Application of Lightweighting Technology to Military Aircraft, Vessels, and Vehicles (2012) / Chapter Skim
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2 Lightweighting Airborne Vehicles
2 Lightweighting Airborne Vehicles
Pages 29-60
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From page 29... ...
Trainers, fighters, and attack aircraft are included in the "fighter" category; primary military vehicles, tankers, and transports are included in "transports." "Primary" and "secondary" assess the relative importance of these capabilities for aircraft design, and the numbers 1 through 3 rank the importance of the attribute for the aircraft type. Military aircraft are driven by performance features (functional capabilities)
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From page 30... ...
Generally speaking, lightweighting of military aircraft will therefore need to be done with an eye to retaining or improving survivability. 2.1.2 Historical and Current Lightweighting Early work on composite and hybrid material systems in transport aircraft attempted to match their properties and design methods to those of aluminum.
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From page 31... ...
After their successful implementation in military aircraft, these materi als began to be introduced into commercial aircraft, as shown in Figure 2-2. Until recently, however, the cost of composite materials limited their application by commercial aircraft.
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From page 32... ...
Translating weight into cost worked well until about 1970, when composite structures began to see greater application in military aircraft. 6 Composite materials offer great potential for weight savings at the same time that they lead to improved performance for military aircraft and lower operating costs for commercial aircraft.
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From page 33... ...
new materials; (2) new manufacturing processes and equipment; (3)
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From page 34... ...
As shown in Figure 2-5, each new composite material has been introduced gradually. As the materials and their manufacturing processes mature and their capabilities are demonstrated, they begin to account for a growing portion of each aircraft type.
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From page 35... ...
Holtzwarth, "Low-Cost Composite Materials and Structures for Air bitmap craft Applications," paper presented at the RTO AVT Specialists' Meeting on Low Cost Composite Structures, Loen, Norway, May 7-11, 2001, and published in RTO-MP-069(II)
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From page 36... ...
Combinations of metallic and ceramic materials that protect the metal with a high temperature resistant coating while retaining the strength and toughness of the metal have been attempted for years. Similarly, inorganic and organic hybrid materials offer "designed" thermal and electrical conductivity and improved mechanical properties.
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From page 37... ...
However, the process is flawed when the prototype aircraft are given limited operational assignments after meeting only a few design requirements -- i.e., before they are battlefield-ready. As described in the second part of Section 2.5.2, the Predator and Global Hawk Unmanned Aerial Vehicles were ATDs that were deployed in Iraq and Afghanistan.
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From page 38... ...
The DARPA Advanced Structural Fiber program24 seeks to increase fiber strength and stiffness by reducing defects in the fibers through advanced processing and by applying atomic control on a massive scale. Before such fibers can achieve meaningful weight savings, resins will need to be developed that can carry the fibers well and without microcracking.25 Each development related to composite materials has lent a capability for the aircraft.
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From page 39... ...
If these new processes overcome the barriers to the use of thermoplas tics and are accompanied by new approaches to solvent sensitivity, the strain-to-failure, durability, and damage tolerance of thermoplastics could improve dramatically. One of the main attractions of pultrusion is its simplicity of tooling and low labor requirements.
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From page 40... ...
Hybrid Materials Hybrid materials could provide some of the benefits of multifunctional materials at relatively low cost -- lower even than the cost of composite materials. Hybrid materials, particularly metal-fiber laminates (shown in 27 Available at http://www.boeing.com/newairplane/787/design_highlights/.
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From page 41... ...
If cost or damage tolerance are large enough drivers to justify a weight penalty, hybrid materials can offer good damage resistance at an affordable price. Airbus is using fiber-metal laminates and has invested heavily in bringing the technology to maturity and to a price that makes it affordable for its A-380.
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From page 42... ...
Recently, additive manufacturing techniques have been developed for metallic materials, notably aluminum and titanium. These techniques make it possible to go straight from the design to the fabrication of parts using systems very much like the three-dimensional printers that heat particles of material and lay them up using a laser to guide and fuse the particles.
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From page 43... ...
Such tooling currently uses (low-cost) composite structures, thus averting mismatches between the coefficient of thermal expansion (CTE)
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From page 44... ...
The savings can amount to 5 percent of the overall structural weight. 2.3.3 Opportunities in Design Trading Off Materials and Manufacturing Processes at the System Level Product design currently begins with conceptual design at the system level.
