What’s in the air? Four experts answer your questions on the latest developments in civil aircraft.
Civil aircraft technology has developed considerably over the past decades, but from outward appearances it takes an expert to detect any changes in most airliners. Is a change on the way? And what technologies are being developed that might affect the way that most of us fly? We put your questions to a panel of experts from academia and industry.
- Chris Gear (CG), chief technology officer and senior technical fellow, GKN Aerospace
- Jessica Kowal (JK), environment, international development and policy, Boeing
- Dr Rob Hewson (RH), senior lecturer in aircraft design, Department of Aeronautics, Imperial College
- Prof Jonathan Morrison (JM), chair of experimental fluid mechanics, Department of Aeronautics, Imperial College
What is the actual means of achieving any of the proposed changes, especially as none of the major players will take the risk of radical change?
CG: I believe these changes will occur when environmental pressures, i.e. oil prices, start to increase, and tougher legislation with tighter regulations on engine emissions and noise come into play in 2030 and again in 2050. Today’s aircraft will need work done on them to achieve these requirements. Until then, OEMs can play safe with products and stay with existing industrialisation. The unknown factor will be China and if it starts to innovate then things might move quicker in the western world, but this is probably unlikely in the next 15 years.
How likely is it that these changes will include a move towards autonomous aircraft?
CG: There will be some move towards autonomous aircraft but mainly in military, not civil, due to safety and passenger discomfort and the security aspects with multi-sensor devices that can be hacked into. I think all the real development will go into military or private aircraft for a long while.
RH: There are already autonomous civil aircraft operating; the rapid increase in the use of remotely operated rotorcraft for filming is one area. DHL has delivered time-critical goods to a pharmacy on the island of Juist 12km from the north coast of Germany by an unmanned aerial vehicle, and both Google and Amazon are exploring the use of such vehicles to deliver packages. I believe large commercial aircraft will have pilots in the cockpit for the foreseeable future, in part due to passenger perception. The level of automation in the control of aircraft is set to increase, with the role of the pilot continuing to become increasingly that of a manager of the complex engineering system.
Is it true that the real medium-term innovations are to be found on the ground with ideas to help reduce greenhouse gas (GHG) emissions from taxiing?
CG: Definitely the application of electrical wheel devices for moving aircraft around the airport would help noise and engine emissions, especially in the large airports we are seeing proposed in Europe and that exist in the rest of the world. There is still more to come from innovations in engine performance and operating temperatures.
RH: There is ongoing research on the powered taxiing of aircraft, most notably the Electrical Green Taxiing System developed by Honeywell and Safran, reducing GHG emissions while the aircraft is on the ground. However, this is only a small part of the large and long-term effort to reduce GHG emissions from civil aviation; recent developments include the development of lightweight composite materials to produce light and very light structures – reducing the amount of fuel and emissions required for the aircraft to fly, the development of materials capable of operating at high temperatures, leading to more efficient thrust, and advanced aircraft aerodynamics – reducing drag, thrust, fuel and emissions. There have also been a number of flights that have operated using biofuel, reducing reliance on oil reserves and potentially decreasing GHG emissions. A number of these biofuels are already certified for normal operational use in aircraft.
JM: GHG emissions can be reduced by improvements to engine efficiency; flight-path management and airframe frictional losses. The last is probably the most challenging, and significant improvements to engine efficiency have already been made. Biofuels offer something for decarbonising flight, but the social impact of growing biofuels on a thirsty, hungry planet is significant.
JK: Rather than focus on one or another innovation as the ‘real’ or ‘best’ opportunity, the broader point is that aviation has to pursue an ‘all of the above’ strategy to meet our ambitious goals regarding the environment.
