Technology for complete automation of the NDE process over a broad spectrum of applications should be a priority research goal. Aircraft structural members are designed to carry a load or to resist stress. The materials development done in support of this nozzle will have. This component must be lightweight, designed for high propulsive efficiency, and include sonic treatment for noise control. In addition, special developments in the inlet, combustor, and exhaust nozzle are required for the HSCT. Orienting fibers in the circumferential direction in the bore would be an efficient use of such materials. Integrating the disciplines of material sciences, mechanics, structural, design, and manufacturing process development will be essential to the success of this enabling technology. constituting from 40 to 60 percent of the airframe weight (AV-8B and V-22, respectively.) Microalloying and particulate reinforcement are promising approaches to make ingot aluminum alloys satisfactory for certain HSCT applications. C. Monocoque structure. The ultimate goal of such programs should be the continuous monitoring of structures for applied loads and damage growth and associated evaluation of residual load-carrying capability. Advantages of magnetic bearings and all-electric accessory systems include elimination of the oil system, elimination of the tower shaft and gearbox, simplified packaging of engine external components, reduced friction losses, higher rotational speeds, active shaft damping, and higher bearing operating temperatures. These advances could lead to their widespread use. In general, the fabrication options available are also variably susceptible to automation, most are energy intensive, and those with fine dimensional tolerances require precise molds. Flight operations per aircraft average roughly 3,000 hours annually and close to 60 hours per week. Although the knowledge of the criticality of certain damage is important in assessing the need for repair, such knowledge is not necessary to develop repair techniques. It is expected that CMCs will provide that necessary increase. Application of composite materials to engine static structures will be highly dependent on the ability to design and manufacture these complex structural shapes and to provide means for determining their remaining life after years of use. With its substantial contributions to both civil and military aircraft developments over the years, NASA can play a pivotal role in establishing consistency in airworthiness standards. At higher Mach numbers, materials with a 300–350°F temperature capability are required. Managing the cost to manufacture these disks will be crucial; ensuring long-term reliability will be essential (through damage tolerance and adequate creep resistance); and providing efficient joining techniques, which allow the rotor to be built up from many individual pieces, will be necessary. Share a link to this book page on your preferred social network or via email. Each technology project should include explicit consideration, at the least, of how it can contribute to the technical basis for airworthiness regulations that will provide safety at minimum cost. Thus, a successful airframe and engine structural design/manufacturing team will cover a spectrum of sub disciplines, consisting of. Currently, polymer matrix composite (PMC) materials have advanced to the point of wide use for fairings and doors, and limited applications in empennage and control surfaces on transport aircraft. Most likely, a major breakthrough in resin technology will be required to achieve the combined technical performance with the ease of fabrication necessary to produce cost-effective airframe structures. PMCs tend to vitiate this objection to sandwich construction. The cost-effective application of composites to primary airframe structures, including wings and fuselages, should be a research program of high priority for NASA. The lack of a general understanding of the failure mechanisms in composite materials and structures inhibits making progress in the latter. Such applications seem most likely in turbine engine combustors, first turbine stages, and nozzles. A necessary adjunct of this is development of tools to reduce the cycle time for generating structural analysis models sufficiently that such analyses for both strength and stiffness can accompany the earliest structure design concepts considered by designers. As in compressor applications, additional turbine structural challenges include developing new design concepts that capitalize on the unique properties of composite materials. This includes a highly reliable structure that requires minimum maintenance and is durable under all applicable environmental influences. - main structure or body of aircraft to which all other components are attached - provides space for crew, passengers, cargo and other equipment. Although not as high as those routinely experienced by engine hot-section parts, portions of the HSCT airframe will be subjected to temperatures beyond all commercial transport airframe experience to this time (except, possibly, the Concorde). Characteristics such as static tensile strength, compression and shear strength, stiffness, fatigue resistance, fracture toughness, and resistance to corrosion or other environmental conditions, can all be important in the design. These recommendations are intended to address the needs of improved aircraft performance, greater capacity to handle passengers and cargo, lower cost and increased convenience of air travel, greater aircraft and air traffic management system safety, and reduced environmental impacts. Specific areas of fundamental research that should be considered for emphasis are outlined below. Some specific recommendations are outlined in the following sections dealing with each class of materials. This has many variations that can contain metals and glass fibers in addition to carbon fiber. Aircraft in this category are of a simple design and intended exclusively for pleasure and personal use. The development of an area known as "damage mechanics" shows promise, but it is currently limited to an assessment of the stress/strain field and not a prediction of residual load-carrying capability and lifetime. Research by NASA emphasizing composites with discontinuous reinforcements is recommended, based on the belief that such