In certain types of aeroplane the empennage is carried on two tail booms emanating from the main body. In some cases the booms and tail plane form what is virtually a portal and in these circumstances a fairly simple approximation may be found for the stresses resulting from fin and rudder side loads. The method adopted follows the treatment given in the author’s paper, “The Stressing of Rigid Jointed Frames.”

The object of the present paper is to draw attention to some of the recent researches which have had as object the improvement of the aerodynamic characteristics of aircraft. Such characteristics can be classified into two groups; those concerned with performance and those concerned with stability and control. In the former group come all those researches which aim at the reduction of drag, while in the latter group come those directed to the attainment of satisfactory stability and control in normal flight, as well as those concerned with the behaviour of auxiliary devices such as flaps and slots which are used under special conditions and in particular during landing and taking-off. The problems associated with flutter also belong to this group. The two groups may be broadly characterised by the words economy and safety.

Theoretical critical stresses have been obtained for four cases in each of which a curved panel has been subjected to a compressive stress, parallel in direction to a generator and uniformly distributed around its top and bottom circumferential edges.

In many branches of engineering, especially the aircraft industry, numerous geometric problems arise which present considerable difficulty to draughtsmen and designers. The object of this paper is to present methods which the writer has developed which enable any problem of the type under consideration to be rapidly solved. The majority of these problems arise in cases where, although sufficient data is provided to enable ordinary three view drawings of a particular part or assembly of parts to be made, angles and lengths have to be found which cannot be directly obtained from this three view drawing.

Wellington, the capital city of New Zealand, is situated in the south of the North Island, among the mountainous masses 2,000ft., high which form the northern shore of Cook Strait. The winds in this latitude are strong and persistent, and this, combined with the venturi effect of the Straits, gives-Wellington a very boisterous climate. The average run of wind per 24 hours is 310 miles and the average number of gales of force 8 or over is in excess of 60 per annum. There is little open ground near the city, and there is no aerodrome site within 30 miles which is free from atmospheric disturbances or topographical defects.

Within recent years the subject of anodic oxidation has been very fully and minutely examined, notably by Bengough, Stuart, and Dr. Sutton, who was responsible for the large-scale experiments carried out at the Royal Aircraft establishment, Farnborough, and who, with his collaborators, has presented a number of excellent papers to the Royal Aeronautical Society, the Institute of Metals, and other bodies. In addition, scientists and industrialists at home and abroad are continuously adding to knowledge of aluminium, its uses and adaptability, and are giving a growing impetus to penetrations into spheres formerly exclusive to steel, brass, copper, tin and timber, each substitution calling for special consideration, so that it is well-nigh impossible for one to broach the subject without impinging somewhere upon the work ol others.

It is known from both theoretical and experimental investigations that St. Venant's assumption on the constancy of the shape of the cross section of girders in pure bending does not hold true in case of thin-walled sections. The greater flexibility than calculated according to ordinary bending theory of initially curved tubes, as experimentally found by Professor Bantlin, was perfectly explained by Professor von Kármán in 1911 on the assumption of a flattening of the section.

In 1927 Brazier with the aid of the variational method determined exactly that the shape of an originally circular thin-walled bent cylinder corresponding to the least potential energy is quasi elliptical and that the cross section of the cylinder, therefore, must flatten, even if the centre line of the cylinder was originally straight. In consequence of the flattening St. Venant's linear law for the curvature loses its validity and the curvature increases more rapidly than the bending moment. For a certain value of the curvature the bending moment is a maximum, and after this value was reached the curvature increases even if the applied moment remains unchanged or decreases, fulfilling thereby the criterion of instability. This instability occurs when the rate of flattening, i.e., the maximum radial displacement of any point of the circumference of the tube divided by the original radius of the tube, will equal 2/9.