Flight, July 1939

THE BIGGEST SHORT
Construction of the New Short “G” Class Described : Three 32-Tonners on Order for Imperial Airways

   FOR reasons which are not difficult to understand, the three Short “G” class boats, one of which is already out of the shops and the other two of which will shortly be appearing, are generally considered to have been built for long-range oceanic work - in particular, for the North Atlantic service. These machines, by their very size, are particularly suited tor such work and will probably, in fact, be used for the North Atlantic services next year. But the wish, in this case, has been father to the thought. Regular commercial crossings of the Atlantic have not unnaturally gripped the imagination of the general public, and for what other reason could a very large new type of civil flying-boat be constructed?
   Actually, the "G" class boat may more accurately be considered simply as a logical development of the well-known and successful "C" class Empire boat, which was designed for and is used on the Empire services. In all probability the early flights of Golden Hind, Grenville and Grenadier will be on the regular Empire routes, and only later will they be put on the North Atlantic - and possibly on the South Atlantic British Airways have unofficially stated that they prefer to use flying boats for the crossing between Dakar and Natal, and the "G" class boat is the obvious type for this service when it starts. A fleet of three is not a very large one and would be only sufficient for operating a service over one or other of the Atlantic routes. Presumably, when these three have been proved in service, additional machines will be ordered.
   Although, as will be gathered from the description, the structure of the new boat is very different from that of the "C" class boat, the general layout is more or less similar, and the machine can best be described as a considerably enlarged “C” class boat that should be something like 20 m.p.h. faster. Apart from the structure, the only real change is in the layout of the navigational compartment, which is very much larger and will carry not only a captain, first officer and radio operator, but also an engineer, at his own station, and a navigator. The four civil-rated Bristol Hercules IVC sleeve-valve engines give a maximum of 5,520 h.p. for take-off at 2,800 r.p.m. The normal maximum will be 1,025 h.p. for each engine - or 1,225 h.p. at 6,000ft. for level flight - and the cruising power will be 850 h.p. at 5,000ft. Three-bladed constant speed airscrews are fitted.
   Superficially the new craft might be described as an Empire boat with its dimensions multiplied by 1.15, but actually the differences between the older boats and the new are considerably greater than that. These differences are more pronounced in the hull than in the wing, the most obvious being the introduction of the type of rear step which has been found so successful in the Short Sunderland military boats.
   In connection with this rear step it is interesting to point out that recent overload tests with a smaller boat have indicated that this type of hull will enable very great loads to be taken oft without excessive runs, and in the case of the "G" class boat this means that the gross weight could well have been a great deal higher than the 73,500 lb. for which the first three machines were stressed. At the time when the machine was designed, however, these overload tests had not been made, and the data available did not justify designing for a greater take-off weight. If more "G" class boats are ordered later, they could, presumably, be strengthened for a greater gross weight, just as the Empire boats were strengthened to a gross weight of 53,000 lb. instead of the original 40,500 lb.
   But even at a gross weight of 73,500 lb. the “G” class boat is very efficient from a structural point of view, as will be realised when it is pointed out that when the first of the “G” class boats, the Golden Hind, was weighed recently it tipped the scales at 38,900 lb. This was, of course, the weight bare, and with a gross weight of 73,500 lb. gives a ratio of gross weight to tare weight of 1.8, a figure well above the average, which means that the machine carries as disposable load 85 per cent, of its own weight. If one takes a large number of aircraft of all types, large and small, a fair average figure is 60 percent, so that in spite of the size of the Golden Hind the structural efficiency appears to be remarkably high. It would seem that the Short engineers have cheated the old "cube law" with a vengeance.
   It is now many years since Mr. Arthur Gouge stated in a lecture that he did not see why the structure weight of large flying boats should necessarily be prohibitive, one of the reasons being that hull weight does not increase with size at the same rate as the wing weight, for instance. In the "G" class boat the wing loading is, of course, relatively high (approximately 34 Ib./sq. ft.), but by no means excessively so, and this has obviously helped in keeping down the structure weight.
   When one inspects the "G" class boats internally, and especially when one has seen them on the stocks, as Flight's representatives had an opportunity to do, it is discovered that tire increase in size has made possible certain changes in structural design which must have had their effect on the good ratio of gross to tare weight. Briefly stated, these changes mostly take the form of using extruded sections in place of the bent-up sheet and strip sections employed in the keel and frames of the Empire boats.

