Learning to fly in the U.S. Army

by E. N. Fales

7. Cedar Wood.—Is used occasionally for fuselage coverings or for hull planking in hydroplanes as it is light, uniform and easily worked. Veneers, or cross-glued thin layers of wood, are sometimes used for coverings.

Laminated or built-up wooden members have been much used for framing and for ribs and spars. The engine bearers are always of wood on account of vibration and are also laminated. In lamination the wooden strut is built up of several pieces of wood carefully glued together. The grains of the different layers run in different directions, consequently a stronger and more uniform stick often is secured. The objection to laminated pieces comes from the weather causing ungluing. Laminated pieces should be wrapped in linen or paper and freshened with paint or varnish from time to time.

Forms.—Attention should be called to the hollowed form of many of the wooden members. In any beam or strut, material at the center of the cross-section is of far less value in taking the load than the material away from the center. Therefore, to secure greatest strength with least weight, it is permissible to lighten wooden members if done understandingly.

Steel.—There is a tremendous difference in the strength, wearing and other desirable qualities among different steels and irons. For airplane work none but the best qualities are allowed. For this reason the use of ordinary iron bolts (as stove bolts) or metal fastenings or wire not standardized and of known qualities should not be permitted. The airplane is no stronger than its weakest fitting. This does not mean that the hardest and strongest steel must necessarily be used, as ease of working and freedom from brittleness may be just as important qualities, but the steel on all metal fittings should be of high-grade uniform stock. A ductile, not too easily bent, mild carbon steel is usually recommended for all steel plate, clips, sockets and other metal parts. If any parts are required to be tempered or hardened it must be remembered that they become brittle and can not afterward be bent without annealing or softening. Tool or drill steel is a name given to uniform or rather reliable grades of steel adapted to heat treatment as tempering or annealing. Often the bolts, clips, nuts, pins, devices and other fittings are of special heat-treated nickel steel which must not be heated locally for bending or for attachment. Such work seriously weakens the steel. The steel is often copper-or nickel-plated and enamelled to prevent rusting. Do not forget that the proper material may be twice as strong as other material which looks the same but which has not received special treatment.

Wires.—Only the highest grade of steel wire, strand and cord is allowable. Manufacturers, as Roebling of Trenton, N. J., manufacture special aviator wire and cord, which is given the highest possible combination of strength and toughness, combined with ability to withstand bending, etc. Steel wire ropes for airplane work are divided into three classes as follows:

1. The solid wire = 1 wire (as piano-wire grade) and known as aviation wire.

2. The strand stay, consisting either of 7 or 19 wires stranded together and known as “aviator strand.” Flying and landing wires on Curtiss.

3. Cord or Rope Stay.—Seven strands twisted together forming a rope, each strand being of 7 or 19 wires and known to trade as aviator cord. The wires are either tinned or galvanized as protection against rust, etc. Ordinarily galvanizing is used, but hard wires and very small wires are injured by the heat of galvanizing and they are therefore tinned.

No. 1. The single wire is the strongest for its weight. Single wires will not coil easily without kinking and are easily injured by a blow, therefore their use is confined to the protected parts of the machine such as brace wires in the fuselage and in the wings.

The strand stay (No. 2) of 7 or 19 wires is generally used for tension wires, as it is more elastic (can be bent around smaller curve) without injury, as the flying and landing wires on the Curtiss. The smaller strands usually have 7 wires, the larger ones 19 wires.