To the limit: how Rolls-Royce readies its engines for extreme environments

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To the limit: how Rolls-Royce readies its engines for extreme environments

A conversation with Rory Clarkson about the extreme environments Rolls-Royce engines must prepare for – and how data makes it possible.

During a commercial flight, the environment an aircraft endures is extreme – even when everything goes according to plan.

When a civil aircraft cruises through the sky, typically at around 600mph, it can reach heights of 40,000 feet – where temperatures can drop to -60 degrees Celsius.

To prepare for the bone-chilling conditions at high altitudes, all Rolls-Royce engines must undergo an exhaustive battery of cold-weather tests at its GLACIER facility in Manitoba, Canada.

But engines must be able to encounter the unexpected – and that’s when Rory Clarkson steps in, to ensure Trent engines are ready for anything. Since 2010, Rory has led the Engine Environmental Protection team, which studies how extreme conditions affect aircraft engines.

According to Rory, when he took over the team ten years ago, they focused on icing conditions – things such as rain, hail and freezing clouds. But all of that changed when Eyjafjallajökull, an Icelandic volcano, erupted in 2010, severely disrupting aviation worldwide.

By analysing colossal amounts of data from Rolls-Royce’s airline customers and the UK Meteorological Office, Rory developed a new computer model that successfully determined the volume of volcanic ash in the air that an aircraft could safely fly in – and for what duration. The model supplanted the old modus operandi: completely avoiding ash at all costs – a costly approach – without compromising safety.

According to The Guardian, grounding so many aircraft cost airlines roughly £130m a day in the wake of Eyjafjallajökull.

But Rory’s model now has the potential to minimise the impact of future volcanic eruptions, by allowing airlines to cease flights only when absolutely necessary. What’s more, his model has provided the basis for research his team conducts into the effects of other atmospheric events, such as sandstorms.

The Rolls-Royce Engine Environmental Protection Team
At a glance

HEADQUARTERS: Derby, UK
THE TEAM: 20 full-time professionals at different Rolls-Royce locations, from Deutschland to Indianapolis.
JOB SCOPE: Study anything in the atmosphere that can impair the performance of or damage our engines.
FOCUS CONDITIONS: Rain, hail, icing, sand and dust, corrosive gases and volcanic ash.
OTHER CONDITIONS: Bird strike, lightning and (recently) tree sap.
AREA OF EXPERTISE: Knowing how much of these focus phenomena are found in the atmosphere – essentially what, where and how much of the stuff.
HOW OUR INSIGHTS POWER TRENT: Study how adverse conditions reach the interior of a Trent engine (and how they behave once inside). We advise the Rolls-Royce team members who design components in an engine – by explaining what we know about these threats. 

Sand and volcanic ash are similar in composition; they also cause similar damage to aircraft engines. Both sand and dust will melt in an engine, as will volcanic ash. And both sand and dust are abrasive and chemically active, as is volcanic ash.

“But [volcanic ash] doesn’t just form crystals – it forms glass,” says Rory. “This glass will go soft and sticky and become very erosive, sticking to the hot parts of the engine.”

Rory adds that some desert sands, particularly in places like the Persian Gulf, will melt at nearly the same temperature as volcanic ash, having a similar impact on engines as the glass particles produced by a volcano. The crucial difference is that, because of their explosive nature, volcanoes more reliably blast these particulates at flying altitudes and beyond – at up to 80,000 feet – and at higher volumes.

“Sand won’t be at concentrations near what a volcano can produce,” he adds. “That’s one of the big differences – there’s a natural limit to the concentrations of sand and dust.”

Rory says that sand and volcanic ash can cause similar damage to engines – corroding and clogging its components. Volcanic ash is more severe, while sand (and dust) are more common, particularly in arid desert regions.

Frosty hazards: high-altitude ice crystals

Frosty hazards: high-altitude ice crystals

Rory says there’s another phenomenon, called high altitude ice crystals, that interests him more than either sand or ash.

