The simple ring frames which are a common feature of metal fuselage construction are being superseded in some large aircraft by more complicated frames in which one or more cross members are added to stiffen the frame.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.

During the lecture on structural testing given by Dr. Pugsley to the Royal Aeronautical Society, reference was made to the work done at Weybridge on the strength testing of aircraft wings, and during the discussion the lecturer suggested that details of this work should be submitted to the Society for publication. This paper attempts to give a brief outline of some of the more interesting developments which have taken place during the war period, together with a few notes on the arguments which led to the adoption of the final form of test gear.

The value of 1 lb. of weight saved in an air liner has been given as equal to 1 lb. of gold in an American paper. This figure has been calculated in a more complete way, and on the assumptions made is reduced to £16 10s. or near enough to one guinea per oz. saved.

1. (1) It is almost always possible to reduce the weight of any component of an aircraft or engine by refining the design. This can be done in many ways, but chiefly by improved material, by reducing dimensional tolerances, by more accurate stressing and by development by mechanical testing. These processes increase the cost and time of manufacture, and as the value of an air liner starts only when it is put into service, and its useful life is settled by obsolescence rather than by wearing out, there is always a practical limit to the time that can be spent on design, development and manufacture. During wartime the resources of the country are pushed to their limit and it is often impossible to get a big enough production of the best materials, o r i o work to fine tolerances; hence we accept an aircraft a good deal short of the ideal. The life of the aircraft is comparatively short and is governed largely by factors outside our control, so that an assessment of the value of weight saving is nearly impossible.

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.

Systematic knowledge of the theorems available for building statically determinate frameworks appears to be restricted in this country to a very small circle. Many engineers are content with the knowledge that a simply-stiff plane framework can be produced by attaching a joint O by bars OA, OB. to joints A and B of a simply-stiff plane framework; and that a simply-stiff space framework can be produced by attaching a joint O by bars OA, OB, OC to joints A, B and C of a simply-stiff space framework. By these simple means, two- and threedimensional simply-stiff frameworks can be built up respectively from the basic triangle and basic tetrahedron.

Most textbooks give no other rules of synthesis, and are content to give as “ proofs ” of the relationships existing between the number of joints j and the number of bars m of a simply-stiff framework (m = 2j—3 in the two-dimensional case and m=3j—6 in the three-dimensional case) the obvious inferences of these relationships from the system of synthesis just described.

The designer of transport aircraft can play a very important rôle in improving the economic efficiency of air transport and the following analysis is devoted to a review of some calculations illustrating this aspect of aircraft design.

Economic efficiency must not be obtained at the expense of other necessary qualities, and it would be as well to touch briefly on some of these before considering cost alone.

1. (a) Safety and Comfort

2. American experience shows these factors to be as important as any. The introduction of a type of aircraft with a good reputation in these respects leads to remarkable popularity.

3. (b) Speed

4. This, the main advantage of air over sea, rail and road transport (reducing a journey of weeks to days, and of days to hours), has a very different importance when reduced to the possible saving of a few further hours or minutes. For usual aircraft engine combinations, it will probably be found worthwhile to increase the cruising speed to that at which economic and safe continuous running of the engines is not exceeded.