Lotus - Elite - Workshop Manual - 1957 - 1963

Dr Andrei Lozzi Machine Design & CAD MECH4460 & 5416 School of Aerospace Mechanical & Mechatronic Engineering The central torsion tunnel, to suit a kit car Handed out: 4pm Thursday 28h March 2013 To be collected: 4pm Thursday 25th April 2013 This assignment should take an average student 16 hours to achieve a pass All students are required to submit a signed statement of compliance with all work submitted to the University for assessment, presentation or publication. You are to design, analyse and build a model of a frame with a tunnel that contributes most of the torsional stiffness to the whole frame for an open two seater kit sport car. The construction is to be made entirely using bamboo skewers of about 3mm dia. glued at the nodes using 5 minute Araldite adhesive. All this material is readily available at most supermarkets. The scale is to be 1/8th, correct to within 5 mm. It is suggested that you make plane jigs on cardboard to assure yourself of reasonable dimensional accuracy. The rectangular prism shown on figure 8 page 4, represents the envelope within which the frame has to be contained. Your model is to be a simple version of a realistic frame, you are to just allow space for two occupants within a structure that is capable of torsional and bending loads between the two axles. No allowance is to be made for suspension, engine, transmission, doors, body shell, seats and other lesser items. Your model is to have, among other elements, two parallel skewers at the locations of the axles shown on figures 8. The torsion tunnel essentially enhances the stiffness of the overall frame by carrying some of the load from one axle to the other. The space required by the occupants is indicated on figure 10 & 11. The necessary opening for the occupant access is shown on Fig 10. They occupants are to face forward and to have reasonable space for their limbs within the frame. The envelope available for the central torsional tunnel is specified on Figure 9. All dimensions are in mm. A commercial kit car frame may be viewed in Bob Halliday’s lab, by arrangement with the workshop manager The frames will be judged based on torsional and bending stiffness, simplicity (mass) and strength. A sample torque is to be applied to one axle and resisted at the other. A bending moment is to be generated by applying vertical forces at the two front lower nodes of the torsion tunnel and resisted at the axles. An analysis of your design may be done SW Simulation or other FEA package. You must submit a report showing how you arrived at your final solution. You may work in pairs but each member’s contribution to the report is to be on separate A4 pages and initialled by the its author. 1 Figs 1 left, 2 below. The brilliant but poorly manufactured 1957-63 Lotus Elite. The monocoque chassis for this car is arrived at by gluing together the outer body shell (top left), to the inner shell (centre) and to the floor pan (bottom), all made as thin fibreglass panels. The engine mounts, seats, door hinges etc. were all bonded directly to the fiberglass monocoque. The concept was brilliant, the car is particularly elegant, simple and extremely light, its roadholding is legendary, but the built quality was very poor. As a collector’s car, it is a nightmare. Figs 3 below, 4 lower right. The car that followed the Lotus Elite was the Elan, shown below. In order to provide adequate strong points for the mounting of engine, transmission and suspension a backbone sheet steel sub-frame was made. This frame can be judged to be stiff and strong in bending but not so in torsion. Torsional rigidity is significantly enhanced once the fibreglass body shell is attached to the sub-frame. Some American texts refer to this sub-frame as “immensely strong”. Somehow American authors and possibly some engineers are not aware that torsional stiffness is important and how it may be achieved. 2 Figs 5 above, 6 far right. The STP Indianapolis turbine car, shown here, reflects ignorance on behalf of the designers. It does not utilise the outer boundary of the car to provide a stiff chassis in torsion and in bending. Placing the driver, structure and engine side by side, maximises cross-section to the air flow and consequently drag. It also unfortunately minimised the polar moment of area of the chassis. American books and journals still laud this as a breakthrough design (yet I believe it was never repeated). Lotus at about the same period had the turbine directly behind the driver. Fig 7 below. This kit car’s frame exhibits a somewhat discontinuous and incomplete space frame. The torsion tunnel in particular is not well braced to contribute to the torsional stiffness of the frame. Compared to the Lotus F1 frames it lacks ingenuity in its attempt to provide rigidity and lightness. See Costin & Phipps 3 Axles The frame must be contained within this envelope Space available for tunnel: 1400 long, 550 high, 400 wide. Front 550 2000 1300 Rear Fig 9 Fig 8 Lower front nodes Opening for occupant access 800x450 800 Fig 10 450 1400 see for example: http://www.madabout-kitcars.com/forum/showthread.php?t=4193 550 Fig 11 1400 4