Comparison of landing-impact velocities of first and second wheel to contact from statistical measurements of transport airplane landings Page: 4 of 23
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NACA TN 3610
had a 40-inch-focal-length lens and was mounted on a plate which could
swivel only in azimuth. The swivel post was rigidly and permanently
attached to a trailer frame. Each corner of the trailer frame was sup-
ported by a jack that permitted adjustment of the vertical angle of the
lens optical axis. By means of these jacks and screw attachments on the
lens barrel, the lens optical axis could be accurately leveled at all
points of the camera traverse.
Statistical data were obtained from landings of the transport air-
planes for which general specification information is given in table I.
All data in the present analysis were obtained from landings on runway 35
at the Washington National Airport. The camera was located 800 feet
from the center line of the runway in line with the region on the runway
at which the greatest number of touchdowns were evidenced by the concen-
tration of tire marks upon the runway surface.
Values of vertical velocities were determined by measuring the
vertical distance through which the wheel'image moved in the time inter-
val of the five motion-picture frames immediately prior to second-wheel
contact, which is equivalent to 4/25 second. Corrections were applied
to the results to account for the distance from the image to the lens
optical axis, and the distance from the camera to the airplane wheel.
Complete descriptions of these corrections and the formulas used are
available in reference 3. With the corrections applied to the results,
the probable error of the vertical velocity is conservatively estimated
to be within 0.50 foot per second.
PRESENTATION OF RESUIWS
The overall results of the statistical analysis combining all flight
conditions and airplane types are presented in figure 2 as frequency
distributions of the vertical velocities V1 and V2 of the first and
second wheels to contact, in figure 3 as a frequency distribution of the
difference in velocities V2 - Vl, and in figure 4 as probability curves
for V1 and V2. Other pertinent results are given in table II. The
probability data were reduced to Pearson type III curves with the aid
of charts presented in reference 4. The experimental probabilities are
shown in figure 4 (and subsequent figures) for the same class intervals
that were used in the corresponding frequency-distribution curves to
indicate the fit of the Pearson curves to the data.
The effect of gusts on vertical velocities is shown in figures 5
and 6. The presence of gusts at the time that the landings were photo-
graphed was determined from airport hourly weather reports. The defi-
nition of gustiness as used herein is in accordance with the criteria of
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Harrin, Eziaslav N. Comparison of landing-impact velocities of first and second wheel to contact from statistical measurements of transport airplane landings, report, February 1956; (digital.library.unt.edu/ark:/67531/metadc57833/m1/4/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.