Paper or plastic?
On 22-09-2011, in The aircraft we fly, by steve
Shopping in grocery stores across the US you are likely to hear this question at check out from the guy whose task it is to place your purchases in your preferred kind of bag (plastic or paper..?). In a way, airframe manufacturers are asking a similar question: plastic or aluminum? The implications are tremendous.
Composite materials have been used in aircraft for several years now, mainly in secondary structures of relatively limited size. Composites are best known for their strength, light weight, resistance to corrosion and difficulty to repair. When Boeing decided to build the 787, they set out to create something truly revolutionary not so much in terms of aerodynamics but in terms of systems and materials. A new, largely electric architecture (replacing bulky hydraulics) was combined with a fuselage built almost entirely of composite materials.
Not to be outdone, Airbus redesigned its A350 project, also giving composites a greater role. There are however fundamental differences in the structures being used by the two manufacturers. While Boeing is building the fuselage from composite barrel sections, Airbus has opted for a more conservative solution, placing composite panels on a frame made of aluminum alloy.
While the A350 is still to see the light of day, the 787 is approaching first delivery to ANA in Japan… after a delay of several years. Only a small part of this delay is directly attributable to the composite construction but there are some important lessons to be learned nevertheless.
First and foremost, the expected weight advantages could only be partially realized. Second, building the barrels (or any large composite elements including the A350’s skin panels) to the required quality including consistency over time is not as easy as some might have thought. Costs are also giving rise to some concern. Another discovery concerns the use of composites on single-aisle aircraft. The kind of composite barrel structure used on the Boeing 787 does not scale easily to smaller aircraft with most of the benefits gone if you try to use it on a 737 replacement.
Of course it is still early and hiccups with any new material or design are to be expected, however, composites are also under attack from another, not unexpected, source. The aluminum industry.
Airframe manufacturers are one of the most important users of fancy aluminum alloys (alongside the car maker Audi which has switched from steel to aluminum for its vehicle bodies several years ago). However, aluminum makers had fallen a bit asleep and were not overly concerned with the increasing percentage of composites on new aircraft. They were woken from their slumber by the 787 and A350 and in the shortest possible time they got their act together with spectacular results.
New aluminum alloys are now being offered that possess surprisingly similar traits to composites. Their strength has grown while their density has gone down so creating even a highly stressed skin part from aluminum will no longer be heavier than the identical element made from composites. These new alloys are also more resistant to corrosion and hence can be used safely in a moist environment. This means a much nicer air quality for long suffering passengers and crew.
The price of the new alloys appears to be very competitive and of course building aircraft from aluminum is a well known craft while repairing aluminum aircraft structures is a cinch compared to repairing composites. The claim of the aluminum industry that there is little sense in switching to composites may sound self-serving but a close look at the details suggests they may have a point.
So, plastic or paper? Or plastic or aluminum?
That the 787 and A350 will continue to be plastic airplanes for as long as they live is not in question. The question is: will they remain a one off, a nice technology effort that did not pay off or are they the first members of the new plastic future?
None of the upcoming new regional jets are changing from aluminum and the Airbus 320NEO family will also remain metal. With Boeing no longer planning a new 737 replacement, going instead for a re-engined 737, it is very unlikely that they will use more composites either. The number of 787s and A350s on order is nice for the respective programs but are miniscule in terms of the impact they are likely to have on the composites industry. With no new large scale aviation application on the drawing board, will the development efforts for those materials progress in a direction of interest for aviation or will they orient themselves towards other, more lucrative uses? Will the environmental impact of the manufacturing process sway the balance in the end towards one or the other of the materials so that the life-time carbon loading of each airframe can be shown as going down?
One of the hitherto less evident elements in the materials debate is the new shape of aircraft emerging as a result of research on new, fuel efficient designs. With the end of tube-and-wings shapes on the horizon and new, extra fine skin surfaces being talked about, a new materials competition might very well enter the fray with the outcome anybody’s guess.
For the time being, hold your equity in both the metals and the composites industry.
