THE publicity recently given in Parliament to the delay in the aircraft building programme scarcely gave due importance to one of its fundamental causes. This expansion in quantity required comes at & time when a radical change is taking place in air-efaft constructional methods, made necessary by fecent research having caused aerodynamic design to demand a somewhat different exterior form. A continued increase in engine-power available, added to improvements in design reducing resistance and giving greater speed ranges, have enabled the speed of flight to increase so that up to 300 miles per hour can be contemplated for certain types of aircraft which constitute the quite normal equipment of the R.A.F. At such speeds as this, the air friction at the surfaces of the various component parts of the machine becomes a much greater proportion of the total resistance than at the lower speeds used hitherto. It now becomes vital to have both correct aerodynamic shape and smooth surfaces if reasonable efficiency is to be attained. In the past, most aircraft has consisted of girder frameworks taking the loads, covered by linen fabric the function of which was to give an airtight surface to react to the air pressure. It is not possible to avoid this cover sagging between its points of support to a certain extent, thus spoiling the correct aerodynamic form. Also the method of attachment, usually sewing, set up excrescences on the surface the roughness of which was appreciable. Thin metal sheeting, with flush riveting, is the obvious improvement upon this, but its weight is intolerable unless it can be made to take some of the induced loads, and allow the interior structure to be correspondingly lighter.