This paper discusses the static longitudinal stability of an aircraft in the simple case when the aerodynamic derivatives are independent of speed. An outline of the basic theory of static stability is given, accompanied by a working document, giving suitable forms for the estimation of neutral points from wind tunnel tests. A worked example is included for a typical case. No attempt is made to interpret the results, but the conclusions include a note on the C.G. margin. Loss of stability stick free, and scale effect are commented on briefly in the appendices.

The differential equation for the deflection of a tapered strut cannot usually be solved by formal methods; we propose to attack the problem in the reverse direction; given the deflection-curve as a polynomial, we find the shape of the longitudinal section for struts of given strength. It will appear that the shapes so found are quite different from those for struts “ of uniform stress ” yet it is possible to get substantial saving in weight for a given strength (for some of the examples up to 11 per cent., the theoretical maximum being 13.4 per cent.

The simple ring frames which are a common feature of metal fuselage construction are being superseded in some large aircraft by more complicated frames in which one or more cross members are added to stiffen the frame. The stress distribution in simple rings is readily analysed by the standard methods for redundant structures, but the direct extension of these methods to more complicated cases leads normally to the solution of a number of simultaneous equations. The method now proposed avoids this difficulty by breaking down the calculation into a number of simple steps and then applying the principle of superposition to combine the results so obtained. In this respect it is equivalent to the Hardy Cross moment distribution method (1) or to Southwell's method of the systematic relaxation of constraints (2) though in many applications the final superposition of loadings is so simple that the full moment distribution or relaxation procedure is not required.

The complexity of much of the mechanical gear used for shock absorption and arresting in aircraft engineering is apt to obscure some of the broad generalizations that may be deduced from the elementary principles of classical mechanics. More particularly does this apply to the distance required to arrest the motion of an aircraft or falling body when the retarding force must not exceed a specified value. This note merely presents some more or less self-evident truths which may be of some value in dealing with new landing and arrester problems.