Abstract:
Analytical-techniques are developed for deriving approximate
solutions to a class of problems that arise in nonlinear flight
mechanics typically when an aeroplane is flying close to a stability
boundary. The techniques are based on pertoz-bation methods and the
method of multiple scales is used to correct for_nonuriformities
otherwise present in the asymptotic expai!,. 3ions. Applications are
mainly concerned with the lateral dynamics of slender aircraft flying
at high incidence. Approximations are derived for both linear and
nonlinear lateral motions that serve to illustrate the importance of
particular parameters in the problem. For the linear theory the
approximations are achieved by reducing the fourth order system to two.
weakly coupled second order systems. The nonlinear theory is mainly
concerned with the effect of aerodynamic nonlinearity on the lateral
oscillation when the latter has marginal stability or instability, as
predicted by the linear theory.
The analytic approximations are extended for use in the problem
of estimating damping moments on aircraft in oscillatory motion. For
this purpose approximations are constructed for the logarithmic
decrement of a nonlinear oscillation that can be used to fit experimental
measurements. Some thoughtis given to-the issue of memory effects in the
representation of aerodynamic forces and moments.
