Li, in Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF/SIF-2014), 2014. Analytical methods for assessing the residual strength of damaged composite components are needed to ensure that only necessarily required repairs are undertaken. Where did the concept of a (fantasy-style) "dungeon" originate? They are typically made from an aluminum alloy structure built around a single spar member or torque tube to which ribs are fitted and a skin is attached. The fuselage is the main structure or body of the aircraft. specifically to other chapters. Fibers from hemp, sisal, and flax are frequently used in automobile interiors. Typical scenarios for LVI are ‘tool drop’ where the impactor hits the target accelerated by gravity from up to a few metres in height and the impact of ground equipment, such as stairs or deicing equipment. A Matlab program has been developed by using the vortex lattice method for the estimation of wing mass, namely the aerodynamic code of TORNADO to calculate the aerodynamic lift forces on a given wing configuration. This can be used to predict the structural residual life of an aircraft grounded in the environment. Which game is this six-sided die with two sets of runic-looking plus, minus and empty sides from? PSE’s are those elements of primary structure which contribute significantly to carrying flight, ground, and pressurization loads, and whose failure could result in catastrophic failure of the airplane. This is to ensure that a damaged structure should not be exposed to an excessive period of time when its residual strength is less than the ultimate. For the structural impact behaviour, improved composites damage and failure models with appropriate finite element (FE) codes are needed and should be validated by structural impact tests at each level of the test pyramid. Of the NDI methods described in this chapter, damage in composites is difficult to detect using eddy current and magnetic particle owing to their low electromagnetic properties, and using liquid dye penetrant because most damage is internal (e.g. Seats are not structure. to more than one chapter and are not specifically covered under They vary Table 6.4 shows the calculated ρ, E, σy, and G values. A gauge wouldn't be a Primary or Secondary structure either. Figure 4-5 shows these units of a naval aircraft. The Airline Transport Association (ATA) classifies that equipment under Chapter 25 Equipment and furnishings. For the wing mass calculation, the following parameters are essential such as density (ρ), Young’s modulus (E), yield strength (σy), and shear modulus (G). (2001). Pilot seat - primary or secondary structure? SHM has the potential to reduce aircraft downtime for routine inspections and reduce design safety factors for damage tolerance because of the early detection of damage. structure of the envelope and gondola of airships. "if I am going to disagree"? Primary and secondary structures are structural systems within the aircraft that have a primary or secondary purpose of transferring a load. The flexibility of the major aerodynamic surfaces (wings, vertical and horizontal tails) adversely affects the effectiveness of the corresponding control surfaces (ailerons, rudder, and elevators). of the aircraft should be established. Wing is a surface providing the lift to the aircraft. Once the damage (greater than the allowable damage size under category 1) is detected, the component is either repaired to restore ultimate load capability or replaced. Hemie fiber has been chosen because of its high Young’s modulus and yield strength. Table 6.2. The propulsion segment mainly produces thrust and, as much as The first option is often used for metal structures, which results in joints that add weight, time and costs during assembly. Glossary. These parameters can be obtained through component or full-scale fatigue testing and through reliability analyses. Primary and secondary structures refers to structural components in an airframe. Internal structure that is safety critical (e.g., wing box) or that is subjected to harsh environments (e.g., stone-spray from landing and take-offs) may receive a topcoat of glossy polyurethane in addition to a primer coating. The interaction of aerodynamic and elastic forces is known as aeroelasticity. They occur in every part of the cell and constitute about 50% of the cellular dry weight. 8.7. These highly-filled topcoats are more prone to breakdown of barrier properties and do not provide the same degree of corrosion protection as do glossy topcoats used on commercial airliners. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. The principal structural units of a fixed-wing aircraft are the fuselage, wings, stabilizers, flight control surfaces, and landing gear. Repairs are needed to restore the design ultimate load capability. Zoning diagram. Each area is dimensioned by several load cases, which result in different materials and material conditions, and a specific distribution of thicknesses over the entire structure. Some NDI techniques can be used to inspect metals but not fibre–polymer composites. They have made a model of civil transport aircraft (Airbus A320-200). This chapter presents HVI test data from gas gun impact tests on advanced composite structures and discusses numerical methods to predict observed impact damage at the structural element level of the test pyramid, which are validated by the tests. Chapter 51, STANDARD PRACTICES AND STRUCTURES - GENERAL. These can be the full generator current capacity. The current methods used by the airlines to repair damage to aircraft composite structure (secondary structure and primary flight controls) depend on the extent of damage, the time available to perform the repair, and the time until the next scheduled maintenance visit. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780081002032500474, URL: https://www.sciencedirect.com/science/article/pii/B9780081009642000198, URL: https://www.sciencedirect.com/science/article/pii/B9781845697044500083, URL: https://www.sciencedirect.com/science/article/pii/B9780081003329000189, URL: https://www.sciencedirect.com/science/article/pii/B9780080969053000371, URL: https://www.sciencedirect.com/science/article/pii/B9780124171534000013, URL: https://www.sciencedirect.com/science/article/pii/B9781855739468500236, URL: https://www.sciencedirect.com/science/article/pii/B9781845693459500062, URL: https://www.sciencedirect.com/science/article/pii/B9780081021316000062, URL: https://www.sciencedirect.com/science/article/pii/B9780128126684000083, Numerical Modelling of Failure in Advanced Composite Materials, 2015, A life prediction method for aircraft structure based on enveloping life surface, Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF/SIF-2014), ASELS describes the safe and reliable life scope for, Morphing Technology for Advanced Future Commercial Aircrafts, Miguel Á. Castillo Acero, ... Yasser Essa, in, Tailor made blanks for the aerospace industry, Tailor Welded Blanks for Advanced Manufacturing, Numerical modelling of impact and damage tolerance in aerospace composite structures, Numerical Modelling of Failure in Advanced Composite Materials, Mines et al., 2007; Toso-Pentecôte et al., 2010, Aircraft Structures for Engineering Students (Fifth Edition), Bonded Joints and Repairs to Composite Airframe Structures, Nondestructive inspection and structural health monitoring of aerospace materials, Corrosion prediction in the aerospace industry, Corrosion Control in the Aerospace Industry, Sustainable bio composites for aircraft components, Naveen Jesu Arockiam, ... Naheed Saba, in, Sustainable Composites for Aerospace Applications, Repair Tolerance for Composite Structures Using Probabilistic Methodologies, Reliability Based Aircraft Maintenance Optimization and Applications. Aircraft & spacecraft structures •Primary structure • Critical load bearing structure of an aircraft/spacecraft that in case of severe damage will fail the entire aircraft/spacecraft •Secondary structure • Structural elements of an aircraft/spacecraft that carry only air and inertial loads generated on or in the secondary structure Definition of primary/secondary structure In order to make a 100% renewable and biodegradable composite material, poly lactic acid (PLA) is considered as a polymer matrix. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. How come planes can endure more positive than negative g's? Apart from that, the secondary use of this force can be applied during landing roll. "No English word can start with two stressed syllables". These carbon fiber-reinforced plastic (CFRP) structures, however, still require assembly with … How can I discuss with my manager that I want to explore a 50/50 arrangement? When does an UAV need an internal structure? Input parameters required for wing box mass calculation. The way forward as discussed by Hachenberg (2002) is to use design analysis to support a limited number of tests at each level of the test pyramid. Ballistic impact is characterised by a local impact response from through-thickness dilatational stress waves. Section 18.2 presents meso-scale composite ply damage and failure models and energy-based delamination models suitable for use in explicit FE codes for prediction of impact damage. Therein we find: §25.785 Seats, berths, safety belts, and harnesses. The universal processes perfectly match the needs of the aircraft industry, where the diversity in parts is huge and the production quantities are low (in the order of 1000). Section 18.4 discusses a test programme on the influence of tensile and compressive pre-stress on HVI damage in composite plate structures, followed by the extension of the FE modelling procedures to pre-stressed panels under impact and prediction of residual strengths and damage tolerance (DT). Table 6.2 shows the mechanical properties of the selected fiber and matrix. In Fig.1, both directions of the abscissa axis (Ny) are positive; they are calendar lives under different states of protective coating. T.H.G. construction features of the fixed-wing aircraft and identify the primary, secondary, and auxiliary flight control surfaces. fittings, load curtains, cables, ballonets, etc. Adhesive bonding is a common method of joining in both primary and secondary structures. When these loads are caused by aerodynamic forces, which themselves depend on the geometry of the structure and the orientation of the various structural