Airfoil with integral de-icer using overlapped tubes

Abstract: A structural member having integral surface de-icing capability and method of manufacture are described. The structural member includes a non-metallic high tensile modulus fiber-reinforced matrix structural backing, thin force and displacement generation means, and a thin high tensile modulus outer skin bonded to said backing and said force and displacement generation means which is positioned between the backing and the skin. The force and displacement generation means may include one or more inflatable tubular members preferably formed into a tube mat having bonded overlapped portions so as to distribute displacement forces. This reduces concentrated stress and fatigue while increasing surface shear forces across the ice accreting surface with each tube actuation. The structural member may be substituted for the aluminum alloy leading edge structural skin typically employed on modern aircraft.

Description: This invention relates to a composite structural member including as an integrated feature a system for separating a solid body such as a layer of ice from the outer surface of the structural member. More particularly, this invention relates to a structural member particularly suitable as an airfoil or leading edge which includes as an integral feature, a force and displacement generation means suitable for de-icing of the outer high modulus skin of the composite structural member when employed in aircraft leading edge surfaces. This invention further relates to an improved force and displacement generation means that can be used integrally with such a structural member, or can be attached to an airfoil or leading edge as part of a separate de-icer assembly. 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 cause 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 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 method for de-icing is typically termed mechanical de-icing. In the principal commercial mechanical de-icing means, pneumatic de-icing, the leading edge zone or wing or strut component of an aircraft is covered with a plurality of expandable, generally tube-like structures that are inflatable employing a pressurized fluid, typically air. Upon inflation, the tubular structures tend to expand substantially the leading edge profile of the wing or strut and crack ice accumulating thereon for dispersal into the airstream passing over the aircraft component. Typically, these tube-like structures have been configured to extend substantially parallel to the leading edge of the aircraft. These conventional low pressure pneumatic de-icers are 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 large 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. 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. Other mechanical means for effecting de-icing include electromechanical hammering such as that described in US-A-3 549 964. 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 US-A-4 690 353. 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 overlying conductor segments causing them to be separated near instantaneously. This distention tends to remove any solid body on the surface of the elastomeric material. Another electromechanical ice removal system is described in US-A-4 875 644, the teachings of which are herein incorporated by reference. Two or more sheet-like arrays, each containing in spaced apart relationship a plurality of parallel ribbon-shaped electrical conductive members, are rapidly and forcefully driven apart when a large magnitude current pulse is fed to the conductors. US-A-4 706 911 and US-A-4 747 575 disclose apparatus for de-icing leading edges in which an impulse of fluid under pressure is utilized to rapidly inflate an inflation tube positioned between a support surface and a sheet-like skin possessed of a substantially elevated modulus. The impulse of fluid is delivered to the inflation tube causing the high modulus skin to dislocate and then stop suddenly. Momentum imparted to the ice accumulations thereby causes additional ice movement which assists in ice detachment and dislodgement. The inflatable tubular structure in certain preferred embodiments is inflated within not more than about 0,1 second and preferably not more than about 0,5 milliseconds. Figure 4 of US-A-4 706 911 describe an ejector/pilot operated discharge valve suitable for use in such pneumatic impulse de-icers. In US-A-4 747 575 and in its Figure 7 there is disclosed a chattering valve for use in a pneumatic impulse de-icer which delivers a rapid series of fluid pressure pulses to the inflatable tube of a de-icer apparatus affixed to a leading edge. Efforts to improve such pneumatic impulse de-icing systems have led to continuing efforts to improve valves for delivery of the desired fluid impulse. In addition to the various improvements needed for airfoil and de-icing mechanisms, known pneumatic de-icers can also exhibit high stress points and bending moments typically near the anchor points of the inflatable tubes. Adjacent anchor points result in a "dead space" or inactive area where, despite actuation or inflation of either tube, no displacement occurs resulting in a high stress concentration. These inactive areas of high stress can cause fatigue in the outer skin particularly for high tensile modulus outer skins made of metal. From US-A-2 506 501 a de-icer for the leading edge of an airfoil is known in which between a substructure and an outer skin two layers of longitudinal tubular elements are arranged. All the tubular elements are parallel to each other and extend in the lengthwise (spanwise) direction of the airfoil. The tubular elements are arranged between the upper and the lower surfaces of the airfoil where the curvature of the airfoil is maximum. A first tubular element is located on the substructure while above this first tubular element and subjacent to the outer skin, two second tubular elements are arranged. The width of the first tubular element is greater than the overall width of the arrangement of the adjacent second tubular elements. Furthermore, a means for separately inflating each tubular element is provided. From US-A-2 937 826 a device for altering the leading edge shape of an airfoil is known which device theoretically could also be used for protecting the leading edges of airfoils against ice accumulation. According to the this known device, between a substructure and an outer skin an inflatable tubular element is arranged which extends in the lengthwise direction of the airfoil. Adjacent to the tubular element there is arranged an air chamber. Both the tubular element and the air chamber are located at the lower side of the substructure of the airfoil. Upon applying fluid under pressure into the inflatable tubular element, the adjacent air chamber is expanded and, as a consequence thereof, is filled with fluid at atmospheric pressure or at a very low pressure. While the wall of the tubular element is reinforced in order to withstand the mechanically strength when inflated, the wall of the air chamber is provided with no reinforcing means. The air chamber is not designed to introduce fluid under high pressure, so that no remarkable contribution to the alteration of the outer skin for cracking ice thereon can be achieved by the air chamber. It is the object of the present invention to provide a de-icing means for the leading edge of a substructure having improved de-icing capabilities reducing fatigue in the outer skin particularly for high tensile modulus outer skins made of metall. According to the invention as claimed in independent claims 1, 10 and 14, a pneumatic de-icer is provided that incorporates an overlap tube design which operates to distribute the ice displacement forces thereby reducing stress concentrations and fatigue in the outer skin, while at the same time increasing the tangential or chord-wise strain in the ice accreting surface, a manufacturing method is likewise provided. An improved de-icer according to this aspect of the invention is suitable for use with an integral leading edge/de-icer structural member as described herein, as well as with conventional pneumatic de-icer apparatus such as the type that can be separately assembled and then attached to an airfoil or leading edge. The features and advantages of the present invention will become more apparent when viewed in light of the description of the best embodiment to the invention and drawings which follow, which together form a part of the specification. In the drawing Figure 1 is a fragmentary sectional view of an airfoil, having a de-icer apparatus depicted in the un-energized state. Figure 1A is an enlarged view of an overlap tube feature according to the present invention, the overlap area being circled in Fig. 1. Figure 2 is an enlarged fragmentary sectional view of the apparatus similar to that shown in Figure 1 in its unenergized state with a layer of ice thereon, and Figure 3 is an enlarged fragmentary view of the apparatus of Figure 2 in its energized state. The present invention provides an apparatus in the form of a structural member having integral surface separation capability which is capable of de-icing a leading edge. The present invention also provides a method of manufacture of such apparatus and a method for de-icing employing such apparatus. The present invention also provides an improved de-icing displacement mechanism and method of making the same. This improved de-icing mechanism reduces stress fatigue in the ice accreting surface while at the same time improving the removal of ice from the surface by increasing surface shear forces over a larger area of the leading edge. De-icing is removal of ice subsequent to its formation upon a leading edge. A "leading edge" is that portion of a surface of a structure which functions to meet and break an airstream impinging upon the surface of the structure. Examples of leading edges are respective forward portions of wings, stabilizers, struts, nacelles, and other housings and protrusions first impacted by an airstream passing over an aircraft while in flight. With reference to Figure 1, an embodiment of a structural member having an integral de-icer is illustrated. In particular, this embodiment incorporates a different arrangement of the inflatable tubes, which arrangement results in improved de-icing performance in different types of leading edge designs, such as, for example, leading edges having ice accreting surfaces susceptible to fatigue. Another advantage of this embodiment of the force and displacement means is that it can be easily adapted for use with a conventional de-icer of the type described hereinbefore that is attached to a pre-existing airfoil or leading edge. It should be noted, however, that certain relative-dimensions of elements shown in Figs. 1-3 have been exaggerated for the sake of explanation. The structural member 10 may be attached or secured to the remainder of the airfoil structure 200 in a conventional manner such as flush fitting fasteners 50. Referring next to Figure 2, an improved de-icer 300 is shown having a surface ply or outer skin 22 that preferably has a high modulus of elasticity. Subjacent the outer skin 22 is an outer or skin bonding ply 24 of