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National Advisory Committee for Aeronautics, Report - Calculation of the Lateral Control of Swept and Unswept Flexible Wings of Arbitrary Stiffness

A method similar to that of NACA-1 Rep. 1000 is presented
for calculating the efecticeness and the rerersal speed of lateral-
control deeices on swept and unswept wings of arbitrary stif-
ness. Precision is made for using either stifness curves and
root-rotation constants or structural influence coefficients in the
analysis. Computing forms and an illustrative example are
included to facilitate calculations by means of the method.

The efectireness of conventional aileron configurations and
the margin against aileron rerersal are shown to be relatively
low for swept wings at all speeds and for all icing plan forms
at supersonic speeds.

Adequate lateral control constitutes one of the more
significant design requirements for airplanes. The ability
of the airplane to enter a roll is determined by the control
pow er and is measured by the maximum available rolling
moment resulting from lateral-control deflection. A meas-
ure of the degree of lateral maneuverability is the helix
angle at the wing tips corresponding to the highest rate of
roll; the lateral maneuverability depends both on the control
power and the damping in roll.

The control power and the damping in roll are affected
by structural flexibility. Control deflection ordinarily gives
rise to aerodynamic loads which tend to deform the m‘ng
structure in such a way as to reduce the loads on it and thus
to reduce the control power.

When the air stream is sufficiently high, the amount of lift which
results from the structural deformation may be sufficient to
nullify the effect of the control deflection. The speed and
dynamic pressure corresponding to this condition are known
as the aileron reversal speed or reversal dynamic pressure,
since at a slightly higher dynamic pressure a control deflec-
tion in a given direction would result in a rolling moment
in a direction opposite to that of the moment on a similar
rigid wing.