Improved leading edge pneumatic deicer assembly

Abstract: A pneumatic deicer assembly 32 for attachment to an airfoil includes a pair of plies 52, 54 which are stitched together with a zig-zag stitch line which periodically crosses over the airfoil leading edge.

Description: This invention relates to a pneumatic deicing system, and more particularly, a pneumatic deicing system having an expansion pattern suitable for improved deicing of aircraft leading edge surfaces. From the beginning of powered aviation, aircraft have been under certain flying conditions troubled by accumulations of ice on component surfaces of aircraft such as wings and struts. If unchecked, such accumulations can eventually so laden the aircraft with additional weight and so alter the airfoil configuration of the wings and control surfaces of that aircraft so as to precipitate an unflyable condition. Efforts to prevent and/or remove such accumulations of ice under flying conditions has resulted in three generally universal approaches to removal of accumulated ice, a process known generally as de-icing. In one form of de-icing known as thermal de-icing, leading edges, are heated to loosen adhesive forces between accumulating ice and the aircraft component. "Leading edges" as used herein means those edges of an aircraft component on which ice accretes and are impinged upon by air flowing over the aircraft and having a point or line at which this airflow stagnates. Once loosened, this ice is generally blown from the aircraft component by the airstream passing over the aircraft. There are two popular methods of heating leading edges. In one approach known as electrothermal de-icing, an electrical heating element is placed in the leading edge zone of the aircraft component, either by inclusion in a elastomeric boot applied over the leading edge or by incorporation into the skin structure of the aircraft component. This heating element is typically powered by electrical energy derived from a generating source driven by one or more of the aircraft engines and is switched on and off to provide heat sufficient to loosen accumulating ice. In small aircraft, a sufficient quantity of electrical power may be unavailable for use of electrothermal de-icing. In the other heating approach, gases at elevated temperature from one or more compression stages of a turbine engine are circulated through the leading edges of components such as wings and struts in order to affect a de-icing or anti-icing effect. This approach is employed typically only in aircraft powered by turbine engines by draining off compressed air having an elevated temperature from one or more compressor stations of a turbine engine. This approach can result in reduced fuel economy and lower turbine power output. The second commonly employed method for de-icing involves chemicals. In limited situations, a chemical has been applied or supplied to all or part of an aircraft to depress adhesion forces associated with ice accumulation upon the aircraft or to depress the freezing point of water collecting upon surfaces of the aircraft. The remaining commonly employed methods for de-icing are typically termed mechanical de-icing. One mechanical means for effecting ice de-icing includes electromechanical hammering such as that described in U.S. Pat. No. 3,549,964 to Levin et al . Concern respecting the susceptibility of the airfoil skin to stress fatigue upon being hammered over extended periods of time have functioned in part to preclude substantial commercial development or adoption of such technique. Another electromechanical ice removal system is described in U.S. Pat. No. 4,690,353 to Haslim et al . One or more overlapped flexible ribbon conductors, each of which is folded back on itself, is embedded in an elastomeric material. When a large current pulse is fed to the conductor, the anti-parallel currents in the opposed segments of adjacent layers of the conductor result in interacting magnetic fields producing an electrorepulsive force between the overlapping conductor segments causing them to be separated near instantaneously. This distention tends to remove any solid body on the surface of the elastomeric material. The principal commercial mechanical de-icing means, however, is termed pneumatic de-icing wherein the leading edge zone or wing or strut component of an aircraft is covered with a plurality of expandable, generally tube-like structures, inflatable by employing a pressurized fluid, typically air, with the deicer being formed from compounds having rubbery or substantially elastic properties. Typically, the material forming the inflatable tubes on such de-icer structures can expand or stretch by 40% or more during an inflatable cycle, thereby causing a substantial change in the profile the de-icer as well as in the leading edge to thereby crack ice accumulating on the leading edge. These conventional pneumatic de-icers require a volume of air to inflate their highly expandable tubes and the time for inflating such tubes typically and historically has averaged from about two and six seconds. The distortion of the airfoil profile caused by inflation of the tubes can substantially alter the airflow pattern over the airfoil and adversely affect the lift characteristics of the airfoil. The rubber or rubber-like materials forming these conventional pneumatic de-icers typically are possessed of a Young's modulus (modulus of