Learning to fly in the U.S. Army

by E. N. Fales

62. Sweepback.—The horizontal angle (if any) that the leading edge of a machine makes with the crosswise or lateral axis of an airplane.

63. Nose Dive or Vol-pique.—A dangerously steep descent, head on.

CHAPTER VII
MATERIALS OF CONSTRUCTION

The materials of construction for airplanes should be of such material, size and form as to combine greatest strength and least weight. With metal parts in particular it may be necessary to substitute less strong material for the sake of getting non-corrosive qualities, ability to withstand bending, ductility or ease of bending, etc. With wood, absence of warping is important as well. The materials which are considered are the following: wood, steel, including wires; special metals as aluminum, brass, monel metal, copper, etc., and also linen and dope.

Strength of Materials.—It is important in a general way to understand the terms used in speaking of strength of materials. Thus we may have strength in tension, strength in compression, or strength in shearing, bending and torsion. Some material fitted to take tension will not take compression, as for example wire; some material, as bolts, are suited to take shear, etc.

In general all material for airplanes has been carefully tested and no excess material is used above that necessary to give the machine the necessary strength.

Tension.—This means the strength of a material which enables it to withstand a pull. Thus wires are used where strength of this kind is required.

Compression.—This refers to strength against a pressure. Wire has no strength for this purpose, and wood or sometimes steel is used.

Shearing.—Refers to strength against cutting off sideways. Thus the pull on an eyebolt tends to shear the eyebolt, or the side pull on any bolt or pin tends to shear the pin.

Bending.—In bending material the fibres on the outside tend to pull apart; those on the inside tend to go together. Thus on the outside we have tension, and on the inside compression. Along the center line there is neither tension or compression, it is the “neutral axis.”