Thus, it appears that with proper design, remarkable cost reductions can be realized in composite part production by introducing automation to replace hand lay-up. For the HSCT airframe structure, specific material requirements are dependent on cruise Mach number, which could range from 1.8 to 2.4. Metallic alloys continue to be used for more than 75 percent of most airframe and propulsion systems by weight. Thus, a successful airframe and engine structural design/manufacturing team will cover a spectrum of sub disciplines, consisting of. The materials systems being considered currently have low ductility in general and, thus, may be difficult to fabricate. However, this area holds great promise for increasing the ability of aircraft operators to assess the health of aircraft and thereby improve operational safety while decreasing maintenance costs associated with currently expensive inspection techniques such as teardown. Substitution of CMCs for metals in engine hot sections is likely to occur in the next decade, and NASA should lead the way. Structural weight is the single largest item in the empty weight of an aircraft and is, therefore, a major factor in the original acquisition and operating cost and in establishing operational performance. Share a link to this book page on your preferred social network or via email. This has many variations that can contain metals and glass fibers in addition to carbon fiber. The cycle selected for advanced engine designs will depend on the temperature level permitted at the exit of the high-pressure compressor. In the sense, however, that no airfoil will develop full lift if its surface cannot maintain shape and smoothness under the pressures it is designed to generate; that no engine will function if its components cannot withstand fuel combustion temperatures and rotation loads; and that no control system can cause aircraft attitude changes if its linkages will not carry the forces that create hinge moments—in that sense, structures and the materials used to build them are first among the enabling, foundation aeronautical technologies. Aeroelasticity considerations in fan blade design continue to pace the technology. Sandwich construction provides the capability of carrying pressure loads and the stiffness to stabilize shear panels of large dimensions, which is necessary if wide spacing of substructural members is to be achieved. Programs dealing with aircraft structural integrity, fleet structural management, and aircraft life cycle management and operation are important contributors in this regard, but technology advances are needed in each of these three parts of life management programs. The alternative could be an unacceptable delay in the certification procedure. There will be an ongoing need for the evolutionary development of conventional metals for the particular requirements of gas turbine engine applications. - main structure or body of aircraft to which all other components are attached - provides space for crew, passengers, cargo and other equipment. To search the entire text of this book, type in your search term here and press Enter. MONOCOQUE In this method, the exterior surface of the fuselage is also the primary structure. Adaptive structures is a relatively recent concept that offers potentially important benefits in aircraft design. The most important conclusions arrived at in the materials and structures discipline are summarized here, without consideration of the auspices under which the advances should be accomplished. Aircraft structural members are designed to carry a load or to resist stress. Aside from a general trend toward greater simplicity, and more lightly loaded structures as aircraft become smaller, there are no unique structural issues specific to commuter aircraft. True. An economic objective of the HSCT program is to achieve an airframe weight reduction of up to approximately 30 percent relative to Concorde-generation designs. Stiffness and strength at moderate temperature are required to carry the heavy ''hoop tension'' created by centrifugal and thermal loads, and light weight is always particularly important in rotating machinery. However, it is important to recognize certain unique aspects of commercial transport service operations and customer relations in dealing with the application of advanced materials and structures to that class of aircraft. This is much lower than the number of man-hours expended for metal parts. The use of composite materials in aircraft is relatively limited, especially in civilian applications, so the base of experience with longevity and durability is limited as well. Primary Structure Secondary Structure Tertiary Structure Primary Structure: Primary structure includes all the portions of the aircraft, the failure of which during flight or on the ground would cause catastrophic structural collapse and loss of control. The metal blades had aluminum honeycomb structure aft of the spar, and the composite blades had NOMEX® honeycomb in the same application. Aluminum-lithium (Al-Li) alloy systems, for example, promise evolutionary benefits in higher stiffness and lower density, with no reduction in structural life. For example, when an airplane is on the ground, the landing gear struts are under a constant compression stress. Examples of Principal Structural Elements typically include: (a) Control surfaces, slats, flaps, and their mechanical systems and attachments (hinges, tracks, and fittings); (e) Skin or reinforcement around cutouts or discontinuities; (a) Circumferential frames and adjacent skin; (e) Skin and any single frame or stiffener element around a cutout; (f) Skin or skin splices, or both, under circumferential loads; (g) Skin or skin splices, or both, under fore and