In aeronautical engineering the strength-weight ratio is so important, apart from the fact that the consequences of structural failure are generally more disastrous, that it becomes essential to investigate the loads and stresses in the various parts of the structures far more accurately and in much greater detail in order that smaller factors of safety may be used.

It is often possible, in the case of structures of a low order of redundancy which have to be designed to meet several different systems of loading, to select by inspection those members which may be considered to be the redundant ones, the elimination of which would result in an increase of the design loads in most of the remaining members. If the members are designed to such increased loads many members of the structure will be overstrong and unnecessarily heavy. The excess of strength of the various members of the complete redundant structure will almost certainly differ, so that the weight of the whole will be increased above the essential in a greater proportion than the strength.