polymeric material. Immediately subjacent and underlying the bonding ply 24 is an improved expulsive force and displacement means 26, which preferably is in the form of a multi-tube mat 400. Immediately subjacent and underlying the force and displacement means is an inner bonding ply 28 of polymeric material. Subjacent and underlying the inner bonding ply 28 is a fiber reinforced composite substructure 30. A layer of ice 18 is shown adhered to the outer ice accreting surface 23 of the outer skin 22. The outer skin 22 is preferably of a high modulus metallic material such as titanium alloy or plastic material such as polyetheretherketone. However, those skilled in the art will understand that when the displacement means 26 is alternatively used in a conventional de-icer boot or assembly, the outer skin 22 and ice accreting surface may be made of an elastomeric material that is substantially more flexible and elastic than the preferred outer skin materials. As stated above the de-icer apparatus 300 includes a multi-tube mat 400 that preferably is prepared as a separate assembly prior to installation in the composite structural member 30. The tube mat 400 includes a plurality of inflatable tube elements 427. Bonding plies 24 and 28 are formed of polymeric material suitable for bonding to the layers on either side. Such compounds are well known in the art and the selection of a particular compound will be predicated upon a number of factors which include operating environment, the nature of the outer ice accreting skin 22 and the underlying force and displacement generation means 26 for the outer bonding ply 24, and for the inner bonding ply 28 the materials used in the force and displacement generation means 26 and the adjacent contiguous layer 29 of the underlying composite substructure 30. Where the outer skin 22 is formed of titanium alloy and the force and displacement generation means 26 comprises inflatable tubular members 27, the outer bonding ply 24 is preferably formed of nitrile phenolic resin in the form of a film such as film adhesive AF32 available from 3M Company. The inner bonding ply 28 in certain preferred embodiments is also formed from such 10 mil thick nitrile phenolic film adhesive. The same 3M product AF32 may be employed for both the outer bonding ply 24 and the inner bonding ply 28 provided it is compatible with the materials of the layers which it is to join. An eminently suitable alternate material for the inner and outer bonding plies 24, 28 and regions 25 is a flexibilized epoxy film such as code EA951 available from Hysol Aerospace Products, Pittsburg, California. Each inflatable member 427 is a tube-like structure typically running the length of the de-icer, i.e., in the spanwise direction of the apparatus and airfoil. Each inflatable member 427 is formed from polymer coated textile fabric. The fabric may be coated on one side only and formed into a tubular member with the coating facing to the outside of the tube or with the coating facing to the inside of the tube provided an adhesion barrier is placed in the inside of the tube during manufacture to prevent adhesive joining of the fabric layers, thereby preventing formation of an inflatable tubular member. Polytetrafluoroethylene (PTFE) film is well suited for use as an adhesive barrier in this application. Each inflatable tubular member 427 serves as a fluid impulse tube. The inflatable tubular members within the apparatus are joined by conduit means (not illustrated) to the remainder of a de-icing system (not illustrated) which includes a timer/controller (not illustrated), a high pressure gas supply (not illustrated), and an impulse delivery valve (not illustrated). A schematic of a suitable control system and high pressure valve for causing fluid impulse inflation of an inflatable tubular member in a structural member according to the invention having integral surface separation capability are described in US-A-4 706 911. Preferred embodiments of gas impulse delivery valves are described in US-A 4 873 647. After the separate tubes are formed with a predetermined length and width appropriate for the particular airfoil design, and prior to curing the tubes 427, the tubes are laid out lengthwise starting with the center or leading edge active tube 427a. Next, the chordwise laterally adjacent tubes 427b are overlapped widthwise along opposite edges 460,462 of the center tube 427a. Thus in this preferred embodiment, the tubes 427 are arranged generally in a configuration in which the tubes extend longitudinally in a spanwise direction along the airfoil leading edge and are placed and overlapped side by side in a chordwise direction. Other orientations of the mat are, of course, possible. As shown in Figure 1, additional lateral tubes 427c may be used depending on the degree of ice removal coverage desired for the leading edge 1. As shown in Figure 1A, each of the inflatable tubes 427 is overlapped widthwise with each tube that is adjacent thereto across the entire span of the tubes. In addition to being overlapped, the laterally adjacent tubes are preferably bonded together in the area of the overlap with the use of a suitable adhesive such as a phenolic cement. A suitable adhesive is the film adhesive AF32 available from 3M Company. Although the tubes 427 are bonded together in the overlap regions, preferably the tubes are not in fluid communication with each other. That is, each tube is separately inflatable as described previously herein, and inflation of one tube preferably does not result in the passage of fluid into an adjacent attached tube. The use of the cement to temporarily hold the mat