Dream factories

The phrase ‘It’s what’s on the inside that counts’ has rarely been more true than in the case of the Boeing 787. Whether parked on the tarmac at Heathrow Airport or on display at the Farnborough Air Show, the newest member of the US aerospace giant’s commercial airliner stable isn’t very likely to gather many second looks: to all but the most discerning aerospace expert, it looks very much like any other medium-to-large passenger plane. It’s only when you get below the skin that it starts to become clear how different this aircraft is from the others surrounding it.

The 787, also known as the Dreamliner, is 50 per cent composite, the first commercial airliner on the market to have that proportion of non-metallic material in its structure; composites comprise major parts of fuselage, tail and wings. With development costs topping some $32billion, the aircraft is claimed to use 20 per cent less fuel than similarly-sized competitors while generating 60 per cent less noise.

Of the rest of the aircraft, 20 per cent is aluminium, 15 per cent is titanium, and 10 per cent is steel.

Many of the systems on the aircraft also represent a significant departure from conventional aircraft design. While most aircraft use pneumatics to operate many systems, using air bled off from the engines, the 787 replaces these with electrical systems, which makes the aircraft less mechanically complex and easier and cheaper to monitor and maintain.

It also has electric brakes, with four modular, independently operating brake actuators per wheel; again, this makes for a less complex system, with no concerns about leaking pneumatic fluid and valves. The brakes can also adjust the force applied to the wheel, slackening off as the brakes cool down when the aircraft is parked; this, Boeing says, increases the life of the brake components.

It’s unlikely that anyone flying on a 787 will notice any of these, however. What they will notice is that it doesn’t have pull-down blinds on the windows; instead, it has electro-chromic windows that darken at the touch of a button. Another maintenance-saving addition — the windows have a 20-year lifespan — these reduce glare without blocking off the view altogether, and allow the cabin crew to dim or brighten the cabin instantly; particularly useful when landing at night.

‘The market was looking for a breakthrough aircraft, not just in terms of its performance but also in terms of the passenger experience and its environmental impact

Todd Nelp, Boeing

The drive to introduce new materials and technologies was a deliberate one, explained Todd Nelp, Boeing’s vice-president for European sales. ‘We recognised over ten years ago, when we started designing this airplane, that it couldn’t just be a bit better than what was out there,’ he said. ‘The market was looking for a breakthrough aircraft, not just in terms of its performance but also in terms of the passenger experience and its environmental impact. We knew from the very beginning that we would have to push technology very hard, maybe even beyond what we were comfortable with.’

In fact, the origins of the 787 lie with a much less conservative-looking aircraft. Responding to a drop in sales of its 767 model and inceased competition for the 747 in the late 1990s, Boeing originally intended to design and build a fast aeroplane, the Sonic Cruiser, that would fly at Mach 0.98, just below the sound barrier; this would be complemented by a new, stretched version of the 747 with composite wings that would improve its fuel efficiency.

The Sonic Cruiser went through several design iterations and several airlines had expressed interest in buying, but the terrorist attacks of 11th September 2001 had a cataclysmic effect on the civil aerospace industry. Airlines became more cautious, particularly of aircraft that would use a lot of fuel. Efficiency rather than speed was the watchword, and faced with declining interest in its new projects, Boeing cancelled both Sonic Cruiser and the updated 747.

Instead, it decided to throw its development effort behind a smaller, fuel-efficient twin-aisle aircraft that would be able to offer a long-haul service from smaller airports than the large hubs served by large aircraft like the 747 or its new European challenger, the Airbus A380. This allowed it to repurpose much of the development work it had already put into its earlier projects, Todd Nelp said.

‘In order to make the Sonic Cruiser viable, we had to use composide materials,’ he explained. ‘We did a lot of work studying their application, and then when we decided that the market would prefer we uese the technology for a more efficient airplane rather than a faster one, we’d got ourselves more comfortable with the idea of using composites. But I think that without having done that work on Sonic Cruiser, I’m not sure the 787 would have used composites to the extent that it has.’

‘Without having done that work on Sonic Cruiser, I’m not sure the 787 would have used composites to the extent that it has

Todd Nelp

Some 25 per cent of the 787 by value is produced, or was developed, in the UK, with engine supplier Rolls-Royce contributing the largest proportion of that. Boeing is quite comfortable working with UK companies, Nelp said. ‘We more or less share a language, and we have a long relationship with many companies here,’ he said.

For its suppliers working on the 787 project, Boeing encouraged them more than usual to come up with new materials or technologies to help it meet its targets of low weight, high efficiency and low noise. ‘Boeing is responsible for the overall design and performance, and for integrating everything that makes the airplane work,’ Nelp said, ‘but we look to suppliers to help us develop the components and systems that are part of that whole. Early on in the product development phase, we’re out talking to the suppliers and understanding where they are with developing their particular technologies, and how we can take advantage of that.’

Within the constraints of certification, suppliers were allowed a fairly free hand. Messier-Bugatti-Dowty, which produces the landing gear of the aircraft, were instructed to bring in ‘what new materials we could, as long as they would help the overall goal of reducing the weight of the landing gear,’ said Matthew Taylor, production programme manager for 787 landing gear.

