Patent Publication Number: US-2010123044-A1

Title: Aircraft Ice Protection System

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/115,264 filed on Nov. 17, 2008. The entire disclosure of this application is hereby incorporated by reference. To the extent that inconsistencies exist between the present application and any incorporated applications, the present application should be used to govern interpretation for the purposes of avoiding indefiniteness and/or clarity issues. 
    
    
     BACKGROUND 
     Ice can accrete on exposed or otherwise susceptible surfaces of an aircraft when it encounters supercooled liquid. When ice accretes on airfoil surfaces, such as wings and stabilizers, shape modifications occur which typically increase drag and decrease lift. And ice accretion on engine inlet lips can disrupt desired flow patterns and/or contribute to ice ingestion. To avoid performance problems during flight, an ice protection system must be able to shield an aircraft from the most extreme icing conditions. 
     SUMMARY 
     An aircraft ice protection system comprises a controller, a plurality of consecutive ice protectors, and information input channels. The ice protectors can be independently controllable by the controller and, depending upon channel-input information, they can operate in either an anti-icing mode or a deicing mode. In this manner, ice protection can be accomplished effectively and efficiently for specific flight circumstances, instead of rigidly expending power that would be required to remedy the most extreme ice impingement conditions. 
    
    
     
       DRAWINGS 
         FIG. 1  is a perspective view of an aircraft having several surfaces protectable by the ice protection system. 
         FIG. 2  is a schematic diagram of one of the aircraft&#39;s surface and the ice-susceptible regions thereon. 
         FIG. 3  is a schematic diagram of the ice protection system, with ice protectors associated with one of the aircraft&#39;s surfaces. 
         FIG. 4  is a schematic diagram of the ice protection system, with ice protectors associated with several of the aircraft&#39;s ice-susceptible regions. 
     
    
    
