The problem of determining the distribution of stress over the various components of a structure such as an aircraft frame is one which has always presented considerable difficulty. For a large proportion of the components calculations of the stresses can only be carried out on the basis of assumptions and approximations, the effects of which cannot be estimated with any degree of accuracy and, since considerations of size and weight impose limitations upon the employment of a large safety factor, there has always existed a need for some practical means of checking the results of calculations or of obtaining more reliable estimates of the stresses.

Wire gauzes are used in air duct systems and wind tunnels for many purposes. Methods of estimating the pressure loss through a gauze currently available are often found in practice to be unsatisfactory. In this paper data obtained by several experimenters are correlated. It is shown that the effect of Reynolds number on pressure drop is similar for a large range of gauze porosities. An empirical method of estimation of the pressure drop is given which can be used with confidence for gauzes of porosity (defined as the proportion of area not blocked by the wires) from 0·27 to 1·00, and over a range of Reynolds number, based on approach velocity and wire diameter, from 20 to 600.

The pioneer rarely receives that meed of praise which is his due, until those days arrive when his pioneering has become a page or so of history. What meed of praise he may then receive is too often made savourless by critics unable to disassociate themselves from the knowledge of their own technical era. The halting speed of pioneering aerodynamic research cannot be judged by the supersonic speed of secret splittings of the atom.

It was R. L. Stevenson who said that to travel hopefully is a better thing than to arrive. In aviation we have arrived at that streamline flow of technical jargon which deludes so many they have at last reached the boundary layer of aeronautical knowledge, so that they find experiments with plates always a little flat, although their curiosity may still be aroused by flying saucers.

The problem of the stress analysis of circular fuselage frames has been investigated by a number of authors; the analyses are, necessarily, rather mathematical in nature although in some cases the final results have been presented in extremely practical form. The present paper offers, in non-mathematical language, a short account of the fundamentals of the problem and a brief guide to the more important published literature. It also develops an approximate method for the analysis of frames using Lagrange's method for minimising a function of several inter-dependent variables. This method is shown to be particularly suitable for the analysis of frames with large cut-outs, about which little has previously been published. In addition, the underlying parameters which determine the stress distribution are deduced from the theory, and the deductions are compared with previously published work. In general, agreement is good. The paper is written throughout with a view to being of practical use in the actual stressing of frames. Numerical examples and explanations of mathematical methods are included in Appendices.

The commonly accepted practice of resolving a velocity V at incidence α into components V sin Λ parallel to the leading edge and V cos Λ normal to the leading edge at incidence α sec Λ is only approximately true and the exact method of resolution is developed here.

In dealing with the aerodynamics of swept-back wings the free stream velocity may be resolved into a constant component parallel to the leading edge and a variable component normal to the leading edge. This is only possible if the constant percentage chord lines are all parallel to the leading edge, that is there is no taper, thickness taper or twist on the wing. This note gives the exact form and the small angle approximations of the velocity components and of the incidence of the component normal to the leading edge.

Vortices are not usually treated by potential theory, but the latter is so well known and of such general application that there seem to be advantages in doing so.

Consider first the potential function

i.e. distance from O.

The minimum comfortable cruising speed of an aeroplane depends on the complexity of characteristics for the design in question, which may be broadly grouped under the headings of stability and control, drag and propulsion.

The store of knowledge relating to such speed is composed, in the main, from experience with aeroplanes powered by supercharged reciprocating engines, for which, at the low powers appropriate to the conditions considered, the brake horsepower and drag horsepower both increase with height at roughly the same rate (constant aeroplane weight and equivalent air speed being assumed). For a turbine-engined aeroplane the brake horsepower (or thrust) decreases with altitude and it might be supposed that this difference would result in a difference between the minimum comfortable speeds of similar aeroplanes driven by turbine engines (either jet or propeller) and by reciprocating engines.