Most of us don’t give aircraft engines much thought. We take aircraft engines for granted,
assuming they will work flawlessly. The manufacturer’s records and reputations assure us. But there
is a lot of work put into getting us so comfortable and reassured.
Aircraft engines are meticulously engineered and manufactured. But once built, the engines
are put through a relentless testing process. Here, we look at how aircraft engines are
tested before production.
Engines will commonly go through water ingestion tests. At Boeing, planes taxi through specially
made water troughs. Manufacturers also force a stream of water into running engines. When
General Electric tests its GEnx engines, it fires 800 gallons of water per minute into
the engine. That water should pass through the engine and out the back without reducing
thrust, proving the engine can handle the fiercest rainstorms.
“These tests assess the correct functioning of engines and thrust reversers, as well as
braking systems when submitted to water thrown up by the wheels in cases of standing water
on the runway,” says Boeing told the BBC’s Katia Moskvitch.
Testers will also shoot ice into running engines to mimic the effects of flying through a hailstorm.
Moving on, birds can also get ingested into engines. Because engines are now so well engineered
and built, bird strikes rarely cause fatalities (except to the bird).
These days, there is one human fatality attributed to bird strikes per one billion flying hours.
But bird strikes do damage aircraft, resulting in $1.2 billion worth of repairs annually.
And, as the US Airways controlled landing in the Hudson River in 2009 demonstrated,
bird strikes can still down a plane. Engine manufacturers have a low tech way to
test engines for bird strikes. In the 1950s, de Havilland invented the chicken gun. It’s
a large-diameter, compressed-air cannon that fired chicken carcasses at the plane, including
into its engines. The desired outcome is for blades to hold
their form after the collision. Since the 1950s, fresh chicken carcasses have been swapped
out for frozen carcasses.
One of the toughest tests of engine reliability is simulating what happens when a blade in
the engine fan comes loose. That shouldn’t happen, but it has been known to occur. It’s
a possible issue if the engine ingests debris. A jet engine shaft can spin at 3,000 revolutions
per minute. If a blade comes off, for whatever reason, it can cause enormous damage to the
rest of the engine, and debris can impact the fuselage.
What engine manufacturers try to do is contain the blade within the engine and allow the
casing to diffuse the energy. During the testing process, a small explosive will get attached
to the base of the blade. They run the engine, detonate the explosive, and ensure that the
blade stays within the engine chamber. These types of tests occur while aircraft remain
safely on the ground.
Part of the engine certification process happens in the air. For that, the engine manufacturers
use modified aircraft known as testbeds. Retired 747 aircraft sometimes find a second
life as testbed aircraft. Rolls Royce and General Electric each have two converted Boeing
747s packed with computers, electronics, and other gear.
With an awkwardly positioned engine, testbed aircraft might look odd, but they are integral
to testing engines. At the end of the day, engine manufacturers,
aircraft manufacturers, airlines, and passengers, all want reliability.
While nothing is perfect, they want to get as close to it as possible. As Airbus says,
it is a matter of going above and beyond what is required.
Before this video, were you familiar with the engine testing process? Let us know in
the comments.