     DESCRIPTION 
     An aircraft  10 , such as that shown in  FIG. 1 , can comprise fuselage  12 , wings  14 , horizontal stabilizers  16 , a vertical stabilizer  18 , engines  20 , and pylons  22 . The wings  14  are the aircraft&#39;s primary lift providers. The horizontal stabilizers  16  prevent up-down motion of the aircraft nose, and the vertical stabilizer  18  discourages side to side swinging. The engines  20  are the aircraft&#39;s thrust-providing means and the pylons  22  serve as underwing mounting means for the engines. 
     As shown in  FIG. 2 , each wing  14 , stabilizer  16 / 18 , engine  20 , and/or pylon  22  has a surface  30  that can be viewed as having a plurality of consecutive ice-susceptible regions  31 - 35 . As is explained in more detail below, the regions  31 - 35  are simply a conceptual mapping tool and they are determined by the placement of ice protection components (protectors  51 - 55  introduced below). The aircraft surface  30  does not need, and probably will not have, any structural features defining regional perimeters or boundaries. 
     In the illustrated embodiment, the regions are arranged in three rows (a, b, c) and each row has five consecutive regions ( 31 ,  32 ,  33 ,  34 ,  35 ). Regions are characterized as consecutive if they precede one after the other in a substantially fore-aft direction. Thus, depicted regions  31   a - 35   a  could be considered consecutive regions, depicted regions  31   b - 35   b  could be considered consecutive regions, and depicted regions  31   c - 35   c  could be considered consecutive regions. 
     Depending upon the aircraft  10  and the particular aircraft component, more or less rows, and/or more or less regions-per-row may be more appropriate. With the vertical stabilizer  18  and/or the pylon  22 , for example, a single row of consecutive regions and as few as two regions may be sufficient. And the congregation of regions in regular (or irregular) rows is certainly not required. In the same regard, the aircraft surface  30  need not be segmented into rectangular or similarly shaped regions as shown; the regions  31 - 35  can comprise a collection of sectors of varying sizes and/or geometries. 
     While the regions appear in a flat array in the drawing, this is simply for ease in illustration and explanation. In most instances, the regions will form a curved profile wrapping around the associated aircraft structure. Specifically, for example, the region  31  will form one end of the curve, the region  35  will form an opposite end of the curve, and the regions  31 - 34  will extend therebetween. 
     If the surface area  30  is on one of the wings  14 , the regions  33  could be curved about the wing&#39;s leading edge, the regions  31 - 32  could be upper regions, and the regions  34 - 35  could be lower regions. The rows could extend spanwise across the wing  14 . An analogous arrangement could be used if the surface area  30  is on one of the horizontal stabilizers  16 . 
     If the surface area  30  is on the vertical stabilizer  18 , the regions  33  could likewise curve around the leading edge. The remaining regions  31 - 32  could be rightside regions and the remaining regions  34 - 35  could be leftside regions. The regions  31 - 33  could be likewise located if the surface area  30  is on one of the pylons  22 . 
     If the surface area  30  is on one of the engines  20 , the regions  33  could be wrapped about the nacelle inlet lip and the rows (a, b, c) could extend radially therearound. With such a circular profile, the regions  31 - 32  could be outer regions and the regions  34 - 35  could be inner regions. 
     Referring now to  FIG. 3 , the aircraft ice protection system  40  is schematically shown. The system  40  comprises an ice-protector grid  50  associated with the relevant aircraft surface  30  and the grid  50  comprises an ice protector  51 - 55  for each ice-susceptible region  31 - 35 . Thus, with the illustrated regions  31 - 35 , the ice protectors are arranged in three rows (a, b, c) and each row has five consecutive ice protectors ( 51 - 55 ). The ice protectors  51 - 55  can each comprise an electrothermal heater that converts electrical energy into heat energy. 
     The ice protection system  40  also comprises a controller  60  that controls the supply of electrical energy to the ice-protector grid  50 . At least some of the ice protectors  51 - 55  can be independently controllable by the controller  60 . An independently-controlled ice protector has its own supply path of electrical energy and this supply can be adjusted by the controller  60  autonomously of the other protectors. 
     At least some of the independently-controlled ice protectors  51 - 55  are multi-mode ice protectors. Each multi-mode ice protector can be selectively operated in one of an anti-icing mode, a deicing mode, and an inactive mode. In the anti-icing mode, electrical energy is continuously supplied to ice protector  51 - 55  for an extended period of time (e.g., greater than 10 seconds) to prevent ice from forming on the corresponding region  31 - 35 . In the deicing mode, electrical energy is intermittently supplied (e.g., for distinct periods of time separated by at least 10 seconds) to the ice protector  51 - 55  to episodically remove ice form on the corresponding region. And in the inactive mode, electrical energy is not supplied (and is not scheduled to be supplied) to the ice protector  51 - 55  for an extended period (e.g., more than 120 seconds). 
     All of the ice protectors  51 - 55  in the grid  50  can be capable of multi-mode operation as this may afford the most embracing portfolio of operational patterns and/or facilitate modular manufacturing and inventory. In many instances, however, certain ice protectors need only operate in one of an anti-icing mode and a deicing mode, regardless of climate conditions and/or flight circumstances. For example, on a wing  14  or stabilizer  16 / 18 , the fore-most protectors  33  could be dedicated anti-icing components and/or the aft-most ice protectors  31 / 35  could be dedicated deicing components. 
