The use of multiplied pressures for automatic altitude adjustments

Standwood S. Sparrow
January, 1922

The efficient performance of an airplane requires that certain adjustments be made as the density of the air through which the airplane passes changes. The safety of the over-dimensioned aircraft engine depends upon careful manipulation of spark advance and throttle opening and a proper control of a variable pitch propeller, if the maximum performance of the supercharged engine is to be obtained. It is evident that there is a real need for satisfactory devices to make such adjustments automatically. Discussed here is a method of automatic compensation which deserves consideration in the design of such devices. Existing schemes for automatic compensation all depend upon some contrivance which functions primarily because of changes in atmospheric pressure. In these devices a leak in the supposedly tight chamber means utter failure. The elimination of this source of danger is one of the aims of the method of altitude compensation described here. The change suggested is to make the source of operation the difference between atmospheric pressure and some multiple of atmospheric pressure instead of the difference between the atmospheric pressure and that of the gas confined in a tight chamber. The design of a device based on this method of altitude compensation is given.

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