Patent Publication Number: US-2013228653-A1

Title: Electrothermal and electro expulsive hybrid ice protection system for engine inlet

Description:
RELATED APPLICATIONS 
     This application claims priority benefit of a provisional application entitled, “Electrothermal and Electro Expulsive Hybrid Ice Protection System for Engine Inlet,” Ser. No. 61/560,995, filed Nov. 17, 2011 and incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     During flight, various portions of an aircraft, such as an engine inlet, can become coated in ice due to cold air containing moisture. This can be detrimental to the aerodynamics and operation of the aircraft. To combat this, heating elements or electro expulsive de-icing systems (EEDS) may be inserted into the engine inlet to de-ice the lip skin of the engine inlet. The EEDS may include actuators which hit or vibrate the lip skin in an attempt to break the ice off of the inlet lip skin. 
     While an EEDS may effectively remove ice formations from the inlet lip skin, significant quantities of small “feathers” of ice residue may still remain attached to the lip skin surface after application of an EEDS firing sequence. Because these “feathers” have very little mass, the impact acceleration of the EEDS actuators is unable to generate sufficient force to overcome the adhesion of the feathers to the lip skin surface. Thus, EEDS alone does not provide ideal ice protection for a jet engine inlet in all possible icing conditions. 
     Another method of removing ice from an engine inlet is through the use of heaters installed within the inlet. However, this requires a large amount of energy to completely melt the ice from the engine inlet and is not as efficient as other ice removal methods. 
     SUMMARY 
     Embodiments of the present invention solve the above-mentioned problems and provide a distinct advance in the art of de-icing of aircraft components. An embodiment of the invention is a hybrid ice protection system (HIPS) for use in an aircraft engine inlet lip to first break ice away from an outer surface of the engine inlet lip and then melt remaining residual ice or ice feathers from the inlet lip. The HIPS may include both an electro-expulsive de-icing system (EEDS) for striking an inner surface of the inlet lip and electrothermal heaters for heating the inlet lip to melt residual ice. The EEDS may have a plurality of EEDS actuators positioned to provide striking force to inner surfaces of both outer and inner walls of the inlet lip. The electrothermal heaters may be positioned to heat the inlet lip at areas between locations where the EEDS actuators provide striking force, so that the EEDS actuators do not strike the electrothermal heaters, only the inner surface of the inlet lip. The HIPS may also include a control system for actuating the EEDS actuators to strike the inner surface of the inlet lip when the inlet is at or below a predetermined temperature and then activating the electrothermal heaters to remove residual ice left on the inlet lip after actuation of the EEDS actuators. 
     Another embodiment of the invention is a method for expelling ice from an outer surface of an inlet lip of an engine nacelle. The method may include the steps of actuating electro-expulsive de-icing system (EEDS) actuators to strike an inner surface of the inlet lip and activating electrothermal heaters to heat the outer surface of the inlet lip between locations where the EEDS actuators strike the inlet lip after actuating the EEDS actuators. The EEDS actuators may be actuated to strike the inlet lip when the inlet lip is at or below a predetermined temperature and/or has a predetermined amount of ice thereon. The electrothermal heaters may only be activated if less than a maximum amount of residual ice build up is present on the outer surface of the inlet lip. Furthermore, the method may include the step of shutting off the electrothermal heaters once a predetermined maximum threshold temperature is reached. Then the method may again repeat the step of actuating the EEDS actuators once the inlet lip outer surface cools and/or a sufficient amount of ice has again built up on the outer surface of the inlet lip. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a fragmentary cross-sectional side view of an engine nacelle comprising an engine inlet lip constructed in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of a hybrid ice protection system (HIPS) configured to be positioned within the engine inlet lip and to remove ice from an outer surface of the engine inlet lip using both an electro-expulsive de-icing system (EEDS) and electro-thermal heaters; 
         FIG. 3  is a perspective view of the EEDS of  FIG. 2  and an actuator support assembly (ASA) for supporting and attaching the EEDS to the engine nacelle of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3 , including the engine inlet lip of  FIG. 1 , the electro-thermal heaters of  FIG. 2 , actuators of the EEDS, and the ASA; 
         FIG. 5  is a close-up perspective view of an actuator end support of the ASA for holding and preventing damage to actuator ends of the EEDS of  FIG. 2 ; and 
         FIG. 6  is a flow chart illustrating a method of removing ice from an engine inlet lip in accordance with an embodiment of the present invention. 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION 
     The following detailed description of embodiments of the invention is intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by claims presented in subsequent regular utility applications, along with the full scope of equivalents to which such claims are entitled. 
