You are working for the Short Brothers aircraft company on the Short 330 aircraf

Question

You are working for the Short Brothers aircraft company on the Short 330 aircraft. The 330 has a rectangular planform wing of total span 74 ft 8 in. There is concern that cracks will form in the main
wing spar near the wing strut connection, which is 15 ft 10 in from the wing tip as shown in the figure below. The total wing area is 453 ft2 and the design wing loading is 50.6 lb/ft2. Assume that this
wing loading is evenly distributed along the span of the wing. The main wing spar has a depth of 14 in and is 0.064 in thick. Assume that the main wing spar carries 75% of the total wing load. Using a factor of safety of 1.5, determine the maximum allowable crack in the main wing spar at the strut brace location. (Material is Aluminum 2024-T3, KIc = 33.7 ksi-in1/2).

Explanation / Answer

Loading = 50.6 * 453   = 22921.8 lb

load carried by main wing spar = 0.75 * 22921.8   = 17191.35 lb

stress in main wing spar = 17191.35 / (14 * 0.064)     = 19.1867 ksi

19.1867   * sqrt (d)   = Klc / F.S.

sqrt(d)    = 33.7 / (1.5*19.1867 ) = 1.1709

maximum allowable crack

d   = 1.3711 inches

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