Test engines like this one in West Palm Beach, Florida, get everything thrown in them from large ice balls to dead birds. (Courtesy: Pratt & Whitney)
By Alexander George
Despite a highly publicized series of accidents this year, air travel is one of the safest ways to move large numbers of people over long distances.
Much of the credit for the extreme rarity of commercial plane crashes goes to extensive regulation, attention to quality control, and extensive testing of modern jets, which cost billions and takes years to develop. Before any passenger steps aboard, the wings get flexed until they snap. The bodies are zapped with electricity to simulate lightning strikes. Test aircraft spend hundreds or thousands of hours in the air.
The testing that goes into certifying the engines that power these aircraft—the engineering marvels that can send a 600,000-pound Boeing 777 over 500 mph—are no less extreme. The engines are designed to suck in air, but they have to be capable of taking on everything else they may encounter in the sky, most notably birds and bad weather. To ensure that’s the case, manufacturers run tests that are as straightforward as they are awesome: They turn on the jets and start throwing things in there.
General Electric, one of the few companies that produces engines for commercial jets, works with the toughest materials in the world. The fans inside a Boeing’s 737 LEAP 1-B engine are made of woven carbon fiber composite, with low-pressure turbine blades made of titanium aluminide, a NASA-grade alloy. Those big blades you see slowly spinning as you board the aircraft? Each one costs tens of thousands of dollars to produce.
But even the strongest and lightest materials in the world can fail, and engineers need to figure out just how that happens. That’s where the fun begins.
(Images: GE Aviation)
First, the easy stuff. The engines need to handle water, so GE will set up a hose and blast a running GEnx engine with 800 gallons of water per minute. When the test goes as planned, all that rain flies through the chamber and out back without diminishing thrust. That means it’ll easily handle the drizzle when flying out of O’Hare.
Ice is slightly more problematic, so much that the FAA requires engines be able to handle several specific varieties of ice formation and ensure they can recover quickly. Besides starting the engines in freezing conditions, testers shoot huge ice balls inside a running engine.
(Images: GE Aviation)
The 2009 US Airways crash landing on the Hudson River did an excellent job reminding the public and regulators that birds can do major damage to jet engines. The big ones can actually bend back the blades at the front of the engine, making it stall or explode. The bird strike test is exactly what you think: a special “chicken gun” fires (already dead) birds into running engines. The goal is for the blades to hold their form after the collision.
The most violent test of all is the “blade-off” procedure. This simulates an event where a single blade at the front of the engine, due to wear, snaps off from the shaft while spinning at over 3,000 RPM. At that engine speed, the blade can quickly become shrapnel and tear through the rest of the plane if the fracture isn’t contained.
To make sure it is contained, engineers rig a small explosive to the base of the blade, which separates it from the shaft. When the test goes well, the blade stays within the engine chamber, while the casing diffuses the energy from the impact. For an extended look at this process, check out this video.
If these images make you nervous about the risks that come with flying, try to remember that these tests are all about making air travel as safe as possible, and they’re an effective tool. And, in the extremely rare event of an engine failure, any modern commercial jet can fly, land, and even take off with only one working engine.
More from Wired: