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Aviation History
1910
1910 - 0144.PDF
(/OGHT RULE 3.—The radius of the circle for rounding off the corners of the blade should be £ the width of the blade. In this case radius = -\a ins. = 5 ins. To avoid com plication the edges have not been rounded off in the diagram. It is easily done, however, by following the methods given. To lay off the propeller blade :— In Fig. 1 set off ab equal to the pitch (= 9-6 ft.) to any suitable scale. . In the diagram this scale is \ in. = 1 ft. Now set out ac at right angles to ab and equal it x diameter = -^ x 8 = 25*12 ft. to the same scale. Divide at into six equal parts at f, g, A, &c, and join fr g, ,h, &c, to b, as shown in Fig. r. In Fig. 2 lay off to a suitable scale 0, p, equal to the radius of the propeller. In this case radius = 4 ft., and scale is 2 ins. = 1 ft. Now divide 0, p, into six equal parts o\ on, on om, &c, and set out the rectangle a, b, c, d, to represent the propeller blade of 40 ins. x 20 ins. whose centre is at Oi (scale 2 ins. = 1 ft.). Now make 1 k, n 0, &c, in Fig. 1 equal to a, bu /L m\, &c, in Fig. 2. FEBRUARY 26, 1910. Now at the same scale (2 ins. = 1 ft.) in Fig. 1 set out ef at right angles to a c, and equal to the thickness of the centre of blade at the root, that is = 1-6 ins. Also at c set out c d = thickness of blade at the tip - -53 in. Join de as shown. Then, at every section,/j g, A, &c, we describe circles with centres at f, g, A, &c, and radii equal to the off-sets on the straight line de, as shown. Now describe arcs of circles touching each of these circles and passing through k i, n 0, &c. Then these represent the sections of the propeller blades at the different points, on, olu, &c, in Fig. 2. They are shown shaded in Fig. 1. Again draw k m, 0 r, &c, in Fig. 1 perpendicular to ac. Take the lengths / m, g r, &c, in Fig. 1 and lay them off on the corresponding section in Fig. 2, that is, ouf, om ky, &c, and draw the curve f gv through the spots so obtained. Draw the same curve on the opposite side of oxpx, namely ex Av Then e^fgx Ax represents the projection of the blade in a vertical plane. That is, it presents the view of the blade when looked at from the "after " side. To get the plan of the propeller we merely project down. This is immediately obvious from the figure. In order not to complicate the plan, only one section has been drawn in, namely, that corresponding to i k in Fig. 1, and to e f in Fig. 2. It must be particularly noticed that the driving or pressure face of the blade is flat, and to avoid a possible mistake the direction of advance of the propeller is given in the plan. The method of making the pro peller and connecting it to the shaft is left to the designer. It can be made in one piece of metal or wood, or it may be built up. In any case, it is important that the sections of the propeller should be the same as the designed sections, and the faces of the blades should be faced up with polished wood if possible. If convenient, the blade should be well polished, and no projections should occur on the surface. If the above rules be carefully worked to, the propeller will do the work it is designed for. SECTION AT 8" rod. • r-4' - 2-0 2-e" 3-4 I GO 1 I Si 51 ~^w k , 16' Design lor •TWO-BLADED 'PROPELLER.- Diam 8 St.. Pilch. 9-& ft,Tfc«Ut 75lbs. at 475 r.pm. and 60 it.per stc. -9-6ft NOTICE.—In response to numerous requests by readers, the series of articles, upon aerial propellers, by " Naval Con - structor," which have appeared in these pages, will shortly be republished in book form. 140
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