     In this description, references to “one embodiment,” “an embodiment,” or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, step, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     A hybrid ice protection system (HIPS)  10  constructed in accordance with embodiments of the present invention broadly comprises both an electro-expulsive de-icing system (EEDS)  12  and electrothermal heaters  14  positionable within an inlet lip  16  of an aircraft engine nacelle  18 , as illustrated in  FIG. 1 . As illustrated in  FIG. 2 , the EEDS  12  may include EEDS actuators  20  and the electrothermal heaters  14  may include inner heaters  22 , outer heaters  24 , and hi-lite heaters  26  which can be selectively activated to provide necessary coverage for specific engine power settings. The actuators  20  may be positioned between the heaters  22 - 26  such that the actuators  20  (or elements attached thereto) do not strike the heaters  22 - 26 , only the inlet lip  16  itself, thereby reducing wear on the heaters  22 - 26  and increasing operating lifetime and reliability. The actuators  20  and heaters  22 - 26  may be arranged and sequenced in a variety of manners, as described below. The HIPS may also comprise a control system  50 , as later described herein. 
     As illustrated in  FIG. 1 , the inlet lip  16  may be configured to attach to a bulkhead  28  of the engine nacelle  18  and may comprise a substantially continuous lip skin having an outer wall  30  and an inner wall  32 . The outer wall  30  may be aligned with and mate flush with an outer inlet skin  34 , which is flush with an outer fan cowl of the nacelle  18 , and the inner wall  32  may be aligned with and mate flush with an inner inlet skin  36 , which is flush with an inner fan case of the nacelle  18 . The inner and outer walls  30 , 32  of the inlet lip  16  may mate at a hi-lite  38 , apex, or substantially rounded end of the inlet lip  16 , providing an aerodynamic surface for a front end of the nacelle  18 . The inlet lip  16  may also comprise and/or be attached to inner and/or outer attachment fasteners configured for attaching the inlet lip  16  to the bulkhead  28 , the outer inlet skin  34 , and/or the inner inlet skin  36 . The inlet lip  16  may also have an outer surface  42  and an inner surface  44 . The outer surface  42  may include outer surfaces of the outer wall  30 , the inner wall  32 , and the hi-lite  38  and the inner surface  44  may include inner surfaces of the outer wall  30 , the inner wall  32 , and the hi-lite  38 . The HIPS  10  may engage the inner surface  44  of the inlet lip  16  in order to break ice off of the outer surface  42  of the inlet lip  16 , as later described herein. The inlet lip  16  may be positioned forward of an engine  46  and engine fan  48  of an aircraft. The engine  46  and engine fan  48  may be attached to the nacelle  18  and substantially surrounded by the inner fan case. 
     As noted above, the EEDS  12  may comprise a plurality of EEDS actuators  20 . Specifically, the EEDS  12  may comprise one or more inner actuators  52  and one or more outer actuators  54 , as illustrated in  FIGS. 3 and 4 . The inner actuators  52  may be positioned slightly aft of the apex  38  of the inlet lip  16  and configured to strike and break ice off of the inner wall  32  of the inlet lip  16 . The outer actuators  54  may also be positioned slightly aft of the apex  38  of the inlet lip  16  and configured to strike and break ice off of the outer wall  30  of the inlet lip  16 . Each of the actuators  52 , 54  may comprise a fixed portion fixed relative to the bulkhead  28  by various supports, as later described herein, and a moving portion configured to actuate toward and away from the fixed portion and toward and away from the inlet lip  16 . 
     In some embodiments of the invention, the inner actuators  52  may be circumferentially offset from the outer actuators  54  by 45-degrees about the inlet lip  16 , as illustrated in  FIG. 3 . For example, there may be four inner actuators separated by a small space circumferentially from each other and four outer actuators separated by a small space circumferentially from each other. By staggering the locations of the small spaces between the inner actuators relative to the small spaces between the outer actuators, circumferentially, the actuators more completely protect the inlet lip  16  and particularly the hi-lite  38  thereof. For embodiments of the invention where there are more or less actuators than described in this example, the offset of the outer and inner actuators  52 , 54  may be more or less than 45-degrees without departing from the scope of the invention. 
