Flight, July 1920

The Olympia Aero Show 1920

The machines

Short Brothers. (STAND 44) Whitehall House, 29-30, Charing Cross, London, S.W.1.

   The Short "Swallow" all-metal biplane, is the outcome of this firm's wide experience in the construction of rigid airships, which has convinced them that this form of construction - employing light aluminium alloys - presents great possibilities in the design and construction of heavier than air craft.
   The construction generally lends itself to rapid production. Practically speaking, all the parts which comprise the making of a complete machine can be stamped out of sheet material. The machine shown is completely built with duralumin, with the exception of the wing spars, which are of steel tubing, and a few other minor parts in which it is found that steel is a more suitable material. The fuselage is a metal shell, similar in construction to the wooden monocoque type, and is virtually a streamline duralumin tube suitably stiffened with bulkheads, rings and longitudinals. Where holes are cut in this shell the edge is suitably stiffened by a roll of sheet duralumin. This structure has been thoroughly tested, and has proved of sufficient strength to withstand the necessary tail loads. The planes are built up with steel tubes for spars with lightened sheet duralumin ribs, the covering being sheet aluminum stiffened by small fluting at certain intervals. Ordinary cable wing bracing is used in conjunction with streamline steel struts. The lower section spars pass through bulkheads in 'the fuselage, which spread the load evenly over the fuselage shell. The undercarriage is of the ordinary vee type, sprung with elastic, and fitted with "Oleo" shock absorbers. The struts are streamline steel tube. The construction of the propeller is entirely novel, the body being an aluminium casting faced with duralumin. The engine, a 260 h.p. Siddeley Puma, is mounted on steel tubes held in position by built up duralumin bearers. No wood or fabric has been used, and great care has been taken to avoid all possible risk of fire, a fireproof bulkhead being fitted aft the engine. The machine is a single-seater single-engined tractor biplane, with “two-bay" wings, having been designed to carry mails or light freight to the amount of 400 lbs. If desired, this space could be designed to take two passengers in place of mails.


The Short Machines

   It goes without saying that the Short all-metal machine is not only the most interesting on this stand but the feature of the show. This is the first time in the history of aviation that a British machine built of metal throughout, even to the wing covering, has been exhibited. It is, moreover, the first time an all-Duralumin - or practically so - aeroplane has been built in this country. It is not strictly true that the Short is built entirely of duralumin, as the wing spars are steel tubes and a few fittings here and there where local conditions demand are steel. Otherwise the machine is of duralumin.
   This metal aroused great expectations when it was first brought out. Later certain shortcomings were discovered - or perhaps it would be more correct to call them peculiarities - which led to a general impression of unreliability of the metal for parts which had to resist loads of any magnitude. This impression has, unfortunately, spread to a considerable extent, and many who would have liked to use duralumin have refrained from doing so on the strength of this reputation. As a matter of fact, the metal is perfectly sound, if only it is properly treated, and it is chiefly ignorance which has precluded its more frequent adoption. Messrs. Short Brothers have, as is of course well known, had extensive experience of duralumin as applied to airship construction, and have thus had ample opportunity of learning what duralumin will and will not do, and the best way of treating and utilising it. The experience thus gained has been made full use of in the Short "Swallow" exhibited at the show.
   The fuselage, which is of excellent streamline shape, is built up of a thin shell of sheet duralumin, formed by riveting together small sheets of the metal, bent over and riveted to circular and oval formers. The formers vary in cross-section, but, generally speaking, they are simple L-sections, with box section formers here and there where local strength is required. The sheets of the covering are divided and joined on the top and bottom centre lines of the body, the only other joints being the circumferential joints of adjacent sheets to one another and to the formers.
   The pilot's seat, the flooring and foot rests for his feet, as well as the supports for the seat itself, are made of duralumin, as are also the four cradles supporting the steel tube engine bearers. The whole engine arrangement is extremely neat and free from complications and obstructions of any sort. The engine has in front of it a radiator shaped to fit the contour of the body, making a very neat nose and fore body. It should be added that there is a duralmin bulkhead separating entirely the engine housing from the rest of the machine, so that the danger of fire is reduced to vanishing point.
   Regarded as a biplane truss the wings are of the ordinary type - that is to say, there are two pairs of struts on each side, braced by stranded cables. Constructionally, however, the wings are as interesting as are the other components of this machine. Steel, in the form of tubes, is employed for the main wing spars. On theoretical grounds objections might be raised against the employment of a circular section beam, as giving a less economical distribution of the material. While this is not to be disputed so long as one considers the beam only, it is more than likely that, taking into consideration the simplicity of the internal wing fittings, rib attachments, &c, the whole structure comes out as light as if "I" or box section spars with more complicated fittings had been used.
   The ribs - speaking of the ordinary ribs and not those of special design to meet local requirements - are simply flat sheet duralumin stampings of somewhat greater depth than the actual aerofoil section used. They therefore project about 3/16 in. above and below the section. Flanged lightening holes are stamped in the ribs at intervals to give lighter weight and greater stiffness. The duralumin sheet wing covering is put on in sheets running from leading to trailing edge, where top and bottom coverings are joined. At each rib the covering sheet is flanged upwards and rests against the projecting portion of the ribs. A channel section strip is placed over the rib projection and over the two flanges of the wing covering, the whole being riveted together at intervals of about 3 ins. A support for the wing covering is formed by bending over to a horizontal position the projecting portions of the wing ribs between rivets, the covering resting on these bent portions which form a sort of intermittent flange of the rib. By this design all the riveting is on the outside, a fact which greatly facilitates the assembly of the wing. Also in case of damage to the covering, the damaged sheet can be easily replaced. In order to add to the stiffness of the covering there are two corrugations stamped in the sheets between ribs, dividing the flat portion between the ribs into three narrow strips.
   The lower wings are joined to roots growing out of the fuselage. Incidentally the covering of these wing roots is a very pretty piece of work. The upper plane, which is in two halves, is attached to a cabane consisting of two inverted V's braced fore and aft by a single tube in the plane of the centre line of the body. The ailerons are hinged to brackets on the rear spar, and have a balance portion in front of the hinge. A similar arrangement is found in the elevator and tail plane, while the rudder is balanced in the usual Short fashion by a projection working in a cut-out portion of the vertical fin.
   The under-carriage has tubular struts, with rubber shock absorbers, and in the angle between the struts there is an oleo dashpot formed by a plunger attached to the axle working in a cylinder, as indicated in one of our sketches. It should be pointed out that the machine is all-metal, even to the airscrew, which is in the form of an aluminium casting faced with duralumin. The machine is stated to be actually a little lighter than one of the same size and power built of wood in the ordinary way, and is claimed to be very much stronger, while being better able to resist the influence of varying climatic conditions. Whether or not it is as yet a commercial proposition has been the subject of a good deal of discussion at the Show. The makers claim that, as nearly all the parts can be stamped out of sheet metal, the machine is actually quicker and cheaper to build than a wood machine, and after all they may be presumed to know better than anybody else the number of man-hours which have gone to its making. That the machine is a long step in the right direction cannot for a moment be doubted, and the firm is to be congratulated upon their foresight in tackling what is undoubtedly a difficult problem, but one which must be solved during the next few years.