     The controller  60  can further be adapted to provide one, some or all of the ice protectors  51 - 55  with a range of power draws (e.g., 100%, 50%, 75%, 25% etc.). These different power draws can be accomplished by direct voltage reduction, if possible and practical. Additionally or alternatively, a range of non-zero power draws can be created by an incessant series of on-off modulation increments (e.g., 150 millisecond increments) summing into a resultant anti-ice or deice time period. 
     The ice protection system  40  further comprises an input-channel constellation  70  comprising a plurality of input channels  71 - 79 . The channels sense, measure, detect, receive, or otherwise obtain information during flight and convey this data to the controller  60 . The controller  60  then controls the supply of electrical energy to the ice protectors  51 - 55  based on this information. 
     An input channel (e.g., channel  71 ) can correspond to outside air temperature (OAT). As a general rule (keeping in mind that real life frequently disagrees with general rules), ice will not form during flight unless the temperature reaches the freezing threshold. This temperature input can be used, for example, in the determination of whether icing conditions are present and, if so, the severity of such conditions. 
     An input channel (e.g., channel  72 ) can correspond to region specific temperatures (RST) of the relevant aircraft surface  30 . When super-cooled drops contact an aircraft surface  30  that is below 0° C., they will freeze. With large super-cooled drops, the freezing process is relatively gradual (due to the release of latent heat) resulting in runback and an increased likelihood of clear ice formation. Tiny super-cooled drops, on the other hand, will freeze on contact, into easily removable lime ice. Troublesome clear ice formation usually occurs at below freezing. While rime ice is most commonly encountered with OATs in the −10° C. to −20° C. range. 
     The input channels  71  and  72  can together convey information to the controller  60  that can help ascertain the chance of clear ice formation. If these channels  71 / 72  collectively signal a high chance of clear ice creation (e.g., an OAT hovering near 0° C. and a RST below 0° C.), the controller  60  can aggressively supply electrical energy to runback-risk regions (e.g., aft regions  31  and  35 ) to curtail such formation. If the channels  71 / 72  instead suggest the strong possibility of rime ice (e.g., an OAT below −10° C. and a RST below 0° C.), less assertive measures can be adopted. 
     Additionally or alternatively, the input channel  72  can relay temperature information regarding areas outside the ice-protected regions  31 - 35 . If non-ice-protected regions of the aircraft surface  30  (e.g., non-heated) are below freezing, runback solidification can be concern. If this challenge presents itself, the controller  60  can strategically deprive the aft-most regions  31  and  35  of heat so as to, for example, build temporary dams to block water flow beyond the protected regions. 
     An input channel (e.g., channel  73 ) can be devoted to data about aircraft altitude (ALT). Icing is rare above 2500 meters because any clouds at this altitude generally contain already-frozen water droplets. If the channel  73  indicates an acceptably high altitude, and no other information signifies icing apprehension, the controller  60  can relax the ice protectors into inactive modes. If the channel  73  indicates a lower altitude, this indication in combination with other data (e.g., OAT readings) can be used to tailor optimum ice protection operation. 
     An input channel (e.g., channel  74 ) can be related to aircraft speed (SPEED). A general rule (again, remembering that general rules often have exceptions) is that the swifter the speed, the warmer the relevant surface  30 , and the less chance of icing incidences. While speed will usually not alone dictate appropriate ice-protection parameters, it may be a helpful ingredient in the overall analysis. Additionally or alternatively, speed inputs can also alert the controller  60  to sudden changes in aircraft travel, and may be a determinative factor in choosing between two otherwise adequate options. 
     An input channel (e.g., channel  75 ) can correspond to the angle of attack (AOA) at this particular point of flight. The angle of attack typically changes significantly during aircraft climb/descent. And in any event, a variance in the angle of attack almost always causes a migration of airfoils&#39; stagnation lines. 
     While anti-icing is persistently viewed as obligatory at a stagnation line, deicing is usually deemed suitable at locations immediately adjacent (i.e., fore) thereto. If multi-mode ice protectors  52 - 54  reside on non-aft regions  32 - 34 , the controller&#39;s knowledge of the stance of the stagnation line allows anti-icing (e.g., very power intensive) to be confined to this location and deicing (e.g., less power consuming) to be employed at adjacent locations. This energy-saving advantage can be further enhanced by the regions  33  and ice protectors  53  replaced with several thin regions/protectors. A strip-like (rather than patch-like) geometry can permit fine-tuned programming of mode selection to closely follow the stagnation shift. 
     An angle of attack can additionally or alternatively influence the relative ice accumulation on the different regions of an aircraft surface  30 . A greater angle of attack, for example, can often cause less ice on upper aft regions and more ice on lower aft regions. The controller  60  can use the conveyed AOA data in the formulation of the best (and probably non-symmetrical) operation of the upper/lower ice protectors. 
     An input channel (e.g., channel  76 ) can correspond to the flight phase of the aircraft  10 . Ice issues generally introduce themselves with the greatest incidence during non-cruise flight phases (e.g., takeoff, climb, and approach). This is because, in part, there is a greater probability of encountering liquid water at the lower altitudes traveled during these phases. 
