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Aviation History
1925
1925 - 0746.PDF
modern instruments, armament, etc. The reason why thetwo types, taken together, form such an excellent combination is, firstly, that both in aerodynamic and structural designthe two types are very nearly identical, and that the majority of fittings, etc., are interchangeable. This applies particularlyto the fuselage fittings, tail skid, wing fittings, etc., so that where both types are used, the number of spares can be reducedto a minimum, which, of course, makes for cheapness. Furthermore the " Grouse II," is fitted with the Armstrong-Siddeley " Lynx " engine, while the " Grebe II " has an Armstrong-Siddcley "-Jaguar" engine. It is, of course,well-known that' the great majority of parts are identical in these two engines, so that the same saving in spares appliesto the engines, i.e., the " Jaguar " is, practically speaking, a double " Lynx," the cylinders, pistons, etc., being identicalin the two types, so that again the number of spares that has to be stocked can be cut down to a minimum, as the great majorityof spare parts can be used for replacing damaged or worn-out parts in either engine. There is, therefore, a great deal ofinducement for those contemplating purchasing aerial equip- ment in Great Britain to give the two Gloster types very carefulconsideration, since coupled with the excellent flying qualities of both types, there is this further advantage of a reduction ofspares. fir As the two Gloster machines are so very similar, the followingdescriptive article may be taken, except where otherwise stated, to apply to both. The photographs and scale drawingspublished this week illustrate the " Grouse II," and photo- graphs and scale drawings of the " Grebe JI " will be pub-lished in our next issue. NOVEMBER 12, 1925 in which the two wings are of the same area and ofthe samewing section. In other respects the two Gloster machines are of orthodox design but they show very clean lines, inwhich the Gloucestershire Aircraft Co.'s racing experience has been made use of in so far as it is applicable to servicetypes of machines. The Armstrong-Siddeley engine is neatly cowled-in, and the streamlined shape is further retained bythe special type of propeller boss which has for several years been a feature of the Gloster machines. In this type ofpropeller the metal spinner usually found is absent and its place is taken by a wooden spinner or enlarged boss builtof wood and integral with the propeller itself, from the laminations of whose blades it is made. • % Another feature of the two Gloster machines, which is not,however, peculiar to these but is incorporated in the majority of modern British service machines, is the placing of the petroltanks in the top plane where fire risk is small, and where, moreover, direct gravity feed to the engine can be provided.In this connection it should be pointed out that our photo- graphs of the " Grouse II,"published herewith, show- the oldertype of tank, whilst the general arrangement drawings might in this respect be regarded as a compromise in that in thefront elevation the new type of tank is shown while the dotted lines in the plan view represent the outline of the older tanks.The type of tank shown in the front elevation is fitted as standard in the latest machines. This type of tank is almostentirely buried inside the wing and therefore offers consider- ably less head resistance than did the older type shown inthe photographs. A further difference which should be pointed out relates to the ailerons of the top plane. In the THE GLOSTER " GROUSE II ": Three-quarter rear view. The two Gloster biplanes under review in the presentarticle are of somewhat unusual aerodynamic design in that "the top plane is of much larger area than the bottom plane,but is of different wing section. Neither section is quite identical with any section of which particulars have beenpublished, but it "may be said that the section of the top plane resembles that known as airscrew 4, while the bottomplane is very similar to airscrew 2. This means of course that, whereas the bottom plane is of the type known as a" thin " section, the top plane is a thick or high-lift section. There seems to be reason to suppose that the excellentflying qualities of the two machines are due in a great measure to this particular aerofoil arrangement. Air. H. P. Folland,who is chief engineer and designer of the Gloucestershire Air- craft Co., has employed this combination further to gainsomewhat in efficiency, by staggering the two wings in rela- tion to one another and by placing the top plane at a slightly-larger angle of incidence than the bottom plane. The result of this arrangement is that a certain amount of foreand aft stability is provided so that the tail of the machine can be kept fairly small. It seems probable that at topspeed the upper wing is carrying nearly the whole load, and by suitable design of the difference in angle of incidenceand stagger, it is possible so to arrange matters that in that case the top plane is flying at a point of its curve wheredrag is small, while the bottom plane, being a thin aerofoil, will also, of course, have a very small drag, with the resultthat the machine approaches monoplane efficiency much more closely than is possible with a biplane arrangement photographs these have their trailing edges in continuationof the trailing edge of the main plane, but in the latest type the aileron projeds slightly, as shown in the plan view ofthe general arrangement drawings. The aileron control of the Gloster machines is somewhatunusual in that only the lower ailerons are operated direct, the movement of these being transmitted to the top planeflaps by a single strut on each side. Xo cables passing over pulleys are employed in the aileron control, tie rods runningto a " T " crank being used in the lower plane from which cranks the tie rods run direct to the controls, short lengthsof cable being used where the controls pass through fibre blocks into the fuselage. The arrangement of the " T "cranks is such that the ailerons are given a differential move- ment, and doubtless this feature has a good deal to do withthe excellent manoeuvrability and the general easy handling of the machine. Before leaving the subject of the aerodynamic design ofthese two Gloster machines, it should be pointed out that in the top plane the master section is employed for part ofthe span only, as the wing is thinned down towards the tips and also at the ends towards the attachment to the centresection struts, or rather to the struts of the cabane, as no top centre section, in the ordinary sense of the tjrm, isemployed. By thinning down the wing in the centre the view from the cockpit is considerably improved and in thecase of the " Grouse II," access to the front cockpit is somewhat facilitated. (To be continued.) 746
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