Method and device for reducing condensate precipitation on the inner surfaces of an aircraft outer skin and adjacent components

Description

[0001] The invention relates to a method for reducing condensate precipitation on the inner surfaces of an aircraft outer skin and adjacent components, wherein the condensate precipitation is reduced by supplying dry air into an upper region of an air gap extending between the upper region and a lower region between the aircraft outer skin and an insulation arranged between a cabin wall and the aircraft outer skin. The invention also relates to a device for carrying out this method.

[0002] Such a method and a device for carrying out this method are known from US 6491254 B1. There, the dry air supplied to the air gap between the aircraft outer skin and the insulation is diverted from an air flow conditioned in an air conditioning system, the other part of which is supplied to the cabin. The air conditioned in the air conditioning system is bleed air from a compressor of an aircraft engine. The dry air supplied to the air gap between the aircraft outer skin and the insulation is supplied to the air gap via lines and flow control valves connected to the air conditioning system and a plurality of air outlet nozzles distributed within the air gap. During cruising flight, an air pressure higher than the air pressure prevailing in the cabin develops in the air gap, preventing cabin air from overflowing through the insulation into the air gap due to the stack effect.The use of compressor bleed air and its treatment in an air conditioning system that also supplies air to the cabin in order to obtain the dry air to be supplied to the air gap requires increased air conditioning capacity, more weight and higher costs of the air conditioning system as a result of the required increase in capacity and thus higher energy consumption of the aircraft.

[0003] In a method known from US 5386952 for reducing condensate formation on the inner surfaces of an aircraft outer skin and adjacent components, cabin air is drawn in near the floor using several dehumidification devices distributed within the aircraft cabin near the floor, dehumidified, and heated. This air is then blown into the air gap between the aircraft outer skin and the insulation at locations distributed along the aircraft's longitudinal direction near the floor. The dry, heated air from the cabin blown into the air gap is distributed within the air gap and has a higher pressure than the air pressure prevailing in the cabin. As a result, air from the air gap re-enters the cabin through the insulation.Although this also prevents condensate precipitation and the resulting ice formation on the cold surfaces of the aircraft outer skin and the adjacent components that border the air gap, the use of devices for dehumidifying and heating cabin air to obtain the dry air that is introduced into the air gap takes up additional space in the aircraft, increases the weight of the aircraft and increases its power consumption and acquisition and operating costs, so that the advantages gained by avoiding condensate and ice formation in the air gap are compensated for by the disadvantages associated with the use of dehumidifying devices to obtain dry air for introduction into the air gap.

[0004] Furthermore, US 2021 / 0122476 A1 discloses a method for reducing condensate formation on the inner surfaces of an aircraft outer skin and adjacent components. In this method, dry air conditioned in an air conditioning system is blown into a space above the cabin ceiling (crown region) via ducts and controllable valves. Air conditioned in this or a separate air conditioning system is blown into the cabin from these or separate ducts simultaneously or alternately with the air blown into the upper space. Thus, in this method, the dry air blown into the space above the cabin ceiling is also provided by an air conditioning system, which in turn is fed with compressor bleed air.Obtaining cabin air, which has a higher temperature and higher humidity than the dry air blown into the space above the cabin ceiling, using the same air conditioning system or a separate air conditioning system requires significant equipment and control complexity, resulting in additional costs and weight. Thus, the advantage gained by avoiding an additional dehumidifier specifically used to extract dry air is offset by the disadvantage associated with the additional equipment and control complexity. Another example can be found in document US 2021 / 339872 A1.

[0005] The object of the invention is to design the method described above for reducing condensate precipitation on the inner surfaces of an aircraft outer skin and adjacent components in such a way that the extraction of dry air into the upper region of the air gap extending between the upper region and a lower region between the aircraft outer skin and an insulation arranged between the cabin wall and the aircraft outer skin takes place with lower equipment and energy expenditure than previously. This method can be considered not only in the construction of new aircraft but also in the retrofitting of existing aircraft. A device for carrying out this method is also to be specified.

[0006] The object of the invention is achieved with regard to the method in that, according to the characterizing part of claim 1, the dry air is obtained by suction from the lower region of the air gap and is guided in one or more lines to the upper region of the air gap, where it is allowed to enter the air gap again.

[0007] With regard to the device, the object of the invention is achieved in that, according to the characterizing part of claim 6, the line or lines has or have one or more inlet openings at the lower region of the air gap, through which dry air in the lower region of the air gap can be sucked out, and in that the line or lines is or are connected to one or more fans which, during operation, generate or generate a pressure difference in the line or lines which moves the dry air from the inlet opening or openings to the outlet opening or openings.

[0008] Advantageous further developments of the method according to the invention are the subject of claims 2 to 7, and advantageous further developments of the device according to the invention are the subject of claims 8 to 20.

