An improved hybrid thermal/mechanical system has been developed to protect airplane wings and other airfoils against the accretion of ice, which degrades aerodynamic performance. The system is designed with particular attention to advanced, high-performance airfoils, which exhibit significant loss of lift when their leading edges and adjacent areas become rough, as they do when ice accretes.
In aeronautical terminology, "anti-icing" denotes the prevention of icing, while "deicing" denotes the removal of ice that has already formed. Anti-icing is the only way to keep the leading edge and adjacent areas of an airfoil aerodynamically smooth in the presence of impinging supercooled water droplets. Deicing is adequate for the area sufficiently downstream of the leading edge, but is not adequate for the leading-edge region because a typical deicing system is not effective until ice has accreted to some minimum thickness, and some residual ice sometimes remains after a deicing cycle.
In the most common approach to anti-icing, one heats the leading edge and adjacent roughness-sensitive area to evaporate the impinging supercooled droplets when flying through a cloud. However, the power demand of a fully evaporative anti-icing system is excessive for most light jet and regional turboprop airplanes. The present hybrid system was developed to enable the anti-icing and deicing of such airplanes at an acceptably low power demand.
This hybrid system includes an upstream thermal anti-icing subsystem, a downstream electromechanical deicing subsystem (see figure), and an electronic subsystem that controls the other two subsystems. The thermal subsystem heats (either electrically or by use of hot gas from the engine) the leading-edge region enough to prevent water from freezing, but not enough to evaporate most of the water. No such heating is performed in the area downstream of the leading-edge region for the following reasons: Water from the leading-edge region runs back along the surface in rivulets, so that most of the downstream area is dry most of the time. As a result, heating most or all of the downstream area in order to heat the wet spots would be inefficient, entailing excessive power demand.
The electromechanical deicing subsystem includes actuators inside the airfoil at downstream locations on the upper and lower airfoil surfaces. These are locations where ice forms by freezing of impinging droplets and of water that runs back from the leading edge. The actuators are basically electromagnetic coils to which large dc pulses are occasionally applied, as required, by discharging energy-storage capacitors, creating a rapid impulsive force. The electromagnetic force causes the actuators to expand perpendicularly to the skin. The airfoil skin momentarily deflects very slightly outward, with high level of acceleration, and returns to its original position. This is the actuation that removes the accumulated ice. Although the momentary pulse power is high, the average power consumed by the electromechanical subsystem is low.
This work was done by Kamel Al-Khalil, Dennis Phillips, and Thomas Ferguson of Cox & Co., Inc., for Lewis Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Lewis Research Center
Commercial Technology Office
Attn: Tech Brief Patent Status
Mail Stop 7 - 3
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Refer to LEW-16412.