Fig. 72.—Detail of Plane Bracing
The main planes are built from birch ¼ in. by ¹/₁₆ in. in cross section, the trailing spar being bent in a jet of steam, so that its ends sweep forward, as shown in the plan view. The ribs are pinned and glued to the spars, the pins being clinched on the under-side. The centre rib is left overhanging the spars, as shown in [Fig. 71], to enable the tin straps (lapped and soldered together as at A) to slide over them and secure the wing to the spar. A section of the joint is given by B. By removing these straps it is thus possible to alter the disposition of the main surface, when it is desired to adjust the elevation of the complete model. [Fig. 71] is a perspective view of the centre rib, the strap being shown black. To move the main plane each clip is forced off the extensions of the centre rib and thus releases the wing. Each clip is cut from tinfoil to the dimensions given at A ([Fig. 71]), being bent to a rectangular shape, and soldered up. B is a section of the joint. [Fig. 72] indicates the method of attaching the diagonal wing bracing, which imparts a dihedral angle of 1½ in. to the plane. A 1½-in. dihedral means that each wing tip is 1½ in. above the level of the spar. An elevation of the main plane is given by [Fig. 73].
Two propellers, of right-handed and left-handed pitch (for the reason, [see p. 36]), must be bent from birchwood 12 in. dia. × 1½ in. wide, by ¹/₁₆ in. thick; a finished view of the two screws is given by [Fig. 74]. For more comprehensive details of air-screw construction see chapters [IV] and [V].
Fig. 75.—Plan of Model
Fig. 76.—Outrigger Details
Fig. 77.—View of Elevator