components to the surrounding airflow, structural distortion results in changes in aerodynamic load, leading to further distortion and so on. How do I place the Clock arrows inside this clock face? 1, the ASELS can be considered as an extension of the ASELC (Sight B) along the coordinate direction of stress level or an extension of the S-N curve (Sight A) along the coordinate direction of calendar life. Many of these are sandwich structures which present particular challenges for design and manufacture. The outer mold-line of military aircraft is typically coated with a low-gloss topcoat. As shown in Fig. You haven't even given a context. If you're going to disagree with everyone why ask the question? It reflects the interrelationships between stress level (S, in MPa), fatigue life (Nf, in flight hours), and calendar life (Ny, in years). 1. A paraglider is a lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure. Copyright © 2020 Elsevier B.V. or its licensors or contributors. lavatory equipment. It is often only necessary to locate SHM sensors in components prone to damage (e.g. Unfortunately, local defects in the coatings system may occur soon after depot repaint or field touch-up due to removal of access panels and other routine maintenance activities. It is often necessary to use two or more inspection methods to obtain a complete description of the type, amount and location of the damage. Adding a smart switch to a box originally containing two single-pole switches. To ensure continuing airworthiness, it is necessary to identify damage severity and detectability as part of the ongoing maintenance process. Best way to let people know you aren't dead, just taking pictures? For the sisal fiber composites, the model could not finish the finite element iteration that can be owed to the lowest value of E. Hemp and flax fiber-based composites drastically increase the weight of the wing box, whereas Ramie fiber-based composites show the reduction in weight of the wing box without compromising structural integrity [9]. Primary Structure. Miguel Á. Castillo Acero, ... Yasser Essa, in Morphing Wing Technologies, 2018. Composites have flown on commercial aircraft primary structures — those critical to flight — for more than 30 years, but only recently have they conquered the fuselage, wingbox and wings, most notably on the Boeing Co.’s (Chicago, Ill.) 787 Dreamliner and the A350 XWB from Airbus (Toulouse, France). Analogously, the use of lighter and better workable materials, specifically suited for these applications, can be another remarkable field of investigation. Table 6.4 shows the calculated wing masses for different natural fiber composites compared with a reference wing box aluminum alloy of the 7000 series. Secondary Structures. I disagree, it is not subject to flight deck (especially since pilot seats are in all aircraft that do not have flight decks), and it is not furnishing. The Shear modulus (G) can be derived from the following equation. Engineering design and damage evaluation – repair criteria for aircraft structures are location dependent depending on whether the structure is considered and … Burst tyre fragments may impact the lower wing skin or fuselage with impact velocities dependent on the tangential tyre speed and typically about 100 m/s, impactor mass can be up to several kg (Mines et al., 2007; Toso-Pentecôte et al., 2010). Does not include structures or equipment assigned Figure 2. Aircraft structures are assembled from many parts (order of 1000 to 10 000 – fasteners not included), which are made from various materials like composites, metal alloys and hybrid materials. Please add a reference, as the definition of primary and secondary structure may greatly vary depending on the context. Primarily for use in cleaning smooth or textured, metallic and nonmetallic surfaces preparatory to processing operations which are sensitive to residual surface contamination. Its selection is dependent on the design philosophy of the aircraft manufacturer. Calculated wing mass of different composites with respect to aluminum. Inspection, damage assessment, and repair requirements differ significantly between these classifications. At the highest level, Chapters 20 through 50 cover Aircraft Systems, 50 - 59 cover structure, 60 - 67 cover Propeller/Rotor, and 71 - 84 cover Power Plant. For primary load-bearing structures, such as the fuselage or wing skin with related safety regulations (FAA AC 23-13A, 2005), validated numerical methods are required to determine impact behaviour. What is the name for the Mitsubishi A6M Zero's one-piece wing/fuselage? He Ren, ... Yong Chen, in Reliability Based Aircraft Maintenance Optimization and Applications, 2017. The corrosion of the aluminum substrate will not occur until the protective coatings are compromised. Change chain with cassette or do nothing? b. crew seats, tables, pilot check lists and food containers, wardrobes, When an aircraft is used so heavily that it exceeds the limits of ASELS, the structural state is considered to be unsafe. Examples of local health monitoring include Bragg grating optical fibre sensors and comparative vacuum monitoring, whereas wide-area monitoring techniques are acoustic