aft loads; (i) Skin and stiffener combinations under fore and aft loads; This site uses Akismet to reduce spam. The simplicity of the structure produced an 86 percent reduction in the number of parts and a 93 percent reduction in the number of fasteners. This is also true for bonded joints in metal structures, particularly when the extended useful lives of commercial aircraft are considered. C. Monocoque structure. It was build with molded plywood, featuring multiple layers that cover a plug in the mold. The exit temperature of the high-pressure compressor and the combustor associated with supersonic cruise translate to an HSCT mission in which 80 percent of operations are at maximum temperature. Alloys capable of superplastic forming continue to promise both economic fabrication of parts with complex curvature or integral stiffeners and weight savings. Gear failures for some helicopter types are the largest single source of fatalities. Lightweight, higher-temperature materials hold the key to increasing compressor exit temperatures. NASA's structures and materials program should emphasize continuing fundamental research to achieve both evolutionary and revolutionary advances in materials and structures, as well as focused technology programs in materials and structures to address specific aircraft system requirements. Competitive designs for advanced rotating parts will depend on such exploitation and on improved understanding of flutter and resonance stress problems and application of magnetic bearing technology. MyNAP members SAVE 10% off online. In multi-engine aircraft the engines may either be in the fuselage, attached to the fuselage, or suspended from the wing structure. It appears that ceramic materials of the silicon nitride and silicon carbide families should receive the greatest attention. This is is in contrast to the FAA  that requires “approved” data for only major repairs and “acceptable” data for minor repairs. The compatibility of desired fiber/matrix volume fraction, resin viscosity, preform density limitations, and fiber wet ability are principal problems of the kind that injection cures encounter. Goals for all of these future products include significant decreases in fuel consumption, significant reductions in engine weight, and reduction in the airlines' operating costs for these engines and their propulsive adjuncts. Simply bonding two precured parts clearly does not produce an integrally stiffened structure. Significant research investments are required to develop the full potential of composite materials for both airframe and engine applications. Research in these areas, however, should be a continuing part of NASA's base program. Relatively thin-walled cylindrical components are frequently wound, using continuous filaments or braids. This situation will continue until major improvements are made in integrating design and manufacturing with composites. Higher allowable temperatures result in higher cycle pressure ratios and associated improvements in core thermal efficiency. Loadunknowns involve both methods of calculation and type of serviceactually experienced.Primary structure for present transport aircraft is designed, basedon average expected operational conditions and average fatigue testresults, for 120,000 hrs. Rotorcraft vibrations can be reduced through aeroelastic tuning of the rotor, but this very complex procedure has not been entirely mastered. Hybrid composite construction does promise the means to do this, with bundles of highstrain-allowable fibers interspersed at intervals among the high-modulus fibers that provide the bulk of structural properties. It is not unusual to do this with uncured skins and either a cured or a partially cured ("B-stage") substructure. Essential to the realization of reduced manufacturing costs with composite structures is a reduction in labor costs sufficient to offset higher materials costs. Consistency among civil, military, domestic, and foreign airworthiness authorities is a major factor in a decision to apply a new material or new structural design approach. Stochastic analysis methods should also receive greater attention to account for more complex operational aspects of advanced aircraft systems. systems as the level of technology increases. Beyond more conventional metallic systems, research efforts in ordered alloys of the TiA1, Fe3A1, and Ni3A1 types should be substantially increased. The highly coupled behavior of the tiltrotor aircraft's rotor and the flexible wing on which it is mounted calls for active control applications to suppress whirl flutter. Composite materials and structures fabrication techniques constitute a major area of uncertainty for the aircraft of the future. The Boeing Model 360 research helicopter demonstrated a large cost reduction over equivalent metal semimonocoque construction by using sandwich composite structure and wide spacing of stiffening members. CMCs offer the high-temperature performance of monolithic ceramics with improved toughness and reliability. The potential of active materials in smart structures (e.g., "shape memory" alloys, piezoelectrics, and thermally responsive composites) seems strong for achieving advanced methods of structural integrity diagnosis for safety improvement and maintenance cost reductions. Environmental factors, however, have been determinative in choosing between skin and stringer versus sandwich construction in metal. Manufacturers are understandably reluctant to undertake a design unless all airworthiness authorities potentially involved have accepted the technical basis of the design. Advanced engine core sizes will continue to get smaller. A structure of carbon fiber set in a plastic. 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