Zoned aircraft de-icing system and method

• US 6,237,874 B1
• Filed: 10/15/1999
• Issued: 05/29/2001
• Est. Priority Date: 09/22/1997
• Status: Expired due to Term

• Current Assignee: Kelly Aerospace Thermal Systems, LLC
• Original Assignee: Northcoast Technologies, Limited
• Inventors: Rutherford, Robert B., Dudman, Richard L.
• Primary Examiner(s): Jordan, Charles T.
• Assistant Examiner(s): DINH, TIEN QUANG
• Application Number:
  US09/419,466
• Time in Patent Office: 592 Days
• Field of Search: 244/134 E, 244/134 D, 244/134 R, 244/123, 244/133, 219/202, 219/535, 219/548, 219/553
• US Class Current: 244/134.00E
• CPC Class Codes: B64D 15/14 controlled cyclically along length of surface

Abstract

An electrothermal zoned de-icing system for an aircraft employs a heat-conducting tape bonded to the leading edge of an aircraft structure subject to an impinging airstream during flight. The heat-conducting tape has a spanwise parting strip area, and first and second ice accumulation and shedding zones. The tape comprises a non-metallic electrical and heat-conducting layer consisting of flexible expanded graphite foil laminated to an outer heat-conducting layer, in which the thickness of the flexible expanded graphite foil layer in the parting strip area is always greater than the thickness of the foil layer in either of the ice accumulation and shedding zones. Therefore, the parting strip area has a decreased electrical resistance, a greater flow of current, and becomes hotter than the zones in which the foil layer is thinner. Because the flexible expanded graphite foil is a monolithic structure that may be shaped, sculptured or layered to form different thicknesses in different areas, only a single control mechanism for a single set of electric terminals is necessary to produce temperature differentials in the parting strip and ice accumulation and shedding zones for a cycled zoned de-icing system.

Claims

1. An electrothermal de-icing system for an aircraft structural member that includes a leading edge subject to an impinging airstream during flight, said airstream passing over an outer surface of the structural member in a fore to aft direction, the system comprising:

a heat-conducting tape bonded to the outer surface of the structural member, the heat-conducting tape comprising a first area that forms a parting strip having a length disposed spanwise along the leading edge, a second area disposed spanwise above and aft of the parting strip forming a first ice accumulation and shedding zone, and a third area disposed spanwise below and aft of the parting strip forming a second ice accumulation and shedding zone, wherein the heat-conducting tape comprises at least two layers laminated to each other under heat and pressure, the layers comprising (i) an outer heat-conducting layer that is an electrical insulator, and (ii) a non-metallic conductive layer connected to a power source, the non-metallic conductive layer consisting of a flexible expanded graphite foil sheet having a first thickness in the parting strip, a second thickness in the first ice accumulation and shedding zone, and a third thickness in the second ice accumulation and shedding zone, wherein the thickness of the flexible expanded graphite foil sheet in the parting strip is greater than the thickness of the foil sheet in either of the first or the second ice accumulation and shedding zones;

an electronic connection for connecting the flexible expanded graphite layer to the power source; and

a programmable controller configured (i) to direct a supply of power from the power source to the flexible expanded graphite foil layer of the heat-conducting tape for a first period of time, to maintain a first temperature of the outer heat-conducting layer at the parting strip that is sufficient to prevent freezing of impinging water droplets and to allow water droplets to flow aft from the parting strip to the first and/or the second ice accumulation and shedding zones of the heat-conducting tape, and wherein the power supply also maintains, in the first period of time;

a second temperature of the outer heat-conducting layer at the first and/or second ice accumulation and shedding zones which is freezing or below freezing to allow formation of ice and an ice-to-surface bond on the outer heat-conducting layer at the first and/or second ice accumulation and shedding zones, and (2) to subsequently direct an increased power supply to the flexible expanded graphite foil layer of the heat-conducting tape for a second period of time, wherein the increased power supply is sufficient to melt the ice-to-surface bond at the first and/or second ice accumulation and shedding zones and to allow formed ice to be shed into the impinging airstream.

2. The electrothermal de-icing system of claim 1, wherein the flexible expanded graphite foil sheet is connected to the power source by a single set of two terminals.

