Effects of icing on performance of a research airplane

The difference between the normal and actual rates of climb of a research airplane is used to measure the effect of icing on performance. The icing conditions were encountered in the course of an extensive series of meteorological research flights in various locations and seasons. Coefficients of lift and drag were determined for the airplane before and after icing encounters, and those coefficients were used to predict airplane performance for various flight conditions. The effect of icing was to increase the drag significantly, while there was little effect on the coefficient of lift. In the course of these flights, characteristics of the icing clouds (such as hydrometeor size spectrum and phase, liquid water content, temperature, etc.) were also measured, and those characteristics are compared to the summaries in the Federal Aviation Regulations and to the data sources on which those summaries were based. Most measurements lie within the envelopes suggested by earlier studies. For volume-median diameters larger than 30 microns, the liquid water contents were substantially lower than indicated by those summaries, but for other diameters measured liquid water contents extended up to and, in rare cases, exceeded the limiting envelopes of the regulations. Two exceptional cases of icing associated with droplets of 40-300 microns diameter are also discussed. The reduction in performance during these cases was anomalously large, although the liquid water content and volume-median diameter did not indicate that these cases should have been potentially hazardous.