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Aviation History
1920
1920 - 1179.PDF
NOVEMBER II, 1920 procedure corresponds to experimental tests, and, if anything, probably overestimates the fuel consumption. With these data Table 2 and Fig. 3 were made. The fuel consumption is seen to be proportional to the weight. a Fig. 4 shows a curve giving the relation between the weight at any time and the corresponding distance flown. Starting with a lull fuel load of 7.870 lbs., giving a total weight of 15,000 lbs., the machine was assumed to travel for a given 6000 straight line. A proof that it should be very approximately straight is given in Part II. Consequences of Flying at Maximum Speed In Table 2A the results for flight at maximum speed aretabulated. The gas consumption is constant and the speed of advance was found to be constant to within about 1 percent. The average value, 106 • 2 miles per hour, was, there- fore, used in the computations. The weight-distance curve (Fig. 4) is a straight line, asthe fuel consumption and speed are very approximately constant. The maximum range is considerably less than under greatest range conditions. The difference is 740 miles. A considerable gain in range is thus attained by flying at the proper angle and hence at proper speed. The useful loads for maximum speed are considerably less than under best range conditions. For an objective 600 miles away the best conditions give a possible load of 4,050 lbs. while at maximum speed this is reduced to 2,430 lbs., a reduction of 1,620 lbs. For convenience, a comparison of the loads and ranges corresponding to them is made in the following tables :— Range in milet. Fig. 5. time interval (two hours) at the weight, speed, gas consump- tion, and thrust corresponding to that weight. During the next two hours it was assumed to fly at new values corre- sponding to the new weight which is equal to the old weight less the fuel consumed in the preceding time interval, and so on. Determination of the Maximum Load for a Given Objective Evidently in case a return trip is to be made without refuel- ling the greatest distance for an objective is equal to or less than half this greatest range. It is easy to determine the greatest possible useful load by means of the weight-distance curve. Fig. 5, in the following way :— Suppose the objective is 600 miles distant. It requires AB-CD lbs. of fuel to get there and GF lbs. to get back after the load is deposited. Since the maximum load is AB lbs. there will be left DE or D'E' lbs. for useful load. Calling the maximum range S, project the points on the curve an xce m 0 Ns J\\ r \ BOMBLatocuw/i: deduced fromWeight- OjstvticeCwre from mil curvt. \ \ an \ — \ \ me \ — \ ... w \ \* mV for s = 600, point D, and s =- S — 600, point F, on the weight axis, the weight included between these two points is the maximum load for that objective. This procedure is quite general. The load decreases to zero as the objective distance increases to half the maximum range, and increases to the maximum load as the objective distance decreases to zero. A curve (Fig. 6) was determined by this method for this machine which gives directly the maximum useful load for any objective. This curve turns out to be practically a o Hour s o l ful l o r IO 7* 4 •+« 0 our s fue l IO 7i 4 en Bomb i loa d i n 3.070 4.270 5.95° <pft O •+H I, I, I Range mum Tota l 1,060 790 420 TABLE at maxi- ,speed Ob - jectiv e 53O 395 210 TABLE Range :ota l r1 510 130 610 Ob - ctiv e 755 565 305 1 1 5, bo C omb i m 1, 2 5 4Range at best Tota l .510 ,130 610 B3 loa d axi m a,030 .738 ,090 speed Ob - jectiv e 755 565 305 ox v ^ f~lt M to Om 3. 4. 5. > Ia loa d O7O 27O 95O Difference in : Tota l 45O 34O 190 ) > > > 1 miles Ob - jectiv e 225 170 95 0 iffer e in l b P 2,040 1,532 860 For the shorter flights the differences decrease, but they are considerable in all cases. The bombing load is increased by almost 190 percent, for maximum range speeds over maxi- mum speed conditions for 10 hours' fuel. Flying at Minimum Power The gas consumption at minimum power is practically identical with that at best range power. While the minimum power is slightly less than the power for best range speed, the speed is also less and the propeller efficiency is also slightly less. The net result is that the time of flight is about the same and the maximum range is diminished. A calculation of the range at minimum power gives 2,400 miles, instead'of 2,480 miles. For flight at minimum power the angle of attack is practi- cally constant and slightly greater than that for foest range speed. . Time Required for any R< nge For convenience, the curves of elapsed time for any dis- tance flown are given in Fig. 4 for both best range speeds and maximum speed conditions. By means of them the time of going and returning from any given objective may be read off. In particular, it is seen that the maximum time of flight under high-speed is 16-4 hrs., as against 38-0 hrs. for best range speed. For a bombing raid on an objective at 600 miles, the total elapsed time to go and return is for maximum speed 11-25 hrs., and for best range speed 18-65 hrs. It will be seen in the following how this time difference may be decreased by flying at high altitudes without changing the efficiency for best range conditions. (To be Continued)
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