THE TREND OF DESIGN

AIR.

THE TREND OF DESIGN

HOW MANUFACTURERS ARE BREAKING NEW GROUND IN AIRCRAFT CONSTRUCTION.

AT no time in the history of aviation have there been so many new ideas in process of development as nowadays. Inventors and designers both in this country and abroad are working along original and varied lines to bring about an increase in safety, greater economy in production costs, running and maintenance charges, and with all these, improvements in general performance.

Those designs which have already reached a practical form have been proved to possess characteristics of definite value, and it seems reasonable to suppose that before many years have passed the more successful productions will have a marked influence in the trend of design of aircraft in general. There is the Autogiro, for example. This highlyunconventional aeroplane is now being built on a production basis. And within a few weeks of its having been placed on the market the Autogiro Company have received a numbet of orders from private individuals in England, on the Continent and even further afield. In addition to this, it has received the “hail mark” of the Air Ministry in having been granted a Certificate of Airworthiness which permits the machine to be used as a ” commercial aircraft” for hire or reward.

This fact is significant because the standards set down by the A.I.D. are easily the most stringent in the world ; before any new aeroplane is granted a certificate, a tremendous amount of calculations have to be gone into, the man-ufacturers’ figures and drawings are checked, and the completed machine is tested over and over again by R.A.F. pilots at Martlesham. If it emerges successfully from its trials it can be taken for granted that there is not much wrong with it.

The Autogiro, however, is not the only newcomer with fresh standards and principles to break into the conventional circle of modern aviation. At Croydon aerodrome General Aircraft Ltd., are busily engaged in building a batch of Monospar monoplanes. These are not experimental machines ; they represent the first issue of a type which without doubt will compel considerable attention as soon as they are put into regular operation. The designer of the Monospar is Mr. Stieger, a Swiss engineer who has been closely associated with the British aircraft industry for several years. At one time he was with the Beardmore Company, and it was while with this concern that he conceived the principle which is embodied in this new machine—the single-spar arrangement of wing

construction. His aim was to produce a cantilever wing of much lower structural weight than that of the orthodox type. In the opinion of many, the monoplane will ultimately wholly supersede the biplane on account of its cleaner exterior and absence of drag-producing excrescences, which makes greater speeds possible. But it has one disadvantage; its structural weight is high.

With the Monospar, however, the system of construction gives the added attraction of a very considerable lightness, while the troubles, which were met with in earlier attempts at making single-spar planes, of lack of rigidity in torsion and poor safety factors, have been completely overcome. The Monospar system consists of a single main member which is strong in bending and which is braced against torsion by an arrangement of struts and ties. The struts take the form of cross-members and are made either as ribs or tubes, and the ends of these are used as the apices of pyramids of tie-rods which run from the top and lower flanges of the spar. These pyramids are disposed along the spar at suitable intervals, and extra members are fitted to deal with the drag and antidrag loads. Mr. Stieger’s early

experimental wings were const ructe d with wooden spars, but the latest type is wholly metal, a n d the assembly has been considerably simplified. The ST.4, as the new Monospar is called,

has its fuselage constructed on the same principle as that of the wings, with a single girder, an arrangement of torsion bracing, and stringers and formers to which the covering is attached. It is a fourseater twin-engined cabin machine, and when it is stated that the tare weight is only 1,250 lb., it will be realised that Mr. Stieger’s system of construction offers very remarkable possibilities in the building of aircraft of low structure weight. These two aircraft form striking examples of the recent evolution to practical form of machines of really original design. Each has been produced with a very definite object in view— the Autogiro as a ” safety ” aeroplane, the Monospar as a craft of high performance and low power. For a great number of years manufacturers have been seeking to improve the controllability of aircraft by overcoming the stall, and introducing features which allow of lower speeds at which manoeuvribility is possible. Research is continually

going on in the matter of wing sections, arrangement of controlling surfaces and so forth, and investigations and theories have resulted in the bringing forth of interesting designs. The Westland Company are working on a tailless monoplane which is based on the Pterodactyl machine which was demonstrated for the first time publicly some years ago. Originally designed and built by Captain Hill, this strange looking machine had a remarkable speed range and an exceptional control at and below stalling speed. The first type was fitted with a 32 h.p. Bristol “Cherub “engine, and a subsequent type in which sundry improvements were made was powered with a Siddeley “Genet.” They thus came in the light ‘plane category. The latest model, which is here illustrated, has a 1/II. ” Gipsy” engine and has much cleaner lines than its prototypes. The tailless type of aeroplane is being favoured quite a deal abroad, especially in Germany where there are now several versions flying and under test. Their evolution, it is interesting to note, has been aided in most cases by preliminary experiments carried out with en gineless models at t and there are of es which appeared first as sailplanes, and which have afterwards been fitted with engines. One such craft is the Hermann Kohl, a cantilever monoplane of 43 feet span. It has a Bristol ” Cherub ” engine driving a pusher propeller, installed behind the pilot’s cockpit. The wings are unique both as regards section and plan contours, the latter being those of an equilaterial triangle. The trailing edge on each side has two hinged surfaces, the outer acting as ailerons, and the inner formed as elevators. To the wing tips are attached vertical fins with normal type rudders. The cockpits are entirely enclosed with the upper fairing continued back to the engine, while the three-wheeled undercarriage is completely faired in. The machine as a whole, thus presents an extraordinarily clean if peculiar appearance. The Hermann Kohl is only one of several of these tailless aeroplanes ; there are others in Germany, France and America. The

latter country has always been prolific as regards new types, and while many of them are freakish, some of them (generally those which bear the stamp of German influence) are highly interesting and are, from all accounts, of promising design. Striking as the advance has been in revolutionary designs of aircraft, the progress which is being made in aero engines is none the less marked. From being unreliable, extravagant, and poor as regards power-weight ratio, the aero power unit has now become phenomenally dependable, and efficient. The last few years has seen a steady rise in power output with a corresponding increase in reliability, and we are now getting to the stage where the heavy-oil engine can be accepted as a practical proposition. The Beardmore Company have done much in this direction so far as British developments are concerned, while two years ago the Packard concern in the U.S.A. produced a Diesel type which gave highly encouraging results. The

Packard engine is a nine-cylinder, air-cooled radial, and is rated at 225 b.h.p. It weighs 510 lbs., which thus gives 2.26 lb. per horse power— a remarkable figure for a heavy-oil engine. In Italy also the Diesel type is being worked upon, notably by the Fiat Company, and definite progress is being made. It is sometimes said that there is a tendency towards stagnation in modern aircraft design. How far from the truth is such an opinion is made

obvious from the foregoing. We are undoubtedly nearing a fresh phase in aviation when it may well be that the aeroplane as we know it to-day will be swept aside, and craft such as those which are just emerging from the drawing-board and experimental stage will take its place. What type will eventually predominate, and in turn become commonplace ? Perhaps in the next five years the trend will be made clear.