The machine adopted for use by the Royal Flying Corps was the Canadian JN4, of simple design and presenting no unusual difficulty in manufacture. As work progressed, however, it became apparent that the type could be largely improved by change of design and fabrication, and there was evolved a machine which, while presenting the same appearance as its predecessor, contained nevertheless certain fundamental and radical alterations. Among other points remodelled were the landing gear—the substitution of the “joy stick” for the former control wheel, the adoption of split trailing edge instead of flattened tubing, and, most important, tail units made principally of metal instead of wood, resulting in an increased factor of safety, especially in the rudder and vertical stabilizer. Progress without change is impossible, and thus it proved in this undertaking.
It will be understood that given soundness of design there remains to be provided good workmanship and the best and most suitable materials. The former was procured without much difficulty, but the supply of the latter involved much thought and experiment, it being always remembered that the ideal machine combines a maximum strength with a minimum weight.
Linen for the covering of wings, etc., was imported first from Ireland, but submarine activity made it imperative that a substitute be secured. It was found at the Wabasso Cotton Company’s mills in Three Rivers, Quebec. Here was secured, for the special purpose required, a cotton fabric of remarkable strength. One inch in width is able to support some eighty pounds, and this with a weight which does not exceed four and a half ounces a square yard. Its adoption was at once successful, and it proved capable, when treated with “dope”—a waterproof and windproof solution with celluloid-like finish—of performing the same service as that of the most expensive Irish linen.
After fabric came wood, the quality of which was required to be above anything hitherto known in the lumber trade. Free from knots, of extreme length, with no “wind shakes,” swirly grain or “pitch pockets,” it seemed at first unprocurable. Ash for the longerons or longitudinals of the fuselage, and spruce for wing beams, wing edges, etc., was of imperative necessity. The market was searched, but what material was available proved to yield but a fraction of its total in satisfactory timber. Then, driven by urgent need, the “I.M.B.” organized a department in Vancouver and began to buy for itself on the shores of the Pacific. That its first purchase was rushed by express in carloads from the Western Coast will indicate how extreme was the pressure for sound material. The illustrations on [pages 32] and [34] give some idea of the magnitude of the operations required to produce that exact quality of lumber which the modern aeroplane demands.
It is interesting to note that even with this admirable supply secured, it was found that certain members were so long that it proved necessary to build them up, and, in the building, the Canadian Aeroplanes Limited evolved a scarfed, saw-toothed splice, since adopted as standard by Britain and the United States. Repeated tests proved that greater strength was thus secured than that of solid lumber of the same dimensions.
The Canadian Aeroplanes Limited propeller is five-ply white oak, glued, compressed and formed up by machinery that is almost human—and took its origin from a lathe designed by Peter the Great to make gun stocks. It is a far cry from Russia to Toronto, but the principle is identical. No “C.A.L.” propeller has shown manufacturing or engineering defect. The successor of Peter’s lathe carves them, four at a time, to one thirty-second of their finished form, and the final touches and balancing are hand work. To anyone who has seen a nine-foot propeller running at 1,500 revolutions per minute, its blade points cutting the air at the rate of eight miles a minute, it will be apparent how fine a workmanship and accurate a design is embodied here.
From wood pass to metal. Fuselage and internal wing bracing is with piano-wire which will stand a pull of a ton, though the members to which it is anchored weigh but a few pounds. Inter-plane bracing will live up to a ton and a half, and the control wires will stand the same test. So accurate are these latter that in process of their manufacture the heated metal is drawn through a forming die made of an aperture in a diamond.
In the autumn of 1918 it was decided to undertake the manufacture of a faster and more modern type of machine—the Avro—and to this object the factory diverted its energies. At the date of the armistice two had been turned out. These machines, equipped with 130 horse-power Clerget engines, promised excellent service, and underwent all tests to the complete satisfaction of all concerned. No less than one hundred additional had been fabricated and were ready for assembly when hostilities ceased.