materials are likely to simplify fabrication. Carbon-carbon composites have high specific strength and stiffness and adequate temperature capability, but exhibit poor oxidation resistance uncoated. NASA's research efforts in structural analysis and design should focus on improving stress and deflection analysis methods; establishing proven structural dynamics and aeroelastic analyses; developing improved life prediction techniques and damage-tolerant design concepts; formulating proven methodologies for optimizing structural designs, including tailored composites; and exploiting adaptive or ''smart structures'' concepts. Both aluminum and titanium matrix composites with silicon carbide type reinforcements (particulate, fiber, ribbon), for example. Differences among airworthiness criteria applied by different authorities in damage tolerance requirements for composites are another area of concern. These include the possibility of panel flutter, large temperature gradients across airframe structures during acceleration and deceleration, and very thin wing sections. Adhesive bonding of aircraft primary structures has been in use for over 50 years and is still in use on current aircraft projects as a direct alternative to riveting. NASA's program of materials and structures research for the HSCT should give high priority to developing basic composite materials, advanced metallic systems, and design concepts and processing techniques for 225–375ºF operations. the best results. Technology advances in materials and structures applicable to commercial transport are, for the most part, transferable to other subsonic aircraft systems. Advanced combustors can be expected to have (1) decreased liner cooling flow or no cooling at all, (2) staged combustors, and (3) turbine inlet temperatures of at least 3000°F. Thus, innovative uses of advanced alloys of titanium, new classes of aluminum, and resin matrix composites that can withstand high temperature will be required if HSCT configurations are to be successful. Structures researchers will have to play a stronger leadership role in working with materials researchers, both in defining priorities among material properties improvements and in adapting advanced materials to innovative structural concepts. The gradual dominance of aluminum as an aircraft material was seen by aluminum manufacturers as only one of a great many potential uses, which included large-scale consumer product manufacturers. Hybrid materials such as those having combinations of glass and graphite reinforcements show significant improvement in tensile fracture properties versus solely graphite-reinforced laminates. This chapter outlines the key areas of research needed and the approaches that research programs should use. One pound added to structural weight requires additional wing area to lift it (all other flight variables being held constant), additional thrust to overcome the associated incremental drag, and additional fuel to provide the same range. HSCT airframes will require application of mixed materials because of the wider temperatures variation that will be experienced by the airframe in normal operations. The families of materials to be considered for engine applications, in the general order of increasing temperature environment, are PMCs, aluminum MMCs, advanced titanium alloys, titanium MMCs, superalloys, titanium and nickel aluminides, intermetallic matrix composites (IMCs), and CMCs. This contrasts directly with metallic structures in which most damage can be seen. In-service inspection and repair techniques must be developed concurrently with component development. Experience has also been excellent with Kevlar/NOMEX® honeycomb structure on the 1,000-gallon external fuel tanks used on Model 234 Chinooks, which have been operating in the North Sea oil fields for many years. The associated propulsion systems in the 2000–2020 time frame have no substantial materials and structures problems that differ from those of other subsonic aircraft. Nondestructive inspection techniques for laminated composite structures are not well developed in comparison to those for metallic structures. Equally important is their promise for active control of internal noise and for reducing structural dynamic loads, stabilizing various aeroelastic phenomena having the potential for destructive instabilities, and improving crew and passenger comfort by reducing vibrations. Testing techniques that are realistic and allow the projection of long-term effects must still be developed. Ultimately, a probabilistic approach will be required with regard to operational loads, routine damage in service, and material properties in the delivered structure, to maximize the potential of many of the advanced materials. This includes sensors, sensor placement tailored to the structure, and automated scanning and interpretation of results. This activity is likely to include many subscale tests leading eventually to near full-scale testing. Repair techniques for aircraft primary structures made of composite materials have been developed but are oriented mainly toward military aircraft. It will include applying this understanding to developing design tools to deal with materials with reduced ductility compared to today's experience. However, no such programs exist for civilian. Damage tolerant structure. Flutter-free blades, both ducted and unducted, depend on developing advanced computational analytical design systems, probably utilizing unsteady CFD techniques. An effort to develop quantitative methods for nondestructive evaluation of composite structures is clearly needed. 