US20150354592A1

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Info

Publication number: US20150354592A1
Application number: US14/828,561
Authority: US
Inventors: Lawrence Binek; Brent J. Merritt
Original assignee: Hamilton Sundstrand Corp
Current assignee: Hamilton Sundstrand Corp
Priority date: 2011-10-24
Filing date: 2015-08-18
Publication date: 2015-12-10
Also published as: US9140272B2; CN103062128A; US20130098045A1; CN103062128B

Abstract

A ram air fan outer housing for directing air from a ram air fan rotor and air from a ram air bypass into a ram air fan outlet. The outer housing includes an outer cylinder with a ram air fan rotor end and a ram air fan outlet end. The ram air fan rotor end and the ram air fan outlet end are at opposite ends of an axis of the outer cylinder. A plenum is joined at a joint region for directing air from the ram air bypass into the outer cylinder. The plenum includes two plenum ridges with one at each of two walls of the plenum. The two walls of the plenum are parallel to the axis of the outer cylinder. Each of the two plenum ridges includes a protruding section of the corresponding plenum wall.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. application Ser. No. 13/279,508 filed Oct. 24, 2011 for “RAM AIR FAN OUTER HOUSING” by Brent Merritt and Lawrence Binek.

INCORPORATION BY REFERENCE

The aforementioned U.S. application Ser. No. 13/279,508 is hereby incorporated by reference in its entirety.

BACKGROUND

The present invention relates to an environmental control system. In particular, the invention relates to an outer housing of a ram air fan assembly for an environmental control system for an aircraft.

An environmental control system (ECS) aboard an aircraft provides conditioned air to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, it is dissipated by the ECS into a separate stream of air that flows into the ECS, across heat exchangers in the ECS, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of air ramming into the aircraft is sufficient to move enough air through the ECS and over the heat exchangers to remove the excess heat.

While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, ram air pressure is too low to provide enough air flow across the heat exchangers for sufficient heat removal from the ECS. Under these conditions, a fan within the ECS is employed to provide the necessary airflow across the ECS heat exchangers. This fan is called a ram air fan.

As with any system aboard an aircraft, there is great value in an improved ram air fan that includes innovative components, such as an outer housing designed to improve the operational efficiency of the ram air fan or to reduce its weight.

SUMMARY

A method for installing a ram air fan outer housing includes inserting a ram air fan housing of a ram air fan assembly into an outer cylinder such that a bearing housing attached to the fan housing is contained within the outer housing. The inserted fan housing is inserted such that the flanged surface of the outer cylinder abuts a corresponding flanged surface of the fan housing. The positioned fan housing is bolted to the outer cylinder. Electrical wires from the fan housing are connected to a terminal box attached to the outer cylinder. A cooling air duct is bolted to a cooling air flange on the outer cylinder. The ram air fan assembly is installed in an environmental control system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a ram air fan assembly incorporating the present invention.

FIG. 2 is a perspective view of an outer housing incorporating the present invention.

FIG. 3 is an end view of the outer housing ofFIG. 2.

FIG. 4 is a side view of the outer housing ofFIG. 2.

FIG. 5 is a cross-sectional view of a portion of the outer housing ofFIG. 4.

FIG. 6 is a cross-sectional view of another portion of the outer housing ofFIG. 4.

FIG. 7 is a cross-sectional view of another portion of the outer housing ofFIG. 4.

