CHAPTER III. RIGGING
In order to rig an aeroplane intelligently, and to maintain it in an efficient and safe condition, it is necessary to possess a knowledge of the stresses it is called upon to endure, and the strains likely to appear.
STRESS is the load or burden a body is called upon to bear. It is usually expressed by the result found by dividing the load by the number of superficial square inches contained in the cross-sectional area of the body.
Thus, if, for instance, the object illustrated above contains 4 square inches of cross-sectional area, and the total load it is called upon to endure is 10 tons, the stress would be expressed as 2 1/2 tons.
STRAIN is the deformation produced by stress.
THE FACTOR OF SAFETY is usually expressed by the result found by dividing the stress at which it is known the body will collapse, by the maximum stress it will be called upon to endure. For instance, if a control wire be called upon to endure a maximum stress of 2 cwts., and the known stress at which it will collapse is 10 cwts., the factor of safety is then 5.
[cwts. = centerweights = 100 pound units as in cent & century. Interestingly enough, this word only exists today in abbreviation form, probably of centreweights, but the dictionary entries, even from a hundred years ago do not list this as a word, but do list c. or C. as the previous popular abbreviation as in Roman Numerals] The word listed is “hundredweight. Michael S. Hart, 1997]
COMPRESSION.—The simple stress of compression tends to produce a crushing strain. Example: the interplane and fuselage struts.
TENSION.—The simple stress of tension tends to produce the strain of elongation. Example: all the wires.