Measurement of Visibility From the Pilot's Cockpit on Different Airplane Types Page: 8 of 24
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'.oA.C.A. Technical Memorandum No. 646
tal circular base-plate divided into degrees there is
placed a second rotatable circular plate, on which a bear-
.ing pedestal is mounted for supporting a vertical semicir-
cular plate arranged to turn about a horizontal axis.
This, vertical plate. is likewise divided into degrees and
is provided with the true bearing devices This consists
of cross hairs and -a head mounted on the end of an out-
rigger. The cross hairs, which .represent the "observation
point," lie at the intersection of the extended axes about
which the horizontal.andvortical plates may be turned, so
that the po-sition of the cross hairs is unchanged by the
rotation. . mirror is mounted on a'universal joint behind
the cross hairs in order to obtain the bearing of a de-
sired point conveniently. This mirror has the advantage
of not requiring the cyo:of theoobserver to be placed-be-
hind the apparatus in the extension of 'tho bearing direc-
tion, which is inconvenient and not always possible when
taking a bearing. The stand used for the first apparatus
serves for mounting this apparatus on the airplane. Only
one person is required for its operation, and bearings of
parts of the airplane lying in front of the windshield
can be easily obtained. It is also possible, with the
same position of the base plate, to measure vertical an-
glos bol-ow the horizon to -580, which has boon found to be
amplo,. 1ioreover, quicker work may be done with this ap-
paratus, so that only about 3 hours were required to meas-
ure a field of vision, while 5 to 6 hours wore required
for the first apparatus. Lastly, its compactness renders
it easier to mount and operate.
3, .Photographic measuringapparatus.- Since the meas-
urement of fields of vision with apparatus of the de-
scribed -construction requires a relatively.large amount
of time, and since taking exact bearings is a strain on
the eyes, it was attempted to determine the field of vis-
ion photographically. The difficulty of this method con-
sists in trying to obtain sharp definition of parts of
the airplane far removed from the observation point, and
as large a photographic angle as possible. A pinhole cam-
era was therefore used. (Fig. 4.) This gave an optical
angle of 1500 with .a.plato 9 X 12 cm (3.54 x 4.72 in.). and
a focal length of 18.5 mm (0.73 in.). The diameter.of the
hole was about 0.2 mm (0.008 in.) and gave a sufficiently
sharp picture. The camera was mounted on the previously
describod stand and was provided with a water level.
Figure 5 shows a photograph of the field of vision of
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Kurz, Gerhard. Measurement of Visibility From the Pilot's Cockpit on Different Airplane Types, report, November 1931; (https://digital.library.unt.edu/ark:/67531/metadc277430/m1/8/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.