elasticity) of approximately 6900 Kpa. The modulus of elasticity of ice is variously reported as being between about 275,000 Kpa and about 3,450,000 Kpa. Ice is known to be possessed of an elastic modulus enabling typical ice accumulations to adjust to minor changes in contours of surfaces supporting such ice accumulations. While the modulus of elasticity of rubber compounds used in conventional de-icers is much lower than the modulus of elasticity typically associated with ice accumulations. The large expansion of conventional pneumatic de-icers has functioned to crack or rupture the structure of the ice accumulations thereby allowing such accumulations to be swept away by impinging windstreams. Fig. 1 illustrates a prior pneumatic deicer 12 formed from a composite having rubbery or substantially elastic properties. The deicer 12 is disposed on an airfoil 14 across a leading edge 15. A plurality of tubes 16 are formed in the composite and are provided pressurized fluid, such as air, from a manifold 18. The manifold 18 is supplied fluid via a connector 20, which transfers fluid from a pressurized source (not shown). Connector 20 is integrated into the deicer 12 during manufacturing. Tubes 16 expand or stretch under pressure by 40% or more during inflation cycles, thereby causing a substantial change in the profile of the deicer (as well as the leading edge) to cause cracking of ice accumulating thereon. Fig. 2 is a cross sectional view of the prior pneumatic deicer 12 illustrated in Fig. 1. The deicer 12 is disposed on an airfoil 14 across leading edge 15. Upon inflation, the tubular structures 16 of prior pneumatic deicers expand substantially along or parallel to the leading edge profile of the wing or strut and crack ice accumulating thereon for dispersal into the airstream passing over the aircraft component. The principal ice removing bending and shearing stresses are therefore exerted primarily in geometrical planes normal to the axis of the inflated tube radius. In geometrical planes containing the axis of the inflated tube radius, however, little or no principal ice removing stresses are produced. Efforts to improve such pneumatic impulse de-icing systems have led to continuing developments to improve their efficiency. Such a deicer is described in US-A-2 025 919 and US-A-2 438 693. The tubes are formed by single inflatable tubes held between a bottom and a top sheet. The tubes are connected to each other only at an end thereof where the fluid conduit is provided. In the deicer of US-A-2 025 919, which represents the prior art as referred to in the preamble of claim 1, the tubes lie side by side forming a non-inflatable zig-zag line between them which crosses the leading edge of the airfoil several times. Another deicer is described in EP-A-0 066 519. The deicer comprises a stretchable top layer and a non-stretchable bottom layer. The bottom layer and the top layer are weaved together by broad weave portions forming parallel tube-like portions between them. It is an object of the invention to improve a deicing apparatus for attachment across the leading edge of an airfoil. This object is achieved, according to the invention, by the features of claim 1. The deicing apparatus for an airfoil having a leading edge includes a first layer of flexible material, a second layer of a stretchable material, wherein the first and second layers are stitched together with stitch lines that zig-zag across the leading edge. When inflated, the deicing system of the present invention has a pattern of inflated portions separated by stitch lines, the pattern being disposed along the leading edge. The inflation pattern of the present invention provides stresses in accumulated ice on airfoil leading edge in directions unavailable heretofore, thereby providing improved deicing capabilities. The present invention is economical to manufacture and facilitates customization of effective deicing capabilities to a wide variety of components. These and other objects, features, and advantages of the present invention will become more apparent in light of the detailed description of exemplary embodiments thereof, as illustrated by the drawings. Fig. 1 is a top view of a prior art deicing system. Fig. 2 is a cross sectional view of a prior art deicing system. Fig. 3 is a top view of a deicer assembly in accordance with the present invention. Fig. 4 is a cross sectional view taken along line 4-4 of Fig. 3, of a deicer assembly in accordance with the present invention. Fig. 5 is a pictorial view, partly in cross section of a deicing system in accordance with the present invention. Figs. 6a-6d are fragmentary top views of second, third, fourth and fifth embodiments of deicer assembly stitching patterns in accordance with the present invention. Fig. 7 is a top view of a sixth embodiment of a deicer assembly in accordance with the present invention. Fig. 8 is a top view of a seventh embodiment of a deicer assembly in accordance with the present invention. Fig. 9 is a top view of a eighth embodiment of a deicer assembly in accordance with the present invention. The present invention provides an apparatus for deicing a leading edge surface. By "deicing" what is meant is the removal of ice subsequent to formation of the ice upon the leading edge. By "leading edge" what is meant is that portion of a surface of a structure which functions to meet and in substantial measure break an