[0009] The invention is based on the observation that during flight, warm and humid air from the cabin flows into the upper region of the air gap through the non-airtight cabin wall and the air-permeable insulation. This is because there is a temperature gradient between the cabin and the upper region of the air gap, which leads to a thermally induced pressure difference, which causes this air flow. Typically, the air flowing into the air gap has a temperature of around 20°C and a relative humidity RH of around 10%. During flight, low outside temperatures prevail, which also cool the aircraft's outer skin and adjacent components behind the insulation. The air flowing into the air gap also cools down. Since cold air has a higher density, it flows downwards behind the insulation, where it would escape from the insulation again if it were not extracted according to the invention.The air flowing downward behind the insulation is dry, having been dehumidified by condensation on the cold aircraft skin and the cold adjacent components. The idea behind the invention is to extract this air from the lower area of ​​the air gap and blow it back in at the top, particularly at the areas requiring protection, thus creating a circulation of dry air. The lower area of ​​the air gap, where the dry air is extracted, represents a "free" or at least "cheap" source of dry air.

[0010] An advantage of the method according to the invention is that the use of the aircraft outer skin as a dehumidification unit and the extraction of dehumidified air is more energy-efficient than the known solutions in which the air is actively dehumidified or fresh bleed air from the engine is used.

[0011] The use of one or more fans in the device according to the invention for carrying out the method is advantageous because a fan typically requires only a few watts, whereas mechanical dehumidification is associated with considerable effort due to the phase change and the already relatively dry cabin air, which has a relative humidity of approximately 10% RH. Fresh air from outside, which has a temperature of approximately -50°C, is also an "expensive" source of dry air, as it must first be compressed to cabin pressure and then conditioned.

[0012] The reduction in condensate precipitation on the cold aircraft outer skin and the adjacent cold components achieved by the method according to the invention also reduces the risk of ice formation, which melts when the aircraft outer skin and the adjacent components become warm again and turns into water that can drip uncontrollably into the cabin and onto the passengers (keyword: "rain in the plane").

[0013] An embodiment is shown schematically in the drawing and is described in more detail below with reference to this drawing, wherein the drawing shows a plan view of a section of the insulation with the cabin wall removed from the cabin.

[0014] As the drawing shows, insulation 1 in the form of a mat is located in the frame fields 2 between adjacent frames 3 of an aircraft (not shown in detail). The insulation is arranged between the cabin wall (not shown) and the invisible aircraft outer skin, with an invisible air gap being formed between the insulation 1 and the aircraft outer skin, which is also bordered by other components adjacent to the aircraft outer skin, such as the frames 3. A schematically illustrated duct network 4 consisting of several duct sections in the form of hoses serves to convey dry air from a lower region of the air gap into the upper region of the air gap. The duct network 4 has a plurality of first duct sections 5 which are guided through passages in the insulation 1 to the lower region of the air gap and have air inlet openings there (not shown).The piping network 4 further comprises second line sections, which include a collecting line 6 and a distributing line 7. The first line sections 5 are connected to the collecting line 6 via multi-way valves (not shown), and the distributing line 7 is connected to several third line sections 8 via multi-way valves (not shown), each of which is guided through passages in the insulation 1 to the upper region of the air gap, where it has air outlet openings (not shown). An intermittently operable fan 9 has its inlet side connected to the collecting line 6 and its outlet side connected to the distributing line 7. The piping network 4 is located largely in the space between the insulation 1 and the cabin wall. The fan 9 is also arranged there. Alternatively, however, it could also be arranged in a space above the cabin ceiling for reasons of space.A first line section 5 and a third line section 8 are arranged in each frame section 2. Alternatively, the arrangement of the first and third line sections 5, 8 with respect to the frame sections 2 can be different, for example for reasons of space or for reasons of more effective air extraction or injection.

[0015] When fan 9 is switched on, it creates a pressure difference in the duct network 4, which causes dry air in the lower area of ​​the air gap to be drawn into the inlet openings of the first duct sections 5 and moved via the collecting duct 6 and the distribution duct 7 to the third power sections 8, where it is blown back into the upper area of ​​the air gap via their outlet openings. Instead of one fan 9, multiple fans can be used if necessary.

[0016] The fan(s) are switched on and off depending on the temperature. For example, the fan(s) are switched on when the outside temperature during flight drops below approximately -7°C, approximately -9°C, or approximately -5°C.

[0017] Tests have shown that the leakage flow behind the insulation layer, i.e., past the cold aircraft outer skin, is approximately 0.7 to 1.4 l / s per frame section. To prevent warm, humid cabin air from overflowing behind the insulation layer, approximately this amount of alternative air had to be applied, although slightly more or less is naturally required depending on the tightness of the cabin wall.