     The EEDS  12  may also comprise a plurality of force transfer units (FTUs)  56  configured to directly impact the inner surface  44  of the inlet lip  16 , as illustrated in  FIG. 4 . The FTUs  56  may be fixed to the movable portion of the actuators  20  and may be positioned and configured to impart actuator impulse force to the inner surface  44  of the lip skin of the inlet lip  16 . The FTUs  56  may be any substantially rigid and durable material that does not damage the lip skin of the inlet lip  16 . For example, the FTUs  56  may each be made of an abrasion-resistant plastic such as polyethylene or the like, providing a rigid yet non-abrasive surface for striking the inlet lip  16 . The FTUs  56  may clip onto, snap onto, or otherwise attach to the moving portion of the actuators  20 . Alternatively, the FTUs  56  may be integrally formed with the actuators  20  and/or the actuators  20  may be made of a material suitable for striking the inlet lip  16  without damaging the inner surface  44 . The use of FTUs  56  on the actuators  20  may be particularly advantageous in embodiments of the invention in which the actuators  20  are made of copper or some other material that could be damaged or cause damage to the inlet lip  16  if allowed to directly strike the inner surface  44  during operation. Furthermore, the FTUs  56  are not bonded directly to the inlet lip  16 , which may allow the inlet lip  16  to be removed without removing the actuators  20  or any structure supporting the actuators  20  and the FTUs  56 . 
     In some embodiments of the invention, the EEDS  12  may further comprise an actuator support assembly (ASA)  58 , as illustrated in  FIGS. 3-5 , for supporting the EEDS actuators  20  and FTUs  56  within the inlet lip  16 . The ASA  58  may include a plurality of standoff fittings  60  and a support structure  62 . The standoff fittings  60  may be made of machined aluminum and may be configured to secure the EEDS actuators  20  to outer chords or other various portions of the bulkhead  28  of the engine nacelle  18  or to other components of the engine nacelle  18  aside from the inlet lip  16  itself. The standoff fittings  60  may be secured to the support structure  62  made of machined aluminum or other such rigid, durable materials. This support structure  62  may be configured to position the actuators  20  and FTUs  56  within the inlet lip  16  such that the actuators&#39; movement is vector-normal to the inlet lip  16  or inner surface  44  at a point where the actuator strikes the inlet lip  16 . The support structure  62  may also be made of metal or some other rigid material and may be one integrally-formed part or may comprise a plurality of support structure pieces mechanically attached to different ones of the standoff fittings  60 . 
     The ASA  58  may also have inner and outer U-channels  64  formed into the support structure  62  and insulated cradles  66  designed to insulate the actuators  20  from the support structure  62 . Together, the cradles  66  and the FTUs  56  may encapsulate the actuators  20 , providing isolation from the support structure  62  and/or the standoff fittings  60  to prevent arcing. The U-channels  64  and/or cradles  66  may also serve as guides for the actuators  20  and FTUs  56 , directing all actuator movement along a single axis or in one degree of freedom normal to the inlet lip  16  inner surface  44  impacted by the FTUs  56 . Furthermore, the U-channels  64  and/or cradles  66  may serve as restraints for the fixed portions of the actuators  20 . The U-channels  64  may be machined, molded, or otherwise formed into the support structure  62 . The cradles  66  may snap into the U-channels  64  and the fixed portions of the actuators  20  may snap into the cradles  66 . This may be accomplished with corresponding protrusions and indentions (e.g., grooves and tabs) in the cradles  66  and the U-channels  64  and corresponding protrusions and indentions formed in the cradles  66  and the fixed portions of the actuators  20 . However, any method of attaching the U-channels  64  with the cradles  66  and the cradles  66  with the actuators  20  may be used without departing from the scope of the invention. 
     As illustrated in  FIGS. 3 and 5 , the ASA  58  may also include actuator end supports  68  designed to hold ends of the actuators  20  stable to prevent damage to these actuator ends. The ends of the actuators  20  may be located at the circumferential spaces between the actuators  20 . Specifically, the actuator end supports  68  may be configured to restrain movement of the fixed portions of the actuators  20  at the actuator ends and may be configured to reduce movement of the moving portions of the actuators  20  at the actuator ends. As illustrated in  FIG. 5 , the actuator end supports  68  may comprise a plurality of spacers  70  and an angled or isosceles trapezoid-shaped stabilizing component  72  configured to prevent movement of the actuators  20  in undesired directions. The configuration illustrated in  FIG. 5  of the actuator end supports  68  may advantageously minimize the actuators&#39; repulsive force at their ends and restrain the ends of the actuators  20  from excessive movement which can lead to fatigue damage of the actuators  20 . However, any configurations of actuator end supports  68  that sufficiently stabilize the actuators  20  at their ends may be used without departing from the scope of the invention. For any actuator end support configuration, keeping the circumferential space between the actuators  20  to a minimum is advantageous, so that circumferential coverage by the EEDS  12  is as large as possible, which is beneficial to the EEDS performance. 
