Abstract:
A dielectric coating is applied to a surface that is prone to icing. Ice detecting sensors are deployed over the surface that is in danger of excessive icing. When sensors detect the presence of ice, a charge opposite that of the ice coating is automatically applied to the surface beneath the dielectric coating. Since ice in its natural state is a negatively charged substance, an identical, negatively charged surface repels or loosens the ice.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally relates to ice formation on aerodynamic surfaces and in particular to icing on airplanes. Still more particularly, the present invention relates to removal of ice formed on the wings of airplanes. 
     2. Description of the Related Art 
     A big problem associated with airplanes is wing icing. Frequently, there are incidents related to wing icing on commercial aircraft. Excessive ice on wings endangers the aircraft and its passengers because the ice reduces the airfoil efficiency of the wing. Methods for dealing with ice adhesion on aircraft vary, though most techniques involve some form of scraping, melting or breaking. For example, the aircraft industry utilizes a de-icing solution such as Ethyl Glycol to douse aircraft wings to melt any ice accumulation. The process is both environmentally hazardous and costly. Some aircraft have permanently installed de-icing mechanisms such as a rubber “boot”aligned along the leading edge of the aircraft wing. The tube is inflated during flight or on the ground whenever icing conditions warrant. This action causes any ice accumulation to break and fall off. Jet aircraft may redirect engine heat onto the wing so as to melt the ice or use heating elements to melt the ice. 
     Propeller driven aircraft are unable to duct heat to the wing surface and rubber boots on the leading edge of wings are not aerodynamically efficient. Also, de-icing costs are extremely high, at $2500-$3500 per application, and depending on conditions, they could be applied up to ten times a day on some aircraft. 
     Therefore there exists a need to provide an apparatus and method to efficiently and automatically remove ice from aircraft wings. It would further be desirable to remove ice without the need for chemicals, boots or heating elements. 
     SUMMARY OF THE INVENTION 
     A dielectric coating is applied to a surface that is prone to icing. Ice detecting sensors are deployed over the surface that is in danger of excessive icing. When sensors detect the presence of ice, a charge opposite that of the ice coating is automatically applied to the surface beneath the dielectric coating. Since ice in its natural state is a negatively charged substance, an identical, negatively charged surface repels or loosens the ice. 
     Ice has certain physical properties which allow the present invention to selectively modify the adhesion of ice to conductive surfaces. First, ice is a protonic semiconductor, a small class of semiconductors whose charge carriers are protons rather than electrons. This phenomenon results from hydrogen bonding within the ice. Hydrogen bonding occurs because the hydrogen atoms of water molecules in ice share electrons with an oxygen atom. Thus, the nucleus of the water molecule - uniquely a single proton remains available to bond with adjacent water molecules. 
     Similar to typical electron-based semiconductors, ice is electrically conductive. While this electrical conductivity is generally weak, the conductivity can be altered by adding chemical agents that donate or accept extra charge-carrying particles, i.e., protons in the case of ice. Another physical property of ice is its “evaporability.” Evaporability of a substance is a function of vapor pressure at the substance surface. In most materials, vapor pressure drops rapidly at the liquid-to-solid interface. In ice, however, there is virtually no change in vapor pressure at the liquid-to-solid interface. The reason for this is that the surface of ice is covered with a liquid-like layer (“LLL”). 
     The LLL has important physical characteristics. First, the LLL is only nanometers thick. Second, it ranges in viscosity from almost water-like, at temperatures at or near to freezing, to very viscous at lower temperatures. Further, the LLL exists at temperatures as low as −100 degrees centigrade. The LLL is also a major factor of ice adhesion strength. The LLL functions as a wetting substance between the surfaces--the principle behind almost all adhesives--and substantially increases the effective contact area between the surfaces. This increase in contact area strongly affects ice adhesion. 
     Generally, water molecules within a piece of ice are randomly oriented. On the surface, however, the molecules are substantially oriented in the same direction, either outward or inward. As a result, all their protons, and hence the positive charges, either face outward or inward. 
     While the exact mechanism is unknown, it is likely that the randomness of water molecules transitions to an ordered orientation within the LLL. However, the practical result of the ordering is that a high density of electrical charges, either positive or negative, occurs at the surface. Accordingly, if a charge is generated on the surface coming in contact with ice, it is possible to selectively modify the adhesion between the two surfaces. As like charges repel and opposites attract, an externally applied electrical bias to the surface that matches that of the charge occurring in the LLL reduces the adhesion between ice and the surface. 
