1. Cross-Reference to Related Patent
U.S. Pat. No. 4,875,644, issued Oct. 24, 1989, entitled "Electro-Repulsive Separation System for De-Icing," by Lowell J. Adams, et al., the disclosure of which is incorporated herein by reference (hereinafter referred to as the "Electro-Repulsive Separation System Patent").
2. Field of the Invention
The invention relates to de-icers for aircraft and, more particularly, to de-icers that operate by deforming ice-accumulating surfaces.
The present invention addresses the foregoing concerns and provides a new and improved planar coil construction especially adapted for use as part of a de-icer. The planar coil according to the invention includes a first sheet-like member defined by a first, continuous, electrical conductor having a plurality of turns and first and second ends. The first end of the first conductor defines an electrical input to the coil, and the second end of the first conductor defines an electrical output. The invention includes a second sheet-like member defined by a second, continuous, electrical conductor having a plurality of turns and first and second ends. The first end of the second conductor defines an electrical input, and the second end of the second conductor defines an electrical output from the coil. The second end of the first conductor and the first end of the second conductor are electrically connected. The first and second sheet-like members are disposed parallel to each other with the turns of the first and second conductors being positioned adjacent each other. The direction of current flow through the turns of the first conductor can be arranged to be substantially the same as that through the turns of the second conductor, or it can be arranged to be substantially opposite that through the turns of the second conductor. In addition, within a sheet-like member the adjacent conductors from the center out have current flow in the same direction, which is of particular importance for electro-repulsive force de-icers.
FIG. 1 is a schematic, cross-sectional view of a prior art mechanical de-icer;
FIG. 2 is a schematic electrical circuit showing how the de-icer of FIG. 1 is activated;
FIG. 3 is a schematic electrical circuit showing how a plurality of de-icers according to FIG. 1 can be installed in a structural member;
FIG. 4 is a cross-sectional view of a de-icer according to the invention attached to the outer surface of a structural member;
FIG. 4A is an enlarged cross-sectional view of a portion of the de-icer shown in FIG. 4.
FIG. 5 is a cross-sectional view of an alternative embodiment of the invention shown in FIG. 4 illustrating another technique for attaching the de-icer to the outer surface of a structural member;
FIG. 6 is a cross-sectional view of an alternative embodiment of the invention showing a metal target used in conjunction with a coil;
FIG. 7 is a cross-sectional view similar to FIG. 6 wherein a so-called displacement void is included as part of the de-icer;
FIG. 8 is a cross-sectional view similar to FIG. 7 wherein the displacement void is disposed adjacent the structural member;
FIG. 9 is a top plan view of a planar coil usable with the present invention;
FIG. 10 is a top plan view of another planar coil usable with the present invention;
FIG. 11 is a top plan view of superimposed planar coils usable with the present invention;
FIG. 12 is a perspective view of a spiral-wound coil usable with the present invention;
FIG. 13 is a schematic front elevational view of the leading edge of a structural member showing one arrangement of multiple de-icers according to the invention;
FIG. 14 is a view similar to FIG. 13 showing an alternative arrangement of multiple de-icers according to the invention;
FIG. 15 is a view similar to FIG. 13 showing yet an additional arrangement of multiple de-icers according to the invention;
FIG. 16 is a schematic electrical circuit diagram for a de-icer according to the invention;
FIG. 17 is a plot of current versus time showing the profile of a current pulse used with the present invention;
FIG. 18 is a plot of displacement, velocity and acceleration versus time showing the movement of a portion of the de-icer according to the invention,
FIG. 19 is a graph of force versus coil current showing the performance of a de-icer in accordance with the present invention compared with prior art mechanical de-icers;
FIG. 20 is an eddy current profile for a one-inch radius coil;
FIG. 21 is an eddy current density profile as a function of time for a one-inch radius coil;
FIG. 22 is a plot of pressure distribution on a metal target as a function of the radius of the target;
FIG. 23 is a plot of pressure distribution on a metal target versus time at various radii;
FIG. 24 is a plot on in-plane pressure per unit target area;
FIG. 25 is a plot of radial distribution of in-plane pressure per unit target area; and
FIG. 26 is a plot of impulse versus target thickness for various target materials.