This is why Boeing’s strategy includes all of the key elements:
- Design and delivery of new, more efficient aircraft such as the 787, 737 MAX and 777X, which will reduce fuel use and emissions by as much as 30 per cent compared with the aircraft they replace;
- Ongoing efficiency improvements of in-service models, such as adding winglets that can improve efficiency by single digits;
- Investment to modernise air traffic management systems, which can improve efficiency by up to 12 per cent for all aircraft using them;
- New software/digital technologies that pilots and airlines can use to save hundreds of pounds of fuel, and emissions, per flight; and
- Development and commercialisation of a global supply of sustainable aviation biofuel that is price competitive with petroleum jet fuel. Using a 50 per cent blend of sustainable biofuel in an aircraft reduces emissions on a lifecycle basis by 25 per cent or more compared with a flight with 100 per cent petroleum.
To the more specific point of your question, there are certainly emissions reductions to be found on the ground, such as ‘one engine taxi’ or electric taxi systems.
For example, Boeing has worked with the Israeli Aerospace Industries (IAI) to certify IAI’s product TaxiBot for the 737. TaxiBot allows aircraft to go from gate to runway and back without using the engines, and thus saving fuel and emissions.
In the UK, Boeing is part of the Sustainable Aviation coalition, which is a partnership of manufacturers, airlines, airport operators and NATS, the air traffic management provider. Ground operations is one area in which Sustainable Aviation is looking for additional emissions reductions.
Are you in a position to look seriously at 3D-printed metal parts? If so, what sort of parts are you looking to use and what real advantages are they bringing? Does the process speed up delivery of an aircraft (very helpful to the customer), bring operational benefits to the customer or is it a combination of these and other factors?
CG: We are very much involved with making additive manufactured aircraft parts and the processes that can be used to make these parts along with the production of the raw powder material that is essential in qualifying the processes and material strength. Additive manufacturing (AM) brings big benefits in material optimisation. The AM process only uses the material needed to make a finished part. It has a very small amount of waste material generated from the process compared with a machined rib where 90 per cent of the billet is removed to get a finished part. The parts being considered are medium-sized components today due to the working section of the machines, but the part complexity is extremely high and it gives you the ability to design and make a part that in the past was impossible to achieve. So the overall weight and costs are much less compared with a typical machined part. The process can seriously speed up the manufacture of parts needed for an AOG [aircraft-on-ground] item.
RH: 3D metal parts are already flying on aircraft; these include brackets attaching components together, printed from both plastic and metal. The metal printed parts are typically aluminium alloys. The advantages are that they do not require as much tooling to manufacture [specialist component-specific manufacturing tools] and can provide new design flexibilities. This allows the design of parts that perform better than those designed to be manufactured using conventional processes. This can lead to unusual structures being designed, some of which have unusual shapes similar to those encountered in nature, for example the branches of a tree or the skeleton of a bird.
Are there any innovations afoot in essential aerospace services – ATC, weather forecasting and so on – that are helping airlines to reduce noise and GHG emissions?
RH: Yes, improved real-time navigation and surveillance is being developed to allow aircraft to fly more directly to their destination, sensing and avoiding other aircraft that may be encountered en route. There have also been studies done on developing cruise descents, where through careful planning of the aircraft arriving at an airport a continuous descent to a landing can be achieved. This means that the time and fuel-consuming ‘hold’ is avoided while the runway is vacated by other aircraft.
JK: Alongside continuous improvement of Boeing’s commercial product line – for example, the Boeing 787 Dreamliner family is at least 20 per cent more fuel efficient, with an equivalent reduction in emissions and a 60 per cent smaller noise footprint than the aircraft it replaces – Boeing is also innovating in digital services we provide to our airline customers and test for potential future use.
For example, the Boeing Fuel Dashboard provides aircraft operators with a comprehensive total fleet view of operational fuel consumption, offering broad savings opportunities. Airlines, business aviation operators and military organisations can gain insight into current fuel usage through all phases of flight. This visibility enables better decision making to reduce fuel consumption, costs and emissions. In addition, we offer real-time weather updates and other types of data analysis to support customers’ fuel-efficiency efforts. In addition, Boeing tested a wide range of software technologies on our ecoDemonstrator 787 in 2014 that can reduce noise and fuel use.
As two examples that also address your original question, the ecoDemonstrator 787 tested:
- Advanced GLS Cat III navigation using a ground-based augmentation station (GBAS), which customises approach paths to reduce community noise and allow greater airport access in some locations; and
- Boeing collaborated with NASA to test its ASTAR Airborne Spacing system.