     As illustrated in  FIGS. 2 and 4 , the electrothermal heaters  14  may be any heaters known in the art sufficient for heating the inlet lip  16  without causing heat-related damage thereto. The heaters  14  may be attached to the inner surface  44  or in near proximity to the inner surface  44  of the inlet lip  16 . Additionally or alternatively, the heaters  14  may be bonded to or embedded into laminate build-up of a composite inlet lip  16 . In some embodiments of the invention, each of the heaters  14  may be divided into three or more segments, such as the inner, the outer, and the hi-lite heaters  22 - 26  noted above. The outer heaters  24  may be positioned in contact with or proximate to the outer wall  30  of the inlet lip  16 . The inner heaters  22  may be positioned in contact with or proximate to the inner wall  32  of the inlet lip  16 . The hi-lite heaters  26  may be positioned in contact with or proximate to the apex  38  or rounded end of the inlet lip  16  and may even continuously extend through a portion of both the outer and inner walls  30 , 32  of the inlet lip  16 , forward of the inner and outer actuators  52 , 54 . The outer heaters  24  may be positioned aftward of the outer actuators  54  and the hi-lite heaters  26  may be positioned forward of the outer actuators  54 , such that the outer actuators  54  are located between the outer and hi-lite heaters  24 , 26 . The inner heaters  22  may be positioned aftward of the inner actuators  52  and the hi-lite heaters  26  may be positioned forward of the inner actuators  52 , such that the inner actuators  52  are located between the inner and hi-lite heaters  22 , 26 . Each of the outer, inner, and/or hi-lite heaters  22 - 26  may be separated into multiple sub elements for ease of manufacturing and installation, and to provide system redundancy. The locations of these heaters  22 - 26 , relative to the EEDS actuator locations, are illustrated in  FIG. 2 . 
     In some embodiments of the invention, the electrothermal heaters  14  may be carbon nanomaterial heaters formed on the inner surface  44  of the inlet lip  16  by spraying or otherwise adhering paint thereto which contains carbon nanomaterial. These nanomaterial heaters may have full contact with the lip skin or the inlet lip  16  as opposed to off-the-shelf flat heaters, which must be cut and carefully laid down to approximately cover desired surfaces of the inlet lip  16 . The nanomaterial heaters may be segmented into the inner, outer, and hi-lite heaters  22 - 26 , as described above, such that they may be separately and independently heated, allowing select portions of the inlet lip  16  to be heated at different times. However, any types of heaters known in the art for de-icing an inlet lip or other aircraft components may be used without departing from the scope of the invention. 
     The control system  50 , as illustrated in  FIG. 3 , may include one or more control systems and may be integrated into or interfaced with a full authority digital engine control (FADEC) of the engine  46  or aircraft on which the HIPS  10  is installed. This may provide the HIPS  10  with access to all of the FADEC sensor readings, such that additional instrumentation (e.g., lip skin thermocouples and the like) are not required. The FADEC may provide the control system  50  with information such as airspeed, total temperature, engine power setting, and other parameters which may govern operating characteristics of the HIPS  10 . Alternatively, the control system  50  may be the FADEC or the HIPS  10  may have its own independent sensing and control means that are separate from the FADEC without departing from the scope of the invention. 
     The control system  50  may comprise any number or combination of controllers, circuits, integrated circuits, programmable logic devices such as programmable logic controllers (PLC) or motion programmable logic controllers (MPLC), computers, processors, microcontrollers, transmitters, receivers, other electrical and computing devices, and/or residential or external memory for storing data and other information accessed and/or generated by the HIPS  10 . The control system  50  may control operational sequences, power, speed, and/or temperature of the actuators  20  and/or the heaters  22 - 26  of the HIPS  10 . 
     The control system  50  may be configured to implement any combination of the algorithms, subroutines, or code corresponding to method steps and functions described herein. The control system  50  and computer programs described herein are merely examples of computer equipment and programs that may be used to implement the present invention and may be replaced with or supplemented with other controllers and computer programs without departing from the scope of the present invention. While certain features are described as residing in the control system or FADEC, the invention is not so limited, and those features may be implemented elsewhere. For example, databases may be accessed by the control system  50  for retrieving aircraft data or other operational data without departing from the scope of the invention. 
