Top 15 Technologies
8.
CNC fiber placement used to create an all-composite fuselage
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The all-composite fuselage boasts weight savings of 20% and allows for a total wall thickness of
only 0.81 in.
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Raytheon Aircraft's new Premier I business jet features an all-composite fuselage manufactured by the Viper CNC Fiber Placement System that was developed by Cincinnati Milacron. This system has allowed Raytheon to reduce the fuselage assembly into two main pieces—forward and aft sections.
With the Viper system, Raytheon has eliminated the hundreds of components and long assembly times that are associated with aluminum aircraft constructions, as well as the tedious fitting and joining of hand-layup composite parts. This monolithic composite construction offers many advantages over traditional aluminum and composite construction methods such as:
- reduced fuselage weight to less than 1000 lb - 20% lighter than a comparable aluminum structure;
- increased cabin space with reduced fuselage wall thickness; and
- automated fuselage production in just over a day.
The all-composite design emerged from customers whose expectations were of increased cabin space and cost reduction without structural material preferences. Fuselage wall thickness of the Premier I was reduced from 3 to 0.81 in. with the change from an aluminum structure to composite. Because of the Viper's capabilities, designers were able to use a sandwich of inner and outer carbon fibers around a honeycomb core to fabricate the fuselage walls. This design results in almost 60% more cabin volume and significant weight savings, which increases the aircraft's range and cruising speed. The Premier I, which is scheduled for certification and delivery in late 1998, offers a cruise speed of 460 knots, 1500-n mi range, and a certification altitude of 41,000 ft. It seats seven passengers plus pilot and its cabin measures 5.4 x 5.5 x 13.5 ft.
Cincinnati Milacron's Viper is a seven-axis system that automates fuselage production through a programmable composite tow placement and in-process lamination. The Viper follows the complex contours of the fuselage with seven axes of CNC motion, constructing composite structures tow by tow. The system automatically lays up tows by feeding, tamping, cutting, and restarting them where window and door openings are to be placed. By using programmable electronic bidirectional tensioners mounted in an air-conditioned creel, the Viper can manipulate up to 24 tows at once—each up to 18 in. wide.
The Viper's tow placement head reaches all 360° of the shell with its computerized rotatable mandrel that can accommodate workpieces up to 13 ft. in diameter. Longitudinal travel of 65 ft. provides enough room for the carriage to move up and down the fuselage length while allowing for the addition of a second mandrel station.
The manufacturing process begins with the inner carbon fiber prepreg tows being placed on the mandrel first. Then operators hand place the honeycomb layer followed by the Viper overlaying outer carbon fiber plies over the top of the structure to form a 70-in. outside diameter fuselage. A final fabric layer with metal filaments to provide lightning strike protection is applied. The fuselage is then cured in a 60 x 75-ft. autoclave. The production cycle of the composite fuselage requires about 24-30 h of machine operation.
Other advantages of the Viper system are:
- Strength—The Viper precisely places composite tow material in the specific locations necessary to meet the aircraft's load requirements, which makes internal stiffeners unnecessary.
- Eliminated assemblies—One-piece construction eliminates many assembly steps entirely, which saves time and expense.
- Less fatigue and corrosion—Carbon fiber is relatively immune to corrosion and fatigue compared to aluminum structures.
Fiber placement technology allows the fuselage of the Premier I to be fabricated in 30 h.
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Raytheon's enthusiasm in composite technology is expressed by CEO, Arthur E. Wagner, "We believe so strongly in investing in this new manufacturing technology that the firm has sought no risk-sharing partners for the Premier I." The company also has plans to use the Viper fiber placement technology on a larger all-composite business jet, the Hawker Horizon. Capable of transatlantic flights, the Hawker Horizon will offer an 84-in., three-sectioned composite fuselage. Its thin-walled composite construction will provide interior dimensions of 72 x 79 in.
Expecting to make its first flight in late 1999 with certification and first delivery in the spring of 2001, the Hawker Horizon will offer a maximum range of 3100 n mi and allow for nonstop flights across the United States and Atlantic.
The all-composite fuselage boasts weight savings of 20% and allows for a total wall thickness of only 0.81 in.
Fiber placement technology allows the fuselage of the Premier I to be fabricated in 30 h.
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