Engine makers are swapping 1960s-era testbeds for more modern airframes to work out next generation powerplants
Engine manufacturers vying for new work in the popular 10,000lb-thrust (45kN) business jet market are trading in their Beatles-era flying test platforms for something from the Nirvana generation.
The equipage of these "new" testbeds offers a small window into the strategy that engine makers are pursuing to capture a corner of the niche that forecasters predict will be a bull market, with as many as 6,000 super-midsize and large executive aircraft built in the next 20 years.
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© HoneywellHoneywell has just retired its ageing Boeing 720 in favour of a 1980s-vintage 757-225 (above) |
Although it is not clear how far to the right the current economic downturn will shove new business jet programmes thought to be on tap - at least one of which was expected to be announced before year's end - competitions for 10K engines are by all accounts continuing and so engine makers are tight-lipped about the particulars of their offerings.
DEFEATED
The only 10K engine selection to date, for Dassault's closely held super-midsize Honeywell TFE731-powered Falcon 50EX replacement, went to Rolls-Royce and its RB282-3 engine in June 2007. Defeated were Honeywell's HTF10000, a higher-thrust follow-on to the company's successful HTF7000 series, GE with a likely derivative of the CF34, Pratt & Whitney Canada with a higher-thrust PW800-series offering, and Snecma with its new 9,500-12,000lb thrust Silvercrest turbofan.
What is known is that at least two of the "big five" engine makers feeding on a steady diet of 10k engine proposals have parked their early 1960s vintage Boeing 720s for something a little newer, and most of the other competitors have already traded up.
Honeywell in June retired its workhorse N720H, a 1961 Boeing 720 powered by four JT3D engines, and began testing its replacement, N757HW, a 1982 Boeing 757-225 with dual R-R RB211 engines. The company had also considered purchasing an Airbus A320, Boeing 747SP or Boeing 767 for the testbed before selecting the 757.
Pratt & Whitney too recently set aside N720PW, a JT3D-powered 1960 Boeing 720, for a refurbished 747SP, the tail number of which P&W will not reveal. The unnamed 747SP will join the company's JT9D-7J-powered 747SP, tail number N708BA, on the flightline in the third quarter of 2009 after being outfitted for flight-test work that will include the P&WC PW810 turbofan that will power the Cessna Citation Columbus. At 8,830lb, the PW810 is considered to be just below the cut-off to be considered a 10K engine.
General Electric's 1960-built Boeing 707 testbed (N707GE) was used for CFM56 testing before being retired in the late 1990s. The company now has a P&W JT9D-powered 747 that it uses for engine testing. R-R too has an RB211-powered 747 (N787RR) for commercial engine research and development work in the USA. The company earlier this year was considering whether to use its 747 testbed for the RB282 flight testing in the 2010 timeframe.
Newcomer Snecma has performed four months of ground tests and nearly a year of follow-on data analysis of its Silvercrest engine core under a $100 million internal development programme to date. Further work is largely on hold awaiting selection by an airframer.
By mid-November Honeywell had flown three test flights with the 757 to explore the flight envelope with a new pylon (sans engine) installed on the right front of the fuselage, clocked to approximate the 11 o'clock position looking rearward. The company is in the process of installing an HTF7000 technology demonstrator "correlation" engine on the pylon for ground-run tests to check out the data recording systems on board the aircraft. Once debugged on the ground, Honeywell will fly four or five test flights and compare data with a nearly identical test run on the 720 late in 2007.
GETTING A REAL JOB
The 757's first "real" job after the correlation work is finished later this year will be to flight-test the HTF7250G turbofan for the super-midsize Gulfstream G250. The 7,445lb engine, a growth version of the Bombardier Challenger 300's 6,825lb-thrust HTF7000 engines, will be mounted to the 757's test pylon for initial flight tests early in 2009, say Honeywell engineers.
While the HTF10000 will take certain technologies "appropriate to that thrust range" from the HTF7000 family, the new engine is largely of clean-sheet design with best-in-class advances to cut noise and emissions whilst maximising thrust-to-weight, says Mike Bevans, senior manager of technical sales for propulsion engines for Honeywell.
Those technologies, which include forward swept fan blades, low-emission combustors and new coatings and alloys, are being tested on a ground-based HTF7000 development engine and in other test assets at the moment.
When it comes time to put the Honeywell's most advanced engine, the HTF10000, through its paces in the coming years, N757HW will be tapped. Structural improvements to the 757 were designed in part to accommodate the HTF10000. Differences between the 720 and the 757 include the position of the test engine, its maximum thrust level and, potentially, its fuel supply. Ian Bell, Honeywell senior flight-test engineer, says the new pylon position was clocked higher on the fuselage from the Boeing 720's approximate 09:30 clock position to avoid flow perturbations on the horizontal and vertical stabiliser. The previous configuration caused a buffet at high and low airspeeds.
The pylon was built to handle 16,500lb static thrust at sea level, although the structure can handle twice that load for safety reasons. The 720's pylon was designed for 12,000lb maximum thrust and is designed to allow room for either a generic test nacelle or the production nacelle, including thrust reversers. Although the fuel supply for the test engine is tied into the existing 757 fuel supply, Honeywell has investigated having independent tanks to test engines that run on alternative fuels.
SORTIES
Bell says the flight-testing campaign for a new engine generally takes 6-12 months and about 100 flight hours to complete, with sorties covering an altitude range of 5,000-45,000ft (1,520-13,720m) and speeds from 150kt to M0.82. Performance, engine operability including surge margin, controls and in-flight starting are evaluated. Bell says in-flight starting will be easier with the 757 due to its superior bleed air regulation system. Engineers executing an air start with the 720 had to "cut off half of the pressurisation system", he says.
P&WC says its new 747SP will also have a pylon mounted on the "upper right side" of the aircraft that will accept engines up to 20,000lb. First testing is likely to take place with the PW810 engine for the Cessna Citation Columbus later next year. The PW810 is set for certification in 2010.
Although they are somewhat exotic, the flying testbeds are not likely to be carrying any highly unusual engines in the near term given the conservative nature of the corporate market. "The emphasis in the last couple of years is a green footprint, including carbon and community noise," says Bevans.
"And to a lesser extent, fuel burn." Honeywell calibrates its technology bearings straight from the source - the company meets airframers every 12-18 months to share technology developments and to receive feedback on engine needs from the user community. While airframers are keen to obtain improvements, they are wary of the exotic. "Nobody wants to be a guinea pig," Bevins says.
Source: Flight International