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. The use of high-speed, large-memory computers permits, in turn, more detailed internal structural loads analysis for each of the many loading conditions and design alternatives, with fine grid analysis determining more precise load paths, stress distributions, and load deflection characteristics for subsequent aeroelastic analysis. It provides space, for cargo, controls, accessories, passengers, and other equipment. Extension of the ACT program to verify large structural components, including cost-effective fabrication as well as structural performance, is essential to bring this technology to a state of readiness for commercial application. Aluminum-lithium (Al-Li) alloy systems, for example, promise evolutionary benefits in higher stiffness and lower density, with no reduction in structural life. Propulsion and avionics are the two most important secondary systems. Although more experience exists with MMCs than CMCs, both are in their infancy with regard to large-scale application. Without this first step, assessing the residual life of such structures will not be possible. To minimize part count in basic fuselage and lifting surfaces, it is necessary to achieve wide spacing between stiffening members or to provide skins with integral stiffeners, or both. It is an important factor in community acceptance. You're looking at OpenBook, NAP.edu's online reading room since 1999. It will probably be necessary for each specialist to become more conversant with the fields in which the others work and, from the earliest stages of design, for all of these specialists to work together in ways that are unprecedented in the aircraft industry. Applied research in structures and materials is virtually always required at some level in developing a new type of advanced aircraft. Various combinations offer differing advantages, depending, for example, on the thermal environment (Figure 9-1). This should include consideration of how compliance with airworthiness regulations can be demonstrated on a practical basis during aircraft certification programs. Graphite/epoxy, for example, is a brittle material. Fabrication technology, particularly for tailored structures, should be emphasized to fully exploit the advantages of MMCs and prevent cost from becoming an insurmountable barrier. composite ppyrimary structure used in a Boeingg commercial aircraft • Boeing 787: Entered commercial service Sept 2010 – Ci f0%fl lihComposites account for >5 0% of total structural we ig h t – Features a graphite-epoxy fuselage, empennage, and wings – Uses ~20% less fuel than other aircraft of similar size, primarily due CMCs in airfoils, disks, and engine cases should allow turbines to be operated at increased temperature without the inefficiencies associated with cooling. Alloys capable of superplastic forming continue to promise both economic fabrication of parts with complex curvature or integral stiffeners and weight savings. primary structure carries flight, ground, or pressurization loads, and whose failure would reduce the aircraft’s structural integrity; secondary structure that, if it was to fail, would affect the operation of the aircraft but not lead to its loss; and B. Materials and structures research and development effort in support of the HSCT needs to be directed toward. Job description and duties for Aircraft Structure Assemblers, Precision. One type is the alpha (α) helix structure.This structure resembles a coiled spring and is secured by hydrogen bonding in the polypeptide chain. Higher bypass fans will operate at lower speeds and may need to be coupled to the low-pressure turbine through a gearbox. Fail-safe structures enable aircraft parts to be produced lighter. In addition, however, there is a continuing and essential need for long-term, fundamental materials and structures research of a generic nature. 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. They vary Also, you can type in a page number and press Enter to go directly to that page in the book. The approach employed is likely to depend on the application. Aircraft structural design, analysis, manufacturing and validation testing tasks have become more complex, regardless of the materials used, as knowledge is gained in the flight sciences, the variety of material forms and manufacturing processes is expanded, and aircraft performance requirements are increased. Rejuvenation and enhancement of NASA's effort on noise for propeller-driven GA products can enable an improvement in the environment of GA airports and can possibly improve the competitiveness of U.S. aircraft in this category. The challenges resulting from this trend involve higher rotor speeds, smaller disk bores, restrictions on maximum low-pressure shaft diameters, and very high-speed bearings. Civilian use of rotorcraft consists primarily of helicopters, although tiltrotor aircraft are under development and proposed commercial versions show promise for the commuter market. Use our Job Search Tool to sort through over 2 million real jobs. accomplished for airframes by taking advantage of the unique properties of composites to drastically reduce the number of individual parts and, thus, greatly simplify assembly processes. As in the case of subsonic transport aircraft, cost-effective application of PMCs for HSCT will require an integration of material advances and structural concepts into cost-effective fabrication methods. Much effort is needed to understand and better control the warping of large, complex parts during cure. Increasing the temperature capability of these alloys another 100°F to meet the higher HSCT requirements is difficult. These differences need to be resolved. Research is needed to increase allowable strain rates and, thereby, part output; to reduce cavitation flaws; and to broaden the classes of superplastically formable alloys available to structural designers. Integration of NDE into the structural concept/design/fabrication processes and automation of the NDE process also require greater attention. CMCs capable of operating to 3000°F are likely candidate materials for the combustor. This class of design problem is particularly important for high-temperature applications. Many NDE techniques are available that will detect flaws and other imperfections with various degrees of accuracy and reliability. Programs in the military sector have addressed the area of "self-diagnostic structures," that is, structures that assess their own health. It is most important to note that current and future materials and structures aspects of aeronautical systems, both airframes and engines, require a new level of collaboration among all of these specialists. Aircraft Structure Chapter 2. Aircraft Structures for engineering students Fourth Edition T. H. G. Megson AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Butterworth-Heinemann is an imprint of Elsevier A. Other areas of concern include improving oxidation resistance, ensuring compatibility of the fiber/matrix interface, and developing CMC fabrication technology. 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