Aircraft from the first world war period were usually wooden framed, wire braced and covered in linen fabric. Aircraft produced in the 1930s were of transitional construction where the wooden frame was replaced by one of tubular steel or, as was to become more common, sections made from formed rolled steel strip. High tensile steel was used so very light, rigid structures could be made.
    The problem that restorers of aircraft of this period face is that steel corrodes and being so thin is almost always unusable a second time around. Fortunately the plates at all the junctions were made of stainless steel and these mostly survive in good order, but the tubes and spars usually need to be replaced.
    The Hawker biplanes had faceted wing spars of polygonal cross section made of rolled steel strip, closed and riveted together, with a high tensile steel web separating upper and lower booms. The machine used for making the booms is called a roll forming mill. Original specification steel for the spars was made for us by a Swiss company who arranged a unique smelt for Aero Vintage. The tubes of the fuselage structure had squared ends where the joint was made with stainless steel plates.
    It was an Air Ministry requirement that these aircraft should be easily maintainable in the outlying reaches of the Empire where welding facilities might not be available. The structure was therefore assembled with close fitting ferrules held together between the plates with flared mild steel tubular rivets. Nowadays neither the tubular rivets nor the high tensile steel strips or tubes are available from stock leading to a major development programme at Aero Vintage Ltd to manufacture the material and recreate machines to produce the sections exactly as were used by Hawkers.
    The squaring of the tube ends was done using a special machine. Using photographs of Hawkers' original machine Aero Vintage designed and built one, and the chance discovery of a set of squaring tools in a South African scrap yard allowed squared tube manufacture to be carried out. Other machines have been installed to manufacture the streamlined tubing used on the wing struts and to make the special tubular rivets.
    Editor's note. Anyone who visits Retrotec/Aero Vintage cannot be but impressed by the high quality of the work carried and the attention to detail in every aspect of design and manufacture. Also noticeable is the quiet working environment; no whining 'windy' drills or chattering rivet guns. To those used only to stressed skin aircraft, the beauty of the tube and wood structures, recreated by their craftsmen exactly as was done at Hawkers between the wars, is most affecting. Just think what it must have been like in a factory filled with lines of these exquisite aeroplanes in peaceful series production.