Fig. 13.—Steel tube strut
with fairing bound on.
Figs. 14, 15.—Interplane struts
spindled from the solid.
the tube by linen tape or fabric, doped and varnished. This strut is of practically equal strength in both lateral and longitudinal directions, and from this point of view is superior to the solid spindled strut, which is usually of great strength in the fore and aft direction, but always possesses a tendency to buckle laterally. [Fig. 14] indicates a hollow plane strut, in which the sides of spruce are spindled from the solid, and glued to a central stiffening piece of ash; while [Fig. 15] is arranged so that a stiffening web is formed in the spindling process. Owing to the rather extensive nature of the latter operation, one does not find many instances of its use. Where the hollow wood struts used are not completely bound with tape or fabric, they should at least be bound at intervals with tape or fine twine, as there is always the possibility of the glued joint failing under the combined attentions of rain and heat.
A type of strut which is now being widely used is that of streamline section steel tubing, drawn or rolled from the round section. It is employed for both the interplane and undercarriage struts, but for the latter has not given entirely satisfactory results, owing to the tendency to buckle under extra heavy landing shocks. This would be more pronounced with a tube of fine section than with one possessing a bluff contour; but in any case, a strut of parallel section, whatever the material, is not well suited to withstand sudden shocks. This point is referred to later. Seeing that progress is being made with the production of a seamless streamline tapered strut this defect should soon disappear.
Fig. 16.—Interplane support from body.
Fig. 17.—Section of built-up strut.