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National Advisory Committee for Aeronautics, Report - Charts and Approximate Formulas for the Estimation of Aeroelastic Effects on the Lateral Control of Swept and Unswept Wings

Charts and approximate formulas are presented for the estima-
tion of static aeroelastic ejects on the spanun'se lift distaibution,
rolling-moment coefiicient, and rate of roll due to the deflection
of ailerons on swept and unswept wings at subsonic and super—
sonic speeds. Some design considerations brought out by the
results of this report are discussed.

This report treats the lateral-control case in a manner similar
to that employed in NAOA Report 1140 for the symmetvic—
flight case and is intended to be used in conjunction with NAOA
Report 1140 and the charts and formulas presented therein.

The lateral control and maneuverability of a wing are
important design considerations. These characteristics may
be affected to a significant extent by aeroelastic action,
particularly at high dynamic pressures and in the case of
thin wings, swept wings, and wings designed for low wing
loadings, because the operation of ailerons and spoilers
usually creates aerodynamic forces which deform the wing.

As a result of these deformations, the angles of attack
along the span often change in such a manner as to produce
lifts which oppose the rolling moment of the aileron or
spoiler; furthermore, these lifts cause additional deforma-
tions which may again reduce the rolling moment, and so on,
until equilibrium is reached. Wing flem‘bility may thus
cause a serious loss in the control power; in fact, if the
dynamic pressure of the airstream is sufficiently high, the
aileron rolling moment may be completely nullified. The
speed and dynamic pressure at this condition are often re-
ferred to as the aileron reversal speed and reversal dynamic
pressure, because at higher dynamic pressures the controls
would have to be reversed in order to roll the airplane.
When wing flexibility causes a loss in lateral control, there is
also usually a loss in the rolling maneuverability, which may
be expressed as the wing-tip helix angle due to rolling and is
affected by changes in both the control power and the damp-
ing in roll.