AIRBUS VERSUS BOEING—COMPOSITE MATERIALS : The sky’s the limit…

In December 2009 Boeing flew the 787 Dreamliner for the first time. One of the major design features of the Dreamliner was its lightweight, a result of the use of composite materials. 50% of the Dreamliner’s structure is made up of composite. Since June 2013 Airbus is flight testing the A350XWB. The latest Airbus now boast a 53% usage of composite material among its long lists of new features.
A composite is a macroscopic (visible to the naked eye) combination of two or more materials which results in a material possessing structural properties none of the constituent materials possess individually. Because the materials are not soluble in one another, they retain their identity. Composite material is already present in our everyday life. Some examples being car bumpers made of glass fibre composite, tennis and badminton rackets made of carbon fibre composite and glass fibre boats.
Composite was first used on commercial aircraft in the 1950’s. 2% of the Boeing 707 was made of fiberglass and in the 80’s Airbus was using 5% composite on the A310-300. Both companies have gradually increased the use of composite through the years. In the 90’s the Airbus A340 was using 10% of composite materials and the Boeing 777 12%. By the turn of the century, the advance made in composite manufacture allowed the aeronautical industry to significantly increase their use of composite. Boeing jumped from the 12% on the 777 to 50% on the 787 while Airbus moved from 10% on the A340 to 25% on the A380 and finally to 53% on the A350XWB.
With its 787 Dreamliner, Boeing became the first airliner to launch a full-size commercial aircraft with composite wings and fuselage. On the exterior surface, the only visible metal is on the leading edges and the engine pylons. The design of the former is driven by bird strike and the latter by engine fire requirements where metals offer some benefits. Most of the metals that make up the remaining 50% are found in very large forgings and castings at the highly loaded joints between the composite structures and where the undercarriage is attached.
Over 70 percent of the A350 XWB’s weight-efficient airframe is made from advanced materials combining composites (53%), titanium (14%) and advanced aluminium alloys (19%). Most of the A350 XWB's wing is made of the lightweight carbon fibre reinforced plastic (CFRP) composites, including its upper and lower covers – measuring 32 metres long by six metres wide, making them the largest single aviation parts ever made from carbon fibre. The nose section uses a mix of 55 per cent aluminium/aluminium-lithium alloys, 40 per cent composites and five per cent titanium.
Several factors are behind this increasing use of composite materials. The price of oil, the change in attitude towards environmental issue (e.g ACARE targets of 50% reduction in CO2, a 50% reduction in perceived noise and an 80% reduction in NOx by 2020) and the predicted increase in airline traffic are all drivers that push the manufacturers to produce light-weight structures.
Composite materials are important to the aviation industry because they provide structural strength comparable to metallic alloys but at a lighter weight. This leads to improved fuel efficiency and performance from an aircraft. Weight reduction is the main advantage of composite material usage and is one of the key factors in decisions regarding its selection. Airbus claims that’s the A350 has a 25% improvement in fuel consumption while Boeing claims a 20% improvement. The use of composite on the two aircrafts have reduced their weight to an approximate 20%. For example, the Airbus A340 having a maximum weight of 275 000kg, uses 9.275kg of fuel for every kilometre. If we apply a 20% reduction in weight the aircraft would consume 8.409kg of fuel for every km. To put this in perspective, over a 10 000 km journey, there will be an approximate fuel saving of 8660kg with a 20% reduction of an empty weight.
The use of composite will also bring a more pleasant environment for passengers as it will allow considerate increase in cabin humidity. The air bled into the aircraft flying at 8000 ft is very low in humidity and increasing the level of humidity is too costly (in terms of money and weight) and an increased in humidity will also cause condensation. In most aircraft condensation occurs on the aircraft aluminium skins and if not controlled properly can cause corrosion. An all-composite structure is less susceptible to condensation and is highly resistant to corrosion. On both the A350 and the 787 Dreamliner, the cabin can be maintained at higher pressure and humidity thus increasing the comfort of the passenger.
This increase in composite usage has also brought a series of concern and changes in the industry. The biggest concern for composite materials on aircraft is the maintenance, repair and overhaul (MRO). Maintenance requirements of composite are very different from those of metals and most MRO companies do not have much experience of maintaining composite structures. There are a number of unknowns regarding advanced material repair and these issues are compounded by lack of standardization regarding training certification, repair techniques, and materials. This is one of the main reasons why Bombardier Aerospace has chosen not to use carbon- or glass-fiber composites in the main fuselage of its composite-heavy C-Series aircraft. The high-cycle aircraft, due to enter service in 2013, is expected to sustain a lot of impact damage from ground support equipment. Since repair and maintenance standards are often based on the performance of metal-based planes, damage is easier to identify and repair in metal portions of aircraft using current techniques.
This uncertainty has been highlighted in 2011 when the Government Accountability Office (GAO) published a report about the safety of repairs and maintenance made to composite structures in the new Boeing 787 Dreamliner. The GAO report identifies four safety-related concerns about repair and maintenance procedures for in-service planes;
(1) limited information on the behavior of airplane composite structures,
(2) technical issues related to unique properties of composite materials,
(3) standardization of repair materials and techniques, and
(4) training and awareness.
Compounding that problem is the fact that composite repair itself deploys up to 60 unique materials, while traditional metal repairs require only a dozen or so, according to one study cited by the GAO report. In addition, technicians are less likely to repair a composite correctly, since the quality of repairs depends primarily on which process they use. The scale of knowledge and supplies that must be kept on hand is thus multiplied several times. Though there's a certain degree of standardization for the repair and maintenance of metals in aircraft, the same is not yet true for composites.
With Airbus and Boeing fighting each other over fuel efficiency, passenger comfort and environmental impact the use of composite of commercial aircraft will keep growing in the future. The experience from the military aircraft will also help scientist to gather more information about the behavior of the composite materials on aircraft. Military aviation has reached a more advanced level concerning the use of composite as they have relatively large development budget and are subject to different regulation when it comes to security.


Commentaires

Both a fascinating and informative article; perhaps you should send it to 'Flight International'. Perhaps the origins and operating philosophies of both Airbus and Boeing should perhaps also be looked at. Airbus came about as result of greater post-war European cooperation though this consortium (Airbus) only set up shop in 1999. A rival of the big US aircraft manufacturers. It wasn't until 2009 that Airbus formally added a military aspect to their aircraft production, though this 'wing' of their operations was initiated in 1999.

As Boeing was set up in 1916 during World War One (Though the US didn't enter the conflict until a year later), military aircraft research and production formed the backbone of it's raison d'etre. It is said that war is the mother of all inventions, indeed this is the case with Boeing; the second largest aerospace and defence contractor in the world, Lockheed Martin being number one.