Boeing's 787 Dreamliner

How Composites And Carbon Fiber Are Used

Boeing Dreamliner. Handout/Getty Images

What is the average density of the materials used in a modern airliner? Whatever it is, the reduction in average density has been huge since the Wright Brothers flew the first practical airplane. The drive to reduce weight in airplanes is aggressive and continuous and accelerated by rapidly climbing fuel prices. This drive lowers specific fuel costs, improves the range/payload equation and helps the environment. Composites play a major part in modern airplanes and the Boeing Dreamliner is no exception in maintaining the decreasing weight trend.

Composites and Weight Reduction

The Douglas DC3 (dating back to 1936) had a take-off weight of about 25,200 pounds with a passenger complement of about 25. With a maximum payload range of 350 miles, that's about 3 pounds per passenger mile. The Boeing Dreamliner has a take-off weight of 550,000 pounds carrying 290 passengers. With a fully loaded range of over 8,000 miles, that's roughly ¼ pound per passenger mile - 1100% better!

Jet engines, better design, weight saving technology such as fly by wire - all have contributed to the quantum leap - but composites have had a huge part to play. They are used in the Dreamliner airframe, the engines, and many other components.

Use of Composites in the Dreamliner Airframe

The Dreamliner has an airframe comprising nearly 50% carbon fiber reinforced plastic and other composites. This approach offers weight savings on average of 20 per cent compared to more conventional (and outdated) aluminum designs.

Composites in the airframe have maintenance advantages too. A typically bonded repair may require 24 or more hours of airplane downtime but Boeing has developed a new line of maintenance repair capability that requires less than an hour to apply. This speedy technique offers the possibility for temporary repairs and a quick turnaround whereas such minor damage might have grounded an aluminum airplane. That is an intriguing perspective.

The fuselage is constructed in tubular segments which are then joined together during final assembly. The use of composites is said to save 50,000 rivets per plane. Each rivet site would have required maintenance checking as a potential failure location. And that's just rivets!

Composites in the Engines

The Dreamliner has GE (GEnx-1B) and Rolls Royce (Trent 1000) engine options, and both use composites extensively. The nacelles (inlet and fan cowls) are an obvious candidate for composites. However, composites are even used in the fan blades of the GE engines. The blade technology has advanced tremendously since the days of the Rolls-Royce RB211. The early technology bankrupted the company in 1971 when it's Hyfil carbon fiber fan blades failed in bird strike tests.

General Electric has led the way with titanium-tipped composite fan blade technology since 1995. In the Dreamliner power plant, composites are used for the first 5 stages of the 7 stage low-pressure turbine.

More about Less Weight

What about some numbers? The GE power plant's light weight fan containment case reduces aircraft weight by 1200 pounds (more than ½ ton). The case is reinforced with carbon fiber braid. That is just the fan case weight saving, and it is an important indicator of the strength/weight benefits of composites. This is because a fan case has to contain all debris in case of a fan failure. If it will not contain the debris then the engine cannot be certified for flight.

Weight saved in blade turbine blades also saves weight in the required containment case and rotors. This multiplies its saving and improving its power/weight ratio.

In total each Dreamliner contains about 70,000 pounds (33 tons) of carbon fiber reinforced plastic - of which about 45,000 (20 tons) pounds is carbon fiber.

Conclusion

The early design and production problems of using composites in airplanes have now been overcome. The Dreamliner is at the peak of airplane fuel efficiency, minimized environmental impact and safety. With reduced component counts, lower levels of maintenance checking and greater airtime, the support costs are significantly reduced for airline operators.

From fan blades to fuselage, wings to washrooms, the Dreamliner's efficiency would be impossible without advanced composites.