These crystals form high in the atmosphere because it’s so cold. Of course, most people know high altitudes are cold, but Rory says most people misunderstand why, usually thinking that it gets colder high in the sky because the atmosphere is thinner.

“The air pressure near the ground is at its highest – because there’s a big mass of air above it,” says Rory. “And as you go up [in the atmosphere], this pressure reduces. But if you then move air or a gas up, from high pressure to low pressure, it will expand – and as it expands it gets colder.”

For a familiar reference point, Rory points to household aerosol sprays. If you’ve ever sprayed on deodorant or suncream from a can, you’ve probably noticed something: it’s cold. Rory says this is the result of the compressed air expanding, which immediately chills it.

As air moves up into the atmosphere, where there is less pressure, it expands and gets cold. And the cold is what causes high-altitude ice crystals.

“These tiny particles, which are up to about a millimetre in diameter, exist in very high concentrations up at cruise altitudes,” he says.

Rory says that these ice crystals find their way into an engine when they are still frozen, and then quickly melt. But when they enter the compressor (the part of the engine that pressurises the air sucked in by the fan at the front), these ice crystals refreeze, forming a big chunk of ice. When it eventually detaches and is sucked into the engine, it can cause a lot of damage to its parts. Because when the aircraft is moving at hundreds of miles per-hour, it’s like throwing a fist-sized ball of ice at that speed into its components.

Over the course of more than 130 million flying hours, the Trent family of engines has already demonstrated its robustness in dealing with this phenomenom and further insights gathered by the team are already being fed into future engine designs.

Rory and his team analyse these and other phenomena to determine what causes them, what damage they cause and how best to avoid or combat them. And while his focus is still on more common hazards – such as ice, lightning and sand – sometimes he and his team are tasked with tackling some truly strange stuff.

Freakish weather, strange sap and strengthening the #PowerOfTrent

Recently, aircraft cruising over the Amazon jungle were discovered to be coated in a mysterious, sticky substance. Rory’s job was to figure out what caused this and how it affected aircraft engines.

“It was a bizarre thing,” says Rory. “There were aircraft cruising above the jungle. And when they landed they were covered in a sort of oily deposit. When they did a DNA test on it, they realised it was tree sap.”

Rory and his team deduced that, in this part of the world, there are very strong convection systems at certain times of year, which push air to high altitudes. The trees, which grow very densely in the Amazon jungle, happen to excrete this sap at the same time – and so the sap was rocketed up into the air, which is how it coated the aircraft.

This time at least, the freak phenomenon caused no particular damage (other than making the engines very dirty).

Though volcanic ash and tree sap are relatively “exotic,” as Rory calls them, the Engine Environmental Protection team approaches these problems as it does more expected perils, such as ice and sand, with a keen understanding of how the weather systems of the world work – and lots of data.

This data collection, gathered both from testing and during commercial flights, is increasingly important. Largely because the planet and its environment aren’t static. New industrial pollutants and changing weather patterns mean the Engine Environmental Protection team must constantly crunch new and huge data sets to make sense of them.

Work done now by the Engine Environmental Protection team means that Rolls-Royce’s next generation of large turbofan engines, will exploit opportunities in their architecture to minimise the impact of these pollutants.

“We are looking at optimal locations for cooling air off-takes and cooling air routing to minimise the quantity of contaminants reaching the turbines,” says Rory.

Moreover, Trent engines will now include sand-resistant thermal barrier coatings, which help prevent these grainy particles from entering the intake and hardening into corrosive glass, as well as hot corrosion-resistant coatings on the nickel alloys, which bolster these components’ defences to harmful industrial pollutants (that can appear suddenly over airports in the wake of new factories).

The Engine Environmental Protection team is doing cutting-edge work on a changing planet; it’s still early days. But in a relatively short time, the organisation has already begun new conversations about how Rolls-Royce should design its engines in future.

But the team’s unique insights, gathered in the field and aggregated into computer models, will continue to inform Rolls-Royce engine designs and maintenance, so that this – the second era of civil aviation – will be the best one yet.

To learn more about the Trent family, visit our Power of Trent hub .

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