Modern jets, such as the 787 and A350 exemplify the switch to composite materials for fuselage
construction. This seems set to stay as the way forward for new aircraft designs.
Although there are challenges, the lower weight of composites offer significant improvements in
efficiency and operating cost. Let’s take a look at composite versus aluminum fuselages.
Did you know that aircraft have not always been made of metal?
Many early aircraft- even those for passengers- used wood and fabric. And not just small
aircraft such as early biplanes – the wooden Howard Hughes H4, known as the ‘Spruce Goose‘
was one of the largest aircraft ever built. It flew once but never entered service.
Low-cost and somewhat low weight, wood was practical. But it was not strong enough for
very high-speed flight. As speeds increased, and certainly as jet engines were introduced,
metal became the better option. With its low weight, low cost,
and relatively high durability, Aluminum was and has been one of the best choices.
While titanium is even better, it’s too expensive. The compromise has been to use aluminum alloys
to reduce the issues of stress fatigue and corrosion. Such alloys have formed the basis
of all jet aircraft fuselages until recently. Small amounts of other metals (like steel or
iron) can be included, but on their own are too heavy and would stress at high temperatures.
Modern aircraft like the Boeing 787 and Airbus A350, have shifted to composite
materials for construction. This follows the trend towards more efficient and lower
emissions aircraft operation in recent years. Interestingly, earlier aircraft had already
started to move this way. The A380 is approximately 20% composite, and the
777 around 12%. Interestingly, the new 777X will retain an aluminum fuselage like its predecessor.
Composite refers to construction from two or more different materials that, when combined,
perform better than the elements by themselves. For the 787, around 50% of the materials used
are carbon fiber reinforced plastic (CRFP) and other composites. Aluminum still accounts for 20%,
titanium 15%, and steel 10%. Airbus, which also makes use of CFRP
in the A350 describes the material as follows: “In CFRP production, thousands of microscopically
thin carbon threads are bundled together to make each fibre, which joins others in a matrix held
together by a robust resin to achieve the required level of rigidity. The composite
component is produced in precisely shaped sheets laid atop each other and then bonded, typically
using heat and pressure in an oven called an autoclave, resulting in a high-quality composite,”
Much of the credit for the move to composites is due to Boeing with the new clean-sheet aircraft
design of the 787. This was lower capacity than the 777 and moved Boeing into the unproven
market for a composite airframe. Airlines reacted positively, though. So much so that Airbus chose
to revise its plans for the A350 and also design a new clean-sheet composite widebody with the A350.
In addition to weight reduction, such materials are also less susceptible
to corrosion and fatigue, reducing maintenance time and cost for airlines.
This resistance to fatigue has also allowed for larger windows - as seen in the 787 and A350.
Composite structures can be molded into any shape,
allowing for separate entire fuselage ‘barrel’ sections to be made in different locations,
rather than aluminum sheets that needed to be bolted together.
Cost can be a drawback to a certain extent. At this time
CFRP components are more expensive to produce than standard metallic parts.
But over time, this can be offset by lower maintenance and operating costs.
There have also been concerns raised about the detection of damage to the fuselage.
Impact damage is not as visible or easy to detect as it is on a metal airframe, although
other tests (including optical, electrical, and acoustic) can check for airframe damage.
Fuselage modification is another challenge. This has been raised as an issue with freighter
conversions – cutting a cargo access door in a composite fuselage is more
challenging than in an aluminum one. It may be easier for a possible A350 freighter, though,
as its fuselage is constructed from composite panels rather than complete barrel sections.
But with the savings in weight and improvement in efficiency, these drawbacks are likely
ones that operators are happy with. Do you think composite structures will be
standard in the future? Or will aluminum always have a place? Let us know by leaving a comment.