Extruded Members
   The keelson, which was a built-up channel-section member in the Empire boats is now an extrusion of what can only be described briefly as an "anchor" section. The stringers, too, are extrusions, the sections being a “T” with a bulbous edge to the vertical limb of the T. One side of the bulb is flattened to facilitate the attachment of sheet webs where such are wanted. In the planing bottom, that is to say, between keelson and chines, the hull frames are made up of plain T-section extrusions and flat sheet. Above the chines, and in the rest of the hull, the frames are of channel section, made up from sheet and strip.
   An unusual feature of the hull design of the "G" class boat is that in the planing bottom the hull frames do not touch the skin, but finish inside the edges of the stringers, to which they are attached by simple angle brackets. This is boat-building practice applied to a large metal hull, and as such is worthy of note. One result is, of course, that when the skin panels curve inwards slightly under loads, as they must do where the loads are fairly high, such as on the planing bottom, no transverse ridges are formed, but only slight fore-and-aft ones, which probably have no effect on water resistance.
   It should be explained here that the T-section extrusion with bulbous "foot" is used in the planing bottom only. Above the chines, and in the rest of the hull, the stringers are extrusions of Z-section, notched for the frames. The planking is in fairly large panels, the edges being joggled for smoothness and flush-riveting being employed everywhere.
   It is obvious that when, as in the. "G" class boat, the stringers only, and not the frames, are in contact with, and attached to, the skin, a certain amount of stabilising of the stringers is lost. In the Golden Hind this is made up for by riveting to the inside (i.e., free) edges of the stringers light strips of shallow channel section. These strips are little more than metal tapes, and are, in fact, used very much in the same way and for the same purpose as the linen tape used to be employed for stabilising the ribs in biplane wings. As far as possible this stabilising strip, which is used at about 6in. intervals, is in continuous lengths and is often taken around corners and bends.
   Of the wing structure it seems only necessary to state that it is similar in general construction to that of the Empire class, so that it will suffice if we recall that the main spar is a box made of corner strips of extruded T-section (the limbs being nearly an inch thick), with tubular girder bracing in the two vertical planes and box ribs with sheet metal covering for the bottom and ”lid” of the box. The trailing edge is of tubular construction, and the whole wing covered with sheet. Gouge-type flaps similar to those of the Empire boats are used, and the four engines are placed in the same relative positions, with "cheese"-shaped petrol tanks in stalled in the wings. There is no fuel in the hull, even when the machine is used for maximum range.
   Short Brothers were the first to introduce the low setting of the out board floats, so that at only a small angle of roll one or other is in contact with the water. This was tested in Maia, where the high position of the centre of gravity caused by the presence of Mercury on top made large angles of heel undesirable. The arrangement proved very successful and has now become a standard feature of all Short boats. It used to be feared that this low setting of the outboard floats might cause the machine to swerve when on the water, but this has not been found to be the case. In the “G” class boats the floats are placed proportionately farther out towards the wing tips than they were in the Empire boats.
   By way of indicating the enormous progress made in flying-boat design during the last ten years it is not without interest to recall that the Short Sarafand, designed to Air Ministry specification R.6/28, was ot 70,000 lb. gross weight and had a wing area of 3,460 sq. ft. (i.e., a wing loading of 20 lb./sq.ft.). With its six Rolls-Royce engines it had a maximum speed of 150 m.p.h. and its range at a cruising speed of 105 m.p.h. was 1,450 miles in still air. The Golden Hind will cruise at approximately 180 m.p.h. and will have, a still-air range of something like 3,406 miles when fitted up for mail-carrying over the Atlantic. If all the disposable load were in the form of fuel it is thought that the maximum range would be not far short of 6,000 miles.
   The only respect in which the Sarafand scored over the Golden Hind was in the take-off. With its much lower wing loading it required a good deal shorter run, although improvements in hull design have largely redressed the balance in the case of the new boats. And with its four Hercules engines giving 1,380 h.p. for take-off, not to mention controllable-pitch constant-speed airscrews, the thrust horse-power available is a much greater percentage of the normal total power than it was in the old six-engined biplane.
   With a machine of this size it is possible to arrange the navigation compartment to provide really ample room for all members of the crew and to organise a correct dispensation of duties. The modern machine, whether civil or military, requires the attentions of a fairly large crew, each member of which must be something of a specialist.
   The “G” class boat will be the first British machine, for instance, to have a separate section for the engineer, who will look after all the incidental engine instruments and controls, and will be in charge of the fuel system, the carburettor heater, arrangements and the cooling shutter controls. Apart from the captain and first officer the other members of the crew will normally consist of a radio operator and a navigator.
   The layout of the "flight deck" is basically similar to that of the “C” class boat, but this “deck” is obviously a great deal roomier and is modified in certain details. On the left, looking forward from the rear of the compartment, there is a partition which effectively covers the control and electrical leads, as well as the auxiliary engine and dynamo system used for emergency battery-recharging. This partition, through which the auxiliaries can be reached by means of a door, has two “desks,” one for the flight engineer and one for the radio operator.
   Behind the flight engineer’s desk there is a panel carrying r.p.m. indicators, manifold pressure gauges, engine and oil temperature gauges, and mixture analysers, while on the desk itself are mixture control levers in their gates, as well as rotating knobs, four on each side, for the fine adjustment of the throttles and the airscrew pitch.
   The engineer also looks after the main fuel cocks, and oil and engine cooler controls which are on the rear bulkhead of the control cabin. In the centre are eight vertically moving levers, six of which control the fuel cocks for the three wing tanks on each side, and two the draining tap and the feed balance for the collector boxes respectively. On either side of these central control levers are lateral moving levers, two on each side, to adjust the engine oil coolers, and control wheels for adjusting tire main cooling shutters and for fuel feed balance testing.

