Page 1 of 3 ME1332: Design Project 1 for A-Teams – Aircraft Fuselage Design 1. BACKGROUND A light aircraft fuselage can be of a truss framework structure for combining lightness and strength. On landing the fuselage is loaded by the inertia of the wings and the reactions through the landing gear. 2. THE CHALLENGE Your team is to design, build and test a suitable 1:8 scale model fuselage structure based on a balsa wood truss construction. The aircraft is like a CFM Shadow Series C-D but is to be designed with a truss structure and the rear passenger seat is replaced by cargo space. (see BM41 at http://www.bmaa.org/files/bm41_6_shadow_cd.pdf) Each team member must show an updated logbook at each Design Lab session to demonstrate their contribution to each of the following: Model fuselage 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. � = �2�2 �� �2 (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.Page 2 of 3 Load B represents that of the main beam/wing/tail plane/motor/propeller assembly on top of the fuselage for which you will provide a string loop for loading. Ensure that the loading points conform to the positions defined in Figure 1. 2.10 The apertures for pilot and cargo access must be as per the dimensions in Figure 1. 2.11 Return all equipment issued and, if you wish, add a team logo/name to the model! 2.12 The framework will be weighed prior to the start of the test and will be loaded until failure occurs. The performance will be assessed per the following performance factor, PF: �� = 100 ����� × ����� ������� ���� (�) ����� ������ ���� (�) (2) Where, using the same units as above: ����� = �(������ ���� − ���������� ����)� + ��(���������� ���� − ������ ����)� Therefore, PF is a larger-the-better measure and it penalises model frameworks that are not accurately predicted in terms of mass and strength. • The maximum allowable mass is 50g and the minimum strength requirement is 30N. • Frameworks that fail to carry the 30N load or have a mass more than 50g will be disqualified and will score zero PF. • The PF will be penalised if points 2.2/2.9/2.10/2.11 are not correctly addressed. Balsa wood Material issued to each team will be limited to: (i) 3.2 mm x 3.2 mm square x 914mm = 6 lengths. (ii) 3.2 mm x 6.4 mm rectangular x 914mm = 10 lengths. (iii) 1.6 mm x 76 mm flat sheet x 914mm (joints only, not to be used in place of truss structure) = 1 length. (iv) Important! You must allow for wastage as no further material will be issued. Table 1: Typical mechanical and physical properties of balsa wood Density [kgm-3] Young's modulus [MNm-2] Tensile strength [MNm-2] Shear strength [MNm-2] Along Grain 150 3100 15 2 3. REPORTS (70%) • SUBMITTED IN THREE STAGES: all sections are assessed and feedback generated after the latter deadline. Marks are only awarded to the students identified on each relevant page. • DO NOT EXCEED MAX page numbers shown. Use Arial, Calibri or Times New Roman font, 10-point or larger. • All sketches must be clear and technical drawings to BS8888. • Calculations must be clearly laid out where specified - typed not hand written. • Report to be on A4 paper, stapled in the top LH corner (no covers, plastic wallets etc.) and the pages numbered. Excess pages will not be read or marked. Deadline for Assignment B: Part B1 (Individual) is 12:00 Friday 3rd FEBRUARY 3.1 Individual author name+ID+TEAM identified in header. Proposed truss design and analysis, including calculations of forces, model mass and failure load estimations, and respective geometric uncertainty calculations. Including framework design (to BS8888). References. (2 pages per student). Deadline for Assignment B: Part B3 (Individual) is 12:00 Wednesday 15th FEBRUARY 3.2 Author name+ID+TEAM identified in page header. Individual team members will also submit their (typed) record of contributions made to Project 1 team meetings by all team members. (1 page)Page 3 of 3 4. MODEL TEST DAY (30%) – Monday 13th FEBRUARY during your designated Design Lab This is the deadline for Assignment B: Part B2. Only team members in attendance will receive this mark. Group presentation before testing. Three-minute presentation giving quantitative evaluation of design solutions and rationale for an improved design State predicted failure load and mass of structure. Test: The model will be placed on two supports with a gap of 600 mm between them and each approx 30 mm wide. Loads of 10 N will be applied at the points B, C and D (see Figure 1). The loads are applied at the discretion of the person conducting the test but shock loading will be avoided. Points B, C and D correspond to the load points of the wing/fuel tank/motor/propeller assembly; pilot; and cargo respectively. Access to the pilot and cargo space is shown and these must be apertures through the structure. The fuselage is 150mm wide maximum. Figure 1: Model fuselage loading points (point B must be above head height) 4.1 One balsa wood model per design group must be submitted for testing in accordance with Sections 2 and 4. 4.2 You must make sure that suitable mounting points for the weight hangers are available. Cord loops at points B, C and D on the framework are suggested but test to see if they are satisfactory. Also, check that the card template can pass into the structure at the pilot's position to represent the access for the pilot. 4.3 The framework should support the loads applied for at least 10 seconds. 4.4 Beyond 30N, additional loads at Point D will be added until the framework collapses. 4.5 The total load before collapse will be recorded and then the performance factor PF will be evaluated. 4.6 The group which achieves the highest performance factor PF will be declared the winner. 4.7 Marks for testing of the balsa wood model will be allocated in accordance with the PF achieved. Individual log books will be regularly inspected