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Aviation History
1928
1928 - 0718.PDF
particularly that known as R.A.F. 30, which is symmetrical,i.e., without centre-line camber. In the design of the machine advantage has been taken of this fact by placing thetop plane at a larger angle of incidence to the centre line than is usually found. This was desirable in order to get a largeangle with the tail skid on the ground, the angle of no lift of the symmetrical wing section, of course, being at 0°incidence. But in placing the top plane at this large angle the pilot's view is at the same time improved, as his eyes areapproximately level with the centre-line of the section, so that he can look both above and below the wing. Added to thisis the fact that although the top plane is built in two halves, there is not the usual cabane for the support of the wing roots,the upper wings being supported from the body by outwardly- raked struts. This absence of a cabane. also slightly improvesthe view, while the slight sagging of the fabric covering over the centre-line joints in the top spars has the effect of slightlyreducing the wing thickness, thus again improving the view. Although a structural rather than an aerodynamic feature,reference may be made here to the somewhat unusual form of AUGUST 2, 1928 at VL = 100), but the section appears for some reason to besubject to considerable scale effect, so that the full scale lift coefficient of the " Starling " is in the neighbourhood of0-6, which enables this section to be used for a reasonably- heavy wing loading without the landing speed becomingunduly high. The minimum drag is low, the section thus being suitable for a wide speed range. Constructional Features Mention has already been made of the fact that the" Starling " is of all-metal construction. This is not strictly true, since the wing ribs are of wood. With that one excep-tion, however, the machine is built entirely of metal as regards its structural parts, although the covering is in theform of doped fabric. The fuselage, like the wings, is of steel construction, butwhereas the wing spars are built up from rolled and drawn strip, the fuselage members are in the form of circular-section steel tubes. At the fuselage joints the longerons are reinforced with tubular sleeves at the points where the [" FLIGHT " Photographs THE ARMSTRONG.WHITWORTH " STARLING " : Three-quarter front and three-quarter rear views. The wing bracing is unusual in that both lift wires run to the front spar. wing bracing employed, and which has been made possibleby the use of the symmetrical wing section : the main lift wires, instead of running to front and rear spars, as is usuallydone, are both taken to a point on the front spar, the rear spar having no lift wire. This arrangement, which at firstsight looks a little alarming, has been chosen so as to concen- trate as much of the wing strength as possible in the frontspar, which is located in a part of the wing section which has ample depth to accommodate it, the rear spar being quite alight affair, and little more than a strong stringer. In the more usual wing section such an arrangement could not wellhave been used, the travel of the centre of pressure under certain conditions throwing a considerable load on the rearspar. With the RAF 30 section, however, the c.p. is almost stationary, and is, moreover, situated fairly far forward, sothat this form of bracing has been rendered possible. Any small loads that may be thrown on the rear spar are transferredto the^ front bay bracing via the interplane struts, which are of " N " formation. While discussing the use of R.A.F. 30 with Mr. Lloyd,Armstrong Whitworth's chief designer, a rather interesting point came to light. In the model form, the maximum liftcoefficient of this section is not very high (about 0-45 or so longerons are pierced by the bolts. The sleeves are merelylengths of tubing of a size to slide over the longerons. The general arrangement of a typical " Starling " fuselage jointis shown in one of our sketches. Bracing is by tie rods in the usual way. To the main fuselage structure is addeda fairing composed of hoops or formers of channel section to which are riveted stringers made from rolled strip.These also are shown by sketches. The fuselage is built in two main sections, front and rear, bolted together aftof the pilot's seat. The wing construction takes the form of steel box sparscarrying wood ribs, the spars being composed of webs and flanges rolled to corrugated sections from flat strip andriveted together. The wood ribs are held to the spars without any form of fastening, the blocks in front of andbehind the bars being so proportioned that a slight pressure on the spar flanges is produced, which is sufficient for locat-ing the ribs. The details of the rib posts and blocks are shown in a sketch, from which it will be seen that postsand blocks are taped together. The front spars are of large dimensions, although even so they do not " fill " the wingsection, while the rear spars are, as previously mentioned, relatively small and light. The normal spar flange is a 662
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