Cirrus Composite Airframes
I found a very interesting Youtube peek inside of the Cirrus airplane assembly factory in Minnesota. While it would be cool to learn more about the actual composites fabrication of the individual parts, there is some great information about part bonding, inspection, and final assembly of the Cirrus aircraft. They use fiberglass and carbon fiber reinforcements to create a very strong and durable fuselage, and it is great to see in action.
Personal jets made of composite materials offer many advantages and unique properties. Design of complex shapes and anti corrosion of aluminum are two advantages. Disadvantages include repeatability and upgrading/modification.
Composites that are properly designed and fabricated can be used in many applications where safety is a big concern. Proper design and inspection during production can create an airplane that can be easily maintained and have a very long life.
Great factory tour courtesy of Aero-TV:
NASA Composite Crew Module
NASA, the space agency for the U.S. government, has investigated the use of advanced composites for use in future vehicle programs. The Composite Crew Module (CCM) has been designed and built as a travel vehicle for astronauts in future space programs to travel. Drawing parallels to the Apollo program, this module will be launched on a rocket and break away as a module.
This technology and material are undergoing testing and evaluation before it is officially accepted for the Orion program. As a partnership between government agencies and public companies, this technology aims to reduce weight and improve performance of the manned vehicles.
From NASA’s website “Led by the NESC, the project team is a partnership between NASA and industry, including design, manufacturing, and tooling expertise. Partners are civil servants from nine NASA Centers – ARC, DFRC, GRC, GSFC, JSC, JPL, KSC, LaRC, and MSFC; the Air Force Research Laboratories; and contractors from Alcore, Alliant Techsystems, Bally Ribbon Mills, Collier Corporation, Genesis Engineering, Janicki Industries, Lockheed Martin, and Northrop Grumman. The CCM team operates in a virtual environment, electronically connecting participants across the country.”
This full-scale structure has strain gauges attached to monitor loads on the structure. It was announced on January 25 that it has passed a battery of stress tests to prove viability.
The structure appears to be made with carbon fiber materials, maybe with some graphite reinforcement and an epoxy resin system. Mention of aluminum honeycomb can be found in the online reading materials. The main pieces are autoclaved, while bonding of the large sections (upper and lower shells) is accomplished outside of the autoclave.
Composites technology is being developed for future space exploration structures and vehicles, and this is good news for the composites industry!
Carbon Fiber in the Chevrolet Silverado ZR2 Concept
At the 2009 Las Vegas SEMA show, Chevrolet introduced their ZR2 Concept pickup truck. This truck is tricked out for off-road capability with all wheel drive and a tricked out suspension. Weight savings improves performance and the designers turned to carbon fiber composites.
Exterior body panels were improved by saving weight by using carbon fiber. These panels include the hood, fenders, tailgate, grille, fascias, fender flares, and rocker panels. The hood and tailgate have used clear-coated carbon fiber to show the weave and give an interesting two-tone look to the vehicle.
The interior is also reported to use carbon fiber in the dash and the door panels.
It is unknown whether this concept vehicle goes into production, but certain elements are certainly becoming mainstream. Aftermarket carbon fiber parts have been popular for years especially on tuner cars. This may catch on for mainstream OEM production. Carbon fiber parts save weight, do not corrode, do not dent, and do not require pigmented paint.
Boeing’s 787
Boeing’s 787 will be the first composites-intensive commercial airliner. Traditionally made from aluminum, carbon fiber composites will work to create a plane that is stronger and lighter with fewer manufactured parts. Carbon Fiber reinforcement with Epoxy resin will be the main construction of these composites, which will make use of an autoclave during processing to control the molding conditions and ensure the quality and durability of the laminate.
Composites will reduce the number of parts for the airplane, and Boeing predicts that the front section alone would normally require using 1,500 sheets of aluminum, which also means drilling between 40,000 and 50,000 holes for the nuts and bolts to attach these sheets together and to the underlying framework. Carbon Fiber composites will allow for the skin and underlying supports to be molded as one large piece. Boeing predicts that assembly line time will be reduced from about three weeks to attach all of this aluminum together to about 3 days to attach the large composites sections together for the entire plane fuselage.
Switching materials has its’ own set of problems to overcome. The customers’ mechanics will need to be trained to repair damage on these composite planes. Damage detection will be important as well. Some will be visible to the naked eye, and other damage will not. Several forms of Non Destructive Testing will be employed to test for damage and wear on the composites body to ensure a safe aircraft.
Composites have been used in aircraft before, but not as extensively in commercial airplane bodies. Existing commercial airplanes have made use of composites in other areas to help make the planes stronger and lighter. Military jets have used carbon fiber composites for many years in their technologies for strength and weight advantages. Private business jets have utilized fiberglass composites for many years in their construction. Homemade kit planes have also made extensive use of fiberglass to make inexpensive craft in personal shops.
The profile of carbon fiber composites will definitely be elevated if Boeing’s 787 becomes as successful as promised.
Wind Blades
The new composites application that everybody is discussing is composites wind blades. The large, three-bladed wind generators have been around for a few decades, mostly in Europe. The U.S. has been catching on in the last couple of years as a way to make cleaner electricity. These windmills are very tall, and have blades that are 100 to 400 feet long, depending upon output rating and location.
The wind blades use glass carbon fiber, resin, and coring to make a long, stiff and lightweight blade that will attach to the hub of the windmill. These blades are very long, requiring huge manufacturing facilities to make them. The transportation of these blades is important as well, as they require specialized trucks and trailers to handle such large pieces. Large cranse are required to lift them into place at the job site. They are relatively heavy, and must be lifted fairly high, requiring a significant lift capacity.
Resin infusion with epoxy resins is the normal manufacturing technique of which I am aware. They use compsite molds that have a constantly changing surface shape due to the complex geometry of the blade. The holy grail for these blades is to make longer blades at lower weight.
This application again demonstrates the advantages of composites. Complex geometry, high strength to weight ratio, and impact resistance are important aspects of wind blades.
There are several manufacturers of the wind blades in the U.S. MFG is a specialty composites molder that has been around for ages and is in the wind blade market. Vestas is another company with operations in the U.S., along with LM Glasfiber, as well as others.
Cutting Layup Reinforcement
When working with reinforcements in the form of a woven mat, cutting is necessary to allow for proper orientation, workability, and strength. The most common way to cut these mats is with industrial scissors. Other methods include rotary cutters, die cutters, and electric shears, but a good pair of oversized, resharpenable, thru-hardened shears (scissors) are the best way to get started.
Woven mats can be cut to size in the dry stage -before the resin is applied- or in the wet stage, when resin is flowing freely. There are benefits and drawbacks to both, and operators usually find their own preferred technique. Cutting mats in the dry stage requires that it gets put together correctly when it is in the wet stage. Handling dry fiberglass is typically more itchy than wet fiberglass, which is sticky. Scissors used to cut wet reinforcement must be properly cleaned in order to be used again.
Many claims are made about the difficulty of cutting kevlar reinforcement. This can be remedied by using a dedicated pair of sharpened scissors only for kevlar. Kevlar is a material that requires a different angle on the blade in order to cut it. I have demonstrated to fellow workers how a fresh pair of scissors will cut kevlar all day, then cut a bunch of fiberglass. But when going back to the kevlar, the scissors will not cut it. Carbon Fiber falls into the category side of fiberglass where it will dull the blades and not go back.
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