emission and acousto-ultrasonics. Access door and panel identification. Everything else on the aircraft is classified according to its primary function (air conditioning, flight controls, etc.) For shorter impact durations under high-velocity impact (HVI), the target response is governed by flexural waves. But that would not help either. Immediate repair is required. Right, so an example: An aerobatic aircraft goes into a manoeuvre, the back support bends, moving the pilot away from controls. Examples of Primary Structure include: Wings Fuselage Tail Landing Gear Wings. Aircraft Structures Definitions A Access panel - removable panel for inspection or maintenance Aft - near of in the direction of the rear of the aircraft ... Primary structure - the parts of the plane in which failure will be causing fatal danger for the passengers Primer It provides space, for cargo, controls, accessories, passengers, and other equipment. Essentially, one of the following decisions must be made: Only needed correction is cosmetic or sealing repair because damage is minor. Table 6.4. Characteristics of materials used in wing box. Structures containing this type of damage are capable of sustaining the ultimate load for the life of the aircraft structure. A wide range of different production processes are used in order to manufacture these parts. These enable cost savings through ‘right-first-time’ design and reduction of experimental tests in the certification process by use of computational analysis, which was a major objective of the industry-led EU project MAAXIMUS (2013). belt frames, stringers, floor beams, floor, pressure dome, scuppers, Why isn't aircraft structure inspection done by robots? Is there a way to notate the repeat of a larger section that itself has repeats in it? Restricted In particular, the manufacture of hundreds of pieces is not sustainable from an industrial point of view and should be strongly limited before such engineering solutions can be actually implemented. ASELS describes the safe and reliable life scope for aircraft structures in service. Primary and secondary structures are structural systems within the aircraft that have a primary or secondary purpose of transferring a load. Category 2: Damage that can be reliably detected at scheduled inspection intervals. Chun H. Wang, Cong N. Duong, in Bonded Joints and Repairs to Composite Airframe Structures, 2016. Park’s Advanced Composite PARTS and ASSEMBLIES for Aircraft and Space Vehicles. How can a hard drive provide a host device with file/directory listings when the drive isn't spinning? On aluminum light aircraft, their structure is often similar to an all-metal wing. Further, the assumption is made that the material is isotropic (Table 6.3). For design of pilot seat, would the seat be considered as primary or secondary structure? Damages outside the scope of the SRM, particularly to critical regions of primary structure, require engineering design disposition and approval by the OEM (or its delegate); this book describes some new design options demonstrated by recent research results. In aircraft structures the reduction of structural weight by using high performance fibers has evolved, but the existing carbon fiber-reinforced polymer composites are nonrenewable. In this chapter, the focus is on carbon fibre composite aircraft structures under HVI that are commonly classified further into soft body impact (hail, birds, tyre rubber) and hard body impact (runway debris, engine parts). Secondary structure could be the leading edge skin … tail cone, fuselage-to-wing-and empennage fillets, attach/attached to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known. See more. From: Numerical Modelling of Failure in Advanced Composite Materials, 2015, Y.T. We use cookies to help provide and enhance our service and tailor content and ads. Recently, advanced computational modeling techniques have been shown to be able to accurately predict the residual strength of composite laminates containing holes of various sizes and shapes (Wang et al., 2011a; Ridha et al., 2014). Aircraft secondary systems are reflected in an extensive industrial infrastructure, with products falling largely into four categories: (1) structural and mechanical, (2) propulsion and power-related, (3) environmental control, and (4) communications and navigation. Includes skins, Two distinct types of aeroelastic problem occur. The primary function of an aircraft electrical system is to generate, regulate, and distribute electrical power throughout the aircraft. Subpart C with the title Structure is broken down into the loads the aircraft must be designed to withstand (flight loads, gust loads, ground loads, etc.). What led NASA et al. In this type of problem, static or steady state systems of aerodynamic and elastic forces produce such aeroelastic phenomena as divergence and control reversal. Changes from one material to another, or from one thickness to another, require separate parts that have to be either joined or made as integral parts. The documents use use a Chapter-Section-Subject numbering system that correlates to a System-Subsystem-Subject. Includes emergency, galley and The use of 3D design models that can be shared