GE, Howmet soar into the record books by establishing a world record of transient thrust. (North America).

The world of aviation was forever changed on November 19 of last year at the General Electric Aircraft Engines' outdoor test complex in Peebles, Ohio.

During testing, the GE90115 commercial jet engine reached an unprecedented 120,316 lb of transient thrust, establishing a new world thrust record. All records are made to be broken, and this one, in fact, was shattered the next day ... the same engine achieved a steady state thrust level of 122,965 lb at standard day conditions.

An integral part of the world-record engine are the high-pressure blade and vane castings that reside within its interior. These components, cast in a high nickel content single crystal alloy by the Whitehall, Michigan investment casting facility of Howmet Castings (Alcoa, Inc.), Darien, Connecticut, transfer the combustion force into the engine's shaft, driving the turbine. Howmet produced nine different castings for the high-pressure section of the engine and one for the low-pressure section.

Thrust is the force that is induced by the engine to make the jet fly at a steady speed. The engine was designed to deliver 115,000 lb of takeoff thrust to power Boeing's longer-range 777-330ER and--200LR aircraft.

"The first stage turbine nozzle takes the high-temperature air from the combustor and directs it at the optimum angle into the first-stage turbine blade row," said Bob Ackerman, manager of the GE9O turbine airfoils for the GE90-115 engine. "As the air exits the first-stage blades it enters the second-stage turbine nozzle, which directs the air into the second-stage turbine blades. The energy extracted by the turbine is used to power the high-pressure compressor."

Howmet first became involved with the GE90 program when it signed a partnership with the engine manufacturer in 1993, which included a Howmet investment into the program.

"General Electric approached Howmet," said Gary Lynn, process engineer at Howmet. "It was looking for a supplier with the technical capability to produce multiple complex configurations using the single crystal metal casting technique and who was also willing to invest in the program."

The key to the single crystal technique is its ability to control the finished components' grain structure, or the specific atomic arrangement of grains that form the crystalline structure of the metal. In metalcasting, three different grain structures can be achieved: equiax, directionally solidified poly-grain and the single crystal.

The equiax technique produces configurations with many randomly oriented grains, similar to a cup filled with ice cubes. This results in weaker boundaries than the parent grains. The directionally solidified poly-grain technique aligns the grains along the preferred direction of the casting, similar to a line of icicles. This results in fewer grain boundaries, which are aligned in a way that gives the casting particular strength characteristics in specific directions.

The single crystal method used for the GE engine's castings produces a configuration in one grain, eliminating all grain boundaries and providing optimum strength characteristics.

"The advantage of this method is the elimination of weak grain boundaries and the option to align the crystal within the component, maximizing its strength characteristics along the important directions of the casting," said Lynn. "We 'grow' the grains through the casting." Howmet uses its own enhanced investment casting process to achieve the structural grain structure in its castings.

Howmet also was involved in the initial design process on both the GE90 base engine and the current -115 version. Howmet representatives are located on site at GE to help facilitate the engineering effort.

"To be able to say that you are involved in an engine like the GE90-115 is pretty incredible," the Howmet team agrees. "Any time your hardware is involved in a world record it gets you excited."