Preliminary investigation of a stick shaker as a lift-margin indicator Page: 3 of 20
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NACA TN 3355
Landing approach. In order to shorten the landing runs or, for the case
of carrier landings, to lower the arresting-gear loads, it is desirable
to approach at as high an angle of attack as possible consistent with
the following requirements: satisfactory stability and control charac-
teristics, sufficient speed for satisfactory engine acceleration and
waveoff, and an adequate margin below the stall to allow for air turbu-
lence and to provide for a flight-path adjustment and flaring. Some
work has been done toward using the stick shaker as a landing-approach-
condition indicator as well as a stall-warning indicator by providing
two stages of stick vibration of different-frequency and amplitude, one
actuated at the angle of attack desired for the landing approach and
the other actuated at the prescribed stall-warning margin. This arrange-
ment does not, however, appear to be entirely satisfactory because it
would supply no indication of the magnitude of variations from the desired
flight condition, which would therefore be difficult to maintain. The
question has arisen as to whether a desired lift coefficient or angle of
attack could be maintained by the pilot with sufficient accuracy if he
were provided with a continuous angle-of-attack or lift-coefficient detec-
tor which would supply a continuous variation of either stick-shaker fre-
quency or amplitude, or both, over the desired range of lift coefficient.
Exploratory tests were therefore made in the laboratory with simu-
lator equipment to determine how well a subject could maintain a given
stick-shaker frequency and amplitude by movement of the stick in an effort
to compensate for an imposed arbitrary change in frequency and amplitude,
simulating, for example, a change such as might be associated with a
change in angle of attack in flight. For these preliminary tests a large
number of discrete changes in either frequency or amplitude, or both,
with change in stick position were used instead of a continuous varia-
tion which could not be obtained with the available equipment. Some
tests were also made to determine the average minimum change in stick-
shaker frequency and amplitude that a subject could detect. The tests
covered an amplitude range from about 0.006 to 0.3 inch (measured near
top of stick) and a frequency range from about 4 to 26 cycles per second.
For the simulator tests a shaker was desired in which the frequency
and amplitude could be varied independently. The available shaker that
most nearly fitted these requirements was a pneumatic device used for
tamping sand in foundry work. The shaker consisted of a double-acting
piston-cylinder combination equipped with a slide valve. The travel of
the cylinder was cushioned at each end by means of springs or rubber
buffers between the ends of the cylinder and the ends of the piston rod
which extended through the ends of the cylinder. The shaker was attached
to the control stick by one end of the piston rod (fig. i).
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Trant, James P., Jr. Preliminary investigation of a stick shaker as a lift-margin indicator, report, February 1955; (digital.library.unt.edu/ark:/67531/metadc57722/m1/3/: accessed December 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.