3. The electrothermal de-icing system of claim 1, wherein the first temperature is about 33°

F. to about 50°

F.

4. The electrothermal de-icing system of claim 3, wherein the first temperature is about 35°

F. to about 45°

F.

5. The electrothermal de-icing system of claim 1, wherein the first time period is about 5 seconds to about 5 minutes.

6. The electrothermal de-icing system of claim 5, wherein the first time period is about 15 seconds to about 2 minutes.

7. The electrothermal de-icing system of claim 6, wherein the first time period is about 30 seconds to about 1.5 minutes.

8. The electrothermal de-icing system of claim 1, wherein the second time period is about 5 seconds to about 2.5 minutes.

9. The electrothermal de-icing system of claim 8, wherein the second time period is about 15 seconds to about 1.5 minutes.

10. The electrothermal de-icing system of claim 9, wherein the second time period is about 30 seconds to about one minute.

11. The electrothermal de-icing system of claim 1, further comprising:

a first temperature sensor in communication with an outer surface of the heat-conducting layer in the parting strip area, and in communication with the controller for real time transmitting to the controller of a first value representing the temperature of the outer surface in the parting strip area of the heat-conducting layer, wherein the controller further comprises a receiving unit for receiving the real time first temperature value;

wherein the controller is programmed to store a first predetermined reference temperature range for the first temperature;

the controller is further programmed to compare the received real time first temperature value with the first predetermined reference temperature range;

the controller is further programmed to indicate an acceptable first temperature when the received temperature value falls within the first predetermined reference range; and

the controller is further programmed to signal the power source to provide more or less electrical energy to the flexible expanded graphite layer of the heat-conducting tape when the received first temperature falls outside the first predetermined reference temperature range.

12. The electrothermal de-icing system of claim 11, further comprising:

a second temperature sensor in communication with an outer surface of the heat-conducting layer in at least one of the first and second ice accumulation and shedding zones, and in communication with the controller for real time transmitting to the controller of a second value representing the temperature of the outer surface of at least one of the first and second ice accumulation and shedding zones, wherein the controller further comprises a receiving unit for receiving the real time second temperature value, wherein the controller is programmed to store a second predetermined reference temperature range for the second temperature;

the controller is further programmed to compare the received real time second temperature value with the second predetermined reference temperature range;

the controller is further programmed to indicate an acceptable second temperature when the received temperature value falls within the second predetermined reference range; and

the controller is further programmed to signal the power source to provide more or less electrical energy to the flexible expanded graphite layer of the heat-conducting tape when the received second temperature falls outside the second predetermined reference temperature range.

13. The electrothermal de-icing system of claim 12, wherein the second temperature sensor transmits to the controller a third real time temperature of the outer heat-conducting layer at the first and/or second ice accumulation zones in the second period of time;

the controller is programmed to receive the real time third temperature value;

the controller is programmed to store a third predetermined reference temperature range for the third temperature;

the controller is programmed to compare the received real time third temperature value with the third predetermined reference temperature range;

the controller is further programmed to indicate an acceptable third temperature when the received third real time temperature value falls within the third predetermined reference range; and

the controller is also further programmed to signal the power source to provide more or less electrical energy to the flexible expanded graphite layer of the heat-conducting tape when the received third temperature falls outside the third predetermined reference temperature range.

14. The electrothermal de-icing system of claim 13, wherein the third real time temperature is about 34°

F. to about 40°

F.

15. The electrothermal de-icing system of claim 1, wherein the flexible expanded graphite foil sheet is a continuous sheet comprising a decreasing gradient of thicknesses between the parting strip and the first ice accumulation and shedding zone and between the parting strip and the second ice accumulation and shedding zone.

16. The electrothermal de-icing system of claim 15, wherein the thickness of the flexible expanded graphite foil sheet in the parting strip, excluding the decreasing thickness gradients, is about 0.005 to about 0.060 inches.

17. The electrothermal de-icing system of claim 15, wherein the thicknesses of the flexible expanded graphite foil sheet in the first and second ice accumulation and shedding zones, excluding the thickness gradients, are the same as or different from each other and range from about 0.001 to about 0.050 inches.

