Self‐Straining in Aeroplane Structures: An Explanation of a Matter that is Frequently Found Puzzling by Students

THERE are many instances in aeroplane design where the structures contain tension cables. If the structure is a “pure frame,” any error in the “truing up” will not occasion any additional forces in the various members; the only effect will be a slight distortion from its correct configuration. If, however, the structure is redundant, it is necessary that these cables be cut (or adjusted as the case may be) to their exact length; if not, the two joints to be connected will have to be distorted, thus causing the structure to become strained before any external loading has been applied. Such a structure is said to be “self‐strained.” The forces in the various members, of course, depend upon the extent of the straining between the two joints concerned.