together prior to cure is preferred for convenience, but not absolutely required. For example, the individual tubes are preferably formed with an adhesive layer applied on the inside of the tubes. This adhesive can preferably be used to provide the bonding layers 24, 25 as previously described herein, as well as the adhesive to bond the overlap regions. The amount of bonded overlap between laterally adjacent tubes may vary depending on the particular application of the de-icer assembly, however, an overlap of about 0,63 cm (a quarter inch) is preferred with tubes having approximately 5 cm (two inch) widths. Such an overlap is adequate to maintain the structural integrity of the mat when the individual tubes 427 are inflated while at the same time permitting an adequate distribution of the active expulsive forces. It is expected that for most applications, the amount of each overlap preferably will not exceed twenty-five percent of the width of each overlapped tube. As described, the mat 400 is preferably built as a separate assembly. The mat can then be installed in the female mold form in the position it will occupy in the resulting structural member, vacuum bagged and further cured in an autoclave to bond the parts together. The cured mat is then removed from the mold and the structural member 30 can be completed. Although preferably the mat is built as a separate assembly outside the mold, it is also possible to build the mat using the overlap configuration during individual placement of the tubes 427 in the female mold prior to cure. However, it is expected that in most situations, this approach will not be as efficient and useful as preparing the tube mat separately prior to installing it in the mold. Figure 3 is similar to Figure 3 and shows the improved tube mat construction in an expanded state. However, the movement of the surface 23 and tubes has been exaggerated in Figure 3 to illustrate the improved distribution of the displacement forces (resulting in lower bending moments and less fatigue) as well as increased shear stress being applied across the leading edge surface (due to all the tubes being at least partially actuated when one tube is inflated) caused by displacement of adjacent tubes when one tube is inflated. In Figure 3, the center tube 427a has been expanded by the application of a high fluid pressure impulse. Although the adjacent tubes 427b are not inflated with pressurized fluid, the adjacent tube surfaces bonded to the center tube 427a are subjected to a displacement force caused by displacement of the center tube 427a. This displacement force is greatest near the bonded areas and decreases laterally in a chordwise direction therefrom. Thus, inflating one tube causes an actuation or displacement of each bonded adjacent tube, which effect results in a distributed shear force being applied to the ice accreting surface 23. In fact, all of the attached tubes will be at least partially actuated. This increased shear force from the mutual actuation of the tubes occurs regardless of which tube or tubes are being pneumatically actuated during a de-icing cycle. Therefore, the strain and displacement forces applied to the surface 23 are distributed over a greater area when each tube is individually inflated resulting in a decrease in bending moments and stress points in the outer skin at the regions near the tube overlaps. However, at the same time, because each tube is partially actuated and exerts a shear displacement force to the surface 23, the chordwise strain applied to the ice accreting surface 23 apparently increases such that, quite unexpectedly, the ice removing capability of the de-icer is improved over a greater area of the leading edge. This is represented in Figure 1 with the shear force lines B. It will be noted that when the center tube 427a is inflated, the tight radius active surface experiences the highest amount of displacement force normal to the surface 23, but the remaining surface of the leading edge also experiences significant shear forces B to help dislodge ice over a greater percentage of the ice accreting surface. Although the invention has been described with reference to certain and preferred embodiments, including the best embodiments, it would be apparent to people skilled in the art of de-icing of aircraft that other variations are possible within the scope of the appended claims. Different adhesive materials may be employed. The individual inflatable tubes or the tube mat in the alternative embodiment may be bonded directly to the outer skin and the substructure without use of separately applied adhesive film bonding layers. The outer metallic skin may be treated to further enhance its hardness or to provide a reduced coefficient of ice adhesion. The outer metallic skin may be provided with a backing layer of fiber reinforced resin to enhance resistance to impact, e.g., hail or bird strikes. A combination of gas pressure impulse and electrically energized force and displacement generating means may be employed in a single part. The composite substructure need not be of uniform thickness or construction throughout the entire contour surface but rather may be locally made of differing dimensions and properties according to the requirements of the intended application. Specifically, the composite substructure may be reinforced adjacent to its point of mechanical joinder to remainder of the airfoil structure. Hydraulic as well as pneumatic fluid pressure may be used for actuating the inflatable members 427. The best manner of tube arrangement for a particular application is empirically determinable by one skilled in the art.

