An accurate knowledge of the strength of materials is more essential in aircraft construction than in any other branch of engineering, as every aircraft component has to be reduced in weight to a minimum compatible with safety. Equally essential in aircraft construction is the use of every available refinement in calculation, although it is not possible as yet to estimate with sufficient accuracy from calculations alone the strength of many of the components. At every stage hv aircraft construction, mechanical tests are therefore made, first to determine the qualities of the materials, then to verify the strength of each part and finally to. check the strength of the complete machine.

Owing to the wide range of my subject and to the limited time available, I propose to deal briefly with some of the aspects of mechanical testing of special importance in aircraft research and development, describing more particularly some of the test apparatus and methods of testing I have had opportunities of developing.