The present invention provides a technique especially adapted for de-icing the leading edges of structural members. De-icing is the removal of ice subsequent to its formation upon a leading edge. A leading edge is that portion of a structural member that functions to meet and break an airstream impinging upon the surface of the structural member. Examples of leading edges are the forward portions of wings, stabilizers, struts, nacelles, rotors, and other housings and protrusions first impacted by an airstream.
FIGS. 1-3 illustrate a known mechanical de-icer 10 and electrical circuitry thereof. The de-icer 10 includes first and second coils 12 that are disposed with a structural member (such as a wing) 14 near the backside of the leading edge thereof. The surface of the structural member 14 is made of metal such as aluminium which will be referred to as the "skin." The coils 12 are mounted to a spar 16 by means of a mounting bracket 18. The coils 12 are circular in plan view. A circular, unalloyed aluminium disk 20 is bonded to the inner surface of the leading edge directly opposite each of the coils 12.
Referring to FIG. 2, each coil 12 is connected in series with an energy storage capacitor 22 and a thyristor 24. A diode 26 is connected in parallel with the capacitor 22. An electrical impulse is initiated by supplying a trigger pulse to the thyristor 24, allowing the capacitor 22 to discharge through the coil 12. Because the thyristor 24 has diode properties, the current follows the first positive loop of the RLC response, after which the thyristor 24 reopens the circuit. This leaves the capacitor 22 reverse-charged. Such reverse-charging reduces capacitor life substantially. For that reason, the diode 26 is placed across the capacitor 22.
Referring to FIG. 3, a typical spanwise installation of the coils 12 within a wing is shown. Each of the coils 12 is separated laterally from other coils 12 by about 16 inches. The coils 12 are supplied a single power unit 28 that includes a transformer 30. The capacitor 22 is connected across the secondary side of the transformer 30. A switching device 32 is connected to each of the thyristors 24 in order to provide a trigger pulse to the thyristors 24.
When the capacitor 22 is discharged through each coil 12, a rapidly forming and collapsing electromagnetic field is created that induces eddy currents in the disk 20 and the metal skin 14. The electromagnetic fields resulting from current flow in the coil 12, the disk 20, and the skin 14 create a repulsive force of several hundred pounds magnitude, but with a duration of only a fraction of a millisecond. A small amplitude, high acceleration movement of the skin 14 acts to shatter, debond, and expel the ice. Two or three such "hits" are performed in short order, separated by the time required to recharge the capacitor 22, and then ice is permitted to accumulate again until it approaches an undesirable thickness. By appropriate control of the switching device 32 the coils 12 can be activated sequentially in order to create a "ripple" effect that is believed to be more effective in shedding ice due to the propogation of skin movement in both chordwise and spanwise directions.
As will be appreciated from the foregoing description, the referenced de-icer 10 depends for its effectiveness upon deformation of the skin. The displacement of the metal surface subject to icing is very limited; typically it requires three impact pulses to remove accumulated ice under all icing conditions. Further, although the skin is displaced only to a limited extent, it is necessary to produce high forces in order to accomplish even that limited displacement. An additional problem is that the forces are "negative" forces in that they apply a tensile load to the leading edge. Aircraft structural members are designed to better withstand compressive loads, rather than tensile loads.
Referring now to FIG. 4, a de-icer according to the invention is indicated by the reference numeral 40. The de-icer 40 is similar to the de-icer 10 in that it employs a coil 42. However, as will be discussed below, the de-icer 40 differs significantly from the de-icer 10. The differences will be apparent from the description that follows.