Claims: De-icer of the type that is attached to the surface of a support structure that together form a leading edge with integral de-icing capability, said leading edge extending in a lengthwise direction and having upper and lower surfaces, said de-icer comprising: a) an ice accreting surface (23), b) at least two inflatable tubes (427a,b,c) extending in a lengthwise direction, each tube (427a, b,c) being completely encircled by textile material in a widthwise direction and coated on at least one surface with polymeric material and c) means for separately inflating each tube (427a, b,c), at least one tube (427a,b,c) overlying a substantial portion of said upper surface of said support structure (30) and at least one tube (427a,b,c) overlying a substantial portion of said lower surface (30), each tube (427a,b,c) being subjacent said ice accreting surface (23) in adjacent lengthwise coextending relationship, each tube (427a,b,c) partially overlapping each adjacent tube (427a,b,c) along a widthwise portion, said overlapping area increasing transfer of chordwise strain in the ice accreting surface (23) from an area overlying a tube (427a, b,c) inflated by pressurized fluid to an area overlying a tube (427a,b,c) not inflated by pressurized fluid. De-icer according to claim 1 characterized in that said at least two tubes (427a,b,c) overlap not more than 25 percent of their respective widths. De-icer according to claim 1 or 2 characterize din that said at least two tubes (427a,b,c) are adhesively bonded together at said overlap portions so that inflation of one tube (427a,b,c,) causes a strain inducing displacement of the other tube (427a,b,c) to increase shear forces in said ice accreting surface (23). De-icer according to any one of claims 1 to 3 characterized in that said ice accreting surface (23) is part of a thin high tensile modulus outer skin (22) and said support structure (30) is a non-metallic high tensile modulus fiber reinforced matrix. De-icer according to any one of claims 1 to 4 characterized in that said at least two tubes (427a,b,c) are adhesively bonded to said overlying outer skin (22) and said underlying support structure (30) by respective layers (24,28) of nitrile phenolic or epoxy, such that said outer skin (22), said at least two tubes (427a,b,c) and said support structure (30) form a leading edge structure having integral surface de-icing capability. De-icer according to any one of claims 1 to 5 characterized by a center displacement tube (427a) and a plurality of laterally adjacent tubes (427b,c) on each side of said center tube (427a) with each tube (427a,b,c) extending lengthwise along said ice accreting surface (30), each of said tubes (427a,b,c) being joined to at least one laterally adjacent tube (427a,b,c) such that adjacent tubes (427a,b,c) partially overlap in a widthwise direction, all of said tubes (427a,b,c) being formed as an integral mat (400) that is structurally bonded to said overlying ice accreting surface (23) and said underlying support structure (30). De-icer according to any one of claims 1 to 6 characterized in that said ice accreting surface (23), said tube (427a,b,c) and said underlying support structure (30) form an integral de-icer assembly that can be bonded to an airfoil leading edge. De-icer according to any one of claims 1 to 5 characterized by at least a third tube (427a,b,c) overlying the support structure (30), said ice accreting surface (23) overlying said third tube (427a,b,c) being subjected to increased chordwise strain upon inflation of a non-adjacent tube (427a,b,c). De-icer according to any one of claims 1 to 5 characterized by at least a third tube (427a), said third tube (427a) substantially overlying a marginal area of said support structure (30) between said upper and lower surface, said ice accreting surface (23) overlying each tube (427a,b,c) disposed on said upper and lower surfaces being subjected to increased chordwise strain upon inflation of said third tube (427a). Structural member having integral surface de-icing capability comprising: a) a non-metallic high tensile modulus fiber reinforced matrix structural composite substructure (30), b) a high tensile modulus outer