US2787694A - De-icing or anti-icing apparatus - Google Patents

Description

United States Patent DE-ICING'OR ANTI-ICING APPARATUS Alexander Gordon Farries, Luton, England, assignor to DrNapier & Son Limited, London, England, a British company Application January 27, 1955, Serial No. 484,466

Claims priority, application Great Britain January 29, 1954 7 Claims. (Cl. 219-19) This invention relates to thermoelectric surface heating apparatus, such as for example de-icing or anti-icing apparatusfor the surface parts of aircraft and the like, which may be exposed. to icing conditions, and of the kind including a thin layer of conducting material which forms a resistance heating element, and is usually sandwiched between two electrical insulating layers. Examples of such apparatus are describedin the specifications of United States copending applications Ser. No. 304,964 and Ser. No. 392,228 in which the conducting material is in the form of a sprayed metal. layer and the insulating layers consist of thermo-settingplastic'material each applied in an uncured state and subsequently cured.

In such apparatus the conductingmaterial is usually in the form of sprayed aluminium or an aluminium alloy in view of its ready availability, ready application by spraying and general suitability for the purpose in question.

In any case, in order to provide the required-length of conducting path in a convenient manner and yet cover the required area of surface the conducting layer is in many casesin the form of a pattern which includes a sereis of relatively wide heater strips either inclined to one another or parallel to one another and separated by narrow gaps and connected at their ends by transverse strips of approximately the same width as the heater strips, so as to form a zig-zag or other non-liner electrical path with the heater strips electrically in series with one another. With this arrangement, it is found that there is a concentration of current and therefore of heat dissipation in the inside of the bends, that is to say, in the case of parallel strips, in the parts of each transverse strip adjacent to the adjacent edges of the heater strips, while the outer parts of the transverse strips and/or the adjacent outer edges of the heater strips remain comparatively unheated.

It is an object of the present invention to provide an arrangement in which such heat concentrations and comparatively cold areas will be avoided and more even heating over the whole of the required area thus obtained.

To this end according to the present invention electrical surface heating apparatus of the kind comprising a thin layer of conducting material constituting a heater element, formed in a patterncomprising at least two heater strips having ends lying adjacent to one another, and connected together electrically in series, includes it connecting conductor element between the adjacent ends of the heater strips, the connecting element being narrower than the two heater strips which it connects and having a lower electrical resistance per unit of length than the heater strips, and contacting the ends of the heater strips over substantially their full widths.

it will thus beseen that each connecting element constitutes inetfect a bus bar by which the electric current flow is distributed over substantially the whole width of the-end of each of theheater strips which it connects.

. Preferably the connecting element is formed at least ice partly of a material having a higher efiective electrical conductivity than that of the heater strips. Moreover the connecting element is preferably so formed thatthe heating efliect per unit surface area of the connecting element is substantially the same as the heating effect per unit area of each of the heater strips.

Conveniently the thickness of the connecting element is greater than that of the heater strips. The width of the connecting element may vary, but it is preferably less than one third, and may be less than one quarter of the width of the heater strips.

In a preferred construction the main heater strips are formed of aluminum while the connecting element is formed at least partly of copper or silver, and the metal may be applied by spraying.

Conveniently however the connecting element comprises an underlayer of the same thickness and material as the heater strips, and a subsidiary upper layer applied over the underlayer.

in one form of the invention the two heater strips are parallel to one another, and the connecting element is arranged transversely across two adjacent ends of the strips.

In another form the two heater strips are arranged at an angle to one another, with the end of one strip abutting the side of. the other strip, and the connecting element is of cranked formation including two parts in con tact with the ends of the two heater strips.

The invention may be performed in various different ways but some specific embodiments will now be described by way 'of example with reference to the accompanying drawings in which:

Figure l is a fragmentary plan view of a bend in an electrical heater element according to a prior proposal,

Figure 2 is a corresponding view of part of a heater element according to the present invention,

Figure 3 is a'somewhat diagrammatic perspective View of the element shown in Figure 2.

