A wing section structure is in the form of a two-cell box in which the vertical spars are connected to the wing: Structural design and Care Assignment, US, UK

UNIVERSITY OF HERTFORDSHIRE
School of Physics, Engineering and Computer Science

Assignment Briefing
A wing section structure is in the form of a two-cell box in which the vertical spars are connected to the wing skin through a set of angle sections as shown below in Figure 1. The geometry is defined using the notation shown.

A1, A2, A3 denote cross-sectional areas of the angle sections, l1, l2, h are lengths of the wing skins between the angle sections and t1, t2, t3, t4, t5 skin thicknesses.
An axis system Oxyz is defined where Ox lies on the axis of symmetry of the section, y is vertically up and z measures spanwise position along the wing with the root being at z = 0.

The wing section is made of an aluminium alloy having the following properties:

Young’s modulus of 70 GPa
Poisson’s Ratio of 0.3
Tensile strength (Yield) of 276 MPa

(1) The section is subject to a positive bending moment 50000 Nm about the x-axis.
(i) Idealise the section (ie determine equivalent boom areas) to simplify the
structural strength analysis.
(ii) Calculate Ixx passing through the centroid.
(iii) Determine the bending stresses arising from the applied bending moment.

(2) For this part of the assignment, you may assume that the design is modified so that the boom areas may be taken as A1 = 650 mm2
; A2 = 1150 mm2
; A3 = 850 mm2
. A shear force
Sy = 30000N in the positive y direction acts at a point 400 mm aft of the front spar of the structure. The booms may be assumed to take all the direct stress and the skins only shear stress.
(i) Determine the shear stresses arising from the applied shear force at the given location.
(ii) Locate the shear centre of the structure. To do this, the steps are as follows:

(a) Calculate the rate of change of twist angle with respect to length from the
results in (i).
(b) Determine the torque necessary to produce the same rate of change of twist angle in the opposite direction. This is done by using the theory of Lecture ASDA2. You will find shear flows q1, q2 and q3 rate of change of twist angle rather than the torque.
(c) Divide the resulting torque by the shear force Sy. This will give the required
location of the Sy to produce no twist relative to its assumed location of 0.4m aft of the front spar of the structure.

(3) The analysis you have just completed has been motivated mainly by looking at the strength of the structure. Briefly discuss what other analysis you think would be necessary as part of the structural clearance of the wing

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