Thermal blanket for gas turbine engine

The thermal blanket can be used for shielding an engine component. The thermal blanket has a window providing visual access to the engine component. The thermal blanket can have a non-transparent portion having an opening extending across the thickness of the non-transparent portion, the opening delimited by an internal edge of the non-transparent portion, and a transparent portion of transparent material in the opening, the transparent portion secured to the internal edge of the non-transparent portion.

TECHNICAL FIELD

The application related generally to gas turbine engines and, more particularly, to thermal blankets therefore.

BACKGROUND OF THE ART

Thermal blankets are used to protect an aircraft and/or engine components from heat caused by adjacent hotter (typically engine) components or in the event of fire. Thermal blankets can be flexible or rigid, and while their primary purpose is typically related to heat resistance or fire retardation, they must also be adapted to their environment of use, where they can be exposed to stress, oil or water, for instance. As well, to be effective, thermal blankets must cover the relevant components, and therefore must be removed if the component requires inspection or maintenance. While existing thermal blankets were satisfactory to a certain degree, there remained room for improvement.

SUMMARY

In one aspect, there is provided an aircraft engine comprising a thermal blanket extending over an engine component, the thermal blanket having a non-transparent portion having a thickness, and an opening extending across the thickness, the opening delimited by an internal edge of the non-transparent portion, and a transparent portion composed of transparent material in the opening, the transparent portion secured to the internal edge of the non-transparent portion, the transparent material of the transparent portion configured for allowing visual access to the engine component across the thermal blanket.

In another aspect, there is provided a thermal blanket for covering an engine component, the thermal blanket comprising a non-transparent portion having a thermal insulation layer sandwiched between barrier layers, and an opening extending across the thickness of the non-transparent portion, the opening delimited by an internal edge of the non-transparent portion, and a transparent portion of transparent material in the opening, the transparent portion having an external edge protruding and secured between corresponding edges of the barrier layers.

DETAILED DESCRIPTION

FIG. 1illustrates a gas turbine engine10of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan12through which ambient air is propelled, a compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases. An engine component22of the gas turbine engine is shielded by a thermal blanket20. The thermal blanket20includes a non-transparent portion24, and a window26which allows visual access to the engine component22. By visual access, what is meant is that the window can allow a person to see the engine component22across the window, independently of the purpose of such visual access, which can be for inspecting the contour of a component, reading a dial, etc.

In this specific example, the engine component is a gear box oil sump area28, including more specifically an oil sight glass29thereof. This is design-specific, and it will be understood that a thermal blanket20having a window26can be useful to allow visual access to a wide variety of engine components in alternate embodiments, such as a bleed valve, an accessory data plate, or an external portion of a component having an appearance which can vary depending on its condition.

Referring now toFIG. 2, an example of a thermal blanket20having a window26is shown in greater detail. The non-transparent portion24of the thermal blanket20has an opening across its thickness. In some embodiments, the opening will have a closed shape, whereas in alternate embodiments, the opening can have an open shape and be positioned along an edge of the non-transparent portion24for instance. A pane30is positioned in this opening. The pane30can be rigid, but could also be flexible and made of a suitable transparent material such as flexible glass, for instance. The pane30constitutes a transparent portion in this embodiment.

Referring now toFIG. 3, it will be understood that the non-transparent portion of the thermal blanket can be made of a traditional layered thermal blanket construction including a thermal insulation layer32sandwiched between barrier layers34,36, with the opening through its thickness defining the window area26. The barrier layers34,36can serve to protect the thermal insulation layer32from the engine environment, or from manipulation, for instance, and can be engineered to be heat-reflective. In some embodiments, there can be more than two barrier layers, but only two are shown herein for simplicity. The internal edge of the thermal insulation layer32is recessed between the internal edges of the barrier layers34. The pane30has an external edge38which protrudes between the barrier layers34,36and which is secured thereto in a sandwich configuration, the external edge38of the pane being adjacent to the internal edge of the thermal insulation layer32in this example.

Turning now toFIG. 4, an alternate embodiment is illustrated. In this embodiment, the internal edge of the thermal insulation layer132is not recessed between the barrier layers134,136. Rather, the external edge138of the pane130is superposed to the internal edge of the thermal insulation layer132, between the barrier layers134,136, in the sandwich configuration. More specifically, one of the opposite faces of the external edge138abuts against a corresponding face of barrier layer134, whereas the other opposite face of the external edge138abuts against a corresponding face of the thermal insulation layer132, and the opposite face of the thermal insulating layer132abuts against a corresponding face of barrier layer136.

The configurations shown inFIG. 3and inFIG. 4both have in common that the pane30,130is secured to the internal edge of the non-transparent portion24,124. The choice of a specific one of these two configurations, or of yet other configurations not illustrated, can depend on various considerations such as the type of non-transparent portion of the thermal blanket and the specificities of the context. Some thermal blanket types can have a thermal insulation layer which has rigidity, and barriers which are supple, for instance. In such cases, it can be preferred to use a configuration such as shown inFIG. 4to harness the rigidity of the thermal insulation layer to hold the pane. Some other thermal blanket types can have barrier layers which are rigid, and an insulation layer which does not exhibit structural resistance. In such other cases, it can be preferred to use a configuration such as shown inFIG. 3, to harness the rigidity of the barrier layers to hold the pane.

Various materials can be used for various ones of the components, in alternate embodiments. Indeed, some thermal blankets can have two rigid sheets of metal forming the barrier layers for instance, in which case the thermal insulation can be provided in the form of powder or ceramic barrier filling the spacing between the sheets of metal, and some other thermal blankets can have barrier layers in the form of flexible sheets of aluminium cloth or silicon cloth (which can be aluminized for instance) sandwiching thermal insulation in the form of thermal wool, for instance. The glass pane can be made of fused silica glass for instance, which has a high heat resistance. The barrier layers can be made of a heat reflective material such as stainless steel, or of a fiberglass fabric embedded with a flame barrier material such as Nextel™ in a sandwich arrangement with insulation material such as wool, ceramic barrier such as ceramic fiber cloth, HSA paper or micro porous insulating material such as min-K™. The companies Unifrax, 3M and Morgan Ceramics are providers of insulation materials therefore.

The pane can be made of fused silica glass or quartz glass. Both fused silica glass and quartz glass offer high temperature resistance, however they perform differently in the optical spectrum. Fused silica glass offers transmission of in the visible and UV portions of the electromagnetic radiation spectrum, whereas quartz glass offers transmission in the visible spectrum. The pane can alternately be made of any suitable material offering the desired transmission of light and a high temperature resistance, and in some embodiments, it can remain satisfactory to use a glass which has a lower temperature resistance than fused silica glass.

The pane30,130can be secured to the non-transparent portion24,124of the thermal blanket in any suitable way. An adhesive can be used between opposite faces of edges which are in abutting contact with one another, for instance. In the embodiments shown inFIGS. 2-4, the pane is provided with a plurality of pinholes extending across its thickness, and along its edge, and a resistant thread, such as a stainless steel thread for instance, can be engaged into the pinholes and used to effectively stitch the pane to the barrier layers (FIG. 3) or stitch the pane to the barrier layers and to the insulating layer (FIG. 4).