Flight, June 1930

THE VICKERS "VIASTRA"
New High-Performance Monoplane

   SOME time ago we announced that West Australian Airways, Ltd., has on order from Vickers (Aviation), Ltd., some machines of a new type, to be known as the "Viastra." These machines are to have an unusually high performance (cruising speed in the neighbourhood of 140 m.p.h.), and a power reserve sufficient to reduce to vanishing point the likelihood of forced landings. It has now become permissible to publish a brief outline of the general design of the new machine, the fuselage of which is illustrated in the accompanying sketches.
   The "Viastra," designed by the Vickers Weybridge staff, is being built at the Supermarine works at Woolston, and will be an all-metal machine, even to the covering of wings and fuselage, in which Duralumin plate is used. The machine is, as the small front elevation shows, a high-wing cabin monoplane. The design has been so planned that the machine can be supplied and used either as a single-engined machine, as a twin-engined or as a three-engined. Furthermore, two distinct types of undercarriage can be provided, a land undercarriage and a twin-float undercarriage. The "Viastra" should thus be extremely adaptable, and in one of its various forms should conform to the particular requirements of almost any operating company. At first sight it may appear somewhat surprising that one and the same machine should be capable of being fitted up for either one, two or three engines, but it should be recollected that with the three-engined arrangement, for instance, the wing loading will be largely increased, but the power loading will be decreased, and the number of engines will reduce the chances of a forced landing, so that the higher wing loading, and resulting higher landing speed, can be tolerated because one is justified in assuming that the machine will only have to alight on a prepared aerodrome. With one engine, on the other hand, the wing loading will be smaller, and the machine should be easier to land in an emergency.
   The "Viastra" is being constructed very largely of Duralumin, in the form of sections of various shapes for the framework, and in sheet form for the covering.
   The forward portion of the fuselage has a frame of Duralumin sections, and is covered with Duralumin plate, a sound-deadening stuffing being used to reduce noise in the cabin. The rear portion of the fuselage also has a Duralumin structure and covering, but not, of course, the stuffing.
   The monoplane wing has Duralumin spars and ribs and Duralumin plate covering. The wing bracing struts are, however, of steel, and are faired to a streamline section.
   The land undercarriage incorporates Vickers' oleo-pneumatic telescopic legs and Dunlop wheels, and Vickers' hydraulic brakes are fitted. These can be operated independently to facilitate manoeuvring on the ground.
   The lay-out of the passenger accommodation may be seen in the sketches. There are two rows of seats, one along each side, of six each side, giving a total passenger capacity of 12. The pilots' cockpit is in front of the cabin and wing, and should give a very good view in the essential directions. Dual controls are provided, and the two seats are placed side by side in the cockpit. Heating of the cabin can be either by electricity or from the exhaust. A novel system of ventilation will be employed, by which the windows in the sides of the cabin remain closed, thereby helping to keep out the noise of the engines. The cabin volume is no less than 640 cu. ft., while the lavatory, aft of the cabin, has a volume of 84 cu. ft. There are two luggage holds, each of 100 cu. ft. capacity.
   Should the machine be required as a fast freight carrier, the chairs can easily be removed and the large hold used for freight and goods.
   The petrol system is of the simple gravity-feed type, with two aluminium tanks placed in the outer wings. All pipe couplings will be of the screwed metal-to-metal type.
   The seaplane chassis will consist of two Duralumin floats supported on a framework of steel tubes. Owing to the wide track the machine should have excellent lateral stability both on the ground and on the water.
   Details of the power plant are not yet available, but the machine may obviously be fitted with almost any type of engines of suitable power. The drawings show radial air-cooled engines, of which several makes and ranges are now available. West Australian Airways use "Jupiters," and it may be assumed that the machines to be sent out to Australia will be fitted with engines of this type.

