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• December 16, 2016 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - Experimental Investigation of the Low Speed Static and Yawing Stability Characteristics of a 45° Sweptback High Wing Configuration with Various Twin Vertical Wing Fins

An investigation was made to determine the low-speed static stability
and yawing stability characteristics of a 45° sweptback high-wing, low-
horizontal-tail configuration with various twin vertical wing fins. In
general, the static longitudinal stability characteristics were not
affected by either upper—surface or lower-surface wing fins. The results
indicated that the directional stability for a high-wing configuration
with twin upper-surface or lower-surface vertical fins located at 70 per-
cent of the wing semispan was smaller at low angles of attack than for
a similar configuration with only a single vertical tail at the rear
of the fuselage. The twin—fin configurations, however, were directionally
stable throughout the angle-of-attack range, whereas the single vertical—
tail configuration was directionally unstable at moderate and high angles
of attack. The twin upper—surface fin configuration was found to be
more directionally stable at low angles of attack but only 50 percent as
effective as the twin lower-surface fin configuration at moderate angles
of attack.

At high angles of attack, the directional stability for the
upper-surface fin configuration decreased as the angle of attack
increased. The positive effective dihedral (at 00 angle of attack)
normally associated with a high-wing fuselage configuration was increased
by the addition of twin lower-surface wing fins at 70 percent of the wing
semispan. As the lower-surface fins were moved outboard, the effective
dihedral was reduced. In the case of the upper-surface wing fins, the
effective dihedral of the complete configuration was made more positive
throughout the angle-of-attack range.

The yawing stability characteristics obtained with the upper-surface
or lower-surface fin configurations were approximately the same at low
angles of attack. At the higher angles of attack, however, the damping
in yaw contributed by the upper—surface fins tended to decrease as the
angle of attack was increased.

Requirements for satisfactory high-speed performance of aircraft
have resulted in configurations that differ in many respects from previous
designs. As a result of these changes, the designer has little assurance
that the low—speed characteristics will be satisfactory for any specific
configuration. The low-speed characteristics of wings suitable for high-
speed flight have been investigated quite extensively. The contribution
of other components of the aircraft, or of various combinations of
components, however, are not well-understood. In order to provide such
information, a series of investigations of models having various inter—
changeable components is being conducted in the Langley stability tunnel.