The de-icer 40 as shown in FIG. 4 is formed in an integral unit that is bonded or otherwise securely attached to the leading edge of a structural member. The leading edge, or skin, of the structural member is indicated by the reference numeral 44. Typically the skin 44 will be made of metal such as an aluminium alloy. The coil 42 normally will be a multi-layer coil comprised of individual planar coil elements (see the discussion that follows with respect to FIGS. 9-11). In all of the embodiments described herein, the coil 42 is a unitary structure that has no portions that move relative to each other. For purposes of the present discussion, the coil 42 will be indicated schematically as a single element. The coil 42 includes a first surface that at rest is in contact with the exterior surface of the skin 44, and a second surface that is spaced from the skin 44. The coil 42 is not bonded to the skin 44, so that it can move away from and toward the skin 44.
The second surface of the coil 42 is covered by a surface ply 46. The surface ply 46 preferably is not bonded to the second surface of the coil 42. The lateral edges of the coil 42 are abutted by a flexible, non-metallic filler layer 48 in order to provide a smooth transition with the contour of the skin 44. The de-icer 40 is bonded or otherwise securely attached to the skin 44 by means of the layer 48. The surface ply 46 is bonded to the layer 48. At the ends of the surface ply 46, the surface ply 46 is bonded or attached by a fastener (not shown) to the skin 44. Accordingly, the coil 42 and the surface ply 46 are able to move away from, and toward, the skin 44 intermediate the portions of the layer 48 that are bonded to the skin 44. It will be apparent from an examination of FIG. 4 that the surface ply 46 not only forms a major portion of the exterior surface of the de-icer 40, but it also functions as a support member for the coil 42 (together with the layer 48) so as to keep the coil 42 properly positioned relative to the skin 44.
The coil 42 preferably is made of unalloyed copper. Reference is made to U.S. application Ser. No. 07/437,489, filed Nov. 15, 1989, Lowell J. Adams et al., entitled "Planar Coil Construction," The present invention provides a planar coil construction especially adapted for use as part of a de-icer that may be attached to the leading edges of structural members. De-icing is the removal of ice subsequent to its formation upon a leading edge. A leading edge is that portion of a structural member that functions to meet and break an airstream impinging upon the surface of the structural member. Examples of leading edges are the forward portions of wings, stabilizers, struts, nacelles, rotors and other housings and protrusions first impacted by an airstream.
Although the planar coil construction of the present invention is described in the environment of a de-icer, it is to be understood that the invention can be used in other environments. For example, the invention could be used as a force-generating element in a vibratory conveyor, as a switching device, or in a variety of other applications. Accordingly, the invention as described and claimed herein shall not be limited solely to use in de-icer applications.
Referring to FIG. 27, a first, sheet-like member is indicated by the reference numeral 210. The member 210 is defined by a first, continuous, electrical conductor having a plurality of turns 212, a first end 214 and a second end 216. The first end 214 defines an electrical input to the member 210, while the second end 216 defines an electrical output from the member 210. The member 210 is formed from a single sheet of unalloyed copper of aluminum having a thickness of about 0.016 inch. The turns 212 have a width within the range of 0.070-0.125 inch.
The first end 214 is disposed at one corner of the member 210, while the second end 216 is disposed at the center. Although the member 210 is illustrated as being rectangular, it could be square, circular, or any other desired shape.
Referring to FIG. 28, a second, sheet-like member is indicated by the reference numeral 220. The member 220 is defined by a second, continuous, electrical conductor having a plurality of turns 222, a first end 224, and a second end 226. The first end 224 defines an electrical input to the member 220, while the second end 226 defines an electrical output from the member 220. The member 220 is formed from a single sheet of unalloyed copper or aluminum having a thickness of about 0.016 inch. The turns 222 have a width within the range of 0.070-0.125 inch. As with the member 210, the member 220 is rectangular, with one end disposed at a corner and the other end disposed at the center.
Referring to FIG. 29, the members 210, 220 are illustrated in a "completely superimposed" arrangement to form a coil indicated by the reference numeral 230. In this arrangement, the turns 212 are disposed immediately adjacent comparable turns 222. The ends 216, 224 are joined as by soldering or welding to form an electrical connection. As will be appreciated from an examination of FIG. 29, electrical current directed into the first end 214 will follow a path through the turns 212 that is in the same direction as the superimposed, adjacent turns 222. The first member 210 typically has 12{fraction (1/8)} turns, as does the second member 220. (An 8{fraction (1/8)} turn member is shown for clarity of illustration). Accordingly, the superimposed members 210, 220 define a coil pair 230 having 24{fraction (1/2)} turns.