DETAILED DESCRIPTION

A ram air fan assembly in an environmental control system (ECS) employs an outer housing to channel air from a ram air fan rotor and air from a ram air bypass into a ram air fan outlet. The outer housing is the single largest component of the ram air fan assembly. The present invention is a ram air fan outer housing that is durable, while also being lightweight. An outer housing embodying the present invention incorporates innovative features that increase durability and ensure a lightweight housing. The outer housing is made of fiber-reinforced polymer composite plies, such as carbon-fiber plies, oriented in a specific sequence of layers, with the number of layers and the overlap of adjacent layers varying as a function of the need for strength. The use of a reinforcing fiber, such as carbon-fiber, in this manner provides a very strong and lightweight structure. The outer housing includes an outer cylinder and a plenum attached to the outer cylinder. Portions of the outer cylinder and the plenum are mechanically reinforced with raised features. Finally, the outer housing is designed with an exceptionally small ratio of a length of the outer cylinder to a diameter of the outer cylinder at a ram air fan outlet. A relatively large outer cylinder diameter at the ram air fan outlet enables efficient fan flow. Keeping the length of the outer cylinder relatively short reduces stresses on the outer housing, particularly at joints between the cylindrical section and the plenum. By reducing stresses, less material is required to reinforce these joints, contributing to a relatively lightweight outer housing.

FIG. 1 illustrates a ram air fan air assembly incorporating the present invention.FIG. 1 shows ramair fan assembly10 includingfan housing12, bearinghousing14,inlet housing16,outer housing18,inner housing20, and a plurality ofbolts60.Fan housing12 includesfan struts22,motor rotor24,motor stator26,thrust shaft28,thrust plate30, andthrust bearings32. Bearinghousing14 includesjournal bearing shaft34 andshaft cap36. Fan housing12 and bearinghousing14 together includetie rod38 andjournal bearings40.Inlet housing16 containsfan rotor42 andinlet shroud44, in addition to a portion oftie rod38.Outer housing18 includesterminal box46 andplenum48. Withinouter housing18 arediffuser50, motor bearingcooling tube52, andwire transfer tube54. A fan inlet is a source of air to be moved by ramair fan assembly10 in the absence of sufficient ram air pressure. A bypass inlet is a source of air to that moves through ramair fan assembly10 when sufficient ram air pressure is available.

As illustrated inFIG. 1,inlet housing16 andouter housing18 are attached to fanhousing12 at fan struts22 by a plurality ofbolts60. Bearinghousing14 is attached to fanhousing12 andinner housing20 connects motor bearing coolingtube52 andwire transfer tube54 to bearinghousing14. Motor bearing coolingtube52 connectsinner housing20 to a source of cooling air atouter housing18.Wire transfer tube54 connectsinner housing20 toouter housing18 atterminal box46.Motor stator26 and thrustplate30 attach to fanhousing12.Motor rotor24 is contained withinmotor stator26 and connectsjournal bearing shaft34 to thrustshaft28.Journal bearing shaft34,motor rotor24, and thrustshaft28 define an axis of rotation for ramair fan assembly10.Fan rotor42 is attached to thrustshaft28 withtie rod38 extending along the axis of rotation fromshaft cap36 at the end ofjournal bearing shaft34 throughmotor rotor24, thrustshaft28, andfan rotor42 toinlet shroud44. Nuts (not shown)secure shaft cap36 tojournal bearing shaft34 on one end oftie rod38 andinlet shroud44 tofan rotor42 at opposite end oftie rod38.Thrust plate30 andfan housing12 contain a flange-like portion ofthrust shaft28, withthrust bearings32 positioned between the flange-like portion ofthrust shaft28 and thrustplate30; and between the flange-like portion ofthrust shaft28 andfan housing12.Journal bearings40 are positioned betweenjournal bearing shaft24 and bearinghousing14; and betweenthrust shaft28 andfan housing12.Inlet shroud44,fan rotor42, and a portion offan housing12 are contained withininlet housing16.Diffuser50 is attached to an inner surface ofouter housing18.Plenum48 is a portion ofouter housing18 that connects ramair fan assembly10 to the bypass inlet.Inlet housing16 is connected to the fan inlet andouter housing18 is connected to a fan outlet.

