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Aviation History
1921
1921 - 0014.PDF
weight of wing structure, equivalent fuselage and equivalent tail unit, in lbs., i.e., Ww + Wp + WT :— 2-2999 c8 -f 5-9257 C2 for all below C = 6-2 2-1684 C» + 5-9257 Ca from C = 6-2toC = 6-7 2-1381 C* + 5-9257 C« „ C = 6-7toC==7-2 2-1083 C + 5-9257 C* „ C = 7-2toC = 7-7 2-3398 C3 + 3-9120 C! „ C = 7-7 to C = 8-3 2-3268 C3 + 3-9120 C* „ C = 8-3toC = 9-o 2-3138 C3 + 3-9120 C1 for all above C = 90 Equations for Constant Weights, Power Plant (dry), • Landing Gear and Control Cables Constant Weight, WK = 81 lbs. WK includes flying and engine controls (including starting mag., switches, and wiring, and doping system), instruments, pilot's seating, wind screen, pumps, cocks, etc., of petrol and oil systems. FIG: 2. Fig. 2 : Cubical tank in 22 S.W.G. tinned mild steel: Weight in lbs. (empty) W = 1 + 1 3 L + 7 7 L> + 4 L». Capacity in gallons =6-2 Ls, L being, in both cases, length of side, in feet. Fuel, Oil and Water : Petrol consumption, 06875 gallon per b.h.p./hour or -4971b. per b.h.p./hour. Oil consumption 00288 gallon, or 0265 H y Nlb. per h.p./hour. Cooling water 1 + 023 H + ~u in gallons ; where H = max. b.h.p. and N = duration in hours. WP, total weight of petrol, oil and water, ,_.,... = 10 -r 23 H + 5298 (H x N), in lbs. Kig. 3 Curve T is ton-miles per gallon for duration of four bours = 1 30^ . C is chord length of wings, in ft. = 08652 J\\ WT is total loaded weight (mul- tiply scale ordinate value by 10) =7 1 Aw -f Ww. LL! is maximum useful load = WT — WE (multiply scale ordinate value by 4). Ww is total wing weight multiply scale ordinate value by 2). WF is total fuselage weight, and WT is total tail unit weight. JANUARY 6, 1921 Control Cables, Wc = 2-29 C, in lbs,. Stress Load, Wg = 7-1 Aw = 7-1 x 13-36 C* == 94-85 C*, . in lbs. Total permissible loaded weight, WT = Ws + Ww. For power loading of 20 lbs./h.p., b.h.p. = -05 WT. Weight of total power plant dry and without tanks WE =3-3 X b.h.p., in lbs. = -165 WT. [WE includes engine (dry) with airscrew hub, exhaust manifolds, engine mounting, engine cowling, radiator (dry; with mounting and shutters, piping for petrol, oil, and water.] Weight of complete landing gear, Wo = -0331 WT. Weight of Tanks " To revert to weight of tanks. I have attempted to get out a formula for tank weights, based more or less on the •results of experience, I have assumed a cubical form for the tank, which is a form easy to make and convenient to instal ;. and as the fuselage is usually of square or rectangular cross section, a larger capacity can be obtained by using tanks of the form of a cube than of a cylinder. .'See Fig. 2). (Capt. Barnwell then deals with the size and weight of tank details, from a consideration of which he deducts the following.—ED.) :— Tank capacity in gallons, G = 6-2 L*. Tank weight in lbs., W,= 1+1-3 L + 7-7 L1 + 4 L»" where L is length of edge in feet. '• Whence we may write:—Weight in lbs., \V = 1 + -71 G* + 229G* + 065 G. Total Weights " We are now in a position to sum up total weights and thence to find the load-carrying value. The total loaded weight, WT , is equal to 7 • 1 Aw + ww. The total weight empty, WK, is of course the sum of the weights of wings, fuselage, tail unit, undercarriage, constant weight, control cables, power plant dry, air screw, and tanks required for 4 hours. To the weight empty, WB, must be added weight of petrol, oil and water for flight duration- required, and also weight of pilot (and other member or members of crew, if any), to give what I shall call the flying weight, WF. Then :— '' Total loaded weight, WT — Flying weight, Wr = useful' load, Lu. , - " Using all these methods, then, 1 have calculated the weights, for chord lengths, C, varying by 55 ft., from C = 3-3 ft. up to C — 11 -o ft., and have run curves for them on a base of Wing Area, of value of 13-36 C*. (See Fig. 3.) "These curves refer strictly to the case of a two-bay biplane of the over-all proportions of the ' Bristol' Fighter, with maximum normal horse-power numerically equal* to one-twentieth of the total loaded weight in lbs., with petrol, oil, water and tankage for 4 hours* duration at maxi- mum normal power, and with ' crew ' consisting of 180 lb. pilot only. Theyalso refer strictly to a stress loading of 7 • I lbs. per - square foot of wing surface, and ' Commercial Class ' strength on this stress loading. The curves run are :—Basic chord length, C, in ft. ; total wing weight, ww, in lbs. ; fuselage weight, wr, in lbs., tail unit weight, wr, in lbs. ; total loaded weight, WT, in lbs. ; useful load, Lu, in lbs. " 1 have not run the curves for power plant weight, WE, nor for landing gear weight, wv, as these are respectively,. •165 and -0331 of WT ; nor have I run the curves for petrol oil and water, for tanks and for air screw. Ton-Miles Per Gallon "One other curve is run on this diagram, the curve to obtain which all the foregoing has been necessitated, namely a curve of ton-miles per gallon, T. Ton-miles per gallon is :— Lo Speed, in miles per hour 2,240 Petrol consumption, in galls, per hour' "It is affected by duration inasmuch as the greater the required duration, the greater the necessary initial weight of petrol, oil and water, the greater the necessary weight of tanks, and consequently the smaller the useful load. In the particular case, for variation in size of an aeroplane, which we are considering, we have kept the horse-power per ib. total weight constant, we have kept the overall proportions constant, we have kept the stress loading constant, we have kept the air-screw efficiency constant. So if the wing loading were constant the speed would be constant. Now the wing loading is not quite constant, because it is the sum of the constant stress loading (per square foot) and of the total wing weight (per square foot), and this latter increases slightly as the size increases. When the wing area is 200-
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