Referring to FIG. 30, two assembled coil pairs 230 have been formed as shown in FIG. 30, and are "partially superimposed" with respect to each other. The resultant coil construction, indicated by the reference numeral 240, includes about 25% of the total turns overlapped at the center of the assembled coil pairs 230.
Referring to FIG. 31A, arrangements of two coil pairs 230 are shown as they might be used in practice to form part of a de-icer. As is explained in more detail in the Electro-Repulsive Separation System Patent, upon supplying a short-duration, shaped, high-current pulse to the coil pairs 230, the outermost portion of the de-icer will be distended as indicated at 242 so as to shatter, debond, and expel any ice that may have accumulated thereon. Referring to FIG. 31B, the coil airs 230 are partially superimposed and an enhanced force will be generated in the region of the overlap where, presumably, the de-icing action will be enhanced. The enhanced distension of the de-icer is indicated by the reference numeral 244.
Referring to FIG. 32, an alternative construction of a sheet-like member is indicated schematically by the reference numeral 250. The member 250, like the members 210, 220, is defined by a first, continuous, electrical conductor having a plurality of turns 252, a first end 254, and a second end 256. Unlike the members 210, 220, the second end 256 crosses a portion of the turns 252 and is disposed adjacent the first end 254 at a location outside the outermost turn 252. The first end 254 defines an electrical input to the member 250, while the second end 256 defines an electrical output from the member 250. The second end 256 is electrically isolated from the turns 252 that are crossed. The member 250 is formed from a single sheet of unalloyed copper or aluminum having a thickness of about 0.016 inch. The turns 252 have a width within the range of 0.070-0.125 inch.
Referring to FIG. 33, an assembled coil construction employing four sheet-like members 250 is indicated schematically by the reference numeral 260. Pairs of the members 250 are separated by dielectric layers 262 as well as the second end 256 of the members 250. The dielectric layers 262 preferably are formed of a material such as two layers of polyamide film, each having a thickness of about 0.003 inch. A suitable polyamide film is available from the E.I. Dupont deNemours & Company under the trademark KAPTON. Before use, the film should be surface-treated by acid-etching, plasma treating or the like to improve adhesion.
Referring to FIG. 34, the members 250 of the coil assembly 260 are shown displaced relative to each other for purposes of illustrating the directions of current flow therein. The uppermost member 250 is shown in solid lines, while the immediately adjacent lower member 250 is shown by dashed lines. As can be seen in FIG. 34, the second end 256 of the uppermost sheet 250 is electrically connected to the first end 254 of the immediately adjacent lower member 250. The output of the lower member 250 is directed through the end 256 to the second end 256 of the lower member 250 of the adjacent coil pair. The lower coil pair members 250 are connected in the same manner as the upper coil pair members 250. However, because the electrical input is to the second end 256 of the lower member 250, current flow through the lower coil pairs is in a direction opposite to that of the upper coil pairs. As shown in FIG. 34, current flow through the upper coil pairs is in a clockwise direction, while current flow through the lower coil pairs is in a counterclockwise direction. Due to the opposing directions of current flow in the upper coil pair and lower coil pair conductors, and because the coil pairs are separated by the KAPTON film 262, upon supplying a short-duration, high-current pulse to the coil 260, the respective upper and lower coil pairs will be forcefully displaced away from each other. This would constitute a force element for an electro-repulsive type of de-icer.
As in the de-icer schematically indicated by FIG. 31A, the displacement of the coil force elements can be utilized in a de-icer to provide de-icing action. If the direction of current flow in the lower coil pair is reversed by electrically connecting the upper coil pair second end 256 to the first end 254 of the adjacent lower coil pair, current flow through the lower coil pair is in the same direction as that of the upper coil pair. The coil pairs thus may be used in an eddy current type of de-icer construction.