     The present embodiment provides a power source connected for applying a DC potential across a dielectric coating formed on the surface. When ice forms on the dielectric coating, a charge is set up by the ice that is opposite to that of the surface beneath the dielectric. Sensors detect the ice formation and cause the power source to reverse polarity, which reduces the adhesion of the ice to the surface. 
     The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective that depicts the leading edge of a wing with a dielectric coating for de-icing in accordance with a preferred embodiment of the present invention; 
     FIG. 2A is a cross-sectional view of the wing of FIG. 1, illustrating a system for de-icing a surface in accordance with a preferred embodiment of the present invention; 
     FIG. 2B illustrates the repelling action caused by polarity reversal in accordance with a preferred embodiment of the present invention; and 
     FIG. 3 is a top view of the wing and system shown in FIG. 2A in accordance with a preferred embodiment of the present invention; and FIG. 4 is a high-level flow diagram that depicts a method for de-icing a surface in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the figures, and in particular with reference to FIG. 1, the leading edge of a wing with a dielectric coating for de-icing in accordance with a preferred embodiment of the present invention is depicted. Wing  102  is shown with dielectric coating  104  applied to the leading edge. Not shown, but detailed in FIG. 2, are sensors that detect the presence of ice. When ice forms on dielectric  104 , the sensors signal a charging circuit (not shown) connected to the wing. In the present embodiment the ice detector is comprised of exposed conductors that, when covered by ice or water, exhibit a change in conductivity. This change in conductivity is detectable and is used to determine whether ice is covering a particular area. 
     When ice covers the coated surface, including the sensors, conductivity between the individual conductors increases. In one embodiment a wheatstone bridge circuit, utilizing the sensors as one of the branches of the circuit, can be used to detect conductivity changes. If a change in conductivity is detected, the charging circuit automatically reverses polarity of the charge on the wing surface to match the polarity of the charge due to the ice coating. The reversal in polarity of the wing surface causes the polarity of dielectric  104  to change and match that of the ice coating. Since like charges repel, this reduces the adhesion of the ice to the wing and the charged dielectric surface repels the ice. 
     Referring now to FIG. 2A, a system for de-icing a surface in accordance with a preferred embodiment of the present invention is illustrated. De-icing system  200  is shown installed on a wing surface to be de-iced. De-icing system  200 , in the present embodiment, comprises sensors  206 , dielectric coating  210 , DC power source  201 , detection circuit  203  and switch  202 . In this embodiment, the surface is a wing surface and a cross-section of the installation shows wing surface  204 . Ice detectors  206  (described in FIG. 1) are shown connected to return cable  208 . When ice  212  forms on dielectric  210 , conductivity between detectors  206  increases due to the ice buildup. This buildup causes a signal to be sent to detection circuit  203 . Detection circuit  203  compares the conductance (in another embodiment, the resistance between detectors is compared and in a further embodiment the capacitance of the dielectric material is measured). An increase in conductance indicates the presence of ice  212 . 
     The buildup of ice  212  also carries an innate charge, in this case a negative charge, on the boundary between ice  212  and dielectric  210 . At first, the negative charge of the ice boundary causes an attraction between ice  212  build up and dielectric  210 . This increases the adhesion of ice  212  to dielectric  210 . Dielectric  210  can be any material that has dielectric properties and one such material is Radar Absorbing Material (RAM). RAM is a thin coating which has a high dielectric strength and is used on aircraft to reduce radar detection. 
     Detectors  206  are installed in dielectric  210  prior to installation. The ends of detectors  206  are exposed and flush with the surface of dielectric  210 . Conductor  208  is connected to all detectors  206 , and each detector is isolated from wing surface  204  and dielectric  210  upon installation. Conductor  208  is connected to detection circuit  203 . Additionally, charging source  202  is connected to wing surface  204  and to a switching circuit  202  that is used to change the polarity of wing surface  204  directly, and indirectly, the polarity of dielectric  210 . When detectors  206  are covered with ice  212 , conductivity between the individual detectors that are covered with ice increases. A signal is sent to ice detector circuit  203  which then causes charging source  202  to automatically reverse polarity of wing  204 . As is well known in the art, surface charges with the same polarity repel and surface charges with the opposite polarity attract each other. 
