Flying through a wind tunnel
Inside a tunnel test facility beside Boeing Field, General Electric engineers are measuring the minutest performance details of a one-sixth scale version of the largest commercial jet engine ever built.
Known as the GE9X, this engine will power Boeing's new 777X and will deliver much of the jet's projected 10 per cent improvement in fuel efficiency.
Boeing will build the aeroplane, featuring a new composite wing, in Everett, Washington. The first is scheduled for delivery to an airline in 2020. But before Boeing's workforce can do its thing, GE must get these tests right.
"We're on track," GE9X program leader Chuck Jackson says as he showed off the wind-tunnel setup.
The small-scale engine fan is installed on a rig that's perched royally at the centre of a cavernous, windowless chamber, its walls padded with polyurethane foam wedges that deaden sound so there will be no echoes.
The rig, which turns the fan shaft at 16,000 revolutions per minute, is pointed at a tunnel opening from which flows an air stream set to simulate takeoff speeds of about 300 kph.
"This is a unique facility," said Jackson. The Boeing wind tunnel is designed specifically for testing jet propulsion systems and leased by GE through the autumn for these tests.
Anthony Opalski, GE's lead engineer for the tests, said testing the small-scale version is done to cut costs.
"We're not spending as much money as we would on full-scale hardware," he said.
The hardware is impressive enough. A tangle of wires emanating from the engine case feeds data to multiple instruments.
Sensors inside and around the rig measure the temperature, speed and pressure of the air flow.
Strain gauges on the fan blades measure the stress on the composite material.
Laser probes measure tiny deflections of the fan blades.
This week, GE is testing the performance of three different sets of fan blades to see which has the best aerodynamic characteristics for its GE9X design.
Within a couple of weeks, the testing will shift to acoustics, as a row of slender microphones, like the upturned beaks of hungry birds, measure the noise of the engine as it goes through its paces.
The sound-absorbing foam wedges that cover every surface give the interior space a surreal look. They ensure that minimal noise bounces back off the walls, floor and ceiling so that the microphones are picking up only the noise coming directly from the engine.
For the convenience of Opalski's team, the engine is mounted sideways on the rig.
Looking from a platform set in a door opening to the side of the rig, it's as if the array of microphones on the far side represent the ground, the engine is skimming over the top of them, and "we're standing in the sky," Opalski says.
Later in the year, the engineers will focus on how the engine reacts to a crosswind, repeating many of their tests after the rig is turned through 90 degrees in the tunnel.
GE already supplies the world's largest commercial jet engine: The massive GE90 that powers the current 777 has a fan diametre of just over three metres.
The GE90 is so reliable that the twin-engine 777 is allowed to fly routes 5.5 hours from the nearest airport.
In-flight shutdowns are exceedingly rare, though should it need to do so, the jet can get home flying on one engine for all that time.
The larger GE9X engine will have a fan diametre about 0.3 metres longer.
Yet because the engine will be more efficient, and because the composite wing of the 777X will be lighter, GE will design it to operate at lower power.
The power of a jet engine is measured in pounds of thrust. One pound of thrust is the force that gravity exerts on a one-pound object.
The GE90 has maximum thrust of 115,000 pounds (52,163 kilograms). The GE9X will have a lower maximum thrust of about 100,000 pounds. Yet the new 777X will carry more than 400 passengers, 50 more than the current 777.
"Less thrust to deliver more passengers," Jackson said.
That's a measure of this engine's appeal to Boeing's airline customers. With the 777X, they are promised a plane that will have 50 extra seats but will burn 10 percent less fuel than the current 777.
GE aims to achieve that with technology improvements developed over the past 20 years since the GE90 entered service.
The GE9X will inherit technology developed for the GEnx engines that power the 787 Dreamliner and also for the LEAP engine that is almost ready for the 737 MAX.
The improvements include a light composite fan case, a combustor that pre-swirls the fuel/air mix before ignition, and new materials in the hot central core of the engine.
Those new materials include ceramic matrix composites (CMCs), made from heat-resistant fibres such as silicon carbide, embedded in a metal matrix.
CMCs have the durability of metal, the strength and weight of fibre, and can withstand higher temperatures than metal.
The stationary ring that encircles the spinning blades inside the GE9X's high pressure turbine will be made from CMCs.
GE will also introduce additive manufacturing on the GE9X, building up some of the small complex shapes within the engine layer by layer, as if on a 3D printer.