In operation, ramair fan assembly10 is installed into an environmental control system aboard an aircraft and connected to the fan inlet, the bypass inlet, and the fan outlet. When the aircraft does not move fast enough to generate sufficient ram air pressure to meet the cooling needs of the ECS, a ram air fan motor controller (not shown) supplies power tomotor stator26 by wires running fromterminal box46, throughwire transfer tube54,inner housing20, and bearinghousing14. Energizingmotor stator26 causesrotor24 to rotate about the axis of rotation for ramair fan assembly10, rotating connectedjournal bearing shaft34 and thrustshaft28.Fan rotor42 andinlet shroud44 also rotate by way of their connection to thrustshaft28.Journal bearings40 andthrust bearings32 provide low friction support for the rotating components. Asfan rotor42 rotates, it moves air from the fan inlet, throughinlet housing20, past fan struts22 and into the space betweenfan housing12 andouter housing18, increasing the air pressure inouter housing18. As the air moves throughouter housing18, the air flowspast diffuser50 andinner housing20, where the air pressure is reduced due to the shape ofdiffuser50 and the shape ofinner housing20. Once pastinner housing20, the air moves out ofouter housing18 at the fan outlet. Components within bearinghousing14 andfan housing12, especially thrustbearings32,journal bearings40,motor stator26, andmotor rotor24; generate significant heat and must be cooled. Cooling air is provided by motor bearing coolingtube52 which directs a flow of cooling air toinner housing20.Inner housing20 directs flow of cooling air to bearinghousing14, where it flows past components in bearinghousing14 andfan housing12, cooling the components. Once the aircraft moves fast enough to generate sufficient ram air pressure to meet the cooling needs of the ECS, ram air is directed intoplenum48 from the bypass inlet. The ram air passes intoouter housing18 atplenum48 and moves out ofouter housing18 at the fan outlet.

As shown inFIG. 1,outer housing18 includesterminal box46 andplenum48.FIG. 1 also shows thatouter housing18 has a ram air fan outlet end and a ram air fan inlet end opposite the ram air fan outlet end.FIG. 2 is a perspective view ofouter housing18, withterminal box46 omitted for clarity.FIG. 2 shows thatouter housing18 further includesouter cylinder70.Outer cylinder70 includesinlet flange72, inlet flange bolt holes74,component channel76,diameter transition78,terminal box opening80, terminal box bolt holes82, coolingair flange84, cooling air flange bolt holes86, outercylinder support ridge88, andoutlet bead90.Plenum48 includesplenum ridges94,plenum flange96, and plenum flange bolt holes98.Outer cylinder70 includes the ram air fan outlet end and the ram air fan inlet end ofouter housing18.Outer cylinder70 has two external diameters, a first external diameter at the ram air fan outlet end and a second external diameter at the ram air fan inlet end.Outer cylinder70 transitions from the first external diameter to the second external diameter atdiameter transition78. Thus, the first external diameter extends from the ram air fan outlet end todiameter transition78 and the second external diameter extends fromdiameter transition78 to the ram air fan rotor end atinlet flange72.Outlet cylinder70 has a single axis running the length ofouter cylinder70 at the midpoint of both the first external diameter and the second external diameter. Once attached to fanhousing12, the axis ofouter cylinder70 is, ideally, aligned with the axis of rotation for ramair fan assembly10 described above in reference toFIG. 1.

FIG. 3 is an end view of the outer housing ofFIG. 2, looking at the ram air fan rotor end ofouter housing18.FIG. 3 shows the circular profile ofouter cylinder70. The axis ofouter cylinder70 is at the center of the circular profile ofouter cylinder70.Plenum48 curves intoouter cylinder70 near a side ofouter cylinder70

