Many disciplines use ‘testbeds’ to evaluate new innovations. These platforms help to scrutinise new technology by simulating the conditions of its applied use.
The automotive world, for example, frequently employs ‘mules,’ the industry slang for testbed vehicles equipped with prototype parts that are under evaluation. These mules are often elaborately camouflaged or otherwise disguised to thwart both interested competitors and overzealous press reporters.
In contrast, in aviation, engine manufacturers test engines in development or under inspection by fixing them to specially remodelled research aircraft. (They also tend to be proudly painted with the insignia of the engine manufacturer). These ‘flying testbeds’ supplement other rigorous forms of evaluation, which range from remote sub-arctic testing facilities equipped with machinery that mimics frosty cloud conditions, to firing chicken carcasses at whirring engine blades to assess their resilience to bird strikes.
Basically, by the time a jet engine is being tested on-wing, attached to a flying testbed, it’s already been through the wringer.
That’s because before any airplane engine can be certified for commercial use, the relevant airworthiness authorities require it to undergo rigorous testing. This includes everything from evaluating the level of fuel burn to assessing how the aircraft handles in zero-G or in severely icy conditions. But some performance can’t be fairly appraised unless the jet engine is actually in the sky, flying at different altitudes and at different speeds.
As flying testbeds involve actually strapping an engine to the wing of an aircraft to power it, no part of the testing process more closely approximates the conditions of commercial flight. And the interiors of flying testbeds are equipped with highly sensitive instruments to monitor the engine’s inflight performance. This technology allows for valuable data to be gathered from flying testbeds as they cruise through the skies, gathering all sorts of information – such as in-engine pressures, temperatures and the location of any strains – while beaming some of this information back to engineers on the ground in real-time.
A Dreamliner come true: developing a bleedless engine
In 2005, Rolls-Royce purchased a Boeing 747-200 aircraft, which was converted by L-3 Communications at their base in Waco, Texas for the purpose of testing a new engine then in development: the Trent 1000. (L-3 Communications needed to install electrical and hydraulic system simulators to approximate the specifications of a Boeing 787.)
In the commercial aviation industry, engine manufacturers most often design their product to be suited for a particular airplane, according to the specifications provided by its manufacturer. For its 787 Dreamliner model, Boeing requested that a “more-electric” engine should power it. By this they meant to adhere to a so-called bleedless design.
A bleedless aircraft seeks to be more energy efficient by eliminating pneumatic hardware. A pneumatic device is one powered by compressed air instead of electricity, from steamliners to the squeaky brakes on big buses to some dental drills.
In years prior to the Trent 1000, most large commercial aircraft were designed to suck surplus air from the engine for cabin systems. The reasoning behind replacing the pneumatics with electricity on the Boeing 787 Dreamliner was for better fuel efficiency.
At first, this may seem counterintuitive – after all, how could electric power be more efficient than compressed air?
But here’s the rub: pneumatic equipment is very heavy. And when you’re engineering something to fly, more weight means more fuel – and that, in turn, means greater CO2 emissions. But removing all the pneumatic ducts, valves and other parts to replace them with modern electrical hardware, weight is saved which can make the aircraft more energy efficient.
By this measure, the Trent 1000 was hugely successful: a Boeing 787 Dreamliner powered by these engines is 20% more efficient than the Boeing 767 it replaced. And its development was hugely enhanced by attaching it to Rolls-Royce’s flying testbed.
Our busy bee: how the Rolls-Royce testbed spurs new advancement
“The use of inflight altitude testing is becoming more and more of a focus of the engine manufacturers,” says Andy Brown, the Flying Testbed Manager at Rolls-Royce. “There’s no way to better replicate the actual conditions during flight.”
Rolls-Royce’s ‘Hefty Bee,’ the local nickname for its flying testbed (based out of Tucson, Arizona), is known to its engineer-caretakers as the ‘spirit of excellence.’ To explain the origin of that unusual name – Hefty Bee is derived from FTB, the industry acronym for flying testbed.
So far, the Hefty Bee has been busier than Rolls-Royce ever expected. It’s racked up more than 800 hours in the sky from more than 250 flights, even though it was originally intended for just 150 hours – and only 25 flights.
“We are seeing things in flight that we are not encountering on the ground, or even altitude chambers. The products are getting so much more sophisticated that inflight testing for optimal performance and operation is imperative.”
Part of the reason for this is that, in general, the equipment for gathering information about an aircraft’s operations has become increasingly more sophisticated, and so the data has become increasingly more useful.
But another reason is that Rolls-Royce has recently had to upgrade some of the hardware on its Trent 1000 engines,
For example, pollutants in the air were causing some premature corrosion of the engine’s turbine blades, meaning they required maintenance earlier than expected. (For a more complete explanation of the affected components and their updates, see here).
Brown explains that, prior to the development of these upgrades, the flying testbed was only being used a couple of times a week. But when the Trent 1000 required further evolution, the Hefty Bee needed to get busy.
“We expanded the team to be able to fly upwards of four times a week,” says Brown. “We also needed more people to handle the analysis of the data. A bigger team allowed us to start flying more during the day and then have the data analysed overnight.”
Data-driven deduction for Trent 1000
Brown says that a single day of engine testing might produce upwards of 20 gigabytes of data. (For some perspective, 20 GB of data is more than the average household in the UK uses in an entire month.)
According to Brown, the information the flying testbed gathers while in flight was particularly useful in identifying the durability issues facing the Trent 1000 engine.
“It was something that we were very much struggling to be able to do – to truly recreate the level of stress on the blades on the ground,” says Brown. “It’s just a different beast operating on the ground.”
Because the flying testbed so closely recreates actual inflight conditions, the data it gathers possesses an unparalleled usefulness, says Brown.
He adds that the testbed helped Rolls-Royce engineers conclude that certain flight conditions – such as a holding pattern, where there is high thrust at lower than cruise altitude – put particular strain on the blades in question, leaving them more vulnerable to premature wear and tear.
But the flying testbed is useful for all sorts of research and development at Rolls-Royce. So even though the Trent 1000 durability issues have largely been identified and are in the process of being resolved, the flying testbed is still taking to the skies regularly.
“We average 25 flights a year, at five hours duration,” says Brown. “And we travel somewhere between 400-500 mph, as you would on a commercial flight. So we end up covering 62,500 miles a year. That’s three times around the world. Overall, in its lifetime, our flying testbed has covered more than 625,000 miles. Obviously, if you do the maths, that’s 30 times around the world.”
These flights often leave the Sonoran Desert in Arizona heading westward to fly over the Pacific Ocean before heading back to base. And while testbeds are capable of landing in any airport, Brown says that many don’t welcome the operational burden of the special operations.
Usually, the best place for a flying testbed to operate out of is a dry environment (so there are fewer days when weather prevents testing) at a facility without too much traffic and near the sea. Proximity to the specific flight corridors for testing, called ‘test tracks,’ essentially designated airways in the sky, is also important.
For all these reasons, Tucson fit the bill. It was the perfect location. And, according to Brown, the locals have even grown fond of it.
“We recently started raising eyebrows with the livery change,” he says, speaking about the flying testbed’s new paint job in 2018.
“I love the look, and so does the Rolls-Royce community. But even people from in town and passersby comment on [it].”
Of course, these comments are likely to continue. Because as Rolls-Royce drives further innovation, the Hefty Bee will be busier than ever in its pursuit of pioneering the IntelligentEngine.
To learn more about the Trent 1000, visit our updates hub.