and wiring disconnects also make the F119 engine much easier to support and maintain. Even the engine support equipment itself has been designed to be lighter and require less space. The F119 has about forty percent fewer parts than previous fighter engines, contributing to its superior maintainability and lowering cost.
“Many of the design features that make the F119 easy to maintain make it easier to assemble as well,” notes Lynn Gambill, chief engineer and director of systems design and component integration for the F119. “The integrally bladed rotor, or IBR, is a good example. An IBR is a one-piece assembly of a rotor and blades. On previous military engines, dozens of blades had to be attached to each rotor disk and then the disks stacked and bolted together. Traditionally bladed disks also have seals and numerous other ancillary parts. With IBRs, we just stack disks. IBRs greatly reduce the part count of the engine as well as the manual labor needed for assembly and disassembly.”
“The captured fastener feature is another good example,” Gambill continues. “External components on the F119 are designed with secondary fastener retention features. Maintainers and mechanics save a lot of time in not handling and accounting for a lot of small loose hardware, like nuts and bolts. Captured fasteners also eliminate safety wire, which saves a lot of labor.”
Testing Success
The F119 has proven its reliability in more than 8,000 engine flight hours of F/A-22 testing. Ground testing has simulated the equivalent of more than six years of operational usage on a single engine. “We took the eighteenth of twenty-five flight test engines off the production line and designated it as our durability test engine,” notes Stone. “It continued to perform to specification after 4,325 thermal cycles, which represent six to eight years of operational service. In the military aircraft engine world, we call that figure a half-life or an inspection interval because the engine is designed for 8,650 cycles, or approximately fifteen years of service.”
“The turbine on this engine has been a shining star,” adds Gambill. “We disassembled the durability engine after we finished 4,325 cycles. The turbine hardware looked great. We saw minimal erosion and oxidation. Historically, turbine blades show large areas of erosion after 4,325 cycles. The F119 has performed so well that we rarely hear about it in public. Ironically, it’s very flattering that the engine is not receiving much publicity.” Testing can simulate years of service in only months by minimizing the non-damaging dwell times at various power settings the engine will see in opera-tion. Engine parts exposed to high-temperature gasses are designed for 4,325 cycles. All other engine parts are designed to last 8,650 cycles. For the F119 to qualify for initial service release, a designation required for operational service, it had to successfully complete the 4,325 cycles in a ground test environment. The F119 completed this milestone in September 2002. The same engine is now being tested for its second half-life.
“We did a lot of other exciting ground tests in 2001,” notes Stone. “The engine ‘flew’ through the equivalent of a monsoon in water-ingestion ground tests. We launched sheets of ice of various sizes into the engine. The ice sheets represented potential ice buildup and liberation if the F/A-22 were to fly through icing conditions. We shot chicken carcasses of various sizes up to eight pounds into the engine to simulate birdstrikes. But the most exciting of all jet engines tests are what we call blade-out tests. We explosively separated half a fan blade at full power to simulate a blade fracture in flight. The requirement is that the engine stay mounted, that it cause no significant secondary damage to the airframe, and that it be safely shut down. Again, the F119 passed the test. The F/A-22 experienced a real birdstrike in April 2002, when a nine-pound loon got sucked into the engine above Marietta, Georgia. The engine didn’t miss a beat.”
F119 Future
As the F119 establishes its standing in the F/A-22, variants of the engine are showing up in other aircraft, such as the F135 in Lockheed Martin’s F-35 Joint Strike Fighter. Pratt & Whitney delivered the first F135 for developmental testing in September. Some alternate applications for F119 engine variants include an F/B-22 fighter/bomber to fulfill the global strike mission and designs for unmanned air vehicles.
The company is also evaluating an F119 axisymmetric thrust-vectoring nozzle for some possible future applications of the F/A-22. The nozzle, which has fewer parts and is less expensive than the current F119 nozzle, could be applied to the F/A-22 around 2009. The new nozzle is one of several innovations that could result from joint Pratt & Whitney and US Air Force improvement programs under consideration for the F119.
“Ten years from now, our improvement programs for the engine should result in increased thrust and increased core life,” notes Gambill. “Technologies, such as turbine durability upgrades developed for the F135, could double the maintenance intervals for the hot sections of the F119. The resulting maintenance interval of ten to fifteen or more years is unheard of for turbine engines.”
“The F119’s durability, performance, and reputation on the F/A-22 program make it attractive for other programs,” concludes Stone. “We like to say that this engine is too good for just one application.”
Eric Hehs is the editor of Code One.