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From page 45... ...
was a joint project of the Air Force Research Laboratory, Office of Naval Research, and five aerospace companies that focused on reducing the risk of using advanced composite materials in aircraft. The program succeeded in lowering the cost of composite structures, which made greater weight reductions affordable, but it was not directly focused on lightweight materials or design.
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From page 46... ...
2.4.2 Incorporating New Materials and Manufacturing Processes in Conceptual Design Through Systems Engineering Approaches Incorporating new materials and manufacturing processes in conceptual design calls for predicting the asmanufactured properties of these materials. Too often, laboratory-based properties have been used that do not match the as-manufactured properties of the material.
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From page 47... ...
Conceptual design is the stage where a manufacturer investigates new materials and manufacturing concepts and determines their payoff for new designs. But decisions on materials and manufacturing processes at this stage are difficult because payoffs are determined at the part level, not at the vehicle level.
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From page 48... ...
Designers must rely on semiempirical methods for predicting the strength of a laminated composite once its constituent properties are determined. New analytical models are also needed to predict the strength of composites based on their geometry, layup, manufacturing processes, and damage condition.
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From page 49... ...
sustain those high altitudes using solar power and batteries alone.44 Even the tiniest aircraft, such as the bioinspired Delfly (Figure 2-14) , must be kept very light -- it weighs only 3 grams and extends 10 cm from wing tip to wing tip -- in order to fly on a peanut-size power source.45 Its flapping wings were modeled after dragonfly wings, which achieve stiffness and strength by being highly corrugated.46 Other sources of ideas for making future UAVs lighter include developing a propulsion system based on automotive fuel cell technology47 and emulating the lightweighting strategies of model airplanes.48 Deployment of Predator and Global Hawk from Advanced Technology Demonstration Program The unmanned aerial vehicles (UAVs)
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From page 50... ...
The lithium in Al-Li 2195 made the initial welds of the external tank far more complex. The repair welds 49 For more information, see "Analysis of International Space Station Vehicle Materials on MISSE 6," available at http://ntrs.nasa.gov/ archive/nasa/casi.ntrs.nasa.gov/20100033233_2010034433.pdf.
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From page 51... ...
SOURCE: NASA Dryden Research Figure 2-13.eps Center Photo Collection, available at http://www.nasa.gov/centers/dryden/images/content/105841main_helios.jpg. bitmap Figure 2-14.eps FIGURE 2-14 TU delft–Delfly.
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From page 52... ...
Solving the transverse strength problem allowed this alloy to be used to fabricate section thicknesses required for the shuttle external tank. Friction stir welding also contributed to the success of this allocation as noted above.
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From page 53... ...
2.5.4 Commercial Aircraft Applications Extensive Use of Composites in the Boeing 787 The Boeing 787 (Figure 2-16) is the first commercial plane to have a composite fuselage.
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From page 54... ...
Composites helped with lightweighting, but the large scale of the composite structure encouraged a conservative design, with the result that so far the 787 has achieved only about half of the anticipated weight reduction. Advanced Materials for the Airbus A350 Weight has so much value for the commercial aircraft customer that Airbus was forced by its customer base to move from a hybrid metallic/composite baseline fuselage to an all-composite baseline fuselage.
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From page 55... ...
55 MODEL DESIGN OPTIONS FOR FORECASTING SYSTEMS FIGURE 2-16 Boeing 787, a primarily composite commercial airliner. SOURCE: Boeing.
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From page 56... ...
2008. "Analysis Methods Used on the NASA Composite Crew Module." American Institute of Aeronautics and Astronautics.
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From page 57... ...
, which included architectural trade studies, optimum honeycomb sandwich design, and optimum composite layups; • Analysis for failure margins of safety for large sheets of material, which included panel buckling, com posite strength failure, and damage tolerance, and sandwich-specific facesheet wrinkling and core shear, and 54 Sara Black.
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From page 58... ...
Kirsch, 2009, "Broad Based Teams, Case Study #1 -- Composite Crew Module." Presented in Project Management Challenge 2009, Daytona Beach, Fla., available at http://pmchallenge.gsfc.nasa.gov/docs/2009/presentations/Kirsch.Mike.pdf; or B.A. Bednarcyk, S.M.
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From page 59... ...
Rusling, 2010, "With No Replacement in Sight, Army's Oldest Helos Keep Going," National Defense, April; and "Army New Kiowa Warrior FOX Model Increases Capability," Defense Daily, October 27.
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From page 60... ...
Processing science will be an integral part of this methodology to ensure that section thicknesses and shapes can be fabricated from the designed resins. • Currently available empirical analysis tools cannot replace the testing required to support composite applications for commercial aircraft.
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