in real-time is now essential for integrating and interconnecting the various innovations the market now requires. have utilized natural fiber composites for load-bearing structures. This type of damage should not grow or, if slow or arrested growth occurs, the residual strength of the damaged structure during the inspection internal is sufficiently above the limit load capability. By continuing you agree to the use of cookies. The use of polymer composite materials in commercial aircraft was first limited to secondary structures such as inspection panels, spoilers or air brakes that do not reduce aircraft structural integrity on failure. The abscissa of Tp1/Tp2 is the effective period of protective coating; structures can be considered to be suffering from pure fatigue damage within this period. After initial screening, hemp, sisal, flax, and remie fibers were selected. Naveen Jesu Arockiam, ... Naheed Saba, in Sustainable Composites for Aerospace Applications, 2018. Table 6.3. Most inspections are currently performed using NDT methods such as ultrasonics, radiography and thermography. The pilot sits in a harness suspended below a hollow fabric wing whose shape is formed by its suspension lines, the pressure of air entering vents in the front of the wing and the aerodynamic forces of the air flowing over the outside. I wouldn't consider it structure as most are designed to be movable on some kind of rail system. Primary and secondary Fairings, access panels and non-pressurized doors require a unique combination of properties and processing. In what kind of context are primary and secondary structure defined? For example, a fwd wing spar or a fwd pressure bulkhead are primary structures. For BVID, quite large areas of damage (typically 25 mm diameter) can be tolerated for older generation carbon/epoxy systems (and brittle high-temperature systems) without failures occurring below the ultimate design strain allowable, generally around 5000 microstrain for quasi-isotropic laminates made of unidirectional (tape) lamina. No repairs are needed. Improvements in manufacturing technology, the development of innovative material systems and a better understanding of their mechanical behaviour have now led to the use of composites for primary aircraft structures that carry flight, pressurisation or ground loads, which are critical for structural integrity. Category 3: Damage that can be readily detected, within a few flights, by operations or maintenance personnel without special skills in composite inspection. J. Sinke, ... R. Benedictus, in Tailor Welded Blanks for Advanced Manufacturing, 2011. Standard Practices, General Procedures and typical repairs applicable The original equipment manufacturer (OEM) generally zones an aircraft component in terms of these regions, and specifies repair limits and the pertinent repair procedures in the structural repair manual (SRM). Thus, while the coating system on-the-whole may provide excellent barrier properties for decades (particularly for interior structure), many opportunities exist for localized mechanical or chemical degradation of the protective coatings. Primary structure is that structure which carries flight, ground, or pressurization loads, and whose failure would reduce the structural integrity of the airplane. This is a main difference between primary secondary and tertiary structure of protein. where X can be any property (ρ, E, σy); Vf, volume fraction of the fiber; Vm, volume fraction of the matrix; f, fiber; m, matrix. area diagram. Some examples include visible impact damage, deep gouges or debonding, and major local overheating damage. Category 5: Severe damage outside design but is self-evident and known to operations, such as anomalous ground collision with service vehicles, flight overload conditions, abnormally hard landings, and so forth. The load exceedance curve is shown in Fig. This is appropriate because the primary control surfaces are simply smaller aerodynamic devices. However, if i have to provide arguments myself, why the hell would I be here? According to the rule of mixture ρ, E, and σy can be calculated by considering individual fiber and matrix. how come V-n diagrams are not symmetric? 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 The plane will crash if the Pilot has a heart attack, too - but it doesn't mean they've become structural! Airbus, through the Thermoplastic Affordable Primary Aircraft Structure (TAPAS) consortium, intends to demonstrate a TPC torsion box, such as that used in horizontal tails, featuring induction welded butt-joint stiffening ribs. (I never move mine, anyway). Ultrasonics, thermography and eddy current inspections are capable of detecting damage and cracks aligned parallel with the material surface whereas radiography is better suited to detecting cracks normal to the surface. structure diagram. To address the structural design requirements, we can refer to 14 CFR Part 25, Airworthiness Standards: Transport Category Airplanes. Soft bodies may disintegrate on impact exhibiting a fluid-like flow behaviour or be highly deformable (rubber), whereas hard bodies usually remain intact after impact. Ballistic impact cases are low mass with often supersonic impact