A criterion for the prevention of spring-tab flutter

Abstract

The present paper advances a formula which can be used as a criterion for the degree of mass-balance necessary for the avoidance of spring-tab flutter. The formula shows that if the tab is of sufficiently light construction, mass-balance may not be required at all; on the other hand, the usual static balance may be inadequate for a tab of high inertia. The criterion comprehends within itself the requirement (given elsewhere) limiting the length of a mass-balance arm. While the formula is based on theoretical considerations (which are set out in the Appendix) the numerical values for the quantities to be used have been deduced from flight experience, which shows excellent correlation with the theory. Two forms for the criterion are given: a simple form suitable for general application, and a slightly elaborated form intended for application to unusually large tabs. The Appendix, besides containing the main analysis, also gives consideration to certain factors which for simplicity are omitted in the main text. In particular it is shown that the 'limiting length' for a balance arm may be generalised to a 'limiting circle' for the position of the balance mass: the circle can often be found from simple geometrical considerations.