Building and Flying an Aeroplane / A practical handbook covering the design, construction, and operation of aeroplanes and gliders

by Charles B. Hayward

Fig. 30. Complete Rib of Bleriot Wing and Pattern from Which Web Is Cut

In the drawing of the complete wing. Fig. 29, the beams are designated by the letters B and E. A is a sheet aluminum member intended to hold the cloth covering in shape on the front edge. C, D, and F are pairs of strips (one strip on top, the other underneath) which tie the ribs together. G is a strip along the rear edge, and H is a bent strip which gives the rounded shape to the end of the wing. The ribs are designated by the numbers 1 to 12 inclusive.

Ribs. The first and most difficult operation is to make the ribs. These are built up of a spruce board 3/16 inch thick, cut to shape on a jig saw, with 3/16- by 5/8-inch spruce strip stacked and glued to the upper and lower edges. Each rib thus has an I-beam section, such as is used in structural steel work and automobile front axles. Each of the boards, or webs as they are usually called, is divided into three parts by the main beams which pass through it. Builders sometimes make the mistake of cutting out each web in three pieces, but this makes it very difficult to put the rib together accurately. Each web should be cut out of a single piece, as shown in the detail drawing. Fig. 30, and the holes for the beams should be cut in after the top and bottom strips have been glued on.

The detail drawing, Fig. 30, gives the dimensions of a typical rib. This should be drawn out full size on a strip of tough paper, and then a margin of 3/16 inch should be taken off all round except at the front end where the sheet aluminum member A goes on. This allows for the thickness of the top and bottom strips. In preparing the pattern for the jig saw, the notches for strips C, D, and F should be disregarded; neither should it be expected that the jig-saw operator will cut out the oval holes along the center of the web, which are simply to lighten it. The notches for the front ends of the top and bottom strips should also be smoothed over in the pattern.

When the pattern is ready, a saw or planing mill provided with a saw suitable for the work, should cut out the 40 ribs (allowing a sufficient number for defective pieces and breakage) for about $2. The builder then cuts the notches and makes the oval openings with an auger and keyhole saw. Of course, these holes need not be absolutely accurate, but at least 3/4 inch of wood should be left all around them.

Nine of the twelve ribs in each wing are exactly alike. No. 1, which forms the inner end of the wing, does not have any holes cut in the web, and instead of the slot for the main beam B, has a 1 3/4-inch round hole, as the stub end of the beam is rounded to fit the socket tube. (See Fig. 23.) Rib No. 11 is 5 feet 10 1/2 inches long, and No. 12 is 3 feet long. These can be whittled out by hand, and the shape for them will be obvious as soon as the main part of the wing is put together.

The next step is to glue on the top and bottom strips. The front ends should be put on first and held, during the drying, in a screw clamp, the ends setting close up into the notches provided for them. Thin 1/2-inch brads should be driven in along the top and bottom at 1- to 2-inch intervals. The rear ends of the strips should be cut off to the proper length and whittled off a little on the inside, so that there will be room between them for the strip G, 1/4 inch thick. Finally, cut the slots for the main beams, using a bit and brace and the keyhole saw, and the ribs will be ready to assemble.

Beams and Strips. The main beams are of ash, the front beam in each wing being 3 1/4 by 3/4 inches and the rear beam 2 1/2 by 5/8 inches. They are not exactly rectangular but must be planed down slightly on the top and bottom edges, so that they will fit into the irregularly-shaped slots left for them in the ribs. The front beams, as mentioned above, have round stubs which fit into the socket tube on the fuselage. These stubs may be made by bolting short pieces of ash board on each side of the end of the beam and rounding down the whole.

To give the wings their slight inclination, or dihedral angle, which will be apparent in the front view of the machine, the stubs must lie at an angle of 2 1/2 degrees with the beam itself. This angle should be laid out very carefully, as a slight inaccuracy at this point will result in a much larger error at the tips. The rear beams project about 2 inches from the inner ribs. The ends should be reinforced with bands of sheet steel to prevent splitting, and each drilled with a 3/8-inch hole for the bolt which attaches to the fuselage strut. A strip of heavy sheet steel should be bent to make an angle washer to fill up the triangular space between the beam and the strut; the bolt hole should be drilled perpendicularly to the beam, and not to the strut. The outer ends of the beams, beyond rib No. 10, taper down to 1 inch deep at the ends.