Flight, April 1924

THE SHORT ALL-METAL LIGHT FLYING BOAT
Two 696 c.c. Blackburne Engines

   IN many ways one of the most remarkable machines of modern times is the little all-metal flying boat now nearing completion at the Rochester works of Short Bros. To begin with, the machine is built entirely of metal (with the exception of the wing covering), and the material mainly used in the construction is duralumin. This, in itself, stamps the machine as being out of the ordinary, as this material has not hitherto been used to any great extent in the construction of aeroplanes. Its application to the construction of a flying boat hull is another innovation in the history of British aviation, and in the Short machine this metal is used both for the framework and for the covering of the hull. Then there is the fact that the machine under review is the first light seaplane to be built in this country, and probably in the world. Not only so, but the twin-engined arrangement familiar from, larger boats has been adopted, although the machine is a monoplane - yet another innovation, at any rate in modern times. It will thus be seen that there is no lack of interest in the light flying boat which, through the courtesy of Short Bros., we were permitted to examine recently, and which forms the subject of the present article
   Before commencing a description of the Short all-metal light flying boat, it will be as well to recall briefly the stages in the development which preceded the construction of the present machine. To begin with, it will be remembered that Short Bros, constructed rigid airships during the War, and that they, therefore, have had considerable experience in duralumin construction. Then, at the Aero Show at Olympia in 1920, they exhibited a biplane two-seater with Siddeley "Puma" engine. This machine, the "Silver Streak," was built entirely of metal, mainly of duralumin, but with steel tube wing spars. Even the wing covering was of duralumin, applied in a very ingenious fashion evolved and patented by Short Bros. The fuselage construction was of simple form, and a feature of it was that the sheet duralumin covering was made to take its share of the stresses set up in the structure. Briefly the principle employed was that the shape, or rather cross-section, of the fuselage was provided by the formers, to which the covering was riveted. The "Silver Streak" was generally admired at the Show, and was recognised as marking a distinct step forward Incidentally the machine was the first all-metal aeroplane to be designed and built in England.
   In modern times the "Silver Streak" has been followed by a later development, the Short "Springbok," in which many of the constructional features of the "Silver Streak" have been retained, while others, notably in the wing construction, have been altered to meet Air Ministry requirements. From the foregoing it will be seen that Short Bros, have done a great deal of pioneer work in this particular form of construction, and it is gratifying to be able to record that the successes attained are being recognised by the Air Ministry, who have for some time been following closely the progress made, and who have now sanctioned the construction of further machines incorporating the special form of metal construction evolved at Rochester. There is thus good cause to think that in this matter of duralumin construction this country will soon take a leading place, as it has already done in steel construction, and that the pioneer work done by Short Bros, will reap the reward it deserves.
   In the meantime the light flying boat which forms the subject of this article should serve as a very good full-scale experiment into the possibilities of the low-power seaplane, as well as demonstrating the merits of the particular form of construction adopted. The way in which this machine came to be built is rather interesting, and a brief reference to its inception may be made here. Two or three years ago a wealthy Australian, Mr. Lebbeus Hordern, purchased from Short Bros, a converted "F.5" flying boat with two Rolls-Royce "Eagle" engines. This machine, photographs of which are published elsewhere in this issue of FLIGHT, was provided with a roomy cabin in which passengers could travel in comfort, and we understand that the machine gave excellent results, and was used quite a good deal out in Australia. Having become interested in the light 'plane type of machine, but desiring a seaplane, and more particularly a flying boat, Mr. Hordern asked Short Bros, if they could supply a twin-engined light 'plane flying boat. Mr. Oswald Short cabled a reply in the affirmative, and after further negotiations the work of designing and building was put in hand. The result is the machine shown in the accompanying scale drawings and photographs.
   The Short light flying boat is a monoplane with thin wing section (R.A.F.15, to be precise), braced by short struts to the hull. The two Blackburne engines are similar to those which did so well at Lympne last year, and are mounted on the wings, each with its streamline cowling behind it. As the engines are mounted fairly far back on the wing, extension shafts have been fitted so as to bring the two tractor screws forward to the leading edge. The propeller shafts are merely extension shafts, as there is no reduction gearing and the propellers run at engine speed. While on the subject of the disposition of the power plant and propellers it is interesting to compare the Short monoplane with the small Dornier "Libelle." Both machines are built of duralumin, but here the similarity ceases, the general designs being quite dissimilar while the detail construction has but few points in common. In the Dornier a small Siemens radial engine is mounted on the centre-section of the front spar, and drives a single tractor screw. In order to get the necessary propeller clearance, and to keep the centre of resistance in reasonable proximity to the centre of thrust, the monoplane wing of the Dornier is raised a considerable distance above the hull, the occupants sitting, in fact, underneath the wing. In the Short machine, on the other hand, the wing is resting immediately on the boat hull, and the two engines are moved out on the wing. Thus the centre of thrust and the centre of resistance are both lower than in the Dornier, while the distance over propeller centres is only about 6 ft. Thus, should one engine stop, the turning moment will probably not be so great but what the rudder can take care of it, although with but one engine running the power loading will naturally be very high, and the machine probably only just able to fly level. Carrying the comparison farther, whereas in the Dornier short "wing roots" growing out from the sides of the hull are used for maintaining lateral stability on the water, in the Short boat wing tip floats of usual shape are employed. Again, the Dornier hull is of approximately rectangular section, while the Short boat has a pronounced "tumble-home" in front, running into a rounded section aft. It is of interest to compare the two machines, because the German flying boat carries two people with an engine of about 55 h.p., while the two Blackburne engines of the Short will probably develop something like 40 h.p. between them, and carry pilot only. Thus both machines represent very economical flying as regards power expenditure, however much they differ otherwise.