Figure 4 is an enlarged diagrammatic sectional view on the line IV-IV in Figure 2 in which the relative dimensions have been distorted for the sake of clarity, and

Figures 5 and 6 are plan views of modifications of the invention.

in the previous construction illustrated in Figure l the adjacent ends of 'two parallel heater strips 1 and 2 are connected by a transverse strip 3 which is of the same thickness and width and formed of the same material as the strips 1 and 2. The resulting current distribution around the bend has been determined by experiment and as shown in Figure 1 it results in a tendency to overheat at the inside 4 of the bend and the formation of cold spots at the outer corners 5 of the bend, This is particularly disadvantageous in surface heaters applied to aircraft surfaces for de-icing purposes, since the hot spots may cause deterioration of the structure, while the cold spots may result in the accumulation of ice.

in the example of the invention illustrated in Figures 2, 3 and 4 the two parallel strips 1 and 2 are connected by a transverse connecting element 6 which has a lower effective resistance per unit of length in the direction of current flow and is of relatively smaller width w, and extends across the full widths W of the ends of the strips 1 and 2. The resulting current distribution is illustrated in Figure 2 and it will be seen that this construction tends to reduce the tendency to the formation of cold spots at the outer corners of the bends. V

The formation of the transverse strip 6 is preferably such that the heating effect and therefore the surface tenr perature of this strip is approximately equal to that of the strips 1 and 2. The total current passed through the transverse strip 6. is the same as that passed by each of the strips 1 and 2 and the heating effect per unit surface area of this strip therefore depends upon the specific resistance of the material, and its width and thickness. By appropriate choice of each of these factors the heating effect may be made to correspond to that of the main strips 1 and 2.

In one particular example the main parallel heater strips 1 and 2 are each 0.5 inch wide and of the order of thousandths of an inch thick and are designed to give heat dissipation at the rate of watts per square inch when passing a current of 10 amps. The resistance of these main heater strips is thus .05 ohm per inch length. In such case the transverse strip 6 is conveniently .125 inch wide, and since its rate of heat dissipation is to be the same at 10 watts per square inch surface area, the resistance per inch of length of this transverse strip must be in the neighbourhood of .0125 ohm. In any case, in order to obtain the required results, the width of the connecting element is preferably less than one third, or one quarter, of the width of the associated heater strips.

The transverse strip 6 may be a separate element applied to the surface and abutting the ends of the strips 1 and 2. Alternatively the main heater element including the parallel heater strips 1 and 2 may be formed with a narrow transverse strip of the same dimensions in plan as the transverse strip 6, and the connecting element may then be built up by the addition of one or more further layers of conducting material 7 as shown in Figures 3 and 4. This construction is particularly convenient where the main heater strips 1 and 2 are applied in the form of sprayed metal, for example sprayed aluminum, in which case the upper layer of the transverse strip 6 may also be applied by spraying and may be in the form of copper or silver or other high conductivity metal.

As mentioned above the invention is particularly applicable to electrical surface heating equipment for use as de-icing or anti-icing equipment on the exposed surfaces of aircraft and similar bodies. In such case the apparatus is preferably built up in the form illustrated in Figure 4. The metallic aircraft skin 8 is first covered by a layer of a synthetic thermosetting plastic adhesive 9 having good electrical insulating qualities. This plastic is preferably applied to the aircraft skin by a spraying process. The main electrical heater element strips 1 and 2 are then applied also by a hot spraying process through a stencil to give the required pattern, and the top transverse element 7 is applied in the form of sprayed copper on top of the end portions of these strips. A further layer 19 of the same synthetic plastic resin is applied over all and the whole structure is then heated to a temperature which will effectively cure the synthetic plastic.

It will be understood that the invention is not confined to connections between parallel heater strips but may also be used in any case where the current path is caused to flow round a bend. For example in Figure 5, a right angled bend is illustrated, and in this case the connecting element 12 between a pair of heater strips 13 and 14 is of L shape in plan, and contacts the ends of both strips, one of which abuts the side of the other. In Figure 6 is illustrated a 45 bend.

It will be seen that the invention enables a uniform temperature to be maintained within fine limits over substantially the whole of the surface to be heated.

It will be apparent also that, since both the heater strips and the connecting elements are applied preferably by metal spraying, the apparatus can be produced with approximately the same ease and has substantially all the advantages as regards appliability by readily available equipment to surfaces of compound curvature, and ease of repair if damaged, of the apparatus forming the subject of United States copending applications Ser. No. 304,964 and Ser. No. 39,228.