opposite plenum flange

96. The surface ofplenum flange96 facing away fromouter cylinder70 defines reference flangeplane B. Plenum48 also curves into flat walls tangent to the radius of curvature ofplenum48 with the flat walls meetingplenum flange96 at a right angle. The center of the radius of curvature for the curved portion ofplenum48 does not coincide with the center of the circular profile ofouter cylinder70. As shown inFIG. 3, one each ofplenum ridges94 is formed on each of two sides ofplenum48, the two sides on opposite sides ofouter cylinder70.FIG. 3 also shows that plenumridges94 protrude such that they are perpendicular to reference flange plane B and are parallel to each other and to the axis ofouter cylinder70. In one embodiment,plenum ridges94 protrude such that planes coincident with the extent to whichplenum ridges94 protrude are between 12.450 inches and 12.470 inches (or between 316.230 mm and 316.738 mm) from a parallel plane containing the axis ofouter cylinder70.Plenum ridges94 provide rigidity to the two largest flat walls ofplenum48, preventing them from buckling under high or low pressure conditions. Alternatives, such as adding stiffing components or thickening the largest flat walls, would add expense and weight. By addingplenum ridges94,plenum48 is able to withstand buckling with little added weight.

FIG. 4 is a side view of the outer housing ofFIG. 2.FIG. 4 showsterminal box46 connected toouter cylinder70 byterminal box bolt100 through terminal box bolt holes82 as shown inFIG. 2.Terminal box46 is also secured toouter cylinder70 by a permanent adhesive. As noted in reference toFIG. 2,outer cylinder70 has a ram air fan rotor end (at inlet flange72) and a ram air fan outlet end (near outlet bead90) at opposite ends of an axis ofouter cylinder70. The outer surface ofinlet flange72 defines reference flange plane A, which is perpendicular to the axis ofouter cylinder70. As also noted above,outer cylinder70 has two external diameters, the first external diameter extending from the ram air fan outlet end todiameter transition78 and the second external diameter extending fromdiameter transition78 to the ram air fan rotor end at reference flange plane A. The second external diameter is determined by the size of the components contained within, such asfan housing12, bearinghousing14,inner housing20 anddiffuser50, and the volume of ram air from the fan inlet to be moved byfan rotor42. In embodiments of the present invention, the first external diameter is greater than the second external diameter to provide efficient flow of ram air from both the fan inlet and the bypass inlet to the fan outlet. However, because the greater external diameter of the first external diameter also increases mechanical stresses onouter housing18, the external length ofouter cylinder70, and thus the external length ofoutlet housing18, is reduced relative to the first external diameter to reduce mechanical stresses onoutlet housing18. Thus, embodiments of the present invention have a ratio of external length (L) to external diameter (D) that is relatively small, the external diameter being the first external diameter ofouter cylinder70 and the external length measured from the ram air fan rotor end to the ram air fan outlet end ofouter housing18 in a direction parallel to the axis ofouter cylinder70, as shown inFIG. 4. In one embodiment, the ratio of external length to external diameter is no greater than 1.5827. In another embodiment, the ratio of external length to external diameter is no greater than 1.5827 and no less than 1.5720. In yet another embodiment, the external length ofouter housing18 is between 26.755 inches and 26.875 inches (or between 679.58 mm and 682.63 mm) and the external diameter is between 16.980 inches and 17.020 inches (or between 431.29 mm and 432.31 mm).

FIG. 4 also illustrates additional details of plenum ridges94 (one shown). In the embodiment shown inFIG. 4,plenum ridges94 are shaped in an inverted “T” to provide suitable rigidity in the two primary dimensions the two largest flat walls ofplenum48, preventing them from buckling under high or low pressure conditions.

FIG. 5 is a cross-sectional view of a portion of the outer housing ofFIG. 4.FIG. 5 shows details of outercylinder support ridge88. As noted above, outercylinder support ridge88 is a portion ofouter cylinder70 shaped for mechanical support ofouter cylinder70.FIG. 5 illustrates that outercylinder support ridge88 is formed by roughly semicircular-shaped protrusion ofouter cylinder70. Much as plenumridges94 are protruding portions of large wall sections ofplenum48 for providing structural support forplenum48, outercylinder support ridge88 is a protruding section ofouter cylinder70 to provide mechanical support forouter cylinder70. In one embodiment of the present invention, outercylinder support ridge88 protrudes between 0.290 inches and 0.310 inches (or between 7.37 mm and 7.87 mm) radially outward from the external diameter ofouter cylinder70. Alternatives to outercylinder support ridge88, such as adding mechanical components or thickening the wall ofouter cylinder70, would add expense and weight. Forming outercylinder support ridge88 intoouter cylinder70 provides additional mechanical strength toouter cylinder70 with little added weight or expense.