18. The electrothermal de-icing system of claim 17, wherein the thicknesses of the foil sheet in the ice accumulation and shedding zones range from about 0.001 to about 0.030 inches.

19. The electrothermal de-icing system of claim 1, wherein the parting strip comprises at least two layered flexible expanded graphite foil sheets.

20. The electrothermal de-icing system of claim 19, wherein the foil sheets have thicknesses that are the same as or different from each other and range from about 0.0025 to about 0.047 inches.

21. The electrothermal de-icing system of claim 19, wherein the layered foil sheets form a decreasing gradient of thicknesses between the parting strip and the first ice accumulation and shedding zone and between the parting strip and the second ice accumulation and shedding zone.

22. The electrothermal de-icing system of claim 1, wherein the flexible expanded graphite foil sheet comprises at least two separate sections selected from the group consisting of a parting strip section, a first ice accumulation and shedding section, and a second ice accumulation and shedding section, wherein the first or the second ice accumulation and shedding sections are separated from the parting strip section by a gap of no greater than about 60 mils.

23. The electrothermal de-icing system of claim 22, wherein the parting strip section or at least one of the ice accumulation and shedding zone sections of the flexible expanded graphite foil sheet comprises a decreasing gradient of thicknesses between the parting strip and the first ice accumulation and shedding zone or between the parting strip and the second ice accumulation and shedding zone.

24. The electrothermal de-icing system of claim 1, wherein the parting strip has a width that is sufficient to accommodate a change in location of an icing stagnation line along the leading edge.

25. The electrothermal de-icing system of claim 24, wherein the width of the parting strip is about 0.25 to about 3 inches.

26. The electrothermal de-icing system of claim 25, wherein the width of the parting strip is about 0.5 to about 2.5 inches.

27. The electrothermal de-icing system of claim 26, wherein the width of the parting strip is about 0.75 to about 1.5 inches.

28. The electrothermal de-icing system of claim 1, wherein each of the first and second ice accumulation and shedding zones comprises an area approximately equal to its respective area of ice accumulation.

29. The electrothermal de-icing system of claim 1, wherein the first and the second ice accumulation and shedding zones comprise widths that are the same as or different from each other and range from about 1 to about 6 inches.

30. The electrothermal de-icing system of claim 29, wherein the widths of the first and the second ice accumulation and shedding zones range from about 1.5 to about 5 inches.

31. The electrothermal de-icing system of claim 30, wherein the widths of the first and the second ice accumulation and shedding zones range from about 1 to about 3 inches.

32. The electrothermal de-icing system of claim 1, wherein the flexible expanded graphite foil sheet has a density of about 50 to about 95 lbs./ft³.

33. The electrothermal de-icing system of claim 32, wherein the flexible expanded graphite foil sheet has a density of about 70 to about 95 lbs./ft³.

34. The electrothermal de-icing system of claim 33, wherein the flexible expanded graphite foil sheet has a density of about 80 to about 95 lbs./ft³.

35. The electrothermal de-icing system of claim 1, wherein the flexible expanded graphite foil sheet has an electrical resistivity of about 2.7×

10<sup>−

4</sup> to about 3.2×

10<sup>−

4</sup> ohm-in.

36. The electrothermal de-icing system of claim 35, wherein the flexible expanded graphite foil sheet has an electrical resistivity of about 3.1×

10<sup>−

4</sup> ohm-in.

37. The electrothermal de-icing system of claim 1, wherein the outer heat-conducting layer is selected from electrically insulating materials having a volume resistivity of about 10³ ohm-in. to about 10¹² ohm-in.

38. The electrothermal de-icing system of claim 37, wherein the outer heat-conducting layer comprises a thermoplastic or a thermosetting material and an inorganic filler that conducts heat.

39. The electrothermal de-icing system of claim 38, wherein the inorganic filler is selected from the group consisting of aluminum nitride, boron nitride, alumina, silicon nitride, and mixtures thereof.

