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Unformatted text preview: ENES 100 Introduction to Engineering Design Spring 2011 1 of 7 Problem Set #5 SOLUTION Due: In class on Mar. 7 (M) or Mar. 8 (Tu) Reading: Chapter 5 of the course text on Hovercraft Motion and Control Problems: 1. In an effort to save some time, your team decided to use the hovercraft base structure design described in detail in Chapter 7 of your ENES 100 textbook. This design consists of identical top and bottom decks made out of pink foam ( foam = 30 kg/m 3 ) which are attached together with 4 identical balsa support bars. Each support bar has a length of 240 mm, a width of 40 mm, a height of 50 mm, and a mass of 100 g. Once built, youve sadly learned that the vehicles structure is not very well balanced. (a) Determine the coordinate distance X from the back of the craft at which you must place a 50 g ballast for the vehicle to be balanced (i.e., for the center of pressure and the center of gravity of the base structure system to be coincident). (b) Suppose instead your team constructed the support bars out of spare foam pieces. At what coordinate distance X should you place the ballast? HINT: Use a spreadsheet tool like Excel to simplify this type of iterative design analysis Solution: (i) Define a coordinate system: X x y ENES 100 Introduction to Engineering Design Spring 2011 2 of 7 (ii) Locate the center of pressure as the centroid of the top deck: gG u g u U U U U u u Note: The location where the hole is cut has no effect on the location of the c.o.p. (iii) Redefine coordinate system with origin at the center of pressure: (iv) Use a spreadsheet to solve the c.g. for each part listed: In general: g u u and u u...
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