Outer cylinder

70 andplenum48 are made of laminations of plain-weave carbon-fiber sheets. Carbon-fibers are known for tremendous tensile strength for their size and weight. Plain-weave carbon-fiber sheets have bundles of carbon-fiber filaments, know as a strand, woven into a sheet using a plain-weave pattern such that half of the strands are oriented in a first direction, for example, a 0 degree direction, and the other half of the filaments are oriented in a second direction, the second direction at a right angle to the first direction, for example, 90 degrees. This weave orientation provides tensile strength in the 0 degree and 90 degree directions. By laminating several sheets together by employing resins noted for strength at high temperatures, structures with high strength and relatively low weight can be built up. In all embodiments of the present invention, all walls ofouter cylinder70 andplenum48 are comprised of at least four layers, or plies, of plain-weave carbon-fiber fabric. The four plies are assembled in a unique laminate stacking sequence to provide excellent tensile strength in more than 0 degree and 90 degree directions. The laminate stacking sequence is such that a first layer and a fourth layer are oriented forty-five degrees from each of a second layer and a third layer, the second layer and the third layer sandwiched between the first layer and the fourth layer. For example, if the first layer has a weave orientation such that its strands are oriented in 0 degree and 90 degree directions (orientation A), then the next two plies in the laminate stacking sequence must have weave orientations such that the strands of each ply are oriented in +45 degree and −45 degree directions (orientation B). The fourth layer in the laminate stacking sequence must have a weave orientation such that its strands are oriented in 0 degree and 90 degree directions (orientation A). This laminate stacking sequence is abbreviated as A-B-B-A, and is employed throughoutouter cylinder70 andplenum48 to create walls with a thickness of, for example, about 0.026 inches (or about 0.66 mm), that are strong, but lightweight.

FIG. 6 is a cross-sectional view of another portion of the outer housing ofFIG. 4.FIG. 6 shows details of cylinder-to-plenum joint92 andplenum flange96. Cylinder-to-plenum joint92 is an important joint where significant mechanical stress associated withouter cylinder70 is transferred toplenum48. Cylinder-to-plenum joint92 includes a unique laminate stacking sequence that interleaves A-B-B-A stacking sequences from walls in adjacentouter cylinder70 andplenum48 to form a lamination of eight layers of plain-weave carbon-fiber fabric. Thus, at cylinder-to-plenum joint92, the laminate stacking sequence is A-A-B-B-B-B-A-A. This laminate stacking sequence with eight layers provides the necessary additional strength to support the level of mechanical stress experienced by cylinder-to-plenum joint92. The interleaving of eight layers extends into each ofouter cylinder70 andplenum48 to a degree sufficient to insure a strong joint. In one embodiment, the interleaving of eight layers extends into each ofouter cylinder70 andplenum48 to at least 0.500 inches (or at least 2.70 mm) beyond any point whereouter cylinder70 orplenum48 forms a tangent to a radius of curvature of cylinder-to-plenum joint92. In another embodiment, the interleaving of eight layers extends into each ofouter cylinder70 andplenum48 to between 0.500 inches and 2.000 inches (or between 12.70 mm and 50.80 mm) beyond any point whereouter cylinder70 orplenum48 forms a tangent to a radius of curvature of cylinder-to-plenum joint92. This laminate stacking sequence with eight layers and weave orientations of A-A-B-B-B-B-A-A provides the necessary additional strength to support the level of mechanical stress experienced by cylinder-to-plenum joint92, while maintaining a lightweight structure.

