Single Strut Systems.
The almost universal arrangement for the small single-seater scout is the single bay, and from this method the progress of design has inclined towards the elimination of as many struts and wires as possible, which has its culminant in the type of truss embodying one strut and one pair of wires, lift and counter-lift, each side of the body. Quite a number of machines have incorporated the single strut assembly, the earliest perhaps being the Brequet, and one also remembers a small Avro scout, the strut in this case being built up with spars and stringers, covered with fabric. The single-lift truss is particularly suited to multiplane construction, where the chord of the wings is narrow, and the bending moment, due to the movement of the centre of pressure, is correspondingly reduced. A disadvantage exists with this form of truss similar to that experienced with the wireless monoplane truss, i.e. the difficulty of maintaining the correct incidence from root to tip. However, some extraordinary machines of recent construction embodying this feature, stand up to active service demands, so that this defect can be of no great moment. A minor detail consists in the circumstance of, for example, a lift wire coming adrift or perhaps being shot away. With the single-lift truss total collapse would ensue, but it is conceivable that the ordinary double-lift truss offers more chances of escape.
Fig. 61.—Wireless wing structure.
Another system which obviates the need for wires is illustrated by [Fig. 61], which was the particular system used on the Albatross “Arrow biplane” of 1912. A drawback is the difficulty of readjustment, which is the probable explanation of its failure to come into extensive use. The direct antithesis of this arrangement, the elimination of struts, is indicated by [Fig. 62]; but as this embodies all the defects of the monoplane system of trussing, even of the attachment of wires to the undercarriage, it must be considered of no practical utility.
Fig. 62.—Biplane truss without interplane struts.