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Aviation History
1910
1910 - 0077.PDF
*!_' .! *a. t i^Pl JANUARY 29, 1910. tfOSKr] DESIGN AND CONSTRUCTION OF AEROPLANES. By J. P. CHITTENDEN and L. H. ROBINSON. (.Concluded from page 59.) THE great difference between the actual and theoretical lift of an arched plane or aerocurve can only be explained by the assumption that a slight reduction of pressure must occur behind the hump on the upper surface of the plane ; this can be proved to a certain extent by taking a thin sheet of semi-flexible material and bending it into an arched form. If a current of air is allowed to pass along the top side, it will be noticed that the back edge has a tendency to lift. It is held by some that this action does not take place, and the stream lines follow the contour of the surface, but considering the simple experiment given above, it seems probable that the former assumption is more correct. Then the total lifting surface total weight of machine = p Dividing the result obtained by the aspect ratio will, of course, give the necessary dimensions for the planes. The theoretical horse-power to drive a given plane through the air is obtained from h.p. = total weight of machine x tan or x V in m.p.h. the formula: ' ZZZ To this must be added the skin friction of the plane, which is generally taken to be about •009 for speeds of from 30 to 40 miles per hour. Apart from losses due to skin friction of the planes themselves, there are also appreciable losses due to struts, wires, &c., owing to the wind pressure against these parts. To find the value of these losses, it is necessary to determine the wind pressure •due to a given speed. In the simple case, when a stream of air of finite cross section impinges normally on a flat surface, the area of the surface being considerably greater than that of the stream, the W w2 pressure per sq. ft. = • or expressed in miles per hour, sub- 0-0807 x 1 -466^ x V2 stituting v = 1 '466 V, then P = —— = '0054 V-. Now, in the case of a strut or an exposed beam, the section of air stream is greater than the surface on which it impinges, so that the change of direction of the air stream is not complete, and it has been found by recent experiments that an average value of P may be taken as equal to 0-oO36 V2. The above remarks apply only to flat surfaces, and by using more suitable sections, such as b or c, in Fig. 7. Too much care cannot be taken to reduce the resistance of parts as much as possible, and all uncovered members should be designed with this in view. Taking the resistance of a flat surtace R = 1 (a), then for a cylindrical section R = -54 b), and for an ichthyoid section R = -2 c). So that the horse-power absorbed by the resistance of these exposed parts may now be obtained by the formula : „ ...Ax -0036 V3 x R Horse-power absorbed = - 375 where A = area of section exposed to wind pressure, V = velocity in miles per hour, R = value for shape of section. By combining these results, the total horse-power required is arrived at, but in practice it has been found advisable to increase R= t R - '54 FIG. 7. R--2 this amount, as a considerable surplus of power is advantageous to meet those emergencies which occur in actual flight. Below is given a table of some well-known aeroplanes, with particulars of weight, surface, aspect ratios, &c. Before leaving the subject of planes, the position of the centre of pressure of the plane in relation to the centre of gravity should be considered, as the balance of the machine in the air is dependent upon this. The position of the centre of pressure of the plane varies slightly with the shape of the plane and the angle of incidence. The position of this point is a matter of experiment, but with an angle of about 50 it is approximately at '2 of the length of the section from the front edge and increases gradually to '35 with an angle of 200. To ensure perfect balance of the machine, the centre of gravity should coincide with the centre of pressure of the plane at TABLE I. Machine. BIPLANES. Wright. I Farman. , Voisin. Curtiss. Cody. Surface of main plane in sq. ft. Weight of machine (total) in lbs. Ratio W/S = lbs. per sq. ft. Span in ft. Aspect ratio Chassis—wheels (W), runners (R), or combined (C) ... Covering material—C = Conti nental, F — Farman, M = Michelin Method of control—W' = warp ing, Ai = ailerons, Au = auto- malic ... Engine— No. of cylinders Revs, per min. ... Horse-power Type of cooling—A = air, W = water ... Ignition—M = magneto, A = accumulator ... Propellers— Number' ... Diameter... ... Pitch No. of blades Revs, per mint Material—W = wood, A = alu - minium, S^steel Drive—C = chain, D~dhect ... 540 1000 1-85 41 ft. 6-3 W 4 1400 '5 W M 9 ft. 450 W c 43° 1200 2-8 34 ft. 6 in. 5-6 445 1310 2"9S 32ft. II 4-9 W 4 1200 5° A M 1 8 ft. 6 in. 4 1000 50 W M 7 ft. 6 in. 4 ft. 7 in. A and S D MONOPLANES. Bleriot. Bleriot R.E.P. 250 700 2-8 28 ft. 6 in. 6-5 W 4 1300 30 W A 1 6 ft. 2 1300 \v D 73 8So 2200 2-58 52 ft. 6-3 W A! W M 150 75o 5 28 ft. 5-2 W 3 1400 25 A A 240 1200 5 W c Ai 3 40 A A 220 1000 4-S 31 ft. 4'3S YV W 7 1400 35 A M 6 ft. 6 in. 6 ft. 10 in. \g ft. 10 in. 6 ft. 7 in. — 4ft. 3£in.!ioft. 1 in. — 2 4 4 4 1400 500 i 1400 A and S D W C A and S D Santos I Dumont. Antoinette "5 392 3" 4 18 ft. 2-8 \\ 2 30 W M 1 1 ft. 6 in. 4 36S 1100 3-02 46 ft. 5-8 Ai 8 1100 5o W A ft. 3 in. ft. 34 in.
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