The latest generation GE9X engine will exclusively power the future giant of the skies, the Boeing 777-X, in versions 9 and 8 and which will replace the B777-300ER currently in service, and that to date (over 4 years before its entry into service) has already gathered orders for over 300 aircraft. A cutting-edge airplane that can carry up to 400 passengers for over 9 thousand nautical miles, thanks to two engines that are the absolute leaders in size in civil aviation.
The GE9X holds an overwhelming part of our technology, as well as the passion and experience of our technicians, engineers and specialists. So far, in the pages of <em>about</em> magazine, we saw the low-pressure turbine modules up close, whose design—as well as the entire module—we’re responsible for. However, we only briefly mentioned that Avio Aero is also responsible for the complete accessory drive train (with Inlet Gearbox, Transfer Gearbox and Accessory Gearbox, connecting shafts and related attachments), and that the first kit was also delivered on time for the FETT (First Engine to Test) at the start of the first week in February.
In fact, the TGB and IGB had already been delivered at the end of last December and in the second half of February, respectively, to be assembled on the Fan Hub Frame (FHF). The latter is another component we're responsible for and it is installed on the engine between the large front fan and the high pressure compressor, the high pressure shaft (HPC shaft) goes through the FHF and the compressor, and the accessory drive train is assembled right next to the high pressure compressor, under the flange, on the outer part.
The GE9X team with the AGB at Avio Aero Rivalta plant
The ADT plays an essential role, allowing the engine and the aircraft to function properly, and supplying energy for a variety of functions, drawing it from the engine itself. The inlet gearbox (called IGB in the jargon) draws motor energy from the high pressure of the engine, and the TGB (the transfer gearbox) transmits it to the accessory gearbox (AGB) on which the accessories are installed.
Coming back to the accessories included in the AGB, these are what allow the engine and aircraft to operate properly (fuel pump, oil pump, hydraulic pumps to activate the flight controls, air turbine to start the engine), as well as various onboard tools and commodities to function and assist pilots and passengers: in particular, the GE9X AGB is the largest ever made by Avio Aero, with only 10 axles to drive 9 accessories (the GE90, the previous engine, has 11 axles to drive 8 accessories). In other words, this AGB can be considered compact for the number of accessories driven, in spite of its enormous size, and, additionally, the fuel accessories are connected to each other via full conduits in an additional small component (fuel adapter) installed directly on the AGB; this improves the engine profile as it reduces the external pipe system. “The reduction in the number of axles,” as Rocco Pellettieri, Project Engineer of the GE9X, explained to us, “not only benefits the weight, but also the cost of the module, and in general the reduction of the part count (number of parts installed in the module) simplifies the entire supply chain. The layout with fewer axles, but more accessories compared with the GE90, was possible thanks to optimization studies, a complex exercise that in any case allowed us to achieve more with less.”
Our design department worked closely with the Aviation team, who were therefore able to benefit from our tremendous experience in this field, and the level of innovation our engineers were able to bring to the table. “As we found ourselves working in the same company alongside our Evendale colleagues, we started dealing with elements that in the past we saw as vendors. In other words, we were able to interface directly with the team in charge of the various specific elements of the engine and accessories, to define the features of the product.” Rocco continued to explain: “For an AGB with such a high number of accessories and an IGB strongly integrated into the core of the engine, the commitment level was really high.”
The accessory drive train is manufactured at the Rivalta plant; in particular, the IGB and TGB, along with various gears for the AGB, go through the Gear CoE, while at the Housings CoE the outer structure of the AGB is processed, whose rough cast piece was manufactured at our Borgaretto plant using the well-known casting process. This process in particular is one of the most challenging ones from an industrial standpoint, due to the complexity of the process and, in the case of the GE9X, in view of its massive size: “to machine the AGB, we had to use our largest machine with a margin of 2-3 cm,” said Luigi Piervirgili, Manufacturing Leader of the GE9X.
In terms of components, of new gears within the AGB, the hardest product to build, and a critical one in terms of quality, is perhaps the bevel gear of the inlet gearbox, which also has a very difficult assembly sequence, that includes parts made by third parties and parts designed at Aviation and not by our engineers. Hence the assembly area is the other CoE in Rivalta, which gave their best performance for this great product.
Instead, the Experimental centers in Sangone—the last Avio Aero site involved in the ADT (accessory drive train) kit of the GE9X—starting in April will have to carry out engineering tests in order to obtain important information on the product before entering the actual certification program, in 2017. Among these engineering tests, of particular importance are the starter tests, which are done for the first time at Avio Aero with the true aircraft accessory, the Air Turbine Starter (i.e. the air turbine to start the above-mentioned engine).
Our team is working to deliver four other IGB and TGB by December, and one AGB in January 2017, the date for the SETT (Second Engine to Test).
Working on this engine has made our engineers and technicians even more skilled, has pushed them to contend with tight schedules and new technologies, allowing them to manage the usual risks with greater control and to accomplish important technical and industrial milestones. “I think one of the most important milestones reached was the introduction of ‘hard turning’, something new in the aircraft world, which is the roughing and semi-finishing on a lathe of already hardened material.” Luigi Adinolfi, Manufacturing Manager, commented: “In short, it means reducing the lead time of a process, until it's similar to that of a copper plating process. Another improvement that comes to mind concerns the milling of the oil pockets for the M55 detail. Improvements and technical progress that to many may seem too specific, but they represent important steps forward for our supply chain.”