air stream impinging thereon. Examples of leading edges would be forward edge portions of wings, stabilizers, struts, nacelles, propellers, rotating wings, tail rotors, and other housings, objects and protrusions first impacted by an air stream flowing over an aircraft in flight as well as spars, struts and other structural elements of marine vessels, towers and buildings. Referring now to the drawings wherein like reference numerals designate like or corresponding parts throughout different views, there is shown in Figs. 3 and 4 a deicing system 30 in accordance with the present invention which includes a deicer assembly 32 comprised substantially of a composite of flexible material. The deicer assembly 32 is formed as part and parcel of an airfoil skin 34 thereby defining the outer contour of the airfoil. The preferred method of integrating the deicer assembly 32 with the airfoil 34 is to provide an indentation (not shown) in the airfoil, manufacture the deicer assembly as a separate entity, and bond or attach the deicer assembly onto the airfoil at the location of the indentation. The preferred bonding means to attach a deicer assembly 32 to the airfoil 34 is to apply an adhesive, such as catalog number 1300L manufactured by the 3M corporation, to both contacting surfaces. The principle inflatable portion of the deicer assembly 32 is a plurality of tube-like passages 36 formed therein and arranged substantially parallel to one another. Tube-like passages expand or inflate when provided a pressurized fluid, such as air. All inflatable tube-like passages 36 are fluidly connected at one end of deicer assembly 32 by a manifold 38 also formed therein. A plurality of zig-zag lines 78 criss-cross across the tube-like passages 36. Manifold 38 is provided pressurized fluid through a connector 40. The preferred construction for deicer assembly 32 is a composite, comprised from bottom (the side of material bonded to the airfoil) to top of: a) a bottom layer or ply 50 of flexible material, such as neoprene; b) a first intermediate, non-stretchable layer or ply 52 of nonstretchable fabric such as nonstretchable nylon which is rubber coated on one side; c) a second intermediate, layer or ply 54 of stretchable fabric, such as stretchable nylon which is rubber coated one side; and, e) a top layer or ply 56 of a tough yet pliable weather impervious material, such as neoprene. An inflation pattern is created by sewing the nylon layers 52, 54 together in a predetermined pattern using thread 60. The preferred material for thread 60 is nylon or kevlar. All lines in Fig. 3 which are created by sewing thread 60 in this manner are illustrated as dotted lines. Layers 54-56 and 50-52 may be bonded together utilizing an appropriate cement, such as catalog number CHEMLOC 220 manufactured by the Lord Corporation. CHEMLOC is a registered trademark of the Lord Corporation. Referring now to Fig. 3, a solid line 70 represents the outer edge of the top layer 56 of the deicer assembly 32. Dashed lines 72, 74 are stitches which represent the outer boundaries of pressurized fluid flow between intermediate layers 52, 54. Pressurized fluid is provided from a source (not shown) through connector 40. Substantially parallel, straight stitch lines 76 represent the stitches which form the inflatable tube-like passages 36, typically arranged substantially along or parallel to the leading edge profile of the airfoil to be deiced, although the lines may also be arranged in other orientations to the leading edge. A plurality of zig-zag stitch lines 78 are provided which crisscross across the horizontal lines 76, with one zig-zag stitch 78 per horizontal line 76. Preferably, the zig-zag lines 78 are shaped similar to a saw tooth waveform to thereby form periodic triangular shaped areas 84 on both sides of each horizontal line 76. It is preferable that the horizontal lines 76 and the zig-zag lines 78 be merged or part of the same stitching pattern by forming loops 80 in the ends of horizontal and zig-zag stitches nearest the manifold 38 in order to prevent separation of the stitch. With this configuration, fluid flows into each tube-like passage 36 between the zig-zag stitch lines as illustrated by arrows 82. Air also flows across stitch lines 76, 78, thereby inflating triangular portions 84, although these portions do not inflate as much as the tube-like passages 36 because of the restricted fluid flow caused by the stitch lines. The inflation pattern created by the stitch pattern of the present invention is best described as "dimpled" or a dimple pattern wherein there is a pattern of high inflated areas and low inflated areas, each inflated area being surrounded by stitch lines which form dimples, or inactive areas, the pattern appearing over the surface of the deicer assembly 32 when pressurized fluid is provided to connector 40. It is to be noted that stitch lines 72, 74, 76, 78 are stitches provided through layers 52 and 54 of the deicer assembly 32. The deicer assembly 32 illustrated in Fig. 3 is configured for being positioned on both sides of a leading edge, represented by line 100. The section of deicer assembly 32 below line 100 would therefore be on one side of the leading edge and a section of deicer 32 found above line 100 would be placed on the opposite side of the airfoil 34. A zig-zag stitch line 102 is sewn through intermediate layers 52, 54 across the leading edge line 100. The