Referring to FIGS. 35A-35G, a schematic view of planar coils according to the invention during their manufacture for an eddy current de-icer is illustrated. It will be assumed that the arrangement shown in FIGS. 35A-35G incorporates the members 210, 220, although the members 250 could be employed with equal facility.
In FIG. 35A, the member 210 is illustrated as it is manufactured initially in an etching operation. In such an operation, a sheet of unalloyed copper is attached to a backing sheet 270. The copper sheet is coated with a substance, such as a photo-resist material, that is impervious to an etching material such as sulfuric acid. The backing sheet 270 also is impervious to the acid. Upon applying the acid to the surface of the copper sheet, copper will be removed in those areas not protected by the photo-resist material. After the copper in the unprotected areas has been removed, the sheet will take the appearance of the member 210 shown in FIG. 27. The member 210 also could be formed in a stamping operation or a matching operation. If desired, the member 210 could be made from a continuous flat-braided conductor.
In order to process the member 210 further, it is necessary to remove it from the backing sheet 270. This result is accomplished by applying a layer of double-sided tape 272 to the exposed surface of the member 210. The tape 272 has a thickness of about 0.0045 inch. A suitable tape 272 can be obtained from Fasson Corporation under the trademark FASTAPE A. Upon lifting the tape 272, the member 210 will be removed from the backing sheet 270. The edges of the tape 272 are trimmed to closely approximate the outer dimensions of the member 210. Thereafter, the exposed adhesive side of the tape 272 can be attached to a layer of dielectric material such as KAPTON film. The dielectric layer is indicated in FIG. 35C by the reference numeral 274. Similarly, the member 220 can be manufactured in an etching process and removed from its back sheet 270 by means of a second layer of double-sided tape 272. Upon attaching the exposed surface of the second double-sided tape 272 to the exposed surface of the dielectric layer 274, the sandwiched coil construction 230 shown in FIG. 35C will be obtained. As shown in FIG. 35G, the layer 274 extends laterally beyond the edges of the members 210, 220 and the tape 272 to form a border approximately 0.25 inch wide that prevents arcing between the edges of the members 210, 220.
In order to protect the members 210, 220 and to provide a dielectric effect, it is desired that the members 210, 220 be encapsulated in some manner. Referring to FIG. 35D, the coil assembly 230 of FIG. 35C is illustrated as being sandwiched between layers 276 of a composite material such as fiberglass/epoxy. A suitable fiberglass/epoxy material can be obtained from Fiberite Corporation under the trademark MXB 7669/7781. After the layers 276 are assembled as illustrated in FIG. 35D, the assembled components are placed in a mold where heat and pressure can be applied so as to conform the coil construction 230 to any desired contour. Although the embodiment illustrated in FIG. 35D is flat, a curved contour should be employed if the coil assembly 230 is to be attached to the curved surface of a structural member. During the application of heat and pressure to the layers 276, it is expected that they will flow at least to a small extent so that gaps between adjacent turns 212, 222 will be filled. The initial thickness of each layer 276 is about 0.010 inch, and the final thickness of each layer 276 is about 0.005-0.006 inch. Also, the edges of the layers 276 will be compressed toward each other to form a tapered configuration that assists in matching the contour of the structural member with which the coil assembly 230 is to be used.
Referring to FIG. 35E, the coil assembly 230 of FIG. 35D is shown as it might be attached to the external surface of a metal structural member 278. The innermost fiberglass/epoxy layer 276 is spaced from the structural member 278 by means of a release layer 280 that permits the coil assembly 230 to move away from and toward the structural member 278. The layer 280 is very thin (about 0.001 inch) and can be obtained from the Richmond Division of Dixico Incorporated under the trademark A5000. A surface ply 282 is positioned over the outermost surface of the exposed layer 276. The ply 282 is secured to the exposed layer 276 by an adhesive such as EA951 commercially available from the Hysol Corporation. If the ply 282 is made of metal such as titanium, aluminum or stainless steel, it should be surface-treated for better adhesion. If the ply 282 is made of a thermoplastic material such as polyetherether ketone (PEEK), surface-treating also is necessary. If the ply 282 is made of another type of thermoplastic material, surface-treating may not be necessary. A metal ply 282 will have a thickness of about 0.005 inch while a non-metal ply 282 will have a thickness of about 0.015 inch. The ends of the layers 280, 282 are attached to the structural member 278 by bonding or any other suitable technique. Typically, an elastomeric support (not shown) would be provided at the ends of the layers 280, 282 in order to provide a smooth transition to the contour of the member 278 and to assist in securing the layers 280, 282 relative to the remainder of the de-icer structure. Regardless of how the layers 280, 282 are connected to the structure 278, it is necessary that at least the layer 282 be able to move away from, and toward, the structural member 278.