In contrast to walls and joints, flanges ofouter housing18 must be much thicker to withstand mechanical stresses associated with the flange connections. As shown inFIG. 6,plenum flange96 is much thicker than the wall ofplenum48. This is achieved by building up plies of plain-weave carbon-fiber fabric in the laminate stacking sequence A-B-B-A, and repeating this laminate stacking sequence until reaching a final target thickness ofplenum flange96. For example, to build upplenum flange96 to a thickness of between 0.100 inches and 0.140 inches (or between 2.5 mm and 3.6 mm) with A-B-B-A stacking sequences having a nominal thickness of 0.026 inches (or of 6.6 mm), between four and five of the A-B-B-A sequences would be employed.

FIG. 7 is a cross-sectional view of another portion of the outer housing ofFIG. 4.FIG. 7 showsinlet flange72 and one of the plurality of inlet flange bolt holes74. Likeplenum flange96 described above in reference toFIG. 6,inlet flange72 must be much thicker than the wall ofouter cylinder70 to withstand mechanical stresses associated with a flange connection. Also likeplenum flange96,inlet flange72 is also created by building up plies of plain-weave carbon-fiber fabric in the laminate stacking sequence A-B-B-A, and repeating this stacking sequence until reaching a final target thickness. As shown inFIG. 7, forinlet flange72, this thickness extends frominlet flange72 into a wall section ofouter cylinder70, where the extra plies drop off until the single A-B-B-A wall thickness ofouter cylinder70 is reached.

The present invention is a ram air fan outer housing that is durable, while also being lightweight. An outer housing embodying the present invention is made out of fiber-reinforced polymer composite plies, such as carbon-fiber plies, oriented in a laminate stacking sequence of A-B-B-A, creating very strong and lightweight walls. By interleaving laminate stacking sequences from the outer cylinder and the plenum across the joint between the two, a strong eight ply laminate stacking sequence is created to handle the mechanical stresses of the joint. Portions of the outer cylinder and the plenum are mechanically reinforced with raised features, such as plenum ridges and an outer cylinder support ridge to provide extra mechanical strength where needed without adding significant weight or cost. Finally, the outer housing is designed with an exceptionally small ratio of the external length of the outer cylinder to the external diameter of the outer cylinder at the ram air fan outlet. The relatively large outer cylinder diameter at the ram air fan outlet enables efficient fan flow. Keeping the length of the outer cylinder relatively short reduces stresses on the outer housing, particularly the joint between the outer cylinder and the plenum. By reducing stresses, less material is required to reinforce these joints, contributing to a relatively lightweight outer housing.

Novel aspects ofouter housing18, includingouter cylinder70 andplenum48 of the present invention described herein are achieved by substantial conformance to specified geometries. It is understood that edge breaks and curved radii not specifically described herein, but normally employed in the art, may be added toouter housing18 to enhance manufacturability, ease assembly, or improve durability while retaining substantial conformance to specified geometries.

Alternatively, substantial conformance is based on a determination by a national or international regulatory body, for example in a part certification or parts manufacture approval (PMA) process for the Federal Aviation Administration, the European Aviation Safety Agency, the Civil Aviation Administration of China, the Japan Civil Aviation Bureau, or the Russian Federal Agency for Air Transport. In these embodiments, substantial conformance encompasses a determination that a particular ram air fan outer housing is identical to, or sufficiently similar to, the specifiedouter housing18 comprisingouter cylinder70 andplenum48, or that the ram air fan outer housing is sufficiently the same with respect to a part design in a type-certified ram air fan outer housing, such that the ram air fan outer housing complies with airworthiness standards applicable to the specified ram air fan outer housing. In particular, substantial conformance encompasses any regulatory determination that a particular part or structure is sufficiently similar to, identical to, or the same as a specifiedouter housing18 of the present invention, such that certification or authorization for use is based at least in part on the determination of similarity.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A ram air fan outer housing for directing air from a ram air fan rotor and air from a ram air bypass into a ram air fan outlet, the outer housing comprising:

an outer cylinder having a ram air fan rotor end and a ram air fan outlet end, the ram air fan rotor end and the ram air fan outlet end at opposite ends of an axis of the outer cylinder; and

a plenum joined to the outer cylinder at a joint region for directing air from the ram air bypass into the outer cylinder, the plenum comprising:

two plenum ridges, one at each of two walls of the plenum, the two walls of the plenum being parallel to the axis of the outer cylinder; wherein each of the two plenum ridges comprises a protruding section of the corresponding plenum wall.

