Some liberties have been taken with the contents of the lecture in relation to the title. Firstly, it is proposed to examine safety in general, for only by this means can airworthiness be seen in its true perspective. Secondly, some trends in airworthiness and inter-related operational matters will be discussed. Finally, crashworthiness is dealt with at some length.

A rapid method is developed for estimating the profile drag of an aerofoil with a known transition point position. The results are in good agreement with previous calculations.

The purpose of this paper is to explain in simple terms the methods employed in, and the principles underlying, the technique of resonance testing and flutter calculations and to place that technique in its proper perspective within the framework of fighter aircraft design. No attempt is made to present original work, or to examine the more advanced aspects of the subject as both of these are considered to be outside the scope of the paper.

The reasons behind the growth in importance of resonance tests and flutter calculations are dealt with first. The technique of ground resonance tests is then given in detail. A few words follow on model resonance tests, the calculation of normal modes, and some aspects of flight resonance tests. The technique of flutter calculations is considered last of all, an attempt being made to give a simple explanation of “ flexure-torsion ” flutter, plus the basic theory of two-freedom flutter leading to the Lagrangian equations. The methods and instruments described in the paper may be regarded as typical, but as the subject is continually evolving they are far from final.

Some present trends in technique are mentioned, together with the difficulties experienced in dealing with the aerodynamic forces in the transonic region. It is essential that these forces be assessed, and the only known method is by experiment.