Measurement of Visibility From the Pilot's Cockpit on Different Airplane Types Page: 4 of 24
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i.A.C.A. technicall I -ndraxndum .No: .646;
III. Principle of' the Method.-
In order to develop amoth6dif6r the measuremont of
visibility, it is firstinecossary to explaini.tho concept.
of "visibility." "Visibility'," with respcCt to.-any object,
signifibes vory gonorally the ability. to- soee this object
from a 'given Viiwpoint. The object may. be-mo.re or loss
concealed' by opaque obstructions between th'e. observer and
the observed object, :i.e., the visibilityt" with :respect
to the object is more or less good.. In order. to ascertain
the "visibility" from" the pilot .'s cockpit o.f: an airplane,
we must determine to what degree the pilot .-..preovented by
parts..pf the. airplane from recognizing external objects.
It is. nocessary to dotormino' the- limits. of, the :pilot's
fio'li o'f vision due to tho opaque part.s of. the airplan,..
Tho eye of the pilot is assumed to' b.e the center of a
sphere of any convenient radius. The boundary .lines of.the
field of vision, are plotted on tho surface of t his sphere.
(Fig. 1.) If the portions 'of the surface of thoe.sphero
which represent the field of the obstructed vio.w are dark-
ened or hatched to differentiate them from- t.he field of.
unobstructed view, a diagram 'of the visibility is obtained.
Furthermore, if the surface of the sphere is provided with
degreo lines similar to the cartographic reprosentation-of
the oarth's surface, a numerical representation of the-
boundaries of vision is obtained. The anglo.s .are referred
to a horizontal plane and to a plane.porpond.icular to. i:t,
both planes being parallel to the flight :path.. Since,. a t
first, only. the visibility in that half .of the sphero ly-
ing in the direction of flight. w- :to. bo. instigated, -the
lines of intersection of- the refcoronc.e:oplans. with the .
surface .of' the sphere wore usod as:.the coordinate axes and
their point of intersoctioi served as:..the origin.
It is possible to determine the total visibility from
a point in all directions by this method of angular' meas-
ureiment. The present investigation .of ..the visibility was
limited, however, to that half of.the-sphere of visibili-
ty lying in front of the airplane, .i..e., the "field of
visibility" was limited by plane passing .through the eye
of the pilot at right angles to: the flight path and to the
horizon.' The field of visibility behind this .plane was
not investigated because, owing to .the. forward motion..of
the airplane, everything lying behind this plane had boon
already.flown over and therefore .no longer-presontod a
source of danger. In spite of this: fact,:the visibility
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Kurz, Gerhard. Measurement of Visibility From the Pilot's Cockpit on Different Airplane Types, report, November 1931; (digital.library.unt.edu/ark:/67531/metadc277430/m1/4/: accessed December 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.