AERONAUTICAL engineers are afflicted by various ‘centres’ which will not stay put. Weights engineers spend much of their time chasing the elusive centre of gravity up and down the fuselage, the aerodynamicist worries about the centre of pressure, and the structural engineer, in addition to these, is cursed with the flexural centre and the shear centre. The main trouble connected with the flexural and shear centre seems to be historical in origin. No real attempt appears to have been made to keep pace with the development of wing structures from the old simple two‐spar, fabric‐covered, constant‐section wing. It is still quite common to see the flexural centre of a wing defined as the point at which a load must be applied, so as to produce bending of the wing without twist. In general, something more precise is required, and, particularly in these days of tapered, swept‐back, stressed‐skin wings, it would seem desirable to review the old definitions and usages of terms such as flexural centre, and flexural axis in order to avoid confusion and possible misstatements or misapplications. The advent of stressed‐skin construction has brought into fairly general use the term shear centre, which is often confused with the flexural centre, although the two points do not necessarily coincide. The use of sweep‐back has caused further confusion concerning the definition of twist. It is hoped that this brief survey may indicate the nature of the confusion that is known to exist—and, perhaps, lead to an authoritative decision, which may standardize terms and definitions.
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