Government/Military Trends
October 2004
Improved Performance: brought to you by composites
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When it comes to handling the unique stresses of flight, metal and aluminum alloys can’t be beat. If you throw enough metal at a problem, it will solve it. Unfortunately, the amount of metal needed to correct a problem may be much too heavy for an aircraft to leave the ground. Weight also compromises performance in other areas, increases fuel use and reduces the amount of payload an aircraft can handle. These issues have brought composite materials to the forefront in aerospace.
Composite materials significantly aid performance in today’s aerospace applications. Consequently the industry is slowly transitioning towards using composites more broadly.
Rotor-wing improvements
Early helicopters were underpowered because of the weight problem associated with using metals. To improve helicopter performance, companies typically take two approaches — develop smaller, more powerful engines that weigh less or lighten the airframe. The development of composite rotor blades and fuselage structures contributed to the successful improvement of helicopter performance.
Prop improvements
Improved performance was the determining factor for JetPROP, LLC, when they selected Hartzell Propeller Inc.’s four-blade composite propeller for the Pratt and Whitney PT6 turbine conversion of the Piper Malibu/Mirage. The blades, made of Kevlar, have a longer life than typical metal blades. They weigh 23 lbs. less than the metal blades used before.
The blades are quieter and smoother than any other blades tested for use in the conversion. They improve high-altitude cruise performance and reduce the amount of erosion from ground operations. Repairs get made by adding material to fix the nicks typical in normal operations. Ease of repair allows for extended use, with some operators putting more than 30,000 hours on the blades.
Polymer research
For military and aerospace industries, researchers are investigating innovative materials to help cope with impact damage during flight. Testing is happening on structural polymers to seal punctures from micrometeorites and space debris, as well as conductive polymers that can restore computer circuits hit by ionic or solar radiation. Christopher S. Coughlin, Ph.D., and others at the Naval Air Systems Command are testing polymer films that will self-heal, closing holes ripped through them by high-speed projectiles (like shrapnel) instantly.
Expanding commercial use
Both Boeing and Airbus are increasing composite material use as a way to save weight and reduce corrosion. Airbus selected GLARE (glass fiber reinforced aluminum) for the fuselage of their next generation aircraft — the A380. Boeing’s development of the 7E7 aircraft may put the amount of composite material in commercial aircraft at 50%, 30% more than any other commercial aircraft.
The ability to provide equal strength tolerance combined with reduced weight over metals make composites attractive for research toward improvements in the way aircraft are built and maintained. This will aid new developments and manufacturing techniques, and will further expand the role of composites in aerospace.