Longitudinal Trim Analysis for Aircraft Icing From the SENS4ICE European Flight Test Campaign

Icing has various impacts on the aircraft flight characteristics. There are several well-known general effects, like the increase of drag due to ice accretion on the airframe or the decrease of lift as well as a highly nonlinear lift behavior during flow separation and reduced stall onset angle of attack caused by ice formation on the lifting surfaces. In addition, icing on the tailplane changes the longitudinal trim characteristics and might lead to premature tailplane stall. To further investigate the longitudinal trim effect of icing caused by different icing conditions, a longitudinal trim analysis was performed based on flight test data gathered during the SENS4ICE European flight test campaign. The analysis focused on the different effects of icing caused by atmospheric conditions with different water droplet size. In this campaign also and especially conditions with supercooled large droplets, which are known to have even more hazardous effects on aircraft flight characteristics, were identified by meteorologists and intentionally intruded by the especially equipped research aircraft. The trimmed aircraft's elevator deflection and total pitch coefficient were analyzed for flight data sets related to different atmospheric conditions encountered during the different flights and compared to the clean (ice-free) aircraft reference flight data. Data were clustered for the certification icing envelopes (appendix C and appendix O), knowing that the ice formations caused are not uniform. Nevertheless, only small deviations from the clean aircraft elevator trim curves are noticeable for both icing data sets, being in line with the pilots' reports after the flights. However, the pitch moment curves show an obvious change of gradient (with angle of attack) for all icing cases.