1684. An Optimization Procedure for a Redundant Wing Structure
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Paper
Abstract
A procedure is described whereby a minimum-weight wing may be obtained by calculating the optimum bending moment of inertia for each of the two spars (or boxes). This is accomplished by forcing each spar to support a proportionate amount of bending moment resulting in the maximum Mc/l stress equal to the damage tolerance allowable for the critical loading condition. The procedure described involves two initial analyses whereby an equation is obtained for the percent of bending in each spar as a function of the ratio of the moments of inertia. From this, a particular ratio of moments of inertia of the two spars is calculated to ensure that each spar is working to its allowable stress. According to the optimal stress theory, any other ratio would result in greater spar weight for bending.
Three cases are used in the examples provided:
* Constant height, same allowable stress
* Different heights, same allowable stress
* Different heights, different materials; therefore, different allowable stresses
This procedure can save at least four weeks of design sizing iterations since it determines the optimum ratio of moments of inertia of the spars without iterations.