40. The electrothermal de-icing system of claim 39, wherein the material comprises polyurethane.

41. The electrothermal de-icing system of claim 1, wherein the outer heat-conducting layer has a thermal conductivity of about 0.1 W/M°

K to about 5 W/M°

K.

42. The electrothermal de-icing system of claim 41, wherein the outer heat-conducting layer has a thermal conductivity of about 0.5 W/M°

K to about 4 W/M°

K.

43. The electrothermal de-icing system of claim 1, wherein the thickness of the outer heat-conducting layer is about 0.001 inches to about 0.030 inches.

44. The electrothermal de-icing system of claim 43, wherein the thickness of the outer heat-conducting layer is about 0.001 inches to about 0.010 inches.

45. The electrothermal de-icing system of claim 44, wherein the thickness of the outer heat-conducting layer is about 0.005 inches.

46. The electrothermal de-icing system of claim 1, wherein the heat-conducting tape further comprises an electrically insulating layer, wherein the flexible expanded graphite layer is disposed between the outer heat-conducting layer and the insulating layer.

47. The electrothermal de-icing system of claim 46, wherein the insulating layer is a component of the heat-conducting tape or is a component of the aircraft surface.

48. The electrothermal de-icing system of claim 46, wherein the insulating layer is a heat insulator.

49. The electrothermal de-icing system of claim 46, wherein the insulating layer has a thickness of about 0.005 inches to about 0.250 inches.

50. The electrothermal de-icing system of claim 1, wherein the structural member comprises a rotor blade or a propeller blade and the heat-conducting tape further comprises an outer erosion-resistant layer bonded to the outer heat-conducting layer.

51. The electrothermal de-icing system of claim 50, wherein the outer erosion-resistant layer comprises a selection from the group consisting of titanium, nickel, aluminum, stainless steel, and alloys thereof.

52. A method for electrothermal de-icing of an aircraft structural member that includes a leading edge subjected to an impinging airstream during flight, said airstream passing over an outer surface of the structural member in a fore to aft direction, the method comprising the steps of:

bonding a heat-conducting tape to the outer surface of the structural member, wherein the heat-conducting tape comprises a first area that forms a parting strip having a length disposed spanwise along the leading edge, a second area disposed spanwise above and aft of the parting strip forming a first ice accumulation and shedding zone, and a third area disposed spanwise below and aft of the parting strip forming a second ice accumulation and shedding zone, wherein the heat-conducting tape comprises at least two layers laminated to each other under heat and pressure, the layers comprising (i) an outer heat-conducting layer that is an electrical insulator, and (ii) a non-metallic conductive layer connected to a power source by a single set of two terminals, the non-metallic conductive layer consisting of a flexible expanded graphite foil sheet having a first thickness in the parting strip, a second thickness in the first ice accumulation and shedding zone, and a third thickness in the second ice accumulation and shedding zone, wherein the thickness of the flexible expanded graphite foil sheet in the parting strip is greater than the thickness of the foil sheet in either of the first or the second ice accumulation and shedding zones;

supplying power to the flexible expanded graphite foil layer for a first period of time to maintain a first temperature of the outer heat-conducting layer at the parting strip that is sufficient to prevent freezing of impinging water droplets and to allow water droplets to flow aft from the parting strip to the first and/or the second ice accumulation and shedding zones, wherein the power supply also maintains, in the first period of time, a second temperature of the outer heat-conducting layer at the first and/or second ice accumulation and shedding zones which is freezing or below freezing, to allow formation of ice and an ice-to-surface bond on the outer heat-conducting layer at the first and/or second ice accumulation and shedding zones; and

subsequently increasing the power supply to the flexible expanded graphite foil layer for a second period of time, wherein the increased power supply is sufficient to melt the ice-to-surface bond at the first and/or second ice accumulation and shedding zones and to allow formed ice to be shed into the impinging airstream.

53. The method of claim 52, further comprising the step of sensing the presence of atmospheric icing conditions prior to the supplying power step.

54. The method of claim 53, further comprising the step of sensing the presence of atmospheric icing conditions during the supplying power and the increasing the power supply steps.

55. The method of claim 53, further comprising the step of repeating the supplying power step and the subsequent increasing power step until atmospheric icing conditions are no longer sensed.