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Aviation History
1928
1928 - 0591.PDF
JULY 5, 1928 BEARDMORE " INFLEXIBLE Three Rolls-Royce "Condor" Engines THE " Inflexible," built at the Dalmuir works of Win. Beard-more and Co., Ltd., is in many ways one of the most remark- able aeroplanes of modern times. With a wing span of158 ft. and a weight of more than 15 tons, this is certainly one of the largest machines actually flying, although typesare reported to be under construction abroad which promise to eclipse the " Inflexible " in point of weight, if not in thematter of wing span. The " Inflexible " owes its inception to the German designerDr. Rohrbach, although the design staff at Dalmuir, headed by Mr. W. S. Shackleton, who has now, for reasons connectedwith his health, transferred to Australia, naturally did a large amount of the detail work. The machine is a high-wingmonoplane, and should be very efficient aerodynamically. The large span assists in reducing induced drag, while thefuselage, in spite of its actual size, forms a very small percen- tage of the wing span. The two wing engines, too, althoughthey are Rolls-Royce " Condors " of 700 h.p. each, appear almost ridiculously small under wings of such large dimen-sions, and altogether there can be little doubt that the aero dynamic design is very efficient. Turning to the structural side, it is much to be regrettedthat Wm. Beardmore and Co. refuse to divulge anything whatever concerning the empty weight of the machine,and of the proportion between tare weight and gross weight. Without knowing anything of these, it is impossible to formany idea as to whether the machine is likely to be of practical use. As an experiment in large-scale research it is certainlyvery interesting, and at least it can be claimed that the machine has flown and is reported to handle very well indeed. Thatin itself is something of an achievement, since the problems connected with the control of such a large machine mightwell have proved somewhat difficult. It might be pointed out that balances of an unusual form are employed so as tolighten the loads on the pilot's controls, while in the case of the rudder a servo-rudder, of the type originated by HerrAnton Flettner, is fitted. This type of servo-rudder has been experimented with a good deal in England during recentyears and appears to perform its functions well. Without going into detail concerning its action, it may be pointedout that the pilot operates the servo-rudder which, under the action of the air forces upon it, in turn actuates the mainrudder. Thus, as the servo-rudder itself can, if necessary, be balanced, it would appear that control surfaces of anysize can be operated. The " Inflexible " is of all-metal construction, and in thisinstance the wing and fuselage coverings are not excepted, as these also are of metal and, in fact, form part of the stress-bearing structure. The fuselage is of rectangular section, with an internal framework of Duralumin, covered with flatDuralumin sheet. The monoplane wing is set at a pronounced dihedralangle, and is, like the fuselage, built entirely of metal, mainly Duralumin. Dr. Rohrbach makes use of a form of construc-tion in which the front and rear spar, together with the wing covering, form a box. to the front and rear of which areattached the leading and trailing edges. By varying the thickness and number of laminations in the covering, thestrength can be proportioned to the stresses at any point. Although the wing is designed as a cantilever beam, there isa single wire on each side bracing it. This wire is, perhaps, to be regarded as a torque wire rather than a lift wire, and isattached to the rear spar, or rather, to the rear corner of the box formed by the two spars and the covering. Thus, ina steep dive, with the centre of pressure situated well aft, the wire helps the wing structure to resist torsion. Of the three Rolls-Royce '' Condor " engines, one is mountedin the nose of the fuselage, while the other two are slung under the wing, some distance outboard. The radiators forthe outboard engines are mounted under the wing, between the engine nacelle and the fuselage. The undercarriage telescopic struts are taken to the wing,while horizontal Vees take the place of the usual single axle. The large Dunlop wheels are provided with brake drums, themechanism being so arranged that the tail skid takes a part in the operation of the brakes As soon as there is a loadon the tail skid the brakes are applied, but should the brake pressure be too great, so that there is a tendency for themachine to nose over, the mere fact of the skid leaving the ground immediately releases the brakes. The " Inflexible " is a very interesting experiment, and theresults of exhaustive tests should be of very considerable value to the future development of the large aeroplane. 539
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