Measurement of Visibility From the Pilot's Cockpit on Different Airplane Types Page: 7 of 24
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6 N.A.C.A. Technical 1 memorandum No. 646
ence plane. Another plate, likewise divided into degrees,
is arr anged to turn about anPaxi-s passing through the '"ob-
"servation point" perpendicilar to the fitrt plate.. At the
bottom' of the turn axis, therefore' at' the "obs~'rvation
point," the end of a thread is fas-tened which m'ay be drawn
toward the- different points of 'the' airplane. The complete
apparatus is mounted on a standd whose -base plate may be
clamped to the pilot's seat. The stand is extensible. and
is provided with universal joints at the points :of. attach-
ment to the base plate and to the apparatus' itself', for
easier adjustment. Moreover, the apparatus "may be turned
horizontally on the stand, in order that it may. 'bo placed
parallel to the longitudinal axis of the airplane.
The visibility measurements are thon mado with this
apparatus , after fastening tho-'base plato. to the' pilot's
seat, by bringing the starting point' of t thread .to-the
chosen observation point. 'Thon with the aid of a w water
1ovol, the referice plane is made horizontal and is rotat-
ed in such a way that the zero direction of the angular
scale is parallel to the longitudinal axis of the airplane.
The measurements 'then follow, in which the thread is ap-
plied point by point to the parts of the airplane limiting
the view, so that the boundary lines of the field of vi.s-
ion may be determined. For reading .the angle, the verti-
cal plate is turned until it-touches the .thread. Then .the
vertical angle may' be read directly and the horizontal an-
gle may be road from the scale on tho bottom plate.
The measurements cannot be made by one person alone,
because one person is required for stretching the thread
and another for reading the angles. .'urthermore, a sag-
ging of the thread was unavoidable when measuring distant
points on the airplane (e.g., the wing tips), which affoect-
ed the accuracy of the moasuromehnts. No measurement of the
points seen by the pilot through transparent objects (for
example, the engine housing seen through the windshield)
was possible with thi's apparatus. Lastly, this apparatus
was only capable of measuring the field of vision above'
the horizon, and had to be inverted for the. rotatable an-
gle scale to be read vertically downward in order to de-
termine points below. the horizon.
2,_Bearinrg anl e-indicator.- The defects in the first
apparatus were ,the cause 'of' building an apparatus desig-
nated "bearing angle-indicator." (Fig.. 3.) It resembles
a theodolite in construction and operation. On a horizon-
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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/m1/7/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.