     The control system  50  may implement the computer program and/or code segments to perform various method steps described herein. The computer program may comprise an ordered listing of executable instructions for implementing logical functions in the control system  50 . The computer program can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, and execute the instructions. In the context of this application, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable medium can be, for example, but not limited to, an electronic, magnetic, optical, electro-magnetic, infrared, or semi-conductor system, apparatus, or device. More specific, although not inclusive, examples of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable, programmable, read-only memory (EPROM or Flash memory), a portable compact disk read-only memory (CDROM), an optical fiber, multi-media card (MMC), reduced-size multi-media card (RS MMC), secure digital (SD) cards such as microSD or miniSD, and a subscriber identity module (SIM) card. 
     The residential or external memory may be integral with the control system  50 , stand alone memory, or a combination of both. The memory may include, for example, removable and non removable memory elements such as RAM, ROM, flash, magnetic, optical, USB memory devices, MMC cards, RS MMC cards, SD cards such as microSD or miniSD, SIM cards, and/or other memory elements. 
     As illustrated in  FIG. 3 , electrical conduits and/or communication conduits  74  may also be secured at or proximate to at least one of the actuator end supports  68  to provide electrical power to the EEDS  12  and/or to provide communication links between the EEDS  12  and the control system  50 . Additionally or alternatively, the conduits  74  may be configured for providing electrical power to the electrothermal heaters  14  and/or for facilitating communication between the control system  50  and the electrothermal heaters  14 . 
     In use, the HIPS  10  may be operated in a sequence that takes into account various sensed or known variables. For example, the HIPS  10  may operate the EEDS  12  and the electrothermal heaters  14  according to the power needs of the aircraft systems or expected ice build up at various locations of the inlet lip  16  surfaces, various speeds, altitudes, etc. In some embodiments of the invention, the actuators  20  may first break ice off of a cold surface of the engine inlet lip  16 , then the heaters  14  may heat the inlet lip  16  to a predetermined temperature before shutting off. This process may be repeated once a sufficient amount of ice builds up again on the inlet lip  16 , as determined by sensors, the FADEC of the aircraft, and/or once a predetermined amount of time has passed. The predetermined amount of time may be based on estimated rates of ice build up in particular sensed or known aircraft conditions. In this example embodiment of the invention, the heaters  14  may be primarily used to remove residual feathers of ice left behind after the EEDS actuators  20  impact the inlet lip  16 . Advantageously, removal of this residual ice may require minimal power compared with prior art de-icing systems that use heaters to melt larger quantities of ice. Furthermore, the heaters  14  may be activated in a pulsing fashion so as to greatly reduce the power required versus a stand alone, continuously operating electrothermal system whose heaters run substantially continuously. 
     The flow chart of  FIG. 6  depicts the steps of an exemplary method  600  for removing ice from an engine nacelle inlet lip  16 . In some alternative implementations, the functions noted in the various blocks may occur out of the order depicted in  FIG. 6 . For example, two blocks shown in succession in  FIG. 6  may in fact be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order depending upon the functionality involved. 
     The method  600 , illustrated in  FIG. 6 , may first include the step of actuating one or more of the EEDS actuators  20  to strike the inner surface  44  of the inlet lip  16 , as depicted in block  602 . Specifically, the EEDS actuators  20  may strike the FTUs  56  attached thereto against portions of the inner surface  44  of the inlet lip  16  located slightly aft of the apex  38  between the hi-lite heater  26  and the inner and/or outer heaters  22 , 24 . This may break off ice building up on the outer surface  42  of the inlet lip  16 . In some embodiments of the invention, the EEDS actuators  20  may be actuated to hit the inlet lip  16  several times to adequately break up and remove a majority of ice build up from the outer surface  42  of the inlet lip  16  prior to activation of the electrothermal heaters  14 . Residual amounts of ice or ice feathers may still remain on the outer surface  42  of the inlet lip  16  after the EEDS actuators  20  break a majority of the ice buildup therefrom. 
     Therefore, the method  600  may further comprise the step of activating one or more of the electrothermal heaters  14  to heat the outer surface  42  of the inlet lip  16  outward of and between locations where the EEDS actuators  20  strike the inlet lip  16 , as depicted in block  604 . This step may be performed after the step of actuating the EEDS actuators  20 , thereby melting residual ice or ice feathers from the outer surface  42  of the inlet lip  16 . For example, the EEDS actuators  20  may be actuated when the outer surface  42  of the inlet lip  16  is at or below a predetermined temperature and/or has a predetermined amount of ice built up thereon. Then, once an adequate amount of ice breaks off of the inlet lip  16  or the EEDS actuators  20  have been actuated to facilitate a predetermined number of strikes of the inlet lip  16 , the electrothermal heaters  14  may be activated to melt the residual ice remaining on the outer surface  42  of the inlet lip  16 . 