In operation, upon supplying a short-duration, shaped, high-current pulse to the coil 230, an electromagnetic field will be generated that will induce eddy currents in the structural member 278 and to a lesser extent in the thin surface ply 282. The eddy currents then will generate electromagnetic fields which will tend to repel the electromagnetic field of the coil 230. In turn, the coil 230, with the surface ply 282 attached, will be forcefully displaced away from the structural member 278. Upon collapse of the magnetic fields, the coil 30 and the surface ply 282 will be forcefully retracted against the structural member 278 to that position shown in FIG. 35E. If the structural member 278 is made of a composite material such as graphite/epoxy instead of metal, a metal target (so-called "doubler") should be disposed on the outside or inside of the member 278.
An additional variation is shown in FIG. 35F. In FIG. 35F, a release layer 284 is disposed intermediate the outermost encapsulating layer 276 and the surface ply 282. Accordingly, the surface ply 282 can move away from, and toward, the coil 230 upon energization thereof. Because the release layer 280 is used in the embodiment shown in FIG. 35F, the coil 230 will move away from, and toward, the structural member 278 if the member 278 is made of metal. If the member 278 is made of a composite member, then the coil 230 will remain in contact with the outer surface of the member 278. In such a circumstance, it may be desirable to eliminate the release layer 280 and bond the innermost encapsulating layer 276 to the member 278 by means of an adhesive such as EA951. Regardless of the material from which the member 278 is made, it will be appreciated that the surface ply 282 always will be forcefully displaced away from, and toward, the member 278 so as to effect a de-icing action.
Referring to FIG. 36, a plot of force versus current is shown for coils constructed and arranged as shown in FIGS. 33 and 34 as a force element for an electro-repulsive type of de-icer. The tests that were conducted to generate the graph of FIG. 36 were laboratory vice tests in which a transducer was disposed intermediate the adjacent coil pairs 250. The lower plot indicated by the reference numeral 286 shows that the force produced by the coil 260 is a direct function of the current supplied thereto. The uppermost curve indicated by the reference numeral 288 shows that disposing a paramagnetic target material (in this case 6061 aluminum, having a thickness of 0.060 inch) adjacent the outer surface of one of the members 250 produced an enhanced separation force. The difference ranges from approximately 19% at lower current levels to 9% at higher current levels. FIG. 36 confirms that coil pairs operating on the so-called "electro-expulsion" principle such as that disclosed in the Electro-Repulsive Separation System Patent have excellent force-generating capabilities, but that such capabilities can be enhanced by the use of a metal target disposed in proximity with the coils. It is believed that this result is brought about by eddy currents that are induced in the target that create an electromagnetic field that interacts with the electromagnetic field generated by the coil 260. In effect, the magnetic target improves or shapes the magnetic field generated by the coil 260. It is believed that the plot 286 would be representative of the force produced by attaching the coil 260 to a composite structural member 278, while the plot 288 would be representative of the results produced by attaching the coil 260 to a metal structural member 278 or by using a metal surface ply 282 in conjunction with 0.060 inch thick metal targets adjacent the coils.
Although the invention has been described in its preferred form with a certain degree of particularity, it will be understood that the present disclosure of the preferred embodiment has been made only by way of example, and that various changes may be resorted to without departing from the true spirit and scope of the invention as hereinafter claimed. It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty exist in the invention disclosed.
Adams, Lowell J., Weisend, Jr., Norbert A., Wohlwender, Thomas E.
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