How modelling, simulation and product lifecycle management tools are making a new generation of lighter, stronger, cleaner and possibly even simpler aircraft.
Today's aircraft engines emit large quantities of heat, noise, particles and gases that make significant contributions to environmental pollution and climate change. This is a problem which the growing number of passenger flights over the last two decades has only exacerbated.
A number of national and regional governments have woken up to the issue, with many agreeing to work with the International Civil Aviation Organisation (ICAO) to limit or reduce aircraft emissions, for example, while the US Federal Aviation Authority (FAA) has implemented a specific programme to determine and reduce the industry's environmental impact.
The European Union (EU) has arguably gone further, setting up the Clean Sky initiative in 2008. This is a €1.6bn research programme jointly funded by the EU and the aeronautical industry. It aims to develop technology for quieter, more fuel-efficient aircraft which will help aircraft manufacturers and airlines meet specific environmental targets: reducing CO2 emissions by 50 per cent, NOx emissions by 80 per cent and noise perception by 50 per cent by 2020 compared to baseline year 2000 levels, with more ambitious goals set for 2050 under the European Commission's Flightpath 2050 Vision for Aviation. The EU has since updated Clean Sky to Clean Sky 2, now given the task of reducing aircraft CO2/NOx and noise emissions by a further 20-30 per cent compared with the 'state of the art' aircraft entering service from 2014 onwards.
Building and flying greener aeroplanes may not in itself be a top priority for aircraft manufacturers and airlines. But utilising lighter, more aerodynamic aircraft with better fuel consumption to reduce the airlines' costs and increase profits in an increasingly competitive market certainly is, and the two objectives dovetail neatly to a certain extent.
"One of the key competitive and regulatory battlegrounds is mitigating environmental impact, alongside the drive to reduce the costs of flight, and those technologies go hand in hand because airlines are trying to reduce the fuel burn," says Robert Harwood, global industry director for aerospace and defence at computer-aided engineering (CAE) software specialist Ansys.
Simulating green prototypes
Modelling and simulation software is playing an important role in the development of greener aviation technology. Engineers use it to test virtual prototypes based on innovative, aerodynamic designs that use lighter construction materials, and to develop new types of engine that reduce fossil fuel consumption, while also validating models against aviation authority certification standards.
Ansys offers tools that help with structural design, simulate wind tunnels using computational fluid dynamics, and model onboard electro-magnetic, fuel, communications, control and load balancing systems, all of which can combine to improve aircraft performance.
Engineers can use the software to help optimise engine flow path aerodynamics, aeromechanics, thermal design and combustion processes alongside rotor, compressor and turbo dynamics for example, while simulating the stress properties of lightweight carbon composites used in the wings and fuselage. And with the increased use of electronic aviation systems within the aircraft itself, designing electrical systems, antennas and other components which feed back performance data in real time is another challenge.
"If you think about the ongoing trend with the Internet of Things (IoT), there are thousands of sensors feeding back diagnostics and statistics all of the time," says Harwood. "It is about how engineers design those systems to show when components are drawing too much power, for example, and feed that in to computer control software critical to energy efficiency. Safety is the top priority, but then it is about optimising all those systems to minimise redundancy, latency and reduce weight."
"The structural design is now more systems-centric so you have to have technology that provides a systems-based digital mock-up to allow engineers to simulate and optimise designs virtually as they develop the aircraft," adds Michel Tellier, vice president of aerospace and defence at Dassault Systèmes.
"Their [aircraft engineers'] challenges are mostly on range, cost, weight and building structures which are more resilient, and the difference between going through thousands of virtual prototypes or designing four physical models [in terms of time and cost] is huge."
Both Ansys and Dassault Systèmes worked with Airbus to help design and validate the carbon composites that make up 50 per cent of the Airbus A380 fuselage, while Dassault has partnered the National Institute for Aviation Research to look at other ways that composite materials can be used in the aerospace industry using its CATIA design and SIMULIA simulation tools, two applications that make up part of the vendor's 3DEXPERIENCE software suite.
"We can simulate pretty much every aspect of the aircraft and its performance capabilities, do virtual multi-physics simulations and create mathematical models," says Tellier. "We make sure that all data can be simulated and that engineers can throw hundreds of missions at the design which can then be optimised."
The Airbus Group (formerly the European Aeronautic Defence and Space consortium, EADS) is working on a hybrid electric propulsion engine system as part of the European Commission's Flightpath 2050 programme.
Developed in partnership with engine manufacturer Rolls-Royce and Airbus, the E-Thrust concept has multiple electric fans arranged in clusters along the length of each wing to produce thrust, with electricity supplied by onboard gas power units that also recharge supplementary batteries. These provide energy storage to enable an emergency landing in case the gas systems should fail.
