STEEL SPARS
Fig. 43.—Rib construction with metal spars.
Fabric Attachment.
Fabric and its attachment is a matter requiring considerable attention, with the great pressure to which modern wings are subjected. In the old days any fabric which was light with a moderate degree of strength was utilized. Nowadays, it is required to stand a certain strain in warp and weft, and rightly so, since the bursting of fabric in flight can only have one result. It is interesting to note that the fabric used on the Deperdussin hydro-monoplane was specially woven with threads running at right angles, forming innumerable squares. The purpose of this was that, should a bullet or any object pierce any one of the squares, damage would be confined to that square, and thereby prevented from developing; but the writer cannot recall any instance of its use to-day.
In covering, the fabric should be tightly and evenly stretched from end to end of the wing, and only comparatively lightly pulled from leading to trailing edge. If too much strain is applied to the fabric crosswise it will result in undulations between each rib. The tendency of fabric to sag between the ribs is accentuated by this, and, of course, matters are not improved upon the application of the dope. It should be remembered that the efficiency of any machine is greatly dependent upon the tautness of the fabric. It should not be stretched too tightly, as the application of the specified coats of dope may result in the fibres or threads of the material being overstrained.
CANE STRIPS SCREWED TO RIBS
Fig. 44.—Attachment of fabric to ribs by cane strips.
With regard to the actual attachment of the covering to the wing framework modern practice is restricted to two methods. The older method is illustrated by [Fig. 44], and consists of strips of spruce, or more usually cane, tacked or screwed to the ribs. It is usual, and certainly preferable, to affix this beading to every rib of those sections of the planes adjacent to the fuselage, as the fabric on these portions is subjected to the slip stream of the propeller, which meets it in a succession of small blows. The fabric in the outer sections need only be affixed to alternate ribs. The alternate method is shown by [Fig. 45]. In this case the fabric is sewn to the