     And regardless of altitude (and even with cloudless skies and temperatures above freezing) icing concerns may lurk within engines  20  during taxing and takeoff. During pre-cruise flight phases, reduced pressure exists within the engine intakes, which can lower temperatures to such a degree that condensation and/or sublimation takes place. If the input channel  76  indicates that aircraft  10  is in the taxiing phase or the takeoff phase, and the channel  71  indicates an OAT less than  10  C, the controller  60  can initiate preventive measures. It may be noted that, during other flight phases, a temperature of 9° C. would not trigger any increased awareness. 
     The flight phase of the aircraft  10  can also be used to reprioritize the deicing hierarchy. The horizontal stabilizers  16 , for example, normally take a back seat to the main wings while in the cruise phase. But these components can become increasingly important during the approach/landing phase of a flight (due to increased pitch control demand). Enter into the equation that the horizontal stabilizers  16  can collect proportionally two to three times more ice than wings (due to the relatively small leading edge radius and the wing-dwarfed chord length); the flight phase becomes quite significant. The controller  60  can be programmed to notch up ice protection on the horizontal stabilizers  16  if the channel  76  conveys that the aircraft  10  is an approach/landing phase. 
     An input channel (e.g., channel  77 ) can be used to provide the controller  66  with information regarding the position of movable parts of the aircraft  10 . These movable parts typically comprise control surfaces hinged or otherwise movably attached to fixed aircraft components such as the wings  14  and/or the stabilizers  16 / 18 . The wings  14  can have, for example, ailerons for roll, flaps or slats for lift enhancement, and/or spoilers for lift reduction. The horizontal stabilizers  16  can have elevators for up-down deflection and the vertical stabilizer  18  can have a rudder for left-right deflection. 
     The positioning of movable parts during can heighten the importance of ice protection on certain aircraft surfaces  30 . For example, if wing flaps are deployed to improve lift coefficient, such deployment will also intensify nose-down pitching moment and thereby amplify the download duty of the horizontal stabilizers  16 . With the input channel  77 , the controller  60  can be notified of part movement and adjust ice-protection parameters accordingly. 
     An input channel (e.g., channel  78 ) can be used to convey cloud characteristics to the controller  60  as the aircraft  10  encounters such cast members. This information could be obtained, for example, by meteorological satellites and screened for alignment with the aircraft&#39;s global position. As icing depends largely upon cloud structures, such data would certainly be beneficial in the controller&#39;s creation of the most advantageous ice-protection strategy. 
     Cumulus clouds (i.e., clouds have heaping cauliflower-like appearances) present the greatest icing concerns worries at OATs between 0° C. and −20° C., with less cause for concern at OATs between −20° C. and −40° C. At OATs less than −40° C., icing fears essentially vanish with cumulus clouds. With a stratiform cloud (i.e., a cloud having a vertically thin layer-like appearance), the most aggressive ice protection steps are necessary at OATs between 0° C. to −15° C., less aggressive steps are necessary at OATs between −15° C. to −30° C., and at less than. Thus, an OAT at −35° C. corresponds to either a medium (cumulus) or low (startiform) alert level depending upon cloud structure. 
     Cloud structure aside, freezing rain and drizzle should be cautiously heeded when the OAT is at or below 0° C. Clear ice is most likely to form in freezing rain, a phenomena comprising raindrops that spread out and freeze on contact with a cold aircraft structure. As clear ice has a tenuous personality, the controller  60  can be programmed to treat potential clear-ice conditions with the utmost care and caution. 
     An input channel (e.g., channel  79 ) can be used to provide information concerning liquid water content in the ensuing airstream. The channel  79  can be fed information by, for example, an instrument sensor mounted on the outside of the aircraft  12 . (See e.g., http://ntrs.nasa.gov/archive/nasa/casi.ntrs/.nasa.gov/20090022002 200902156.) A liquid water content up to 0.125 g/m 3  could correspond, for example, to trace intensity with barely perceptible ice formations on unheated aircraft surfaces. The controller  60  therefore could be programmed to rest the ice protectors  51 - 55 . A liquid water content of 0.125 g/m 3  to 0.25 g/m 3  and a liquid water content of 0.25 g/m 3  to 0.60 g/m 3  could correspond to moderate ice intensities and the controller  60  could be adapted to bolster its attack upon receiving such data. Channel-conveyed LWC data upwards of 0.60 g/m 3  could trigger the controller  60  in a watchful stance whereat it monitors icing conditions with escalated diligence. 
     In the ice protection system  40  shown in  FIG. 3 , the ice protectors  51 - 55  are associated with one aircraft surface  30  and the controller  60  optimizes the ice protection of the regions  31 - 35  of such surface based on data input through the channel constellation  70 . As shown in  FIG. 4 , the ice protectors  51 - 55  for several of the aircraft surfaces  30  can be controlled by the same controller  60  based on the channel-input data. The latter arrangement may facilitate overall aircraft power optimization, as it allows the controller  60  to take into consideration the aircraft&#39;s overall ice protection needs. 
     One may now appreciate that with the aircraft ice protection system  40 , the ice protectors  50  can be operated so as to most effectively and efficiently addresses the flight circumstances, instead of rigidly expending the power required to remedy the most extreme ice impingement conditions. 
     Although the aircraft  10 , the aircraft surface  30 , the system  40 , the grid  50 , the controller  60 , and/or the channel constellation  70  have been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In regard to the various functions performed by the above described elements (e.g., components, assemblies, systems, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.