A 1:8 scale balsa wood model will be built and tested to compare with the predicted load capacity of the fuselage.

| April 13, 2018


A 1:8 scale balsa wood model will be built and tested to compare with the predicted load capacity of the fuselage. Limited material quantities will be issued to teams:   2.1  Generate a Specification that includes criteria for selecting the best design.   2.2  Design a truss framework having the minimum weight to withstand the loads at the positions shown in Figure 1. The two truss sides are joined by cross-members whose mass is to be accounted for. There must be sufficient cross-members to prevent twisting of the structure.  2.3  Use standard pin-jointed analysis techniques to predict the load at which the truss will fail under the testing procedure described in Section 4. Each member of the team should propose and analyse their own truss design proposal, including calculations of the estimated model weight and estimated failure load. The maximum load that will be applied is 100N. Loads will be applied using weight hangers at the points indicated in Figure 1.  2.4  Buckling of the framework struts is the most likely failure mode and to manage this, you may need to increase the stiffness of the framework members under compression or reduce their length. The buckling loads may be calculated using the Euler strut buckling formula.      𝑃𝑃=𝑃𝑃2𝜋𝜋2𝐸𝐸𝐸𝐸 𝐿𝐿2        (1)   Where P is the buckling load; E is the modulus of elasticity for the material; I is the smallest second moment of area of the section; L is the length of the strut; and P2 is a constant which depends on the type of end supports for the strut. In a strut pin jointed at both ends, P2 = 1 but you must research the value applicable to your design.  2.5  Assess the effect of geometric uncertainty as described in the lecture sessions, i.e. the effect of variations in material and truss dimensional tolerances on predicted failure.  2.6 Select the best design based on objective selection criteria and improve the selected design, possibly combining it with ideas coming from the other unselected designs.    2.7  Produce a technical drawing of the final design including the predicted failure load and mass. If additional calculations are required to predict failure load and mass, because of the improvements made with respect to the selected design, do not report the calculations (but include the predicted values).  2.8  Construct your model using the balsa wood, materials and tools supplied. All the construction work must be performed within the timetabled hours. See relevant workshop technician for availability.  2.9  Provide string loop mountings at the loading points shown in Figure 1, on which to attach weight hangers, e.g. string. Ensure that you have strong loading points and that the hangers will not bottom-out on the test rig.

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