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Aviation History
1925
1925 - 0534.PDF
l AUGUST 20, 1925 THE BEARDMORE W.B. XXVI A Two-Seater Fighter of Unorthodox Design and fitted with 375 H.P. Rolls-Royce " Eagle IX THE first " large " aeroplane to be designed by Mr. W. S. Shackleton after joining William Beardmore and Co., Ltd., and which is now nearing completion, is the W.B. XXVI, which forms the subject of our scale drawings this week. The machine is of somewhat unusual design, and incorporates a number of interesting features. The W.B. XXVI was specially designed for use as a high-performance two-seater fighter, and Mr. Shackleton chose the biplane arrangement, partly on account of its greater rigidity and lower weight, and partly to provide a better field of view. At the same time he has made an attempt to equal, or at any rate approach, the monoplane type in aerodynamic efficiency by the sup- pression of wing bracing wires and by using a large gap/cord ratio. Unfortunately, photographs of the finished machine are not available, but the scale drawings give a very fair idea of the general arrangement, while certain features, not readily detected in the scale drawings, are shown in the photograph of the wind tunnel model. It will be seen that the flat-sided fuselage is of fairly small cross-sectional area, and is not directly attached to either upper or lower plane, the top plane roots being anchored to cabane struts from the top longerons, and the lower plane centre-section bolted to a fin built integral with the bulkheads of the fuselage. vertically, an angle of 10 degrees only beyond the vertical being obstructed by the fuselage. In order to improve the field of fire aft, the vertical fin is of the cantilever type with- out external bracing, while the tail plane is braced by one strut on each side, running to the lower longerons. There is thus no risk of the gunner accidentally shooting away any bracing struts of the tail. The Fuselage The fuselage is built up of spruce longerons with bulkheads of spruce and three-ply. The covering is in the form of birch three-ply, so that once the fuselage is erected there is no trueing up to be done to it, and it should require a minimum of attention in service. The fuselage is subsequently covered with fabric to protect the joints, and is painted and doped to give a watertight surface. The fin carrying the lower plane, etc., is, as already mentioned, built integral with the fuselage bulkheads so as to obtain the necessary rigidity in the wing structure. A fireproof bulkhead is fitted at the front of the fuselage, and all parts forward of this are of steel. The engine bearer is of simple and rigid type and is specially designed to allow of the rapid removal of the com- plete engine anit. The engine is a 375 h.p. Rolls-Royce " Eagle IX," totally c.owled-in with the exception of the exhaust collectors, and a The Beardmore W.B. XXVI, 375 h.p. Rolls-Royce "Eagle IX " engine. This photograph shows the win^tunnel 111111 ' " fniodel oT the machine. The biplane wings are rigidly braced by three struts on each side, one being the interplane I-strut with forked ends, and the other two compression struts running from the top longerons to the lower wing spars. The attachment to the fuselage is by pin joints, so that the wings can be quickly dismantled and re-erected. Furthermore, no adjustment of any kind is necessary after the final trueing up of the machine, the wings being rigidly locked in position merely by inserting the necessary bolts and pins. This feature should be particu- larly valuable in the field, and should save a great deal of time. The pilot's and gunner's cockpits are placed very close together, so that the closest co-operation between them should be possible, and the view from both cockpits should be particularly good, the more so as the top plane is thinned- down towards the centre so as to enable the crew to look over or under it with a minimum of obstruction. The armament consists of three Beardmore-Farquhar machine guns : two fixed guns firing through the propeller and controlled by the Constantisco interrupter gear, and the third operated by the gunner and mounted on the usual Scarff gun-ring. The rear gun is so mounted in relation to the wings and fuselage that it can be operated almost through- out the entire upper hemisphere, while in a downward direc- tion, owing to the fact that the gunner's cockpit is aft of the trailing edge of the lower plane, the gun can be fired almost particularly neat nose has been made possible by employing a special type of Lamblin radiator. This radiator is located on the leading edge of the bottom centre section, a position which combines the advantage of good accessibility with very small drag. Tiie petrol tanks ate mounted in the top plane, one ahead of the front spar and one aft of the rear spar, on each side, and arc shaped to follow the curves of the wing section. Owing to the height above the carburettor, chis arrangement of the tanks simplifies the petrol system by giving direct, gravity feed, and the fact of having a set of tanks on each side should considerably minimise the risk of the machine being brought down by machine pun bullets piercing all the tanks. Wing Structure Although differing somewhat in size, the upper and lower planes are of identical construction, each comprising two box spars of spruce with ribs made of spruce and three-ply. The whole of the wing, from the leading edge to the back spar, is covered with ply wood, a form of construction which gives great resistance against drag forces and stiffens the wings considerably against torsional loads. Ailerons are fitted on both top and bottom planes, and are operated by direct-acting rods and cables, the whole of the mechanism being carried inside the wings, with sliding doors for adjustment and inspection of various parts. The two lift struts running 534
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