     FIG. 2B illustrates the repelling action caused by polarity reversal, in accordance with a preferred embodiment of the present invention. Wing surface  204  automatically changes polarity from, in the present embodiment, a positive polarity to a negative polarity in response to potential applied to wing surface  204  from DC source  201 . This causes the polarity of the surface of dielectric  210  to also reverse from a positive polarity to a negative polarity. Ice  212 , having negative polarity  214  at the boundary to dielectric  210  and ice  212 , is then repelled by negative polarity  213  of dielectric  210 . This repulsion causes the adhesion between ice  212  and the dielectric  210  to reduce and actually begin movement of ice  212  away from dielectric  210 . 
     FIG. 3 is a top view of the wing and system shown in FIG. 2A in accordance with a preferred embodiment of the present invention. Wing surface  204  is coated by dielectric  210 . Ice detectors  206  are connected with the detector circuit via conductors  208 . Conductivity is determined between the various detectors  206 . If the conductivity is low to zero, there is either no or very little ice covering the dielectric  210 . If the conductivity is high, there is ice covering at least two of ice detectors  206 . 
     Referring now to FIG. 4, a method for de-icing a surface in accordance with a preferred embodiment of the present invention is depicted. A more complete understanding of the method for de-icing is obtained by viewing FIG. 3 in conjunction with FIG.  4 . The process begins with step  400  which depicts a determination of the area to be controlled by the deicing mechanism. The process proceeds to step  402 , which illustrates ice detectors  206  being installed. In this embodiment, ice detectors  206  are the exposed ends of conductive wires that are used to measure conductivity or resistance and are connected to the detecting instrument via ribbon conductors  208 . The process passes to step  404 , which depicts RAM coating  210  being applied to a surface that will be de-iced by the present invention. The RAM coating  210  completely covers all but the exposed ends of ice detectors  210 . Generally, RAM  210  is applied on specific, strategic sections of a wing for radar avoidance. In this application, RAM  210  may be applied in locations on the wing that are prone to ice build-up. 
     The process continues to step  406 , which illustrates installation of the wing surface charging system. The charging system is a low voltage, low direct current charging source with a switching circuit that is capable of being automatically reversed upon receiving an appropriate signal from the ice detecting instrument. The process then passes to step  408 , which depicts ice formation on the wing surface. This step occurs when the wing surface is in flight and subject to ice formation. The process proceeds to step  410 , which illustrates the ice detection system detecting the ice build up and a further comparison of the conductivity between ice detectors  206  and the detection system sending a signal to the charging source. 
     The process continues to step  412  which depicts the charging source, in response to the signal, reversing polarity on the wing surface. The charging source maintains the new polarity on the wing surface, until the ice begins to separate from the surface. A decrease in conductivity between ice detectors  206  indicates loss of ice coverage on the dielectric  210  and causes detector circuit  203  to signal switch  202  to return to the old polarity. The method then passes to step  414 , which illustrates the ice being repelled from the wing surface. Generally, the time required for the ice coating to separate from the wing surface is short, measured in milliseconds, due to the wind speed over the wing surface. The number of times the polarity is reversed depends on whether ice is still detected on the wing surface. If ice is detected, detector circuit  206  causes the switch to change polarity of the wing surface from positive to negative until no ice is detected. The DC source then returns to maintaining a normal, positive polarity of the wing surface. 
     Alternatively, a timer can be included that causes polarity to reverse periodically for a predetermined period of time. As described above, the time for each period of polarity reversal can be very short. In addition, the system may be manually operated by an aircraft operator. For instance, in case the ice detectors fail and ice is observed coating the wing, the system may be manually overridden. The polarity is switched from positive to negative and back until the ice separates from the wing surface. 
     The present embodiment provides a power source for applying a DC potential across a dielectric coating formed on the surface. The potential reverses polarity on the dielectric coating and repels ice from the surface of the coating. Rather than distorting the airfoil to separate the ice utilizing a rubber boot, as in the current art, the present invention causes the innate polarity of the ice to cause separation. The invention operates automatically upon sensing the presence of ice. Also, a manual override can be provided to activate the polarity reversal according to observed icing conditions. No expensive chemicals are necessary because the adhesion of the ice is reduced so that the ice may be easily removed without harm to the wing surface. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.