The landing gear incorporates titanium in two major components — the truck beam, through which both the axles run; and the internal cylinder of the main shock absorber. It also uses composites in the side-braces of the gear, which would normally be made from steel.

‘We get a specification at the start of the project, which is the maximum weight allowable for the landing gear, the size of the space it has to fit into, and the parameters and specs for the aircraft, its size, weight and the loads the landing gear will experience,’ Hall said. ‘We had experience within our group of developing and using composites — one of our sister companies, Aircell, uses them in lightweight engine nacelles.’ Moreover, he added, the company benefitted from working with the Advanced Manufacturing Research Centre at Sheffield University, a Boeing-funded organisation, which has special expertise in machining titanium.

‘Titanium has two big advantages — its very high strength-to-weight ratio, and its very high resistance to corrosion,’ Taylor said. ‘We don’t have to treat or paint the surface of titanium components at all.’

For Boeing, the process of introducing new materials changes through the course of a project, Nelp said. ‘In the case of Messier-Dowty and their composites, we were quite involved in the work that they did, when it came to actually designing the component and certifying it in our airplanes,’ he said. ‘In general, at the start of the project we’re quite open, depending on supplier capabilities. As we get to a defined product, we get more prescriptive until finally the certification process of integrating the components and making sure that they comply with regulation demands that we be very involved.’

One way that composites have changed the way the aircraft functions is in the wings, which are thinner, curvier and more flexible than conventional aluminium structures, deflecting upwards at the tips to a noticeable degree during flight. Another member of the UK supply chain, Qinetiq, provided wind-tunnel testing services for the aircraft structure, using a pressurised wind tunnel that can scale up so that a scale model of the 787 would experience the same proportional aerodyamic loading as the full-scale aeroplane. The model had to have wings which reflected the position they take up during take-off and landing.

One of the main goals of the tests carried out by Qinetiq was to reduce the noise produced on take-off and landing, and the noise transmitted to passengers. Traditonal soundproofing materials tend to add weight to the aircraft, so Boeing had to find new ways to reduce the noise. These include a sound-absorbing liner to the engine nacelle — the streamlined shell encasing the engine — and scalloped trailing nacelle edge which changes the characteristics of the jet exhaust stream. Boeing has also introduced mechanisms to control the turbulent fow of air over the surface of the aircraft, which induces drag (increasing the fuel consumption of the aircraft) and transmits sound to the aircraft interior.

‘I’ve flown for ten hours on one, and I felt great

Randy Tinseth, Boeing

Other comfort features inside the aircraft include higher humidity, cleaner air, windows 30 per cent larger than a 767, and 2000ft lower apparent altitude inside the cabin, along with increased ceiling height owing to a redesign of the overhead hand baggage lockers. ‘You’ll feel better after flying in a 787; all of these features reduce fatigue,’ said Randy Tinseth, vice-president for the marketing activities of Boeing’s commercial division. ‘I’ve flown for ten hours on one, and I felt great.’

Power system

The Trent 1000 engine with which the Boeing 787 was developed is the latest of Rolls-Royce’s long-running Trent series of turbofans to enter service. Developed specifically for the 787, it incorporates a series of technological innovations intended to improve its efficiency, reduce its weight, and keep the mechanical complexity of the aircraft low.

‘The development programme for an engine like this takes many years,’ said Mark King, president of civil aerospace for Rolls-Royce. ‘There are 18000 parts in a turbofan engine and we invest some £900million in R&D each year to make each of those parts better than the one that was in the previous generation of engine.’

In terms of performance improvement, the Trent 1000 is 15 per cent lower in fuel consumption than the first Trent generation and 3dB quieter, which equates to halving the sound levels at the human ear.

‘This is the most successful entry into service of a new engine that we’ve ever had

Mark King, Rolls-Royce

Trent engines are built at Rolls-Royce’s factory in Derby, then those destined for Boeing aircraft are flown to Seattle where they are ‘podded’ — fitted into their nacelles — before being installed onto the aircraft at Boeing’s final assembly plant. ‘We have a dedicated team at Seattle for the flught testing of the new aircraft, and we also have a production team which comes into operation when the aircraft goes into full production, making sure the engines are podded, delivered and so on,’ King said,

To illustrate the complexity of the components inside the engine, King focused on the turbine blades, which are grown as single crystals inside a vacuum furnace, with internal passages formed inside the crystal as it grows. The blade has internal and external cooling channels and a ceramic heat resistant coating; these, along with the single-crystal structure, — which means it has no internal junctions between crystals along which heat can travel — means that it can operate at some 400°C above the melting point of the alloy from which it is formed.

The Trent 1000 entered service in January, and its introductory period is ‘the most successful entry into service of a new engine that we’ve ever had,’ King commented. ‘That’s really useful when companies like British Airways and Virgin Atlantic order Dreamliners and want to decide which engines would be the best,’ he added.

Trent 1000

The data

Length            4.74m

Diameter            2.85m

Dry weight            5765kg

Maximum thrust 240-330kN

Thrust-to-weight ratio                       6.189:1

Bypass ratio            11-10.8:1