enly as to produce dangerous
air stresses upon the surfaces, in which case there is a possibility of
collapse.

If an upside-down flight is desired, the engine may, or may not, be
throttled down at point A. If not throttled down, then the elevator must
be operated to secure a course approximately in the direction B. If it
is throttled down, then the course must be one of a steeper angle than
B, or there will be danger of stalling.

Diagram p. 88.--This is not set at quite the correct angle. Path B
should slope slightly downwards from Position A.

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.

BENDING.--The compound stress of bending is a combination of compression
and tension.

The above sketch illustrates a straight piece of wood of which the top,
centre, an