2. The outer housing ofclaim 1, wherein the plenum ridges protrude to planes parallel to each other, and between 12.450 inches and 12.470 inches (or between 316.230 mm and 316.738 mm) from a parallel plane containing the axis of the outer cylinder.

3. The outer housing ofclaim 2, wherein the plenum ridges each form an inverted T shape.

4. The outer housing ofclaim 1, wherein the outer cylinder further comprises:

an outer cylinder support ridge extending along at least a portion of the outer cylinder in a plane perpendicular to the axis of the cylinder, and comprising a protruding section of the outer cylinder wall.

5. The outer housing ofclaim 4, wherein the outer cylinder support ridge protrudes between 0.290 inches and 0.310 inches (or between 7.37 mm and 7.87 mm) radially outward from the outer cylinder wall.

6. The outer housing ofclaim 1, wherein a ratio of an external length of the outer cylinder to an external diameter of the outer cylinder at the ram air fan outlet end is no greater than 1.5827, wherein the external length of the outer cylinder is a distance from the ram air fan rotor end to the ram air fan outlet end in a direction parallel to the axis of the outer cylinder.

7. The outer housing ofclaim 1, wherein a ratio of an external length of the outer cylinder to an external diameter of the outer cylinder at the ram air fan outlet end is no greater than 1.5827 and no less than 1.5720, wherein the external length of the outer cylinder is a distance from the ram air fan rotor end to the ram air fan outlet end in a direction parallel to the axis of the outer cylinder.

8. The outer housing ofclaim 1, wherein an external length of the outer cylinder is between 26.755 inches and 26.875 inches (or between 679.58 mm and 682.63 mm) and an external diameter of the outer cylinder at the ram air fan outlet is between 16.980 inches and 17.020 inches (or between 431.29 mm and 432.31 mm).

9. The outer housing ofclaim 1, wherein the joint region extends into each of the outer cylinder and the plenum to at least 0.500 inches (or at least 12.7 mm) beyond any point where the outer cylinder or the plenum forms a tangent to a radius of curvature of the joint region.

10. The outer housing ofclaim 1, wherein the joint region extends into each of the outer cylinder and the plenum to between 0.500 inches and 2.000 inches (or between 12.70 mm and 50.80 mm) beyond any point where the outer cylinder or the plenum forms a tangent to a radius of curvature of the joint region.

11. The outer housing ofclaim 1, wherein

the outer cylinder includes walls comprised of a laminate stacking sequence of a plurality of adjacent layers of plain-weave fiber-reinforced polymer composite;

the plenum includes walls comprised of a laminate stacking sequence of a plurality of adjacent layers of plain-weave fiber-reinforced polymer composite; and

the joint region is comprised of a laminate stacking sequence of a plurality of adjacent layers of plain-weave fiber-reinforced polymer composite, the joint region laminate stacking sequence formed by interleaving the plurality of adjacent outer cylinder layers in the joint region with the plurality of adjacent plenum layers in the joint region.

12. The outer housing ofclaim 11, wherein

the plenum laminate stacking sequence comprises at least four adjacent layers of plain-weave fiber-reinforced polymer composite, each layer of the four adjacent layers having a weave orientation such that a first plenum layer and a fourth plenum layer are oriented forty-five degrees from each of a second plenum layer and a third plenum layer, the second plenum layer and the third plenum layer sandwiched between the first plenum layer and the fourth plenum layer; and

the joint region laminate stacking sequence comprises at least eight adjacent layers of plain-weave fiber-reinforced polymer composite, the joint region laminate stacking sequence formed by interleaving the four adjacent outer cylinder layers in the joint region with the four adjacent plenum layers in the joint region.

