The tail is built up from split bamboo, ⅒ in. by ³/₃₂ in. in cross-section, and the rudders are framed up from No. 20 gauge piano wire. The ends of the rudder frames are forced through the longerons, and the ends bent back in alignment with them; they are then bound to the longerons with black three-cord carpet thread. The rudders are covered after being fixed to the outriggers. When it is necessary to adjust them, the piano wire will be found sufficiently ductile to admit of a warp being placed thereon.
Fig. 147.—Front Elevation of Compressed-air-driven Model
Eleven ribs connect the spars of the top plane and nine those of the lower, the camber of each being the same; that is, the same depth of camber is maintained throughout. Before the wings are covered, the angle-plates to which the inter-struts are fixed must be bound on; and these are cut from No. 30 gauge sheet tin. They should be cut less in width than the spar to which they are attached, in order that their sharp edges shall not cut through the binding. To prevent the plates from moving, they should be lightly sunk into the wing spar with two centre-punch dots, and a film of glue should also be spread over the face of the plate coming in contact with the spar.
The inter-struts are streamlined in cross-section ([see Fig. 149)]; but they are to be left rectangular in section at their ends, to provide a flat surface for the plates to bed home on. The ends of the plates are turned back over the binding, which may be of the light machine variety.
The lower ends of the inter-struts are cut off to the same angle as the dihedral on the lower plane, to avoid distortion of the plane. Spruce or American whitewood may be used for them, the greatest cross section being ½ in. by ⅛ in. The greatest cross-section is situated at the middle of the strut, whence it tapers to ³/₁₆ in. by ⅛ in. [Fig. 149] shows the attachment of the inner strut to the wing spar. In [Fig. 150] are shown the brackets forming the guides for the axle, and also the supports for the rubber shock-absorbers. Piano wire is used for them. The width of the guide should be such that the umbrella-ribbing, which constitutes the inner portion of the axle, rides freely within it. The wheel axles are cut from No. 16 gauge piano wire, and they are soldered to the umbrella-ribbing, being sunk into the channel of the latter, bound with No. 30 gauge tinned iron wire, and then soldered.
Ordinary elastic, as used for a rubber-driven model, can be used as the shock-absorber, and it should be neatly and fairly loosely bound to the vertical guide, the axle of course being first seated therein. In order that the absorber brackets may maintain a vertical position, their ends are shaped to a form similar to the letter U. They are wire-bound to the skids and lightly soldered.
Fig. 149.—Details of Inter-struts.
