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Question: four helical compression springs have to be designed as one...

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Four helical compression springs have to be designed as one of the components to support the dynamic force of remote controlled helicopter landing pad. The weight of the landing pad is calculated to be 1200N and will be equally distributed in all the springs. The designed maximum weight of the helicopter is 600N. When the helicopter lands on the pad, each spring compressed by a length of 25mm. The spring will be made of squared and ground ends, ASTM A232 spring wire. Use 10% of clash allowance. Use No-2. Using a safety factor of 1.3, solve the following problems by considering the fatigue loading. Check for possible buckling. Use Figure 9, 10 and 11 (a) Calculate the diameter of the wire. (5 marks) (b) Calculate the diameter of the spring. (S marks) (c) Calculate the number of active coils (N). (5 marks) (d) Calculate the free length of the spring (LF). (5 marks) (e) Discuss the importance of the calculated wire and spring diameter in resisting fatigue failure of the spring. (5 marks) 0.80 0.76 0.65 0.60 0.53 0.43 65 103 10 106 0.40 0.20 0.20 0.40 min S 0.60 0.80 Figure 9
18 1.8 0.5 (shear correction only use for static loading) K.-1 + 16 1.7 K-4 10.615 ishear and curvature 4C-4C corrections, use for fatigue loading 1.6 12 10 8 1.3 6 1.2 Preferred range, ends ground ← Preferred range, ends not ground- 1.0 10 12 14 8 Spring index, C-Dd 6 Figure 10
Wire diameter (in.) 0.080 0.0040.008 0.020 0.040 0.200 0.400 0.800 450 3000 400 2500 350 ASTM A313 (302) ASTM A228 music wire (cold-drawn steel) 300 2000 ASTM A401 (Cr-S eel)N ASTM A229 ASTM A227 ASTM A230 1500IN(ol-tempered carbon steel) ASTM A232 (CVa steel) 200 ASTM A229 toil-tempeired carbon steel) ASTM A227 (cold-drawn carbon steel Inconel alloy X-750 (spring temper) 150 1000 ASTM B159 (phosphor bronze) 100 ASTM A313 (302 stainless steel) 500 50 2 3 4 5 6 7891 2 3 45 6 7891 2 3 4 5 6 7 891 0.10 1.0 10.0 100.0 Wire diameter (mm) Figure 11
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