Calculations Showing the Influence of Aerodynamic Damping on Binary Wing Flutter
The influence of damping is examined by comparing the flutter critical speeds and frequencies obtained using the complete equations of motion and those obtained when all the damping terms are omitted. The calculations are made for binary flexure-torsion flutter of a wing in incompressible flow and the comparisons extend over ranges of values of the principal parameters. When the ratio of air density to wing density is high, the damping terms are found to raise the flutter speed by a large amount. But when the ratio of air density to wing density is low, a condition often occurring in practice, it appears that, over a wide range of parameter variation, the flutter speed obtained in the absence of damping is reasonably close to that obtained from the complete equations. Further experience is obviously needed before any general conclusions can be re~¢hed, but the present results offer some hope of reducing either the extent of, or the accuracy needed in, the aerodynamic information used for wing flutter calculations. It is pointed out that with constant aerodynamic coefficients the flutter speed for an undamped system is independent of the wing density.
A graphical representation of the binary flutter equations normal co-ordinates
A graphical representation of the solution of the flutter equations for a binary system is developed in which the effect of aerodynamic damping is separated into two parts. This division is thought to make the significance of the relative sizes of the damping coefficients more comprehensible. The method is applied to some typical binary systems and some general properties of binary systems are derived. It is shown that nearly-equal direct damping coefficients and small damping couplings lead to near-maximum flutter speeds and that, in general, the lower the air density the lower is the equivalent airspeed for flutter. The simplifications made in the frequency-coalescence' theory of flutter are clarified.
Linear elastic stability
Elastische Systeme konnen im wesentlichen in konservative (und zwar 1. nichtgyroskopische und 2. gyroskopische) sowie nichtkonservative (3. dissipative, 4. zirkulatorische und 5. instationare) Systeme eingeteilt werden. Eine Analyse der funf Kategorien zeigt, dass die bei Stabilitatsuntersuchungen ublichen statischen Verfahren nur in der 1. und in beschranktem Masse in der 3. Kategorie zulassig sind, wahrend die ubrigen Systeme kinetisch behandelt werden mussen.