Flight, September 1930

VICKERS "VIASTRA I"
Three Armstrong Siddeley Geared "Lynx" Engines

   FOR several years it has been universally accepted that in order to secure immunity from forced landings the power plant of an aircraft should be divided into at least three individual units. Mathematicians have proved, at least to their own satisfaction, that with such an engine arrangement and a certain power reserve enabling the machine to fly on any two engines, forced landings should not occur. There is, however, a tendency nowadays rather to doubt the validity of this argument, and to advance as a counter to it that when one engine of a three-engined machine fails, the other two have to be run so nearly full out that they, in turn, are liable to break down. And it is sometimes pointed out that with the same percentage of power reserve, or perhaps a very slightly greater, the single-engine installation could, for the same weight, be made so reliable that it would be quite as free from forced landings as the three-engined.
   The argument does not really appear any nearer to being settled than it was several years ago, and in support of the single-engined power-plant system its advocates may point to the fact that the world's long-distance records have been established by single-engined machines. The whole problem being still very much open to discussion, and operational conditions, and consequently operators' requirements, differing materially according to the route operated, anything which can be done definitely to settle the vexed question, single or multi-engined aircraft, must be heartily welcomed. It is safe to say that nothing in modern times has promised to contribute so much towards a solution as the new " Viastra," recently finished by Vickers at the Supermarine works at Southampton. This machine, a brief illustrated description of which appeared in FLIGHT of June 27, 1930, has been very cleverly designed not only to take a wide variety of power plants, but to use these either in single units, in two units, or in three. Furthermore, the machine will shortly be available either as a landplane or as a twin-float seaplane. It would be difficult to imagine a simpler way of obtaining direct practical comparisons on the subject of power-plant installations. It might have been thought that to achieve this versatility the designers would have to make so many compromises that in one or other of its forms the machine would suffer from some drawback or other, either in performance or pay load. We have been privileged to examine the detail performance and weight estimates of the machine in a number of alternative forms, and in all cases both pay load and performance appear to be not only up to the average, but in many cases well above it.
   The first "Viastra" to be finished at Southampton and to undergo preliminary tests at Hamble before going to Weybridge for more exhaustive trials, is a three-engined machine fitted with Armstrong Siddeley geared "Lynx" engines. This machine, known as the Vickers Lynx Viastra I, has a tare weight (equipped) of 6,980 lb. (3,170 kg.) and a gross weight of 10,650 lb. (4,840 kg.), so that the ratio of gross to tare weight is 1-527; or, in other words, the machine carries as disposable load 52-7 per cent, of its tare weight. This is a, good figure for a three-engined monoplane of high performance (cruising speed 120 m.p.h.). It is true that some years ago the Vickers designers produced a machine with an even better ratio, the "Vellore," but that machine was a single-engined biplane with relatively low performance and very low wing loading.
   Taking the geared "Lynx" engine at 235 h.p. maximum, the disposable load of 3,670 lb. represents 5-2 lb./h.p., which must be regarded as a very economical figure for a machine with such a high cruising speed. The proportion of pay load to fuel load - or, in other words, range - can, obviously, be chosen to suit the requirements of the particular route on which it is intended to use the machine. With fuel for 300 miles at cruising speed (two-thirds power) the pay load (i.e., disposable load over and above weight of fuel crew, etc.) is 2,460 lb., or 3 1/2 lb. per horsepower (on maximum power). This range roughly corresponds to the London-Paris route with which most people are familiar, and thus gives a very good idea of the operational economy of the "Viastra I.”
   In aerodynamic design the "Viastra I" does not at first glance look very much out of the ordinary. It is a braced high-wing monoplane with wings of rectangular plan form and constant section. In view of the fact, however, that performance estimates indicate that a top speed of about 140 m.p.h. may be attained, the drag of the machine must be low. For example, assuming the estimated maximum speed of 140 m.p.h. to be attained, the Everling "high-speed figure" works out at 19-6, which is exceptionally good for a three-engined machine. It is to be assumed that the drag reduction resulting from fitting the engines with Townend rings has been taken into account in estimating the performance, and the effect of this reduction is presumably considerable, otherwise it is a little difficult to account for the low drag.
   It is, perhaps, from a structural point of view that the "Viastra I" is most interesting. Designed to have a good ratio of gross to tare weight - or, in other words, a low structure weight, cheapness of production has been kept prominently in view, as well as a minimum of upkeep cost. The fundamental principle adopted in the structural design is that the skin or covering must take its part in the work of sustaining the loads. It will be recollected that some years ago Vickers Limited acquired the British rights for using the Wibault patented forms of construction, and that several machines were built closely resembling the original French design. Since then, however, Vickers have expanded and improved the Wibault system a good deal, and in the "Viastra” may be said to be incorporated the latest experience of the firm in truly all-metal construction.
   The fuselage of the "Viastra I" incorporates a skeleton framework strong enough to carry its load, but needing the support of the metal skin to stabilise it. In a general way it may be said that the system consists in using Duralumin longerons of angle section, braced by vertical and diagonal Duralumin members of angle section, T section and channel section, according to local loads and stresses. Riveted to this framework is a Duralumin skin, put on in vertical strips having fore and aft corrugations for stiffening purposes. The production of these corrugated strips has been reduced to a very simple operation at the Vickers works, and the system helps very materially in cutting down the cost of production of the machine.
   The floor of the cabin, etc., portion of the fuselage is strengthened by transverse floor bearers projecting downwards from the main fuselage structure. These bearers consist of top and bottom channels joined by a "wandering web" of a type similar to that used in the wing spars. The external covering, of corrugated Duralumin, is then riveted to the bottom of these floor bearers.
