The Effect of a Gap Between Elevator and Stabilizer on the Static Stability and Maneuverability About the Lateral Axis in Flight Page: 4 of 10
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N.A.C.A.. Technical Memorandum No. 701 3
The results of closing the gap were distinctly notice-
able on the general behavior of the airplane by a lower
stick force and enhanced elevator effect. Although no -.
tail landings could be made with gap open, the elevator
effect, with gap closed, was such as to make the tail skid
touch the ground ahead of the wheels.
The size and the method of closing the gap is indi-
cated in Figure 2. A strip of varnished linen is glued to
stabilizer and elevator.
In Figure 3 the lift coefficients are plotted against
the elevator displacement with open and closed gap for the
same c.g. position. The change in elevator displacement
with the lift factor aS/ca is shown in Figure 4 versus
the c.g. position, along with the magnitude of the static
stability by fixed control acm/aca.* According to figure
4 the limit of the static stability with fixed control
lies, for open gap and full throttle, at 26.7 c.g. posi-
tion, at 28.6 per cent of the mean wing chord with closed
gap and at 34.9 and 36.9 per cent of the mean wing chord
in throttled flight.
The static elevator effect is d = 0.024 for open
gap in flight with full throttle and = 0.012 with
throttle closed. With gap closed the static elevator ef-
fect is ---= 0.034, with throttle open and dcm = 0.015
with throttle closed.
Figure 5 exhibits the results of stick force measure-
ments with open and closed gap. The reduction in stick
force by closing the gap amounts to about 1.5 kg (3.3 lb.)
in flight with open throttle, or about 60 per cent by low
dynamic pressures, and 30 per cent by high dynamic pres-
sures. The improvement in throttled flight lies within
The moments impressed by the weight of the elevator
control affect the forces which the pilot exerts on the
*According to experience and in agreement with thbo6retical
considerations the relationship of Ecm/aca to c.g. posi-
tion r is approximately
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Hübner, Walter. The Effect of a Gap Between Elevator and Stabilizer on the Static Stability and Maneuverability About the Lateral Axis in Flight, report, March 1933; (digital.library.unt.edu/ark:/67531/metadc63551/m1/4/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.