Patent Application
20130037122
This disclosure relates generally to an aircraft auxiliary system and, more particularly, to influencing back pressure at an exhaust of the aircraft auxiliary system.
Auxiliary systems are used in many aircraft. One example auxiliary system, an auxiliary power unit (APU), mounts to structural members within a tail cone of the aircraft. Aircraft skin secured to the structural members encloses the APU within a cavity. Other auxiliary systems are located in other areas of the aircraft.
An inlet duct extends from an outer surface of the aircraft skin to the auxiliary system. Fluid communicates to the auxiliary system through the inlet duct. A door may selectively cover an opening to the inlet duct to restrict flow to the auxiliary system. An exhaust duct communicates exhausted fluid from the auxiliary system.
As known, back pressure is a function of the air flowing over outwardly facing surfaces of the aircraft skin interacting with the exhausted fluid. If the back pressure is relatively high, the efficiency of the auxiliary system may undesirably decrease. For example, relatively high back pressure levels can reduce flow through the APU, which inhibits the ability of the APU to cool an aircraft cabin.
An exemplary pressure influencing assembly for an aircraft auxiliary system includes an inlet opening to an aircraft auxiliary system and an exhaust opening from the aircraft auxiliary system. Both the inlet opening and the exhaust opening face at least partially radially away from an axis. The exhaust opening is positioned within a flowpath from the inlet opening.
An exemplary pressure influencing assembly for an aircraft auxiliary system includes an aircraft auxiliary system arranged within a cavity established by an aircraft skin. The aircraft auxiliary system has a rotational axis. An inlet duct communicates an inlet flow radially through an inlet opening in the aircraft skin to the aircraft auxiliary unit. An exhaust duct communicates an exhaust flow radially through an exhaust opening in the aircraft skin away from the auxiliary power unit. The inlet opening is at least partially circumferentially aligned with the exhaust opening.
An exemplary method of influencing back pressure on an aircraft auxiliary system exhaust includes exhausting a flow from an aircraft auxiliary exhaust, and disrupting a flow over an outer surface of an aircraft auxiliary system using an inlet opening, an inlet door, or both. The disrupting is to influence back pressure on an exhaust of the aircraft auxiliary exhaust.
The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows:
Referring to
The APU 10 includes a gearbox 22 through which a generator 26 is mechanically driven in response to rotation of a shaft-mounted compressor and turbine about an axis A.
Air from the exterior of the tail cone 18 is supplied through an inlet duct 30 to the compressor of the APU 10. The compressed air from the compressor is expanded across the turbine, and expelled through an exhaust duct 34. A person having skill in this art and the benefit of this disclosure would understand the general operation of an APU.
An outwardly-facing surface of an aircraft skin 38 faces away from the cavity 14. The outwardly-facing surface provides an aerodynamic outer mold line, or contour, of the tail cone 18. In this example, the inlet duct 30 and the exhaust duct 34 are both secured to the aircraft skin 38.
A vertical stabilizer 42 extends upwardly from the tail cone 18. The tail cone 18 has an axially extending crown 44 that bisects the vertical stabilizer 42. The vertical stabilizer 42 is an interruption in the surface of the aircraft skin 38 because the vertical stabilizer 42 protrudes from the relatively consistent outer mold line.
An inlet opening 46 is established within the skin 38. The inlet opening 46 provides a path for air to enter the inlet duct 30.
A door 50 is pivotally attached or hinged to an aft side 54 of the inlet opening 46. The door 50 is selectively opened and closed to control airflow through the inlet opening 46 into the inlet duct 30. A controller 58 connected to an actuator 62 may be used to move the door 50 between open and closed positions, or positions that restrict flow and positions that permit flow.
An exhaust opening 66 is established in the skin 38. The exhaust opening 66 provides a pathway for exhausted fluid from the APU 10 that has moved into the exhaust duct 34 to exit the tail cone 18.
In this example, air moves through the inlet opening 46 and the inlet duct 30 along a path P1 when the door 50 is in an open position. The door 50 helps direct or “scoop” air into the duct 30 through the inlet opening 46.
Exhausted fluid moves away from the APU 10 through the exhaust duct 34 through the exhaust opening 66 in a path P2.
Notably, fluid communicating along the paths P1 and P2 has a radial component over at least some of the paths P1 and P2. That is, fluid does not communicate in an exclusively radial direction along the entire duct 30 or the entire duct 34 relative to the direction of flow through the APU 10.
Also, the direction of fluid flow through the inlet opening 46 and the exhaust opening 66 has a radial component. The inlet opening 46 and the exhaust opening 66 face, at least partially, radially away from the axis 12, which facilitates fluid flow in the radial direction through the inlet opening 46 and the exhaust opening.
As can be appreciated, the tail cone 18 and the cavity 14 have a generally oval cross-section that tapers toward an aft end 68 of the tail cone 18. The cross-section is circular in some examples.
The tail cone 18 has an upper portion 70 and a lower portion 74. The aft end 68 is located at the vertical boundary between the upper portion 70 and the lower portion 74. The aircraft skin 38 of the upper portion 70 faces upwards, and the aircraft skin 38 of the lower portion 74 faces downwards.
Upwards and downwards, as used in this disclosure, refer to relative to a horizon when an aircraft having the APU 10 is in level flight or on the ground.
In this example, the inlet opening 46 and the exhaust opening 66 are both located in the upper portion 70. Thus, the inlet opening 46 and the exhaust opening 66 both face upwards.
The inlet opening 46 and the exhaust opening 66 are circumferentially offset from the axially extending crown 44 of the tail cone 18. More specifically, the example inlet opening 46 and exhaust opening 66 are circumferentially centered at a 2 o'clock position relative to the axis A (
The vertical stabilizer 42 is at a 12 o'clock position. Thus, the vertical stabilizer is not an interruption in the surface of the aircraft skin 38 that is between the inlet opening 46 and the exhaust opening 66.
The example exhaust opening 66 is positioned within a flowpath of air moving from the inlet opening 46. That is, some or most of the air that has moved over the inlet opening 46 generally moves toward the exhaust opening 66.
Although the example inlet opening 46 and exhaust opening 66 are circumferentially aligned, other examples may include some circumferential misalignment. For example, the inlet opening 46 may be circumferentially centered at a 1:30 position and the exhaust opening 66 circumferentially centered at a 2:30 position. In such an example, at least some of the inlet opening 46 is still circumferentially aligned with at least some of the exhaust opening 66.
In other examples, no portion of the inlet opening 46 is circumferentially aligned with the exhaust opening 66. That is, the inlet opening 46 may be circumferentially spaced from the exhaust opening 66. In such example, the inlet opening 46, the door 54, or both, still disrupt airflow near exhaust opening 66 because the exhaust opening 66 is still positioned within a flowpath of air from the inlet opening 46. In such examples, the flow moves a bit circumferentially as the flow moves toward the exhaust opening 66.
Referring to the highly schematic view of
Although the above disclosure describes the auxiliary power unit 10 as the auxiliary system, those skilled in this art and having the benefit of this disclosure will understand other aircraft auxiliary systems that could utilize the inlet opening 46 and exhaust opening 66. For example, an aircraft environmental control system or fluid discharge system may benefit from lowering an inlet pressure relative to an outlet pressure.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.