   The hull of the Short light flying boat is of a construction very similar to that first introduced in the "Silver Streak" - that is to say, the frames and "timbers" are rings of duralumin, of L-section, to which are riveted the plates of the covering. The longitudinal stringers do not run through, but merely serve as stiffeners between rings. In the forward portion the plain rings receive the addition of a built-up plate conforming to the transverse shape of the steps or planing bottoms, which latter, as in wood construction, are separate structures and open at the rear so that water can run out when the machine is in the air. The structure inside the hull is entirely confined to these rings, and the whole makes one of the most astonishingly simple structures we have ever seen. The simplicity and "clean" appearance are, perhaps, the most marked features of the design.
   Rings of rather heavier construction are used where external components are attached, as, for instance, where the main planes and tail planes are attached, but even this addition is taken care of without spoiling the simplicity. The space inside the hull is entirely unobstructed, the formers projecting inward from the skin only a couple of inches or less, and there being no other structural members.
   The pilot's cockpit is in the extreme nose, and consequently he obtains an excellent view forward. In addition to the usual controls, engine controls, etc., with which the machine is provided, there is a starting lever, or rather two - one for each engine. These levers, except for the fact that they are operated by the hands, act exactly like a kick-starter on a motor-bicycle. At the time of our visit to the works the arrangement was being tested on the bench, and it was found quite easy to start the Blackburne engine by this means. Thus, on the little flying boat the pilot should be able to start his engines without assistance, a fact that might well be of the utmost importance on a cruise.
   While speaking of the boat hull of this machine it should be mentioned that when the hull was finished it was taken out on the water, a load of about 800 lbs. was put on board, and the hull was left for 24 hours. At the end of that time it was found that literally only an egg-cup full of water had leaked in. The question of water-tightness is, therefore, not apparently a difficult one to solve in metal construction. This in spite of the fact that, unlike Dornier practice, no fabric is used in the seams of the Short boat. How a hull built in this manner will behave after extensive use, with a few bumpy landings, etc., still remains to be seen, but there seems to be very good reason to believe that the duralumin hull will be at least equal to the wooden hull in this respect. Where the metal hull undoubtedly does score is in the total absence of water soakage. We believe that in the case of a large flying boat the amount of water that soaked into the hull amounted to no less than 600 lbs. It will thus be seen that for a boat that is to spend most of its time moored on the water this question of soakage is of the utmost importance, and this fact alone should entitle the all-metal hull to very careful consideration.
   The wings of the Short light flying boat are also of metal, the spars being of corrugated sheet construction and the ribs simple channel sections with lightening holes cut in them. The covering will, however, be fabric doped in the usual way. The two wing halves are bolted to the top of the hull, and are, as already mentioned, braced by two struts on each side. The ailerons are of large area, running the whole length of the wing and being of fairly large chord. They are operated by cranks on the inner ends of the aileron tubes by rods running vertically down into the interior of the hull.
   The tail surfaces are of normal shape, and are built of metal tube spars with channel section sheet ribs. The covering is fabric.
   To facilitate handling ashore a pair of large-diameter wheels are supplied with the machine. These are carried on an axle which can be pushed into a tube running across the hull in line with and slightly above the main step. Thus one man should be able to handle the machine with ease. For flying the wheels are, of course, unshipped and left behind, or may be carried inside the hull if the user expects to need handling the machine ashore on his journeys.
   The Short light flying boat is of more than ordinary interest, and when the flying tests, etc., take place shortly we hope to be able to publish photographs and a report of the trials.
   The main dimensions, etc., are shown on the general arrangement drawings. The total loaded weight is expected to be between 800 and 900 lbs., and the speed (estimated) is about 68 m.p.h., with the engines running at 2,500 r.p.m. The two-bladed propellers are of 4 ft. 3 ins. diameter, and run at engine speed. Assuming a total loaded weight of 850 lbs. the wing loading becomes 4-34 lbs./sq. ft., and if the total horse-power is assumed to be 40 b.h.p. the power loading will be 21-25 lbs./h.p. Thus the power loading is by no means exceptionally high, and judged solely on power loading the machine should be able to fly level on one engine, i.e., with a power loading of 42-5 lbs./h.p., especially as the design is a very "clean" one.