[0018] It was further determined that the condensation problem only occurs when the temperature of the outer skin falls below the dew point of the cabin air. The cabin air typically has a relative humidity of 10-15% at 23°C during flight. This corresponds to a dew point temperature of approximately -7°C. The air circulation system is only activated below this temperature. In the simplest case, the control can be achieved with an on / off switch that activates the system with a fixed flow rate when the temperature falls below a certain threshold.

[0019] Of course, the invention is not limited to the illustrated embodiments. The above description is therefore not to be considered limiting, but rather illustrative. The following claims are to be understood as meaning that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define "first" and "second" embodiments, this designation serves to distinguish between two similar embodiments without establishing a priority.

Claims

1. Method for reducing condensate precipitate on inner surfaces of an outer skin of an aircraft, the condensate precipitate being reduced by supplying dry air into an upper region of an air gap, which extends between the upper region and a lower region, between the outer skin of an aircraft and an insulation (1), the insulation being arranged between a cabin wall and the outer skin of an aircraft, characterized in that the dry air is obtained by sucking it off from the lower region of the air gap and is conducted in one or more lines to the upper region of the air gap, where it re-enters the air gap.

2. Method according to claim 1, characterized in that the dry air is sucked off at a plurality of outlet points of the lower region of the air gap that are spaced in the longitudinal direction of the aircraft and, at a plurality of inlet points of the upper region of the air gap that are spaced in the longitudinal direction of the aircraft, is allowed to reenter it, the dry air being guided between the outlet and inlet points through a network of lines (4) comprising the plurality of lines, in which network a pressure difference which moves the dry air from the outlet points to the inlet points is generated.

3. Method according to claim 2, characterized in that a volumetric flow of dry air in the range between 0.7 I / s and 1.4 I / s is sucked out of the air gap at each outlet point and / or in that a volumetric flow of dry air in the range between about 0.7 I / s and about 1.4 I / s enters the air gap at each inlet point.

4. Method according to any one of claims 1 to 3, characterized in that the dry air is sucked off from the lower region of the air gap and / or the dry air is supplied to the upper region of the air gap intermittently.

5. Method according to any one of claims 1 to 4, characterized in that the dry air is only supplied to the upper region of the air gap at a predetermined outside temperature of the air surrounding the outer skin of the aircraft, or in that the dry air is only supplied to the upper region of the air gap at an outside temperature of the air surrounding the outer skin of the aircraft of about 0°C or less or about -7°C or less.

6. Device for carrying out the method according to any one of claims 1 to 5, comprising one or more lines for supplying dry air through one or more outlet openings of the line or lines to an upper region of an air gap, which extends between the upper region and a lower region, between the outer skin of an aircraft and an insulation (1) arranged between a cabin wall and the outer skin of an aircraft, characterized in that the line or lines has or have one or more inlet openings at the lower region of the air gap, through which dry air can be sucked off in the lower region of the air gap, and in that the line or lines is or are connected to one or more fans (9) which, in operation, generates or generate a pressure difference in the line or lines, which moves the dry air from the inlet opening or openings to the outlet opening or openings.

7. Device according to claim 6, characterized in that the fan or fans (9) is or are intermittently operable and / or in that the fan or fans (9) is or are arranged in a space above an upper section of the cabin wall.

8. Device according to claim 6 or 7, characterized in that the inlet openings are located at first line sections (5) extending below the insulation (1) and / or in passages in the insulation (1) between the air gap and a space between the insulation and the cabin wall and are connected to second line sections arranged in the space between the insulation and the cabin wall and / or in that each inlet opening and / or each outlet opening is or are respectively arranged in the region between two frames.

9. Device according to any one of claims 6 to 8, characterized in that the outlet openings are located at third line sections (8) which run above the insulation and / or in further passages in the insulation (1) between the space between the cabin wall and the insulation (1) and the air gap and are connected to the second line sections.

10. Device according to claim 8 or 9, characterized in that the second line sections are connected to the first line sections (5) via first valves.

11. Device according to claim 9 or 10, characterized in that the second line sections are connected to the third line sections (8) via second valves.

12. Device according to any one of claims 8 to 11, characterized in that the fan or fans (9) are each connected to the second line sections on its or their inlet side and its or their outlet side.

13. Device according to any one of claims 8 to 12, characterized in that the second line sections have a collection line (6) which is connected to the first line sections (5) and / or in that the second line sections have a distribution line (7) which is connected to the third line sections (8).

14. Device according to claim 13, characterized in that the distribution line (7) is connected to the outlet side of a fan (9) and in that the collection line is connected to the inlet side of the fan (9).

15. Device according to any one of claims 10 to 14, characterized in that the first valves and / or the second valves are each multiple-way valves.