Today, the public tends to take flying for granted. We think of travelling across an ocean in a matter of hours as a matter of course. But the engineering that makes it possible deserves a closer look.
Because an aircraft engine is not an easy thing to build.
For a sense of scope, consider that each of these intricate marvels must undergo an exhaustive battery of tests to prove their worth – which is to say, to evaluate their performance and receive the necessary safety certifications.
The rigour of this process, and the lengths engine-makers will go to test and experiment with their products, is hard to overstate.
“Each Rolls-Royce engine is a masterpiece of engineering,” says John Bates, a retired US Air Force Colonel with 27 years experience as an aerospace engineer.
“You can be assured that the testing for any jet or turbofan engine is exhaustive,” says Bates. “Any imaginable test that can be humanly done is done. It doesn’t matter how expensive it is – if it’s going to preserve an aircraft, they’ll do it.”
To illustrate the great lengths that civil aerospace engine manufacturers will go to test their wares, let’s head north. Way, way up north. To the GLACIER (Global Aerospace Centre For Icing and Environmental Research) Facility, where Rolls-Royce sends its engines for cold-weather testing.
Taking a cold, hard look at an aircraft engine
When Rolls-Royce is evaluating a new engine, they strap it inside an Antonov, a behemoth Soviet-era transport aircraft (the largest ever made), and fly it to Winnipeg, Canada. Then it’s a 10-hour drive up to Thompson, Manitoba, a small subarctic mining town where temperatures regularly dip below 40 degrees centigrade during the winter season.
It’s brutal. When you inhale air that’s 40 degrees below zero, every breath penetrates your lungs, sharp as a dagger. In fact, when it’s this cold, even your eyeballs can freeze solid.
“With all the cold-weather clothing on you can’t be outside for more than 15 minutes,” says Chris Pattinson, Head of Test Operations & Execution at Rolls-Royce.
So why doesn’t Rolls-Royce just simulate that kind of cold? And, crucially, does it really need to be that cold?
“For many years, we would actually put our engines in freezers, for want of a better word, and simulate cold conditions,” says Pattinson.
“However, we need to be able to do this testing in far more representative environments. Icing testing is reliant on cold weather and icing cloud conditions. Plus, there are not many places in the world that can achieve this. We needed an outdoor test facility where you’re exposed to real-world conditions. That’s what GLACIER offers us.”
The GLACIER facility, in partnership with the National Research Council of Canada, is operated by an organisation called MDS AeroTest. Its general manager, Troy Ramnath, says Thompson is uniquely well-suited for the sort of work he oversees.
“Now, I’m not a meteorologist,” says Ramnath. “But I do know that one of the reasons Thompson was selected is its location – it’s in this critical sweetspot, where the highs and lows of the North American jet stream cross over.”
According to Ramnath, Thompson’s weather vacillates at fairly predictable intervals. It’s hit with very cold weather snaps of four to five days, where the daytime high and low temperature is consistent. Then, if it warms up a bit, usually that temperature will remain stable for a comparable spell. This regular temperature variation allows his team at GLACIER to perform tests for a range of icing scenarios and certifications – from the conditions in the upper atmosphere, to taxiing down a sleety runway when there’s high moisture in the air.
“So, at warmer sub-zero temperatures, where the humidity is higher, that’s where you have worst-case scenario of ice build-up on the intake and engine fan,” says Rammath. “When you’re actually taking off down the runway, getting up to speed, that’s where your ice will shed. Chunks of it break off the intake and are sucked into the engine – the engine acts kind of like a giant ice crusher. [With these tests] they want to demonstrate that the engine can withstand this worst case scenario – repeatedly.”
Cloud-making and team building: just another day at GLACIER
But it’s not just on the ground that aircraft can encounter frosty hazards. Clouds may look like harmless white wisps, but they can wreak havoc, bearing chunks of ice the size of apples.
To ensure all their engines can endure flying through these sorts of clouds, absorbing icy blows without a hitch, Ramnath says the GLACIER facility creates their own.
“Basically, the engine is docked into the test stand. Then the icing tunnel has a series of horizontal bars, and each houses an air line and a water line. So there are specific nozzles in each spray bar, for the water flow rate, temperature and the airflow rate. Both are controlled by a software interface, which NRC oversees and continually adjusts during each engine test,” says Ramnath.
According to Ramnath, while MDS AeroTest operates the GLACIER facility, they do not design the tests – nor do they learn the results. The specifications come from the engine manufacturer and then the results are sent back to them.
“For example, Rolls-Royce correlates how much water and air are required to generate a cumulus cloud for a specific testing condition.”
Pattinson says this sort of cold-weather test is critical for demonstrating to the regulatory authorities that the engine can tolerate the build-up of ice, and then shed it without affecting engine performance and reliability.
“We test the engines in much harsher environments than they would typically face,” says Pattinson. “Cold-weather testing demonstrates the reliability of our products far beyond the conditions these engines need to operate under during normal service.”
According to Pattinson, another test that Rolls-Royce runs at the GLACIER facility is called a ‘Cold-Start test.’ Essentially, these are to evaluate whether an engine can effectively start in even the most testing locations.
“Imagine you’re at El Alto Airport in La Paz, Bolivia. That’s one of the world’s highest international airports, at around 13,000 feet in altitude; it’s typically a cold place,” says Pattinson. “So, you’re on the first flight home in the morning, it’s 6:05am, and the pilot accelerates the engine to maximum power for takeoff. You can imagine the engine oil and other lubricants – they become very viscous at these extreme conditions. We need to demonstrate that the engines will operate reliably in these extreme conditions.”
Yet, despite the freezing tests these engines undergo, the most remarkable thing about the GLACIER facility isn’t the cold. It’s the warmth.
“The team at GLACIER is great,” says Pattinson. “And I think Troy is right, it’s like a family. Working in these most extreme conditions, you need to work together and you rely on each other to make the testing a success. When you have worked all day to hit the most exacting test conditions and the engine performs well, the feeling is brilliant.”
“We have barbeques, we all go bowling,” says Ramnath. “When you’re doing this kind of work, everyone plays their part.”
It takes a large team, countless hours and brutal cold to appropriately test an engine’s resilience. But this is just one example of one facility (called a ‘testbed’) where Rolls-Royce puts its aviation products through their paces. Because at 40,000 feet, there’s no room for error.
To find out more about Rolls-Royce’s tough engine tests, take a look at another testbed – one that operates high in the sky.