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Aviation History
1934
1934 - 1393.PDF
JANUARY 25, 1934 THE AIRCRAFT ENGINEER SUl'PLEMFWT TO FLIGHT IN THE DRAWING OFFICE LAYING OUT LINES AND PLATING BY K, HALEY. IN getting out a set of lines for either an ordinary " fairing," drawing, or plating up a monocoque fuse- lage, it is impossible to get them correct unless the 7 are faired in three views; putting a line in " to eye " is hopeless. Only a few years ago, when 90 per cent, of the fuselage fairings were done in wood, it was quite a common sight to see a skeleton fairing in position, with pieces glued on here, and pieces cut out there, to allow the stringers to lie fair, proving that the lines were far from accurate. Imagine plating a ship with f-in. plating and the lines not being fair. No doubt this procedure was satisfactory to a degree, as when the fabric was put on the general appearance was pass- able, but now that we are familiar with metal moiio- coque fuselages the writer is of the opinion that it is worth the trouble to fair the lines properly in the first place, and eliminate any error, or endeavour to do so. In the following article the writer will try to describe the method employed in laying out lines, half-block model, and shell expansion, for a metal fuselage. The section on lines will, of course, apply equally to a set of " fairing lines " for an ordinary fairing drawing. Lines To begin with, endeavour to lay out the drawing paper for the lines to as big a scale as possible, and the whole bench can, and should be, utilised, unless the machine is extremely short. A steel straight-edge, 6 ft. long, is a useful tool when laying out lines and a set of splines or battens, with at least a dozen lead weights are essential. If time will permit, the cartridge paper should be pinned down the night before and allowed to stretch. Set down the " datum line," or " thrust line," as in Fig. 1, also centre line in plan and " body plan." Draw in outline in profile and plan, the plan being only drawn in the bottom half of the lower drawing. Subdivide the total length between the nose and the sternpost, into an equal number of " stations " (if possible, these stations should be a multiple of the frames or fairing formers). Number these stations 0, 1, 2, 3, etc., from the left-hand side. The number of stations will depend on the total length, and whether the fuselage has a lot of curvature in its length. At the ends, especially the nose, half-stations can be in- serted for fairing purposes only. Having laid out the outline in profile and half-plan, draw in the shape of the widest station (usually at half-length) on the " body plan," to the left hand of the centre line, station 5, fig. 1. Next, draw lines enclosing the width and total depth on the body plan, as A, B, C, D, Fig. 1, and divide this figure into equal parts from " 0," both vertical and horizontal, the horizontal lines being numbered from the base upwards, and the vertical lines numbered from the centre line to the right and left. The horizontal planes will be known as such, and the vertical lines will be called " buttocks." Mark off the intersection of these horizontal lines with the profile and the intersection of the buttocks with the plan out- line, as at " XX " and " YY," Fig. 1. Now we are ready to transfer the height above and depth below the datum of each station to the body plan, also the half-width. Having chosen the middle station and marked same previously, mark off other stations on the body plan thus:—All stations forward of the middle station mark off to the left of the centre line of the body plan, and all stations ait of the middle station mark off to the right of the centre line. On the body plan we now have the height and depth of each station on its centre line and the half-width along the datum about " 0." These positions are " lifted " off the profile and plan with strips of paper about £ in. wide. Next proceed to lightly outline the shape of each station on the body plan after having noted an - necessary flats that may occur, such as a bomber's window on the bottom surface, etc The shape of the sections will otherwise be largely governed by the shape of the middle section. After all the stations and half-stations (if any) have been drawn in, proceed to draw in the diagonals as OB, OC, 0A, 0D, Fig. 1. Fairing The real " fairing " has not yet been carried out, and we now proceed to fair our " body plan." Taking a strip of paper place same along the hori- zontal plane No. 1, and mark off the centre line on the strip and all the intersection points of all stations that cut this line. Transfer these points on the strip to the bottom half of the " plan " and mark off the half-width of each station. Place a batten through these points with weights thereon, and lightly draw a line through them. Proceed as above for all the horizontal planes. Do not attempt to correct shape unless there is an obvious bump, as it may be due to quite another cause. The alteration to another line later on may bring any irregular lines in the early stages to their correct spots. Now, with another strip of paper placed on Buttock No. 1, mark off the intersection of all the stations fore and aft, i.e., each side of the centre line on the " body- plan." Transfer these points to the profile and mark off these points at each station. The ends; of these /*•***• FIG.I. .M*
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