Connections in Use.
Fig. 47.—Interplane strut attachment.
The illustrations given indicate the varying degrees of practice, taking as the standard for comparison the early Wright socket, [Fig. 47]. Although somewhat crude it was quite suitable for the purpose, especially as the wing warping system in the Wright machines necessitated a fair amount of flexibility in the joints. It serves also to illustrate that some advancement has been made in constructional work. The advantages of rapid erection and dismantling have been realized and provided for in most machines since the early days of the industry, and it is not surprising, therefore, that the salient characteristic of the joint ([Fig. 48]) used by S. F. Cody on his famous biplane was portability. The interstrut terminates in a kind of fork, which in turn is pinned to the head of a special bolt slotted to receive it. The fact that the wiring lugs were improvised from chain links is interesting.
Fig. 48.—Interplane strut attachment.
The method of packing the wings for transport consisted in detaching the two outer cellules from the central structure, when the removal of one set of wires enabled the planes to be folded one against the other. It is possibly of interest to record the fact that in the military trials of 1912 this machine was taken down and re-erected in 51 minutes, quite a good performance taking into account its large dimensions. Although this attribute is scarcely necessary at the present time, it will be undoubtedly required by the sporting owner of the future with limited storage facilities. The fitting shown
Fig. 49.—Interplane strut attachment.
by [Fig. 49] is only suitable for machines with light wing loading. The plate forming the anchorage for the wires is pressed out, the lugs bent to the different angles, and then attached to the spar by an eyebolt, to which is fixed the plane strut, the ends of the latter being capped with steel tube of streamline section. A similar arrangement is that shown by
Fig. 50.—Interplane strut attachment.
[Fig. 50], the lug plate being pressed out and bent, but in this example the strut terminates in a socket of oval steel tube welded to the plate. It is connected to the spar by a bolt passing through the centre of the socket, the strut end fitting over this.
Fig. 51.—Interplane strut attachment.
The practice of anchoring wires to eyebolts, as in [Fig. 51], forms the nucleus of many strut connections, but as a method cannot be recommended. Continual strain on the wire has a resultant in the bending over of the head of the eyebolt as in [Fig. 52]. As a point of fact the use of the eyebolt is distinctly elementary, and gives the impression of a makeshift. The fitting illustrated by [Fig. 53] constitutes an advance on the previous arrangements dealt with, and is also indicative of modern practice.
Fig. 52.—Interplane strut attachment.
Fig. 53.—Interplane strut attachment.
The main body of this clip is a stamping from heavy sheet-steel, bent up to the section of the spar, the bolts, it will be noticed, passing horizontally through it. The anchorage for the wires is formed by lugs, which have a direct pull on the bolts, and is so arranged that a slight clearance exists between lug and spar.
Fig. 54.—Plane strut attachment.
The plane-strut is shod with steel tubing, and connected to the fitting by a bolt, as shown. Of the strut connections described so far, hardly one can be said to conform to the leading principle of the ideal fitting, i.e. the secure attachment to the spar without piercing the latter for bolts. [Fig. 54] gives a fitting which is as good a solution of the problem as is constructionally possible. The basis of this connection is the lug-plate, to which is welded the strut-socket, the whole being fastened to the spar by four bolts, which are let in the flange of the spar just half their diameter, and tighten on a washer-plate on the opposite side. Lateral movement along the spars is thus adequately prevented, although the outer strut-socket might conveniently be bolted right through the spar, without materially reducing the strength thereof. This is made possible by the fact that the wing spars, disregarding the small wash-out at the extreme tip, are generally parallel in depth from root to tip, the amount of material at the point of intersection of the plane-strut being in excess of that necessary for the stresses concerned. Another attachment achieving similar results is shown in the diagram ([Fig. 55]), forming an example of the fitting employed on the pre-war Avro biplane. It will be noticed that in this case two bolts only are used for the connection, the pull of the flying or lift-wires being counteracted by the duplicated wires taken from the washer-plate to a fitting located on the single central skid of the undercarriage.
Fig. 55.—Interplane strut attachment.