What I claim as my invention and desire to secure by Letters Patent is:

1. Electrical surface heating apparatus for an exposed aircraft surface and of the kind comprising a thin layer of conducting material constituting a heater element on said surface, formed in a pattern comprising at least two heater strips having ends lying adjacent to one another, and connected together electrically in series, and including heat-emitting connecting conductor element between the adjacent ends of the heater strips, the connecting element being narrower than the two heater strips which it connects and formed at least partly of a material having a higher effective electrical conductivity than that of the heater strips such that the heating effect per unit surface area of the connecting element is substantially the same as the heating effect per unit area of each of the heater strips, said connecting element contacting the ends of the heater strips over substantially their full widths and said connecting element avoiding cold spots by providing substantial temperature uniformity in the connect ing element.

2. Electrical surface heating apparatus for an exposed aircraft surface and of the kind comprising a thin layer of conducting material constituting a heater element on said surface, formed in a pattern comprising at least two heater strips having ends lying adjacent to one another, and connected together electrically in series, and including a heat-emitting connecting conductor element between the adjacent ends of the heater strips, the connecting element being narrower than the two heater strips which it connects and having a thickness greater than that of the heater strips such that the heating effect per unit surface area of the connecting element is substantially the same as the heating effect per unit area of each of the heater strips, said connecting element contacting the ends of the heater strips over substantially their full widths and said connecting element avoiding cold spots by providing substantial temperature uniformity in the connecting element.

3. Electrical surface heating apparatus for an exposed aircraft surface and of the kind comprising a thin layer of conducting material constituting a heater element on said surface, formed in a pattern comprising at least two heater strips having ends lying adjacent to one another, and connected together electrically in series, and including a heat-emitting connecting conductor element between the adjacent ends of the heater strips, the connecting element being narrower than the two heater strips which it connects and having a lower electrical resistance per unit of length than the heater strips such that the heating effect per unit surface area of the connecting element is substantially the same as the heating effect per unit area of each of the heater strips, said connecting element contacting the ends of the heater strips over substantially their full widths, said connecting element avoiding cold spots by providing temperature uniformity in the connecting element and the main heater strips being formed of aluminium while the connecting element is formed at least partly of a material selected from the group comprising copper and silver.

4. Electrical surface heating apparatus for an exposed aircraft surface and of the kind comprising a thin layer of conducting material constituting a heater element on said surface, formed in a pattern comprising at least two heater strips having ends lying adjacent to one another, and connected together electrically in series, and including a heat-emitting connecting conductor element between the adjacent ends of the heater strips, the connecting element being narrower than the two heater strips which it connects and having a lower electrical resistance per unit of length than the heater strips such that the heating effect per unit surface area of the connecting element is substantially the same as the heating effect per unit area of each of the heater strips, said connecting element contacting the ends of the heater strips over substantially their full widths, said connecting element avoiding cold spots by providing temperature uniformity in the connecting element and the connecting element comprising an under- 5 layer of the same thickness and material as the heater strips, and a subsidiary upper layer applied over the underlayer.

5. Electrical surface heating apparatus as claimed in claim 1 in which the two heater strips are parallel to one another, and the connecting element is arranged transversely across two adjacent ends of the strips.

6. Electrical surface heating apparatus as claimed in claim 1 in which the two heater strips are arranged at an angle to one another, with the end of one strip abutting the side of the other strip but electrically insulated therefrom, and the connecting element is of angled formation including two parts in contact with the ends of the two heater strips.

7. Electrical surface heating apparatus according to claim 2 in which the two heater strips are parallel to one References Cited in the file of this patent UNITED STATES PATENTS 1,172,025 Homan Feb. 15, 1916 1,996,522 Norris Apr. 2, 1935 2,527,720 Guyer Oct. 31, 1950 2,622,178 Glynn Dec. 16, 1952 2,622,828 Lucas et al. Dec. 23, 1952 2,627,012 Kinsella et a1 Jan. 27, 1953 2,641,675 Hannahs June 9, 1953 2,648,754 Lytle Aug. 11, 1953 2,665,090 Holdaway et a1 Jan. 5, 1954

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