Aircraft Performance Degradation - the Effects of Inflight Icing upon Lift, Drag and Propulsive Efficiency 2011-38-0073

Data is presented from a number of flight research aircraft, which have been involved in the research of the effects of inflight icing, in a variety of atmospheric supercooled droplet and mixed-phase icing environmental conditions. The aircraft Types considered cover both Pneumatic and Thermal Ice Protection Systems (IPS). Icing includes supercooled droplet impact icing upon airframe and propeller blades and cold-soaked frost icing. The drag effects of inflight icing, from mixed-phase small and large droplets encountered during the course of SALPEX cloud physics research operations, upon a Fokker F-27 turboprop transport aircraft, have been analyzed. Furthermore, during the course of AIRS 1.5 and AIRS II inflight icing flight research operations, the NRC Convair conducted aerodynamic characterization maneuvers, following and during icing accretion in a wide range of environmental conditions of altitude, air temperature, LWC and droplet spectra. The correlation of the effects of inflight icing accretion on the drag of the NRC Convair, with full droplet spectral parameters, for which the small (FSSP) and large (2D) portions of droplet spectra have been combined, has been analyzed. The changes to profile drag, C_Do, lift-dependent drag, k, and lift-curve slope, a, were analyzed initially for correlation with Ta, LWC and FSSP MVD. With the airframe IPS ON, ΔC_D

increases did not correlate with SLW exposure. Maximum Δk and Δa degradations correlated with each other, and with air temperature. With airframe IPS OFF, maximum Δa degradations correlated with exposure to SLW, whereas maximum ΔC_D

and Δk correlated with exposure to small droplet conditions. Furthermore, correlation of the aerodynamic parametric effects with LWC and the full-spectra droplet spectral parameters of 50VD (or MVD, when defined as median volumetric diameter), 80VD, 95VD and spectral width, approximated as maximum droplet diameter. When combined with LWC, the parameters of 95VD and maximum droplet diameter provided the better correlation of C_D

, k and a icing-induced effects, essentially limiting canyons in the contour cross-plot of effects. The analysis also highlighted the need to include the full droplet size distribution for the determination of the most detrimental icing accretion environmental regimes. The effects of icing upon propulsive efficiency have been directly measured and correlated with atmospheric conditions. Finally, the drag effects of SLD icing upon an aircraft with high lift devices deployed has been analyzed and correlated with atmospheric conditions.