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787 special: Power to spare

Hamilton Sundstrand’s APU, designed solely to generate electrical rather than pneumatic power for the 787, is gearing up for flight tests in April

Hamilton Sundstrand has dispatched an APS5000 auxiliary power unit (APU), complete with a mock-up 787 tailcone, to Fairbanks, Alaska for the start of winter tests as part of the preparation for flight tests on the real thing in 2007.

An earlier APU has already been delivered to the company’s Airplane Power System Integration Facility (APSIF) test facility (see P58) in Rockford, Illinois where it is being used to generate power for the 787’s electrical system, while another unit is being prepared for qualification tests. “Technically we’re doing pretty well,” says president of Hamilton Sundstrand aerospace power systems Tim Morris. “The unit is meeting its performance targets and doing well on noise.”

The company has nine engines in the APS5000 test campaign overall. Aside from the Alaska-bound unit in the 787 tailcones, another is being set up for ETOPS testing, installation compatibility tests and maintenance demonstrations.

© Hamilton Sundstrand 
Hamilton Sundstrand's APS5000 APU does not have a load compressor and drives dual 225kVA generators through a gearbox

Unlike previous APUs, the 787 unit is designed solely with the intent of generating electrical rather than pneumatic power and does not therefore have either a load compressor or a bleed system. Rated at 1,100shp (500kW), and driving dual 225kVA generators through a large gearbox, the APU was started electrically using a starter/generator for the first time on 31 October 2005 at its power systems facility in San Diego, California. The APU itself is also controlled electrically, using a system similar to that developed for the APS2300 used on the Embraer 170. Goodrich turbine fuel technology division supplies the drive-integrated fuel injection system for the APS5000, which includes both fuel atomisers and flexible manifolds. The APU incorporates a single-stage centrifugal compressor with a pressure ratio in excess of 8:1, and a two-stage power turbine section. Other features include a low-emissions combustor and a low-noise eductor oil-cooler, which will duct the exhaust aft and upwards to reduce ramp noise.

“It’s a simple design and it’s not a derivative, though it is similar in layout to other APUs before it,” says Morris, who adds that both Pratt & Whitney and Pratt & Whitney Canada assisted with development of core engine components. “One of the things we told Boeing when we worked on the original proposal was that we’d get all the technologies of UTC [United Technologies] involved,” he adds, saying that target average time between overhaul/repair is 15,000h which the company describes as a “significant step change from current generation APUs”. Hamilton Sundstrand is scheduled to deliver the first APU to Boeing for flight testing in April 2007 and the first production APU around October 2007.

Controls and nacelles

Advanced third-generation digital engine control systems are in final development for the 787, with General Electric (GE) and Rolls-Royce having divided down traditional partner lines for their electronic engine controllers (EEC). GE selected FADEC International, a joint venture set up in 2003 between BAE Systems and Hispano-Suiza, to supply a “FADEC [full authority digital engine control] 3” controller for the GEnx that was based on the design adopted for the GE90-115B as well as the latest CF6 and CFM56 variants and the GE-Pratt & Whitney Engine Alliance GP7200.

The FADEC 3 governs engine fuel flow, interfaces with the thrust reverser, and performs advanced functions such as electronic overspeed protection. Using an ethernet-based data communications network, the controller is designed to be expandable to accommodate new functions, while the company says the advanced on-board monitoring will provide enhanced diagnostic capability for the entire engine system, including the FADEC, reducing the occurrence of “no fault found” incidents.

Goodrich was selected by R-R to develop a next-generation system for the Trent 1000 that has six times the control power and 50% of the weight per function of earlier FADECs, while having a 50% better reliability rate. “This has got more crunching power,” says Goodrich engine control systems vice-president Simon Burr. “Architecturally we’ve gone back to first principles and really set about designing a box to deal with electronic obsolescence. It’s a direct read across from the design used in the updated T56 for the latest [Northrop Grumman E-2D] Hawkeye,” he adds.

Compared with earlier designs developed for the RB.211 and Trent 800 – which are made up of three separate boxes – and a second-generation, single box integrated unit used on the Trent 500, the Trent 1000 device is contained in a flatter housing with just three cards per channel in place of 16 in its predecessor. Goodrich engine controls systems president Marc Duvall adds that the heart of the new EEC is “our own Goodrich proprietary processor, which we’ve been steadily evolving”. The EEC has to “cope with some unique requirements”.

Meanwhile, Goodrich is preparing to install new automated fibre-placement machines in its dedicated 787 composite engine nacelle production site in Riverside, California in September as it readies itself for the jump to serial manufacturing. Similar machines at the US National Center for Advanced Manufacturing in Louisiana were earlier used to build pre-production components for initial test.

Goodrich also recently delivered the first thrust reverser assemblies to both GE and R-R for use in ground tests of the GEnx and Trent 1000 engines respectively, and is “about 30% delivered through more than 30 articles”, says the company’s 787 product development vice-president Jeff Rogers.

Aggressive ramp-up

“In September we will have our own machines, and we think we’ve got a plan synched up with the 787 production build-up,” says Rogers, who adds that Goodrich is “comfortable” with its initial plan to use two Ingersoll machines. However, more machines are being considered to match Boeing’s studies for further acceleration of the production rate to 12 a month or beyond. “It is an extremely aggressive ramp-up for the front edge of a programme, but our biggest concerns are the supply chain and raw materials.” Goodrich gets most of its pre-impregnated composite materials from Hexcel and, to a lesser degree, Cytech. Another focus is on titanium, a special grade of which is required for the high-temperature exhaust areas of the nacelle.

Aside from the exhaust system and thrust reverser, Goodrich is also responsible for the fan and inlet cowls, the latter based on the “acoustically smooth” splice-less design first tested on Boeing’s 777 Quiet Technology Demonstrator in 2005. The first two nacelle systems for the initial flight-test 787 are scheduled to be delivered to R-R in the first quarter of 2007. ■

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