Composites In Aerospace

Their Advantages and Future in Aerospace Applications

Composite Materials are Used to Build Aircrafts. shaunl/E+/Getty Images

Weight is everything when it comes to heavier-than-air machines, and designers have striven continuously to improve lift to weight ratios since man first took to the air. Composite materials have played a major part in weight reduction, and today there are three main types in use: carbon fiber-, glass- and aramid- reinforced epoxy.; there are others, such as boron-reinforced (itself a composite formed on a tungsten core).

Since 1987, the use of composites in aerospace has doubled every five years, and new composites regularly appear.

Where Composites are Used

Composites are versatile, used for both structural applications and components, in all aircraft and spacecraft, from hot air balloon gondolas and gliders to passenger airliners, fighter planes, and the Space Shuttle. Applications range from complete airplanes such as the Beech Starship to wing assemblies, helicopter rotor blades, propellers, seats and instrument enclosures.

The types have different mechanical properties and are used in different areas of aircraft construction. Carbon fiber, for example, has unique fatigue behavior and is brittle, as Rolls-Royce discovered in the 1960's when the innovative RB211 jet engine with carbon fiber compressor blades failed catastrophically due to birdstrikes.

Whereas an aluminum wing has a known metal fatigue lifetime, carbon fiber is much less predictable (but dramatically improving every day), but boron works well (such as in the wing of the Advanced Tactical Fighter). Aramid fibers ('Kevlar' is a well-known proprietary brand owned by DuPont) are widely used in honeycomb sheet form to construct very stiff, very light bulkhead, fuel tanks, and floors. They are also used in leading- and trailing-edge wing components.

In an experimental program, Boeing successfully used 1,500 composite parts to replace 11,000 metal components in a helicopter. The use of composite-based components in place of metal as part of maintenance cycles is growing rapidly in commercial and leisure aviation.

Overall, carbon fiber is the most widely used composite fiber in aerospace applications.

Advantages of Composites in Aerospace

We have already touched on a few, such as weight saving, but here is a full list:

  • Weight reduction - savings in the range 20%-50% are often quoted.
  • It is easy to assemble complex components using automated layup machinery and rotational molding processes.
  • Monocoque ('single-shell') molded structures deliver higher strength at much lower weight.
  • Mechanical properties can be tailored by 'lay-up' design, with tapering thicknesses of reinforcing cloth and cloth orientation.
  • Thermal stability of composites means they don't expand/contract excessively with a change in temperature (for example a 90°F runway to -67°F at 35,000 feet in a matter of minutes).
  • High impact resistance - Kevlar (aramid) armor shields planes, too - for example, reducing accidental damage to the engine pylons which carry engine controls and fuel lines.
  • High damage tolerance improves accident survivability.
  • 'Galvanic' - electrical - corrosion problems which would occur when two dissimilar metals are in contact (particularly in humid marine environments) are avoided. (Here non-conductive fiberglass plays a roll.)
  • Combination fatigue/corrosion problems are virtually eliminated.

The Future of Composites in Aerospace

With ever increasing fuel costs and environmental lobbying, commercial flying is under sustained pressure to improve performance, and weight reduction is a key factor in the equation.

Beyond the day-to-day operating costs, the aircraft maintenance programs can be simplified by component count reduction and corrosion reduction. The competitive nature of the aircraft construction business ensures that any opportunity to reduce operating costs is explored and exploited wherever possible.

Competition exists in the military too, with continuous pressure to increase payload and range, flight performance characteristics and 'survivability', not only of airplanes but of missiles, too.

Composite technology continues to advance, and the advent of new types such as basalt and carbon nanotube forms is certain to accelerate and extend composite usage.

When it comes to aerospace, composite materials are here to stay.