• Version
• 149 Downloads
• 3.21 MB File Size
• 1 File Count
• January 9, 2017 Create Date
• January 9, 2017 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Charts and Approximate Formulas for the Estimation of Aeroelastic Effects on the Loading of Swept and Unswept Wings

Charts and approximate formulas are presented for the estimation of
aeroelastic effects on the spanwise lift distribution, lift—curve slope,
aerodynamic center, and damping in roll of swept and unswept wings at
subsonic and supersonic speeds. Two types of stiffness distributions are
considered, one which consists of a variation of the stiffness with the
fourth power of the chord and one which is based on an idealized constant-
stress structure. Some design considerations brought out by the results
of this paper are discussed.

A knowledge of the spanwise lift distribution and of some of the
aerodynamic parameters associated with it is required.for the design of
a wing structure. Under certain conditions, such as high dynamic pres—
sures, thin wings, swept wings, or wings designed for low wing loadings,
the spanwise lift distribution may be affected to a significant extent
by aeroelastic effects in somewhat the following manner.

A wing which carries a certain lift necessarily deforms under that
lift. If the angles of attack along the span are changed as a result of
this deformation, the lift carried.by the wing is changed as well; in
turn, this change in_lift causes a change in the deformation of the wing
and hence another change in lift, and so on, until an equilibrium condi-
tion is reached. The changes in the magnitude and the distribution of
the lift are reflected in changes of the wing lift-curve slope, the wing
bending and rolling moments, the spanwise center of pressure of the lift,
and, on a swept wing, the longitudinal center of pressure. Since the
lift produced by a given change in angle of attack-is proportional to the
dynamic pressure, the various aeroelastic effects tend to increase with
dynamic pressure. In fact, for certain wings a sufficiently large dynamic
pressure may 'produce a condition of instability in which the change in
lift caused by deformation is greater than the. amount of lift required
to produce the deformation” so that a given deformation will tend to _
increase until the structure fails. This phenomenon is aeroelastic
divergence; since it involves only torsional deformations in the case
of unswept wings, it is.often referred to as toraional divergence.