13. The outer housing ofclaim 1, wherein the outer housing is comprised by a ram air fan assembly, wherein the ram air fan assembly further comprises:

a fan housing;

a fan motor attached to the fan housing;

a fan rotor;

a thrust shaft connecting the fan motor to the fan rotor;

an inlet housing connected to the fan housing;

a bearing housing attached to the fan housing; and

an inner housing attached to the bearing housing.

14. The outer housing ofclaim 13, wherein the outer housing is connected to the fan housing and contains the bearing housing, the inner housing, and a portion of the fan housing.

15. A ram air fan outer housing for directing air from a ram air fan rotor and air from a ram air bypass into a ram air fan outlet, the outer housing comprising:

a plenum joined to the outer cylinder at a joint region for directing air from the ram air bypass into the outer cylinder, wherein the joint region is comprised of a laminate stacking sequence of a plurality of adjacent layers of plain-weave fiber-reinforced polymer composite, the joint region laminate stacking sequence formed by interleaving the plurality of adjacent outer cylinder layers in the joint region with the plurality of adjacent plenum layers in the joint region, wherein the joint region laminate stacking sequence comprises at least eight adjacent layers of plain-weave fiber-reinforced polymer composite, the joint region laminate stacking sequence formed by interleaving the four adjacent outer cylinder layers in the joint region with the four adjacent plenum layers in the joint region,

the plenum comprising:

two plenum ridges, one at each of two walls of the plenum, the two walls of the plenum being parallel to the axis of the outer cylinder; wherein each of the two plenum ridges comprises a protruding section of the corresponding plenum wall, and

walls comprised of a laminate stacking sequence of a plurality of adjacent layers of plain-weave fiber-reinforced polymer composite, wherein the plenum laminate stacking sequence comprises at least four adjacent layers of plain-weave fiber-reinforced polymer composite, each layer of the four adjacent layers having a weave orientation such that a first plenum layer and a fourth plenum layer are oriented forty-five degrees from each of a second plenum layer and a third plenum layer, the second plenum layer and the third plenum layer sandwiched between the first plenum layer and the fourth plenum layer.

15. The outer housing ofclaim 1, wherein the plenum ridges protrude to planes parallel to each other, and between 12.450 inches and 12.470 inches (or between 316.230 mm and 316.738 mm) from a parallel plane containing the axis of the outer cylinder.

17. The outer housing ofclaim 1, wherein the outer cylinder further comprises:

18. The outer housing ofclaim 1, wherein a ratio of an external length of the outer cylinder to an external diameter of the outer cylinder at the ram air fan outlet end is no greater than 1.5827, wherein the external length of the outer cylinder is a distance from the ram air fan rotor end to the ram air fan outlet end in a direction parallel to the axis of the outer cylinder.

19. The outer housing ofclaim 1, wherein the joint region extends into each of the outer cylinder and the plenum to at least 0.500 inches (or at least 12.7 mm) beyond any point where the outer cylinder or the plenum forms a tangent to a radius of curvature of the joint region.

20. A method for installing a ram air fan outer housing comprising an outer cylinder and a plenum attached to the outer cylinder, the outer cylinder comprising a flanged surface perpendicular to an axis of the outer cylinder, the method comprising:

inserting a ram air fan housing of a ram air fan assembly into the outer cylinder such that a bearing housing attached to the fan housing is contained within the outer housing;

positioning the inserted fan housing such that the flanged surface of the outer cylinder abuts a corresponding flanged surface of the fan housing;

bolting the positioned fan housing to the outer cylinder;

connecting electrical wires from the fan housing to a terminal box attached to the outer cylinder;

bolting a cooling air duct to a cooling air flange on the outer cylinder; and

installing the ram air fan assembly in an environmental control system.