Aircraft Structures

Module aims

The structural principles developed in the second year are applied to thin-walled surface structures representative of parts of airframes.  These structures deform under transverse loads and are prone to instability under compressive or shear loading and the students will learn how to analyse the effect of such loads. Modern aircraft structures are frequently made of laminated composite materials and the course will give the basic theory for how to extend the theory of homogeneous plates to composite laminates.

Learning outcomes

By the end of this course the student should be able to:

(i) Analyse the St Venant torsion of an open tube and obtain expressions for the torsional stiffness and the shear strains.

(ii) Calculate the stress distribution in a thin-walled closed tube loaded by shear forces and to develop methods for finding the shear centre.

(iii) Describe the modification of the stress distribution due to the presence of booms and to develop the beam/pure shear panel idealisation.

(iv) Evaluate the deflection of a closed cell as a consequence of bending and shear strains and to develop expressions for the warping displacements of the cross section due to torque, leading to axial constraint stresses.

(v) Extend the work done on a single cell tube to the case of a multi-cell tube loaded by transverse shear forces and calculate the influence of taper

(vi) Describe the function of fuselage frames and to calculate the stress distribution in the fuselage near a frame due to a concentrated load.

(vii) Describe the fundamentals of plate theory and to be able to calculate deflections in thin plates under transverse loads using Navier’s method and Rayleigh-Ritz energy method.

(viii) Apply the Rayleigh-Ritz method to study the buckling of flat plates under a compressive load and to note the results for shear buckling.  

(ix) Illustrate the postbuckling characteristics and the effect of plate curvature.

(x) Describe the principle of plate stiffening in order to increase the buckling load.  

(xi) Describe the modes of instability and the use of data sheets to study the buckling of plate assemblies.

(xii) Describe the micro- and macromechanics of an orthotropic composite ply.

(xiii) Evaluate the in-plane stiffness and bending stiffness of laminates made of orthotropic plies, and to understand the effect of various coupling phenomena in laminates.

(xiv) Experimentally determine the properties of aircraft structures and materials

Module syllabus

  • Open Thin-Walled Tube Under Torsion: Stiffness, strains and the membrane analogy.
  • Single Cell Tube Loaded by Shear Forces: Stress distribution and twist. Shear centre.
  • Boom/Shear Panel Idealisations: Simplified modelling of assemblies of skin, stiffeners and spars 
  • Deflection of a Thin-Walled Tube:  Due to bending shear and torsion. Warping of the cross section.
  • Multi-Cell Tube:  Stress distribution and twist due to transverse shear forces. Influence of taper.
  • Frame in Fuselage:  Stress distribution in frame and fuselage under a concentrated load.
  • Plate Bending: Small deflection of thin plates. Moment/curvature relationship, stress distribution, stress resultants.
  • Rayleigh-Ritz method: The use of energy methods to obtain an approximate solution.
  • Plate Buckling:  Influence of compressive stresses and shear stresses.  Postbuckling behaviour.
  • Stiffened Panels: Global and local buckling modes. Use of data sheets for interaction of plate assemblies.
  • Fuselage Buckling:  Between frames due to bending moments, Brazier effect.
  • Orthotropic Composite Plies: Micro- and macromechanics. Transformation of properties between coordinate systems.
  • Laminates: Use of ply properties to calculate laminate stiffness. Relation between forces and deformation in laminates and various coupling phenomena.

Pre-requisites

AERO40007 Mechanics
AERO40008 Structures 1
AERO50008 Structures 2

Teaching methods

Lectures are presented using a combination of the blackboard, overhead projector and pre-printed notes. Tutorial classes are also held to discuss selected questions on the tutorial sheets.

Assessments

Examined Assessment
3 hour written examination in Summer term (80%)
Mechanical Properties of Composites Lab (10%)
Bending/Torsion of a Wing Structure Lab (10%)


 

Reading list

Core

Supplementary