Pratt & Whitney's PW6000 development is about to reach the critical first flight milestone
Guy Norris/EAST HARTFORD
Around the test rigs and stands at Pratt & Whitney's Willgoos power station-like test site in Connecticut, the excitement is almost palpable. "We're getting back into the smaller-engine market and I like to think it will blaze new trails for us in the aerospace business," says Bill Korzec, operations manager for the Willgoos site, as he stares at X-872, a PW6000 test engine about to begin simulated high-altitude runs.
For P&W, success is critical for the PW6000 and, in many ways, disproportionate to its power size and likely market penetration. Although aimed at a relatively narrow thrust bracket of between 16,000lb and 24,000lb (71kN and 107kN), it provides far more than simply a successor to P&W's ubiquitous, but increasingly obsolescent, JT8D family.
Based on core technology developed from the US Air Force's Integrated High Performance Turbine Engine Technology (IHPTET) programme, the PW6000 also provides the platform for P&W's 21st century commercial revival strategy. After years of dependence on the JT8D and a strong focus on the higher-powered PW2000 and PW4000 families, the company felt frozen out from the new-generation narrowbodies by CFM International's CFM56. The company thought its partnership in the International Aero Engines V2500 was not bringing in volume business, particularly since IAE's failure to secure a place on the Next Generation Boeing 737 in the mid-1990s.
Since then, however, some things seem to have changed. Although P&W originally planned to spin-off a V2500/CFM56 successor from the PW6000 called the PW8000, it later backed off from this and officially keeps the target thrust for this geared fan derivative deliberately vague. Although many believe it will still be aimed at the 150-seat market, the latest official plan is for a larger version to compete with the Rolls-Royce Trent 500.
Whatever the outcome, the future significance of both new developments is evident. With the PW6000 as its base, the PW8000 continues to be the cornerstone of P&W's future small-engine strategy. The concept is designed to be variable and to be scaled "up and down" to form a geared fan portfolio ranging from 25,000-100,000lb thrust "at some stage", says P&W programmes vice-president Bob Leduc.
To break into the intensively competitive 100-seat field with an all-new engine, P&W sought two major requirements: a new aircraft application and game changing operating costs. It secured the former when Airbus Industrie selected it in September 1998 for the A318. This shortened A319, formerly dubbed the A319M5, survived the long and sometimes bitter campaign to launch the AE31X project with Alenia, Aviation Industries of China and Singapore Aerospace Technologies.
The second requirement's value has become apparent since launch. Although Airbus subsequently began offering the CFM56 on the A318, the promise of lower costs with the new P&W engine has lured all but one of the airlines that have ordered the 100-seat twin to choose the PW6000. "We will basically be about one third the price of the CFM56," claims P&W large commercial engines single-aisle marketing manager, March Young. "We are confident about that. This market is much more cost sensitive because it is in the low-margin operating arena. That's why we made this a big issue."
Cost is being driven down by a low part-count design philosophy. The high-pressure compressor (HPC), for example, has only six stages and the entire engine has just over 2,000 blades and vanes compared to more than 3,000 for a CFM56. Of these, fewer than 1,000 are classed as "high volume" parts such as HPC and HP and low pressure (LP) turbine blades that would be "consumed" during a shop visit. Another is the use of the "ETOPS [extended-range twin-engined operations] out of the box" proving processes honed for the PW4000 on the Boeing 777.
"Even though operators won't be likely to use the A318 for ETOPS flights, and the engine won't be certified for ETOPS, we are developing it as if it will be," says Young. P&W expects the initiative to uncover potential problems before entry into service and "the traditional introductory 'hump' will disappear". The engine will be among the most rigorously tested in P&W's history.
This philosophy is also being applied to building maintenance experience before service. The plan is to introduce the engine with the maintenance costs of a much more mature engine. Based on a take-off derate of 10%, ambient temperature of 18¡C, an hours per cycle flight leg of 1.4, average utilisation of 240h/month and a labour rate of $60/h at January 1998 prices, P&W claims its total maintenance cost per hour will be around $69 for the PW6122 (designation for the A318 version), against $90 for the CFM56-7B20, $90 for the CFM56-5B8/B9 (selected for the A318) and $102 for the Rolls-Royce BR715-21 as used on the 717-200.
Importantly for Europe's heavily legislated skies, P&W also claims the edge environmentally. Tests indicate adequate nitrous oxide emissions (above the BR715, but below those of the CFM56), a better unburned hydrocarbon level than all but the BR715, and comparable carbon monoxide. It also expects to be quieter than the competition on cutback and approach, while conceding a few decibels on sideline measurement to the BR715.
Testing times
After selection in September 1998, P&W launched into detailed design and sketched out an ambitious test and development effort almost 40% shorter than previous programmes. As it turned out, development and programme issues at both P&W and Airbus have extended the schedule, with first flight of the PW6000-powered A318 sliding from its original mid-2001 target to January 2002.
Despite the slippage, P&W says the revised targets are firm: certification to FAR33 is on schedule for October 2001, European JAR25 and USFAR25 certification in October 2002 and entry-into-service on the A318 due the following month.
The first engine to test, designated X-872, was "lit off" in early August last year. Two more test engines, X-871 and X-873, have joined the programme. Sea level and altitude performance tests, as well as operability and engine starting tests, have been conducted on X-872, while the other two engines have been devoted to stress testing the 24-bladed, wide-chord titanium fan, as well the low- and high-pressure compressors. They have also conducted HPC diagnostic tests, nacelle ventilation, endurance and operability work. A formidable array of 18 test rigs continue to be heavily involved in the programme and have either completed, or are working on, tests of the combustor, lube system, bird ingestion and fan containment, accessories, hail extraction and bearings, among others. Around 10,000h of testing is expected to be amassed during the programme overall, of which 3,200h will be built by the nine test engines that will eventually be involved.
Two of the nine are flight test engines in final assembly. One of the pair, X-874, is due to appear at the Farnborough air show in July before beginning test work later this year, while the second engine, X-875, will be fitted to P&W's 720B testbed in preparation for a first flight in August. The flight test engine will verify nacelle ventilation, fan stress, operability, in-flight starting, inlet compatibility and transients as well as overall performance and heat rejection. The second flight test engine will take to the air in February next year.
Extra low and high pressure rotor stress tests are set to begin on the second-build version of X-871 this June, while build 3 will test LP turbine stresses in September and build 4 will map HPT stress in December.
Engine X-872 is starting a new phase of high altitude tests: X-873 is getting further endurance testing. Engines and rigs are also checking design changes made to combat faults and problems encountered. These vary from a strengthened retaining ring in the HPC, modified after sixth stage platform seal problems, to a revised oil static draintank design. Tests to fine-tune the fan blade design will continue throughout this year with three configurations under evaluation. The changes are mainly aerodynamic and not structural, the basic design having already undergone initial 0.7kg (1.5lb) and 1.1kg bird strike tests. The final design will be tested with a 2.75kg bird in September.
With flight tests looming, P&W is eager to keep the momentum going by looking for new applications. Top of a very short list is Bombardier's BRJ-X regional jet, deemed "a perfect fit" for the PW6000. Securing this on top of the A318 could provide P&W with the perfect start to its 21st century power play.
Source: Flight International