     Next, the method  600  may comprise a step of shutting off the electrothermal heaters  14  at a predetermined maximum temperature threshold, as depicted in block  606 . In some embodiments of the invention, the heaters  14  may be operated until the inlet lip  16  outer surface temperature thermocouples measure a specific temperature or maximum threshold temperature, at which time the heaters  14  may be deactivated until the next cycle. However, a heater activation time required to achieve a necessary surface temperature may be determined as a function of free stream total temperature, airspeed, and/or other parameters as necessary such that successful operation of the HIPS heaters  14  may be conducted without the use of monitoring thermocouples attached to the inlet lip  16 . 
     Then, the method  600  may include the step of determining if the outer surface  42  of the inlet lip  16  has cooled and/or has accumulated a sufficient amount of ice, as depicted in block  608 , and actuating the EEDS actuators  20  once one or more of these conditions has occurred. A variety of estimated, sensed, or pre-determined variables may be used to determine when to again actuate the EEDS actuators  20 , as in block  602 . For example, the EEDS actuators  20  may be actuated again at a predetermined length of time after shutting off the electrothermal heaters  14 , once sensors or other variables indicate that the outer surface  42  of the inlet lip  16  has cooled again to a predetermined temperature, and/or once a predetermined amount of ice builds up again on the outer surface  42  of the inlet lip  16 . The method  600  may be repeated a plurality of times as needed throughout operation of the aircraft, as illustrated in  FIG. 6 . However, note that various sequences may be employed by the HIPS  10  without departing from the scope of the invention. Furthermore, the sequence of independently actuating the EEDS actuators  20  and independently activating the electrothermal heaters  14  may be determined by the HIPS control system  50  or FADEC based on various flight conditions. 
     At high engine power settings, a stagnation point of airflow entering the engine  46  may move to a point on the outer wall  30  of the inlet lip  16 , while at low power settings the stagnation point may move to a point on the inner wall  32  of the inlet lip  16 . This movement of the stagnation point may directly influence impingement of water droplets and, therefore, a location of ice accretion. The inner, outer, and hi-lite heaters  22 - 26 , as well as the inner and outer EEDS actuators  52 , 54 , can be selectively activated to provide necessary coverage for these different engine power settings, further reducing the power requirements of the system. For example, the outer EEDS actuators  20  may be activated to remove ice building on the outer wall  30  of the inlet lip  16  at a high engine power setting, followed by activation of the outer and/or hi-lite heaters  24 , 26  to remove residual ice from the outer wall  30  of the inlet lip  16 , while the inner heaters  22  and the inner EEDS actuators  52  may not be used or may be used at more distant time intervals than the outer actuators and heaters  54 , 24 . 
     The primary ice removal method of the HIPS  10  may be the EEDS actuators  20 , with a secondary removal of residual ice accomplished by low-power pulsing of the HIPS heaters  14 . Thus, the heaters  14  require relatively little power to remove only residual ice. Advantageously, test observations show that ice breaks away more effectively on a cold surface (such as that from HIPS  10 ) when struck by elements of the EEDS  12  than on a heated surface. The HIPS  10  described herein also requires fewer actuators than prior art systems because the EEDS actuators  20  are able to be conformed to a complex curvature of the inlet lip geometry. The EEDS actuators  20  may extend  90 □ around a circumference of the inlet lip  16 , reducing part count, weight, and gaps in actuator coverage. Typical prior art actuators are unable to conform to a compound curvature and, therefore, must be separated into more elements. 
     Although the invention has been described with reference to the particular embodiments, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention. Specifically, the HIPS  10  is described herein for use on an aircraft engine inlet, but the apparatus and method described herein could be used for de-icing any aircraft skin. For example, other potential applications may include ice protection of wings and tail surfaces, turboprop or piston engine inlets and cooling openings, propeller blades, radomes and nosecones, wind turbine blades and nacelles, and other surfaces susceptible to ice accretion in service. Furthermore, the HIPS  10  can additionally or alternatively be operated as an independent EEDS-only or electrothermal-only system if desired, and with appropriately designed control systems could be tailored to suit the needs of specific conditions.