Characterizing the Supercooled Large Droplet Environment with Corresponding Turboprop Aircraft Response

Abstract

This continuing study evaluated turboprop aircraft performance response to various environmental conditions. These conditions included clear air, warm rain, ice only, mixed phase, and supercooled drops encountered during 19 separate ights. Supercooled droplets consisting of cloud, drizzle, and rain sizes were the main focus of this study. Aircraft response was quanti ed by rates of change in aircraft rateof-climb capability, lift and drag coef cients and, lift over drag ratio. The aircraft performance parameters were compared to environmental hydrometeor parameters, such as 80% volumetric diameter (80VD) * liquid water content (LWC), quantifying the environmental conditions. Results show that encounters with supercooled drizzle drops, or ZL, resulted in maximum rates of performance degradation. These high rates of degradation forced the pilot to take evasive action within 5 min of entering these hazardous conditions. The Wyoming King Air experienced substantial increases in drag and stall speed, substantial decreases in climb capability, and signi cant lift degradations while encountering ZL. Encounters with supercooled cloud and rain-sized drops resulted in minor to low rates of performance degradation, whereas encounters with supercooled drops in low ice particle concentrations resulted in only minor rates of degradation. In addition, aircraft response to high ice particle concentrations and low liquid water, following a ZL encounter, resulted in rapid performance recovery, possibly because of erosion of ice on the airframe. Aggregates of needles and hexagonal plates led to the highest rates of recovery, whereas cold, clear air resulted in the lowest rates of recovery. Furthermore, ight analyses facilitated quantifying ZL horizontal extents and encounter frequencies. For example, ZL measured by a one-dimensional cloud probe during atmospheric research ights exceeded 0.05 g/m 3 twice per 10 ight hours over a horizontal length of 29 km. The results presented herein show a strong relationship between aircraft response and environmental parameters utilizing the largest drops in the hydrometeor distribution (80VD * LWC and ZL LWC). The results suggest that the most severe icing is actually caused by drizzle-sized drops as opposed to freezing rain. In addition, the results suggest that activating the de-icing boots (with typical chordwise coverage) after a ZL encounter may have little effect on aircraft performance recovery. Nomenclature C D = aircraft drag coef cient C L = aircraft lift coef cient D = aircraft drag L = aircraft lift

Climatic Characteristics and Determination Method for Freezing Rain in China

“…Supercooled warm rain process refers to that when there is no warm layer greater than 0 ∘ C, the size of supercooled cloud droplets (diameter larger than 40 m) increases by collision-coalescence, which is the main mechanism for the formation of freezing drizzle. Supercooled warm rain process mainly occurs in the upper air or mountainous area, which is one of major reasons for aircraft icing [11,12]. Huffman and Norman [13] as well as Bocchieri [14] conducted statistical analysis of the freezing rain in America and pointed out that more than 60% of freezing rains are formed by melting process.…”

A climatological study of surface freezing precipitation in Europe

“…aircraft water content measurements of 0.1-0.3 g m -3 for rain and about 0.1 g m -3 for drizzle). Ashenden & Marwitz (1998) proposed the classification of liquid hydrometeors in terms of median volumetric diameter (50% mass achieved in the particle distribution), diameter corresponding to 80% mass achieved, maximum diameter, and liquid water contents for different diameter ranges defining supercooled cloud drops, drizzle drops and rain drops. The International Meteorological Vocabulary of the World Meteorological Organization (WMO, 1992), which applies to the SYNOP reports used in this study, defines:…”

Two-Dimensional Airfoil Performance Degradation Because of Simulated Freezing Drizzle

“…(SLD ) regions have been reported by Ashenden and Marwitz, 1,2 where they showed high rates of aircraft performance degradation in freezing drizzle (30-400 mm diameter) and low rates of performance degradation in icing conditions caused by cloud drops (<40 mm diameter) and freezing rain (>400 mm diameter). To examine these conditions closer, wind-tunnel tests were conducted in two phases to determine the performance degradation of a scaled two-dimensional NACA 23012 airfoil (outboard wing section of the Wyoming King Air).…”

“…In addition, researchers have shown that cycling the de-icing boots after a freezing drizzle encounter may result in no noticeable bene t to aircraft performance. 2 The observed performance degradation from the various ice shapes are because of ice-shape geometry and impingement limit variations alone. The surface roughness for all simulated ice shapes was identical and, therefore, not a factor when evaluating the airfoil performance degradation.…”