skin (22), c) thin force and displacement generation means including at leat two inflatable tubular elements (427a,b,c) extending in a lengthwise direction along said outer skin (22), d) each tubular element (427a,b,c) being subjacent said ice accreting surface (23) in adjacent lengthwise coextending relationship, each tubular element (427a,b,c) partially overlapping each adjacent tubular element (427a,b,c) along a width-wise portion, said overlapping area increasing transfer of chordwise strain in the ice accreting surface (23) from an area overlying a tubular element (427a,b, c) inflated by pressurized fluid to an area overlying a tubular element (427a,b,c) not inflated by pressurized fluid, and e) said tubular elements (427a,b,c) being connectable to a fluid impulse inflation means with each tubular element (427a,b,c) being inflatable independently of adjacent bonded tubular elements (427a, b,c). Structural member according to claim 10 characterized in that inflation of one of said tubular elements (427a,b,c) causes movement of said outer skin (22) and causes movement of adjacent tubular elements (427a,b,c) to increase chordwise strain in said outer skin (22) and distribute fatigue stresses over a greater surface area of said outer skin (22). Structural member according to claim 10 or 11 characterized in that laterally adjacent tubular elements (427a,b,c) are adhesively bonded together along said edge portions which are less than or equal to 25% of a tubular element's width. Structural member according to any one of claims 9 to 11 in combination with an airfoil, the structural member being secured to said airfoil to form the leading edge thereof. Method of making a tubular fluid displacement de-icer for a leading edge, the method comprising: a) forming an ice accreting outer skin (22), b) forming a multitube force and displacement mat (400) by laying adjacent inflatable displacement tubes (427a,b,c) in a lengthwise direction and parallel to each other, and joining said tubes widthwise in an overlapping manner, each tube (427a,b,c) being subjacent said ice accreting outer skin (22) in adjacent lengthwise coextending relationship, each tube (427a,b,c) partially overlapping each adjacent tube (427a,b, c) along a widthwise portion, said overlapping area increasing transfer of chordwise strain in the ice accreting outer skin (22) from an area overlying a tube (427a,b,c) inflated by pressurized fluid to an area overlying a tube (427a,b, c) not inflated by pressurized fluid, c) forming a support substructure (30), and d) curing and bonding said combined outer skin (22), said force and displacement mat (400) and said substructure (30) at elevated temperature and pressure to provide said de-icer. Method according to claim 14 characterized in that the step of forming said force and displacement mat (400) includes the steps adhesively bonding a plurality of said tubes (427a,b,c) to form said mat (400) prior to curing said tubes (427a,b,c), and curing said displacement mat (400) in the configuration it will assume in the completed de-icer prior to bonding it to said outer skin (22) and that support substructure (30). Method according to claim 14 or 15 characterized in that said outer skin (22) is formed of a high tensile modulus material and said substructure (30) is a composite structure formed of a plurality of layers of reinforcing filaments in a polymeric matrix. Method according to any one of claims 14 to 16 characterized in that said de-icer is integrally formed in a leading edge structural member (30). Method according to any one of claims 14 to 17 characterized in that said de-icer is attachable to a leading edge structural member (30). Method according to any one of claims 14 to 18 further including the steps of applying an inner bonding layer (28) to said force and displacement mat (400) and applying an outer bonding layer (24) to said outer skin (22), said bonding layers (24,28) being applied prior to said step of curing and bonding the combined elements.

Inventors: RAUCKHORST RICHARD LAWRENCE, RAUCKHORST, RICHARD LAWRENCE
Applicants: GOODRICH CO B F, THE B.F. GOODRICH COMPANY
Application year: 1993
Main classification: B64D15
IPC codes: B64D15