A Simplified Icing Model for Simulation and Analysis of Dynamic Effects.

摘要

Ice accretions on aerodynamic surfaces are a major concern during flight. In this research effort, glaze ice is being modeled and its effects on aircraft dynamics analyzed. This type of ice builds up as a clear layer on aerodynamic surfaces and other components such as antennas and intakes. Glaze icing is dangerous because as the amount of ice increases, it alters the shape and properties of the aerodynamic surface. Wind tunnel tests of this type of icing and data analysis have shown that the main effects of icing consist of decrease of lift coefficient, reduction of stall angle of attack, increase in drag coefficient, reduction of control surface effectiveness, and degradation of stability characteristics. In some instances, icing can produce significant gravimetric alterations and aerodynamic control surface lockage.;Based on these conclusions, a simplified icing model has been developed as part of a simulation package for aircraft health management instruction. The objective of this simulation package is to offer an interactive educational environment for experimentation, demonstration, and analysis of flight at both nominal and abnormal conditions. This icing model is expected to provide computationally effective tools primarily for the study of dynamic effects of ice accretions on aircraft performance, handling qualities, and pilot workload. Experimental wind tunnel data under icing conditions were used to develop regression models for the lift and drag coefficients. Linear variation with time in icing was considered for the degradation of stability and control derivatives.;The simplified icing model has been integrated with a business jet real-time simulation model since this type of aircraft is frequently subjugated to icing conditions. The impact of icing on aircraft is analyzed via simulation and observation of modal parameters. During steady state flight, linearization is performed to obtain stability matrices and their eigenvalues are used to determine and study the modal parameters on both the longitudinal and lateral-directional channels. In addition, the performance analysis studies the aircraft capabilities to maintain steady level symmetric and asymmetric flight. Also, an examination of the aircraft longitudinal and lateral-directional handling qualities compared to specifications for Class II aircraft in phase B flight conditions was considered.;Numerical simulations have revealed that the icing model behaves qualitatively as expected. While the time under icing conditions increases, the aircraft becomes much more difficult to control and a steady level flight condition can no longer be maintained after approximately three minutes when the throttle command saturates. Continued exposure to icing conditions results in approaching stall conditions and/or loss of altitude. The modal parameter analysis shows a degradation of handling qualities for both longitudinal and lateral-directional channels. The largest relative degradation is recorded for the damping ratios of the phugoid and Dutch roll. However, it is the short term oscillation that experiences a degradation by one level of handling qualities on the Cooper-Harper scale.