A New Ultrafast Thermometer for Airborne Measurements in Clouds

Abstract

A new aircraft device for measuring temperature in clouds is described. Its sensor is a resistance thermometer made of platinum-coated tungsten wire 5 mm long and 2.5 ?m in diameter. The sensor is located on a rotatable vane behind a thin rod aimed at protecting it against the impact of cloud droplets, which according to limited experience gathered until now seems to be sufficiently effective as an antiwetting protection for the speeds of motorgliders. Contrary to the massive housings usually adopted in other constructions, the rod creates only negligible disturbances in the thermodynamic properties of the ambient air. The time constant of the sensor is of the order 10?4 s, which permits measurements of temperature in clouds with a resolution of a few centimeters, depending on aircraft velocity. The thermometer was tested in a wind tunnel, and on an Ogar motorglider and a Do-228 aircraft. Its present version performs fairly well at low airspeeds of up to about 40 m s?1. For faster aircraft further improvements seem necessary. The paper presents a detailed description of the instrument, discussion of test results, and examples of centimeter-scale features of temperature fields in clouds measured with the thermometer.