   With the exception of the metal covering, and the difference in wing rib construction resulting therefrom, the wing construction of the "Viastra I" follows fairly closely that of previous Vickers machines. The system of wing construction has already been fairly fully described in FLIGHT (see issue of September 15, 1927), and it will suffice if we here confine ourselves to a brief summary of the features.
   The main wing spars have flanges of flat Duralumin strip, laminations being added as and where local stresses demand. These flange strips are riveted near their edges to angle section corner strips, and the "wandering web," i.e., a web of strip Duralumin which runs in zig-zag from front to rear face of the spar. By the fact that the web crosses in this manner, it forms diagonal diaphragms between the top and bottom flanges, and diaphragms of the ordinary type become superfluous. This type of spar has been found to give very good results from a strength/weight point of view, and is relatively very cheap to manufacture.
   The wing covering in the "Viastra I" is in the form of Duralumin panels of standard width, corrugated in a fore and aft direction, and with the free edges at the sides of each panel turned up. These free edges are then riveted to the rib flanges, which are flat strips placed vertically. The construction will be clear from an examination of the sketch above, which shows a view inside the wing. The rib webs are Warren girders of Duralumin tube, slotted at the ends to fork the rib flange strip. It will be seen that the wing spars do not occupy in depth the whole of the aerofoil section, and that the rib flanges are supported from the spar flanges on simple bent plate clips. To stiffen the wing covering, angle strips running at right angles to the wing chord are placed at intervals. These strips are interrupted at the rib flanges, as shown in the sketch.
   The centre section of the wing is built integral with the fuselage, the construction being visible in one of our photographs. The concentrated stresses from the wing spars are taken by a tubular structure in the roof of the fuselage, this structure taking the form of a plain transverse tube to which is attached the apex of a vee formed by two other tubes.
   Externally the two wing halves are braced by steel tubes, the arrangement of which can be seen in the general arrangement drawings and photographs. From the point on the front wing bracing strut, to which is attached the telescopic leg of the undercarriage a diagonal strut runs to the top longeron of the fuselage.
   Bristol-Frise type ailerons are fitted, the type of bracket supporting them being shown in one of the photographs above. The first "Viastra I" to be built is in addition fitted with Handley Page automatic slots.
   The power plant of the "Viastra I" consists of three Armstrong-Siddeley geared "Lynx" engines of 235 h.p. each. The engine mountings have been so designed that a variety of different engines can be fitted, and the wing engines can be removed altogether and the machine used as a single-engined type. In that case the central engine will of course be one of much greater power than the "Lynx."
   The petrol is carried in two tanks in the wings giving direct gravity feed. A new type of tank has been evolved and is we believe used for the first time in the "Viastra." This type of tank consists of two identical halves joined in the middle. At the joint the tank plating is flanged up and the two halves are held together by a series of bolts and slotted sleeves, with a packing between the two flanges to make a petrol-tight joint. The oil tanks are of different shape, but of the same form of construction. In the petrol tanks a loose framework inside serves both to strengthen the tank and to act as a baffle to prevent surging of the fuel. This framework is so designed that the two halves of the tank shell slip over it when the tank is being assembled.
   The undercarriage of the "Viastra I" is of the "split" type, with oleo-pneumatic shock absorbers, Dunlop wheels and Vickers hydraulic brakes. These can be operated together or separately, and a tail wheel with castor action allows of turning the machine in a very small circle on the ground.
   The biplane tail is of unusual design, in that it is, so to speak, of the single-spar biplane type. The two rudders at the ends of the horizontal tail surfaces are pivoted around vertical tubes which remain stationary, serving as the vertical struts of the biplane tail system. In construction, the biplane tail is very similar to the main wings, i.e., of all-metal construction, even to the covering.
   The cabin of the "Viastra" is of large dimensions (length, 20 ft. 3 in.; width, 5 ft.; height, 6 ft. 1 in.), and when the machine is used as a passenger carrier there is seating accommodation for 12 passengers, six along each side of the cabin. The ventilation system is novel, in that each passenger has an adjustable ventilation shutter placed near his seat. The windows can therefore be kept closed, which in itself reduces the amount of engine noise which reaches the cabin. With metal covering it was to be expected that "drumming" might be somewhat pronounced, and to reduce this the designers have introduced in each small panel in the fuselage wall a tiny bag filled with sand.
   Aft of the cabin is the lavatory, very neatly arranged, with a door which alternatively shuts off the lavatory from the cabin, or, when passengers are emplaning or disemplaning, the lavatory from the entrance. Reached by a separate external door behind the lavatory is a large luggage compartment. This is fitted with a specially strong, false floor, which can be raised, as shown in one of our photographs.
   The cockpit of the "Viastra" is ahead of the wing and well protected by windscreens. The view from the cockpit is good in all important directions, and when the machine is used as a twin-engined type, the view is, of course, even better. Dual controls are provided in front of the two side-by-side seats. A door in the rear wall of the cockpit communicates with the cabin.
   As the "Viastra I" has not yet been through the type tests at Martlesham Heath, actual performance figures cannot be given, but it is thought that the estimated top speed of 140 m.p.h. will be reached, and it is certain that the estimated cruising speed of 120 m.p.h. will be attained,

Flight, June 1931

SPECIAL TYPES AT THE DISPLAY

"VIASTRA”

   THIS is an all-metal commercial monoplane fitted with three Bristol "Jupiter VI" engines of 450 h.p. each. The covering of wing as well as fuselage is of metal (Duralumin), so that the machine can remain in the open for long periods without damage.
   The cabin has accommodation for 12 passengers, and, in addition, the machine carries 800 lb. of luggage.
   The Viastra has a wing span of 70 ft. (21.3 m.) and a gross weight of 12,950 lb. (5,900 kg.). The normal range is 300 miles (485 km.) at a cruising speed of 130 mp.h (210 km./h.). The landing speed is 66 m.p.h.(106 km./h.) and the maximum speed 152 m.p.h. (245 km./h.).