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Aircraft Loading And Structural Layout (Aerospa... TOP

Topology optimization has become an effective tool for least-weight and performance design, especially in aeronautics and aerospace engineering. The purpose of this paper is to survey recent advances of topology optimization techniques applied in aircraft and aerospace structures design. This paper firstly reviews several existing applications: (1) standard material layout design for airframe structures, (2) layout design of stiffener ribs for aircraft panels, (3) multi-component layout design for aerospace structural systems, (4) multi-fasteners design for assembled aircraft structures. Secondly, potential applications of topology optimization in dynamic responses design, shape preserving design, smart structures design, structural features design and additive manufacturing are introduced to provide a forward-looking perspective.

Aircraft Loading and Structural Layout (Aerospa...

Examples in aircraft structural design and analysis topics:Investigation in the numerical representation of damage on CFRP stiffened panels and behaviour under combined loading;Delamination growth of carbon fibre composites under fatigue loads;Experimental testing and numerical analysis of aircraft bolt jointed sandwich composites;Strength prediction via testing and/or numerical simulation of bolted joints on fibre reinforced laminates;Composite design considerations for trailing arm landing gears;Fatigue behaviour of bolted joints on CFRP laminates following pull through failure;Simulation of thermal residual stresses of CFRP wing;Fatigue of buckled composite stiffened panel;Dynamic Indentation of composite laminates;Numerical modelling of through-thickness reinforced composite laminates;Direct measurement of traction-separation law in fatigue damage of adhesive bonding;Composite joints reinforced by composite fasteners. ModulesKeeping our courses up-to-date and current requires constant innovation and change. The modules we offer reflect the needs of business and industry and the research interests of our staff and, as a result, may change or be withdrawn due to research developments, legislation changes or for a variety of other reasons. Changes may also be designed to improve the student learning experience or to respond to feedback from students, external examiners, accreditation bodies and industrial advisory panels.

To provide you with an understanding of the theories of Fatigue and Fracture Mechanics and show how these structural concepts are applied to the design and testing of aircraft structures and Airworthiness Certification.

Abstract:This paper presents an investigation into the gust response and wing structure load alleviation of a 200-seater aircraft by employing a passive twist wingtip (PTWT). The research was divided into three stages. The first stage was the design and analysis of the baseline aircraft, including aerodynamic analysis, structural design using the finite element (FE) method and flutter analysis to meet the design requirements. Dynamic response analysis of the aircraft to discrete (one-cosin) gust was also performed in a range of gust radiances specified in the airworthiness standards. In the second stage, a PTWT of a length of 1.13 m was designed with the key parameters determined based on design constraints and, in particular, the aeroelastic stability and gust response. Subsequent gust response analysis was performed to evaluate the effectiveness of the PTWT for gust alleviation. The results show that the PTWT produced a significant reduction of gust-induced wingtip deflection by 21% and the bending moment at the wing root by 14% in the most critical flight case. In the third stage, effort was made to study the interaction and influence of the PTWT on the symmetric and unsymmetrical manoeuvring of the aircraft when ailerons were in operation. The results show the that PTWT influence with a reduction of the aircraft normal velocity and heave motion by 1.7% and 3%, respectively, is negligible. However, the PTWT influence on the aircraft roll moment with a 20.5% reduction is significant. A locking system is therefore required in such a manoeuvring condition. The investigation has shown that the PTWT is an effective means for gust alleviation and, therefore, has potential for large aircraft application.Keywords: wing structure; passive twist wingtip; gust alleviation; aeroelastic stability

Part two looks at the fuselage in more detail. We will discuss the various structural components that make up a typical fuselage design and discuss the types of loading that the fuselage must be designed to withstand.

A snapshot of the highest-level breakdown of CFR Part 23 is shown below. The regulations are divided into several subparts which cover every aspect of design and operation including airframe structure (including design envelope and loading), propulsion, design and construction, and minimum demonstrated performance. An aircraft can only be awarded a Type Certificate if it is shown to comply to all aspects of the intended certification.

An airplane in flight is subjected to forces and moments that are continuously changing as the aircraft moves through the air. The structure must be designed strong enough to withstand the worst combination of loadings that define the edges of the design envelope.

When thinking about inertial forces it is important to consider how the mass is distributed through the aircraft. We often lump the entire aircraft mass at the center of gravity (c.g.) when drawing free-body diagrams to show the forces acting on the aircraft. In reality the mass is distributed throughout the aircraft and so an engine sitting on the wing can be thought of as its own mass, located some distance away from the aircraft c.g. This engine experiences its own inertial loading in a turn, and the structure that connects the engine to the wing must be made strong enough to withstand the local stresses induced in the turn.

A typical flight profile includes a take-off, climb, cruise, descent, and landing. This introduces a set of cyclical airframe loads which are broadly repeated each time the aircraft flies. Metal fatigue is a condition whereby a structural failure will occur below the static strength of the material due to tiny cracks that form as a result of repeated cyclical loadings. A fatigue analysis is an important component of an overall aircraft stress analysis.

The aircraft structure must be designed to withstand a certain load factor during normal operation, such that no permanent deformation or structural damage will occur when this load factor is reached. Design load factors are specified for different classes of aircraft and can be found in the airworthiness regulations. A typical light aircraft certified under Part 23 is certified to operate at a positive load factor of between 3 and 4 (limit load), and a negative load factor of between -0.5 and -1.5.

The atmosphere is very seldom completely still and is usually characterized by turbulence, gusts, and other disturbances. These all contribute to the total loading on the aircraft, and very often a gust loading case forms a limiting point of the design envelope. It is important that the structure be designed to withstand a combined load case where a gust impacts the aircraft during a high-g manoeuvre in accordance with the relevant airworthiness regulation.

Moving from a global picture of loading, we now classify the specific types of loads that are introduced into the structural members of the airframe. There are four categories of loading that can be introduced into a structural member: axial, shear, bending, and torsion. Different types of structure (spars, stringers, skins etc) are designed to carry the different types of loads introduced during flight. That way the various airframe components work together to resist and distribute the applied loading.

There are three common design philosophies associated with the structural layout of a typical aircraft. The most common design philosophy in use today is the semi-monocoque design, which evolved from the earlier truss and monocoque designs.

The earliest aircraft structures were built with a space frame or truss construction. Before the Second World War it was common to use wood as the primary structural material, with a fabric covering stretched over to provide the aerodynamic shape. Later truss structures were built from steel tubing like that seen on the Piper PA-18 Cub fuselage. A truss structure is a simple but inherently inefficient design, as the aerodynamic covering contributes mass but provides no real stiffness to the design. All the load is therefore carried in the truss members.

A monocoque structure is a single-shell design where the skins that make up the shell carry all the loading and contribute all the structural rigidity to the design. This can result in a light structure if properly designed, as no substructure is required to support the load-bearing skins. There are however two major downsides to a monocoque structure. The first is that the skin must be designed with very intricate curves and shapes to avoid buckling of the skin under loading. This requires a complicated and expensive manufacturing process to complete. The second is the difficulty in the incorporation and distribution of point loads into the structure. Typical point loads introduced into an airframe structure are those generated at engine mountings or the landing gear attachment points. Monocoque designs have largely been replaced by semi-monocoque structures as steel was replaced by aluminium as the primary airframe material.

A typical semi-monocoque structure consists of longitudinal members (stringers, longerons, spars), which carry bending and support the skin against buckling, transverse members (frames, ribs) which carry transverse shear and provide a means for point load introduction, and skins which carry in-plane shear loads and introduce that load into the substructure. All structural members in a semi-monocoque structure work together to resist deformation and to transfer the applied loading. 041b061a72

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