航空研究所長距離機の基本航續性能實測結果

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The range, kilometres per kilogram of fuel, of the Koken long-range monoplane was measured for several speeds in level flight at heights between 1000m. and 2000m. The total weight at the tests was from 5000kg. to 6000kg., i. e., from 55 to 65 percent of the fully loaded weight. Two wooden propellers and one variable-pitch propeller tested had the following dimensions: [table] The wooden propellers, having nearly same dimensions, proved to have also nearly same aerodynamic characteristics by the tests. For the variable-pitch propeller, we selected the higher pitch as high as possible, without regard to the aerodynamic efficiency, in order to test to what limit the fuel consumption can be reduced in flight. The measured ranges were reduced to the standard condition on the density basis, as the effect of density on fuel consumption was considered to be prevailing over that of pressure, and plotted againt c_z. Figs.9, 11 and 12 are for wooden propeller and undercarriage retracted condition, Figs. 8 and 13 also for wooden propeller, but undercarriage down condition, and Fig.10 for variable-pitch propeller and undercarriage retracted condition. As shown in these figures, the test results with undercarriage retracted agree fairly well with those calculated from the wind-tunnel test data for c_z/c_x and η and the bench test data for the fuel consumption, so we can estimate, by the extrapolation of the curve of the calculated results, the range at the most economical speed, which was not actually measuaed in the tests. Thus we reached the conclusions that, with undercarriage retracted, the Koken longrange monoplane, fitted with the wooden propellers, can cruise per kg. of fuel with the most economical speed (c_z=0.6), at the heights of 1000〜2000m, 3.9km. and 3.3km. at the total weight of 5000kg. and 6000kg. respectively, and when fitted with the variable-pitch propeller, 5 percent increase is obtained on the above figures of range. The test results showed that by pulling down the undercarriage the range decreased about 20 percent over the weight and speed range tested accompanying an appreciable decrease of the economical speed due to the shifting of the incidence angle of maximum lift-drag ratio to a higher value. The out-put of the engine in flight was, moreover, estimated from the measured number of revolutions and boost pressure, using a revolution-boost-power diagram based on bench tests, and applying corrections due to atmospheric pressure, temperature and mixture ratio. The mixture ratio was taken as the ratio of the directly measured fuel consumption to the air consumption estimated by a revolution-boost-air consumption diagram. Using the estimated values of the engine out-put, the specific fuel consumption and consequently the "Weitflugzahl" ηc_z/c_x were calculated. The specific fuel consumption with the wooden propellers, was from 190 to 210 g/FP/h over the weight and speed range tested. Though these values seem to be not so low for our special engine, further reductions on the consumption can be expected at larger total weights, where torque is higher for the same number of revolutions. By the use of the variable-pitch propeller, the consumption was decreased to 170〜180 g/FP/h. The marked decrease of the fuel consumption was due to the reduotion of the number of revolutions, resulting from the use of an extremely high pitch. The "Weitflugzahl" was plotted against c_z in Fig.14 for wooden propelier and undercarriage down, in Fig.15 for wooden propeller and undercarriage retracted, and in Fig.16 for variable-pitch propeller and undercarriage retracted. By the extrapolation of the calculated curve with which the test results agreed well, we can conclude that the maximum value of the "Weitflugzahl" is greatest with wooden propeller and undercarriage retracted, and in this case it attains to 15 or more. The value corresponds to the maximum lift-drag ratio of 19 or more, assuming, from the wind-tunnel test results, the propeller efficiency of 79%.
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航空研究所長距離機の基本航續性能實測結果

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