velocities arising from weapons with application to security protection systems. P3 define, primary, secondary and tertiary aircraft structure M3 explain how the provision of drains, materials selection, jointing compounds, surface protection and stringer design help reduce the risk of corrosion damage to the base of an aircraft fuselage P4 explain the provision for protecting the aircraft airframe and its systems in The compartment above the floor and between the forward passenger Some examples include barely visible impact damage (BVID), small delamination, porosity, small scratches, and so forth. One involves the interaction of aerodynamic and elastic forces of the type described above. Concluding remarks in Section 18.5 are followed by future trends, sources of further information and references. Aluminum aircraft structure undergoes one or more surface treatments to prevent the onset of corrosion. Redistribution of aerodynamic loads and divergence are closely related aeroelastic phenomena; they are, therefore, simultaneously considered. They are equipment. Even though there is a possibility of damage growth and residual strength degradation under hygrothermal cycling conditions, this appears to be a serious concern only under severe cycling conditions. Foreign object debris (FOD) such as runway debris, stones or metal fragments could impact aircraft when launched by a tyre or by jet blast from another aircraft, as discussed in Chadwick et al. NDI methods have the capability to detect certain (but not all) types of damage in metals and composites. Thus, the residual strength assessment of a structure following impact damage can be performed similarly by using these advanced computational methods. Anyway, it seems pretty obvious that there's nothing intrinsic in your average pilots seat that relates to the flyability of the aircraft so I don't see how it could be considered structural. The wing box weight has been calculated by using the material properties of the natural fiber composites, and they have compared the results with a reference wing box made of an aluminum alloy. HVI scenarios usually occur in flight or on take-off and include bird strikes or impact by hail, tyre rubber, engine fragments or runway debris. What's the significance of the car freshener? Aircraft structures are vulnerable to impact damage resulting from impact by hard or soft bodies, such as steel fragments, birds, burst tyre rubber or hail. Also in process is a … Bird strike regulations require the airplane to safely continue its flight after impact with a 4-lb bird (8 lb on the empennage) at design cruising speed VC (EASA CS25, FAA 14 CFR 25: §§ 25.571 and 25.631). the compartments for equipment, passengers, crew, cargo, plus the OEMs as well separate that equipment from structural airframe components as well. Diagram of an aircraft structure enveloping life surface. It has proven satisfactory in attaching stiffeners, such as hat sections to sheet, and face sheets to honeycomb cores. Within this section is the necessary design requirements for seats, etc. Fig. Such interactions may exhibit divergent tendencies in a too flexible structure, leading to failure or, in an adequately stiff structure, converge until a condition of stable equilibrium is reached. Allowable strength versus damage size. The surface D1-Nc1-Nc2-D2 is a boundary limit designed to prevent unexpected fracture of a structure due to corrosion fatigue damage. This requires the development and validation of computational methods to support the design of a composite aircraft under the full range of flight and service loads defined in the airworthiness specifications. … Structural repair is required (if feasible) because strength is reduced below ultimate design allowable, or has the potential to be reduced in subsequent service. If an aircraft is grounded in different environments in full life circle (the corrosion properties relevant for high altitudes can be ignored), different ASELSs corresponding to these environments should be used for the prediction of residual life. Looking at the Chapter definitions we find (emphasis mine): Those removable items of equipment and furnishings contained in the Why do Arabic names still have their meanings? Not being able to unbuckle, the aircraft crashes, as a result of structural failure. delaminations) and does not break the surface. Building algebraic geometry without prime ideals. Structural health monitoring (SHM) is emerging as an alternative to conventional NDI, in which sensor systems are used with little or no human invention to monitor aircraft for damage. The first category encompasses aerodynamic controls and actuators (mechanical or fly-by-wire systems), doors, engine nacelles and … Difference Between Primary and Secondary Structure of Protein (Protein Structure) Proteins are the most abundant organic molecules of the living system. Adhesive bonding is a common method of joining in both primary and secondary structures. For civil aircraft structures, gust load is mainly considered as the critical load case [73]: where ɛ is the actual load, ɛLL is the limit load, and ɛUL is the ultimate load, ɛUL = 1.5ɛLL.
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