Norwegian Spruce.
This wood is also known as spruce fir and white deal, and is grown principally in North Europe. Selected balks can be obtained to weigh no more than 30 lbs. per cubic foot, which compares very favourably with silver spruce. It can be obtained in average lengths, but it is subject to the presence of small hard knots and streaks of resin, although the writer has seen consignments with very few knots. A material known as Baltic yellow deal and Northern pine is procured from the same source, and is more durable than Norwegian spruce. It is inclined to brittleness when dry, and is heavier than white deal, weighing about 36 lbs. per cubic foot. The recent shortage of silver spruce has led to the employment of Norwegian spruce for items such as fuselage struts, hollow fairings to tubular struts, the webs and flanges of the plane ribs, and generally for those components for which long straight-grained lengths are not absolutely essential.
For fuselage struts, where the chief consideration is stiffness, to resist the bending strain produced by inequalities of wiring, fittings, etc., it may actually give better results, being slightly more rigid than silver spruce—at least that is the writer’s experience of it. In addition, very little increase in weight would result, as this wood can be obtained of almost the same weight per cubic foot as silver spruce. The defect usually met with in this wood, of knots occurring at intervals, would be of no great detriment, the lengths needed for the fuselage struts being approximately 3 feet and less, and it would therefore be easily possible to procure wood of this length free from knots. The other items enumerated are of varying lengths, which, with care in selection and conversion, could be arranged for. The practical application of this would be the increased amount of silver spruce available for such highly stressed items as wing spars, interplane struts, and longerons.