preferred pattern for stitch line 102 is what can be described as a slanted or skewed square wave. It can be seen that two tube-like passages 36 are provided on either side of the leading edge line 100 and therefore on either side of stitch line 102. In this manner, a series of inflated passageways 75 are provided directly across the leading edge 100 of the airfoil about perpendicular to the leading edge, thereby providing improved deicing characteristics directly on the leading edge 100 and improving deicing of the airfoil by initiating a wave of ice accretion starting from the leading edge 100 and spreading on both sides of airfoil 34. Referring now to Fig. 4, the inflation pattern across leading edge 100 consists of a series of high inflation areas or passageways 75, created by zig-zag stitches 60. Referring now to Fig. 5, a deicing system 96 in accordance with the present invention includes a deicer assembly 32 attached to an airfoil 34. Deicer assembly 32 is comprised of a bottom gum layer or ply 50; a first intermediate, non-stretchable layer or ply 52; a second intermediate, stretchable layer or ply 54; and, a top layer or ply 56. Tube-like passages are formed by stitching layers 52 and 54 together in a predetermined pattern consisting of a plurality of parallel stitch lines 76, each parallel line having a zig-zag stitch line 78 which criss-crosses thereover. The combination of parallel straight lines 76 with zig-zag lines 78 creates a dimple type pattern when deicer assembly 32 is inflated by pressurized fluid provided from a fluid source 97 through a line 98. The dimple pattern has highest inflated points 90, intermediate inflated points 92 and lowest inflated points 94 between stitch lines 76, 78. A zig-zag stitch line 102 periodically crosses over leading edge 100 to thereby form inflated passageways 75 when the system is inflated. Referring now to Figs. 6a, 6b, 6c and 6d, wherein stitch patterns in accordance with a second, third, fourth and fifth embodiments of the present invention are generally similar to the stitch patterns illustrated hereinbefore in the previous figures and are thus indicated by reference numerals corresponding to those discussed above, except that 200, 300, 400 and 500 "prefixes" are utilized. In Fig. 6a, a second embodiment for the zig-zag stitch pattern 202 across leading edge 100 of the present invention is a square wave shape. In Fig. 6b, a third embodiment for the zig-zag stitch pattern 302 across leading edge 100 of the present invention is a sine wave shape. In Fig. 6c, a fourth embodiment for the zig-zag stitch pattern 402 across leading edge 100 of the present invention is a slanted or skewed square wave shape, wherein some of the zig-zag stitches are double stitches, which prevents fluid from accumulating in the area 403 between stitches, thereby creating an inactive zone when the deicer is inflated. In Fig. 6d, a fifth embodiment for the zig-zag stitch pattern 502 across leading edge 100 of the present invention is a saw tooth wave shape. It is to be noted that the scope of the present invention is not to be limited by the particular stitch patterns illustrated and that other patterns not shown hereinbefore may be utilized for similar deicing results. Operation of the deicing system 30 is as follows. Pressurized fluid is provided by a source (not shown) through connector 40, into the manifold 38 and into each tube-like passage 36 and triangular area 84, wherein the modulus of elasticity of the material of deicer assembly 32 allows for expansion thereof, thereby causing a contoured airfoil surface which causes ice accumulated on top of the surface to be dislodged. Referring now to Fig. 7, wherein a deicer assembly 632 for a deicing system in accordance with a sixth embodiment of the present invention is generally similar to the deicing systems illustrated hereinbefore in the previous figures and is thus indicated by references numerals corresponding to those discussed above, except that a 600 "prefix" is utilized. Deicer assembly 632 includes a plurality of tube-like passages 636 formed therein and arranged substantially parallel to one another. Tube-like passages expand or inflate when provided a pressurized fluid, such as air. Alternate tube-like passages 636 are fluidly connected at one end of deicer assembly 632 by a manifold 638 also formed therein. A line 670 represents the outer edge of the fabric layers of the deicer assembly 632. Lines 672, 674 are stitches which represent the outer boundaries of pressurized fluid flow between intermediate layers. Pressurized fluid is provided from a source (not shown) through connector 640. Substantially parallel, straight stitch lines 676 represent the stitches which form the inflatable tube-like passages 636, arranged substantially along or parallel to the leading edge profile of the airfoil to be deiced, although the lines may also be arranged in other orientations to the leading edge. The deicer assembly 632 is configured for being positioned on both sides of a leading edge, represented by line 600. A zig-zag stitch line 602 is sewn through the intermediate layers across the leading edge line 600. The pattern for stitch line 602 is what can be described as a double slanted or skewed square wave. In this manner, a series of inflated passageways 675 are provided directly across the leading edge 600. Referring now to Fig. 8, wherein a deicer assembly 732 