Air Temperature Nomogram: A Rapid and Accurate Method for Obtaining True Air Temperatures from Indicated Air Temperatures for Aircraft Resistance Thermometers

Abstract

CONVENTIONAL aircraft thermometers are of the platinum‐resistance type, comprising one arm of a Wheatstone bridge network. The meter connected to the network is graduated on a temperature scale and different values are due to changes in the resistance of the platinum element. These arise from variations in the temperature of the air immediately in contact with the element or its protective casing. Any indicated temperature is a measure of the temperature of the air in contact with the thermometer. It is also the temperature of those parts of the aircraft over which the air is moving at the same speed as it is flowing past the thermometer. Since the air does not flow at the same speed over all parts of the aircraft it is clear that by mounting thermometers in different positions on an aircraft, different temperatures will be obtained. Due mainly to kinetic heating none of these will be the true temperature of the air in the free stream—i.e. away from the influence of the aircraft—and to obtain the free stream air temperature it is necessary to apply corrections. For many purposes, particularly meteorological research, it is important to be able to obtain true air temperatures from indicated air temperatures quickly and accurately and it is with this purpose in mind that the diagram to be described was devised and constructed.

Citation

Durbin, W.G. (1961), "Air Temperature Nomogram: A Rapid and Accurate Method for Obtaining True Air Temperatures from Indicated Air Temperatures for Aircraft Resistance Thermometers", Aircraft Engineering and Aerospace Technology, Vol. 33 No. 11, pp. 326-328. https://doi.org/10.1108/eb033479