The need for a device to measure flight resistance, engine and propeller power, and efficiency during flight grew in proportion to the demand for increased flying capacity in military types of aircraft. Here, a dynamometer hub was inserted between the engine and the propeller. Taken as a whole, the tests that were conducted show that though the dynamometer is a sensitive instrument liable to numerous derangements, it is undeniably useful even in its present form, when handled with care and skill. Facilitating, as it does, the possibility of maintaining the fixed position of the engine, the blocking out of the weight effect when the plane is in the sloping position, and the possibility of taking direct measurements of force at the point of transmission, the dynamometer appears to be by far the best solution of the problem of a flying test bench, utilized as a hydraulic balance with the smallest possible measuring stroke and the least tendency to oscillation.
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