For long-haul flights, can we get a supersonic, quiet, beautifully designed, clean aircraft, for example an electric Concorde, at an affordable price with maximum comfort for all passengers? Can we make flying a wonderful experience again with the added bonus of zero-pollution [noise, GHG and so on]?
JM: The energy density required for supersonic flight is much greater than that for subsonic flight.
CG: Not for a long time unless you want to go outside the atmosphere in a rocket device, but the take-off and landings will be noisy.
I’d like to ask the panel how feasible they think the concept of electrically powered civil flight is – particularly given Airbus’s growing interest in the technology.
CG: Definitely going to happen in smaller vehicles with less range over the next decade, possible in civil craft if the energy storage systems can be made light enough, can recharge in flight and are safe to operate. We are still a long way from finding an energy source with that much power and that duration that is not a combustion device today. The probable step could be a hybrid solution that can provide the burst of power for take-off and charging while in flight. The weight of the electric motors will also be a factor and the possible development of new materials for these motors.
JM: The real challenge is the energy density required. It so happens that fossil fuel provides this – as would nuclear, but I wouldn’t advocate that. Electrically powered aircraft would require much improved battery efficiency – and batteries are heavy. There are composite materials being developed that offer much more efficient energy storage.
JK: Boeing continually researches technologies to power civilian flight, including electric-powered aircraft.
Having said that, commercial aircraft will require liquid fuel for the foreseeable future because no other energy source – such as electric, solar or hybrid – has been shown to provide enough thrust to get a large aircraft off the ground any time, anywhere. This is in part why Boeing has taken a leadership role in developing and commercialising sustainable aviation biofuel, which represents the single largest opportunity for aviation to reduce its emissions by using an alternative fuel.
We work with partners – airlines, governments, researchers, fuel producers and non-governmental organisations – on six continents to make progress on this.
When it’s sustainably produced, aviation biofuel cuts CO2 emissions by 50 to 80 per cent on a lifecycle basis compared with fossil jet fuel. Approved aviation biofuel is blended directly with petroleum jet fuel, and aviation biofuel actually performs as well as or better than Jet A, with higher energy density and a lower freeze point. Let me know if you want more information about biofuel development.
‘Fluidic flight controls’ – these were demonstrated on a model aircraft as part of the BAE Systems FLAVIIR project. Are we going to see this kind of flight control on passenger aircraft, for the sake of lower maintenance or any other reason?
JM: I was involved in the FLAVIIR project. Fluidic controls are usually employed as replacement of flaps so that the aircraft has reduced signature to radar. It is therefore more likely to be developed for military applications.
Ingestion of the boundary layer has been suggested over the years, by individuals such as Fabio Goldschmied and David Birkenstock, as a means of reducing wake drag at the rear of the fuselage. Substantial fuel savings have been claimed. Are these schemes considered to be realistic by the industry, and if so then what research is currently under way?
JM: The only boundary layer suction scheme that has been developed over a number of years is that applied to the leading edge of a wing. This is known as hybrid laminar flow control (HLFC), where leading-edge suction reduces boundary layer growth as well as delaying transition.
Transition increases friction drag by a factor of four or five, so HLFC may be effective here. Generally, the energy applied to boundary layer suction is likely to be more than the benefit in removing the boundary layer.
How will emerging and future manufacturing techniques – for example 3D printing – shape the development of civil aircraft in the future?
CG: They will certainly be in parts of airframes and engines today and this will grow over the next 10 years. The effect will be as replacement of existing items or cost-downs or simplification to one part from many.
Once we start looking at new products and opportunities, then they will have a big impact on the design of products and how we solve some of the restrictions that today’s processes prevent us from optimising in our structures.
What limits innovation? Is it the regulations that are clearly necessary for safety? Is it lack of investment? How could the SpaceX of aviation come into being?
CG: I would say investment limits innovation but regulations are a real way of creating innovation as they force you to reconsider the design solutions and set new boundaries to tackle; without them nothing would develop.