Fuel Supplies
   Incidentally, the fuel system is somewhat complicated by the fact that any one of the six tanks must be able to feed all or any of the four engines. There are two fuel distributor centres. On the rear bulkhead are the four Televel gauges for measuring the fuel supply in each tank, both when the machine is in level cruising attitude and when it is on the water. In all, the six flat cylindrical tanks can carry a maximum of about 3,600 gallons, giving a range, with minimum load, of about 3,200 miles. The first boat. Golden Hind, will be a special long-range type in which the entire tankage will be used; the second machine, Grenadier, will be a medium-range type capable of 2,000 miles non-stop carrying twelve passengers and mail; and the third, Grenville, will be a comparatively short-range machine to carry twenty-four passengers and mail over a distance of 1,000 miles. Any one of them could fly something like 6,000 miles non-stop, or, alternatively, carry some 150 passengers on a short run.
   The two sides of the recess carrying the radio operator’s “desk” are designed to take the receiving and transmitting equipment, leaving only the essential dials and controls in view. The whole of this partition, with the alcoves, is quite one of the neatest installations of the kind which we have seen.
   The navigator’s position, again looking forward, is on the right of the machine opposite the radio operator’s station. He will have ample light and space for his work, and almost immediately above him is the hatch through which a retractable dome emerges. When celestial sights are required, this dome is merely raised, and the navigator, while standing on the floor of his compartment, can take them in comfort.
   When not at the controls, the captain takes a position immediately behind the first pilot's seat, where there is a little table for his use. In front of him is a window with optically corrected glass so that he himself may take sextant sights, either as a check on those obtained by the navigator or for practice. Except for those used by the pilots, all the seats are of the swivelling type.
   The control and instrument layout in the pilots' compartment have been arranged so that crews experienced with the Empire boat shall notice no great change. The instrument placing is identical, and, as far as possible, the engine and trimming controls are similarly arranged.
   Various items have, however, been tidied up; the engine control bank is somewhat more neatly arranged, though the throttle, mixture and airscrew controls are still in the same relative positions. On the pilot's left is the complete lighting control panel, and the various trimming cranks are arranged in the roof in such a way that they can be reached from either seat, with the Gouge flap control and its indicator on a panel to the left.
   Electrical equipment in a craft of this size must be comprehensive, and Rotax are responsible for the greater part. In addition to such major items as magnetos - eight, of course - starters (four) and generators (two) there are a wing-flap operating motor, radio converter, Rotax-Eclipse airscrew ant-icing pump, Rotax-Harley landing lights, and Rotax-Weston cylinder pyrometers. In addition, this firm is responsible for the general lighting equipment.

Span 134ft. 4in. (41 m.)
Length 103ft. 2in. (31.4 m.)
Wing area 2,160 sq. ft. (201 sq. m.)
Weight empty (equipped) 37,700 lb. (17,100 kg.)
Crew 1,000 lb. (454 kg.)
Fuel and oil (long-range version) 28,000 lb. (12,727 kg.)
Payload 4,250 lb. (1,927 kg.)
All-up weight 73,500 lb. (33,340 kg.)
Wing loading 34 Ib./sq. ft. (166 kg./sq. m.)
Power loading 13.3 Ib./b.h.p. (6 kg./h.p.)
Maximum speed 209 m.p.h. (337 km./hr.)
Cruising speed (70 per cent, power at 5,000 ft.) 180 m.p.h. (290 km./hr.)
Maximum range 3,200 miles (5,150 km.)
Makers Short Bros. (Rochester and Bedford), Ltd., Rochester, Kent.

Flight, November 1939

Britain's Civil Aircraft

SHORT

   Later and larger than these machines are the "G" class boats which have four Bristol Hercules IVC engines giving a maximum combined take-off output of 5,520 h.p. The ”G” boat measures 134ft. 4in. in span and weighs 73,500 lb., the weight empty (equipped) being 37,700 lb. On 70 percent, power the cruising speed is 180 m.p.h., the maximum attainable being 209 m.p.h. In general design the machine resembles the earlier Short commercial machines. Apart from the structure the only real change is in the layout of the navigational compartment, which is very much larger and will carry not only a captain, first officer and radio operator, but an engineer, at his own station, and a navigator. This compartment should be of great value on flights of over 3,000 miles which can he easily undertaken by the “G” class boat.
   Before the war the company had under construction three large commercial landplanes, with Bristol Hercules engines. One of these was to operate at more or less normal heights and the other was to have a pressure cabin for high-altitude work. At 25,000ft. a cruising speed of 275 m.p.h. was anticipated.

Short Bros. (Rochester and Bedford). Ltd., Rochester, Kent.