for a deicing system in accordance with a seventh embodiment of the present invention is generally similar to the deicing systems illustrated hereinbefore in the previous figures and is thus indicated by references numerals corresponding to those discussed above, except that a 700 "prefix" is utilized. Deicer assembly 732 includes a plurality of tube-like passages 736 formed therein and arranged substantially parallel to one another. Tube-like passages expand or inflate when provided a pressurized fluid, such as air. All inflatable tube-like passages 736 are fluidly connected at one end of deicer assembly 732 by a manifold 738 also formed therein. A line 770 represents the outer edge of the fabric layers of the deicer assembly 732. Lines 772, 774 are stitches which represent the outer boundaries of pressurized fluid flow between intermediate layers. Pressurized fluid is provided from a source (not shown) through connector 740. Substantially parallel, straight stitch lines 702 represent the stitches which form the inflatable tube-like passages 736, which are arranged at an angle theta with the leading and zig-zag across the leading edge 700. In this manner, a series of inflated passageways are provided from one side of the airfoil, across the leading edge 700 to the other side of the airfoil. Referring now to Fig. 9, wherein a deicer assembly 832 for a deicing system in accordance with a seventh embodiment of the present invention is generally similar to the deicing systems illustrated hereinbefore in the previous figures and is thus indicated by references numerals corresponding to those discussed above, except that a 800 "prefix" is utilized. Deicer assembly 832 includes a plurality of tube-like passages 836 formed therein and arranged substantially parallel to one another. Tube-like passages expand or inflate when provided a pressurized fluid, such as air. All inflatable tube-like passages 836 are fluidly connected at one end of deicer assembly 832 by a manifold 838 also formed therein. A line 870 represents the outer edge of the fabric layers of the deicer assembly 832. Lines 872, 874 are stitches which represent the outer boundaries of pressurized fluid flow between intermediate layers. Pressurized fluid is provided from a source (not shown) through connector 840. Substantially parallel, straight stitch lines 802 represent the stitches which form the inflatable tube-like passages 836, which are arranged at an angle theta with the leading and zig-zag across the leading edge 800. In this manner, a series of inflated passageways are provided from one side of the airfoil, across the leading edge 800 to the other side of the airfoil. Unlike deicer assemblies illustrated hereinbefore, deicer 832 is configured specifically for leading edges and does not cover other areas of the airfoil.

Claims: A pneumatic deicing apparatus for attachment across the leading edge line (100) of an airfoil (34), said apparatus comprising: a bottom ply (50) of a first fabric, a top ply (54) of a stretchable second fabric, pressurized fluid is provided between said bottom and top plies (50,54) to thereby inflate said top ply (54), and said top ply (54) and said bottom ply (50) form inflatable portions with a non-inflatable line (102;402;502;602;702;802) between the inflatable portions, said line (102;402;502; 602;702;802) being a zig-zag line extending traverse to the leading edge line (100) of the airfoil (34) and periodically crossing over the leading edge (100), characterized by said top and bottom plies (54,50) being stitched together with at least one stitch line (102,402,502, 602,702,802) using thread (60) forming said non-inflatable line, the stitch line (102,402,502,602,702,802) allowing flow of the fluid therethrough from one portion to another, and the top ply (54) being inflated around said stitch line (102,402,502,602,702,802). A pneumatic deicing apparatus according to claim 1, wherein said zig-zag stitch line (702) is shaped as a slanted square wave. A pneumatic deicing apparatus according to claim 1, wherein said zig-zag stitch line (502) is shaped as a saw-tooth wave. A pneumatic deicing apparatus according to claim 1, wherein said zig-zag stitch line (302) is shaped as a sine wave. A pneumatic deicing apparatus according to claim 1, wherein said zig-zag stitch line (202) is shaped as a square wave. A pneumatic deicing apparatus according to claim 1 or 5, wherein a plurality of stitch lines (402,403) are substantially parallel. A pneumatic deicing apparatus according to one of claims 1-6, wherein said bottom ply (50) is comprised of nonstretchable nylon and said top ply (54) is comprised of stretchable nylon. A pneumatic deicing apparatus according to one of claims 1-7, further comprising: a base layer (52) disposed beneath and attached to said bottom ply (50), and a surface layer (56) disposed above and attached to said top ply (54). A pneumatic deicing apparatus according to one of claims 1-7, further comprising: a base layer (52) comprised of a first elastomer and disposed beneath and attached to said bottom ply (50), and a surface layer (56) comprised of a second elastomer and disposed above and attached to said top ply (54).

Inventors: FAHRNER ALAN JOHN, WEISEND NORBERT ADRIAN JR, FAHRNER, ALAN JOHN, WEISEND, NORBERT ADRIAN, JR.
Applicants: GOODRICH CO B F, THE B.F. GOODRICH COMPANY
Application year: 1993
Main classification: B64D15
IPC codes: B64D15