The aircraft are also designed with sleeker airframes to reduce weight and drag by decreasing the size of the vertical tail and improving payload distribution.
Built as a technology demonstrator, the first working prototype is the two-seater E-Fan introduced at the Paris Air Show in 2013, which has been undertaking test flights for almost a year. It sports two electric motors with a combined power of 60kW, each of which drives a variable-pitch fan to provide static thrust of 1.5kN. The motors are turned by a series of 250V rechargeable lithium-polymer batteries housed in part of the wings parallel to the cockpit.
The E-Fan is currently intended to be sold commercially as a pilot training aircraft, but Tellier says its development is just the start of a longer journey that will eventually see its technology components incorporated into larger, passenger aircraft.
"It [E-Fan] is just a technology stepping-stone, licensed and fabricated as a pilot trainer, but that is not Airbus' core business – their intention is to get regional airlines using this technology 20 years from now," he explains. "It is really about identifying core technologies that can be brought to maturity to support large-scale production and proliferation."
Tellier says that Dassault Systèmes software is playing an important role in the design of both the E-Fan and Airbus's other activity as part of the E-Thrust initiative. He says designing and simulating hybrid electrical aircraft from the ground up is much simpler than for traditional aircraft due to the relative simplicity of the architecture overall.
"If the whole thing is electrical you do not have huge fuel tanks in the wings, pressurisation or power systems which are powered by sucking bleed air out of the engines," he said. "There is no redundancy in terms of hydraulic systems. Switching to all-electric gets rid of half a dozen systems and all the redundancies that go with them so you get a significantly lighter, safer and less complex aircraft."
High power electric motor
Elsewhere Airbus is also working on the E-Star, a proof-of-concept serial hybrid- electric conversion of a Diamond Aircraft HK36 Super Dimona motorglider which uses a generator set based on an internal combustion engine as a range extender to augment electrical power from an onboard battery.
This project is part of a long-term research partnership with Siemens initiated in 2013. The company envisages that the technology will eventually be used in helicopters and larger aircraft able to carry up to 100 passengers to help reduce fuel consumption and emissions by up to 25 per cent and drive environmental performance.
The latest development saw Siemens announce in March 2015 that it has produced an electric motor weighing just 50kg that can deliver a continuous output of about 260kW, a 5kW/kg power-to-weight ratio far in excess of standard industrial motors, which the manufacturer believes will support aircraft take-off weights of up to two tonnes.
The company did not say which specific modelling and simulation software it used for the motor's design, but went on record that its development was possible only by analysing all the components of its previous electric aircraft motors and incorporating optimised improvements prior to construction using a range of computer simulation methods before applying the findings in order to produce the lightest and strongest set of components possible.
Siemens acquired Belgian modelling and simulation software specialist LMS for a reported €640m in 2013. LMS has a long heritage of providing model-based systems engineering tools to the aerospace industry, and its software has since been integrated with Siemens' own finite element modelling (FEM/FEA) and multibody dynamics simulation tools alongside the German company's product lifecycle management (PLM) software.
The simplification of data exchange between multiple modelling and simulation tools which are typically used in large-scale design projects, and in some cases the integration of PLM software, is particularly important in aircraft manufacturing. And being able to transfer information from one model to another and make that process simple from a design perspective is critical to building complete virtual prototypes that combine different elements to demonstrate overall behavioural characteristics.
"You have to have very good data exchange," says Harwood. "When the aerodynamics team takes the detailed engineering CAD model they do not care about all the nuts and bolts, they just take the geometry and simplify the hell out of it to get what they need. The structural team will take that model but they need other details, and these are just two disciplines. So you have all these child models and individual teams configuring those models, and the design cycle for each happens at a different pace. Somewhere, you have to bring these together and keep them concurrent and that is a huge challenge."
The Airbus A350 XWB programme approached this problem by using Dassault's 3DS 3DEXPERIENCE platform to produce a single 3D systems-based digital mock-up of the new wide-body aircraft, a project involving hundreds of different suppliers and thousands of engineers. This too presented challenges, not only in terms of scale but also the coordination of people and processes and the use of a common 'digital' language that enabled all the different modelling and simulation tools used by Airbus and its commercial partners in different countries to talk to each other.
"Imagine in the past you had people that designed parts and systems, then other people who took those, built simulations then verified them. The big change on the Airbus XWB is that what the engineers designed is directly simulatable, there is no intermediate [process] anymore," said Tellier. "So they went to a high-definition 3D master and that was the only thing they produced. They manufactured, simulated, validated and released off that and went from a CAD drawing, alphanumeric type scenario to this virtual aircraft."