Aircraft air inlet with airflow guide to prevent flow...

Aeronautics and astronautics – Aircraft power plants

Reexamination Certificate

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Reexamination Certificate

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06293494

ABSTRACT:

PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 50 093.9, filed on Oct. 30, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to an air inlet or intake for an aircraft that essentially comprises an intake or inlet opening that is recessed into the outer fuselage skin of an aircraft in the airflow lengthwise direction, so that the entire inlet cross-sectional area is flush with or recessed into the outer surface of the aircraft skin. The air inlet leads into an air channel that is connected to an air suction source, so that the air inlet provides outside air that is sucked from the exterior of the aircraft into the air suction source, such as an auxiliary power unit or the like. The downstream edge of the air inlet, with reference to the airflow direction during flight of the aircraft, is bounded by an air inlet lip that extends flush with and forms an extension of the outer surface of the fuselage skin. The air inlet is suitable to be used for connection with all systems of an aircraft that demand a flow of external air, whereby the air inlet is to provide an optimal utilization and recovery of pressure and a minimum interference drag or resistance, both during flight and during ground operations of the aircraft.
BACKGROUND INFORMATION
Various air inlet systems and particularly ram air inlets are known in the field of aircraft construction. These air inlet systems include recessed or recessible air channel inlets that are arranged on various aerodynamic surface areas of the aircraft. These inlets serve to deflect at least a portion of the boundary layer airflow from the exterior of the aircraft during flight thereof, so that the boundary layer air can flow into the interior of the aircraft in a suitable airflow channel, to be used by any one of a number of different systems of the aircraft.
Also, a so-called NACA sink inlet or intake developed by the National Advisory Committee for Aeronautics (NACA) is also known in the art, and is often used in aircraft for various air suctioning systems. Examples of such systems installed in aircraft include the auxiliary power unit (APU) intakes, air conditioning pack ram channel inlets, belly fairing ventilation inlets, and the like. These NACA sink inlets installed typically in aircraft primarily serve to provide exterior air to smaller power plants or auxiliary devices, for example in the form of ram air inlets for providing cool air to the air conditioning packs. Such a NACA sink inlet is also conventionally arranged in the belly fairing of the aircraft of the Airbus family for providing external air for cooling the bleed air extracted from the jet engines in corresponding heat exchangers of the air conditioning systems. In order to provide air to the auxiliary power unit (APU), a NACA sink inlet having parallel side walls is installed in the bottom surface or belly of the fuselage in the area of the horizontal tail surfaces of the aircraft. Additionally, a so-called pack bay ventilation inlet is provided to ventilate the air conditioning pack bay and also for tempering the aircraft structure. This pack bay ventilation inlet is typically arranged in the forward portion of the belly fairing. Moreover, two sink inlets are typically provided on the cowling of an engine, whereby one of the inlets serves to provide cooling air for carrying out the first stage cooling of the bleed air extracted from the engine, and the second inlet provides air for ventilating the intermediate space between the engine and the cowling. Another use or arrangement of such an air inlet is as a wing tank inlet, for providing air for ventilating the fuel tanks and thereby achieving a pressure equalization. In this context, the wing tank inlet is arranged on the bottom exterior surface of the respective wing.
All of the above described different air inlets have an inlet geometry, especially including inlet edges or an inlet lip against which the relative wind flows as the aircraft is in flight, such that this inlet geometry generates a pair of air vortices which transport the energy-rich air of the boundary layer into the inlet. In this manner, during flight of the aircraft, a useable pressure recovery is achieved for the air guide channel system arranged downstream of the air inlet, which serves to provide an air mass flow transport. The amount of turbo-machine or turbine engine suction power that would otherwise be necessary can be considerably reduced or completely eliminated through the use of such air inlets. Namely, the necessary aerodynamic energy of the air supply for the above mentioned auxiliary aggregates or systems of the aircraft is solely provided by the motion of the aircraft through the surrounding air during cruise flight of the aircraft, or more accurately is provided by the aerodynamic flow of the surrounding air relative to the air inlet edges or lips of the NACA sink inlets. However, when the aircraft is operating on the ground, either parked, taxiing or rolling for take-off or landing, this aerodynamic flow of the surrounding air is completely non-existent or is insignificant and therefore does not provide the above described effects. During this period of time of ground operations, the required volume flow of external air is sucked through the respective air inlet such as a NACA sink inlet, for supplying the respective auxiliary system of the aircraft.
Present
FIG. 1
shows the airflow situation in connection with a NACA air inlet
1
′ for the situation when the aircraft A′ is flying forward in cruise flight. As shown in
FIG. 1
, the flow of outside air
5
′ flows smoothly from left to right, whereby a portion
53
′ of the outside air is sucked smoothly into the air inlet
1
′. The nose portion
6
′ of the inlet lip
3
′ faces directly into the incident flow, whereby the airflow is divided into a portion
53
′ that flows into the air inlet
1
′ and a portion
54
′ that continues to flow along the exterior of the aerodynamic surface of the aircraft fuselage.
In comparison to the above described flow condition that exists during forward flight of the aircraft, a completely different flow pattern exists around the air inlet
1
′ during the ground operations of the aircraft. Such a flow condition and situation is illustrated in present FIG.
1
A. In this condition, there is no longer a general flow of the relative wind from left to right along the outer aerodynamic surface of the aircraft. Instead, the outside air
5
′ is substantially stagnant and is sucked from all directions, i.e. from the left and from the right and from all directions underneath the aircraft, into the air inlet
1
′ by the suction that prevails in the air guide channel C′ connected downstream of the air inlet
1
′. As a result, outside air
5
′ being sucked from the right in
FIG. 1A
fully flows around the 180° curved or rounded surface of the nose portion
6
′ of the inlet lip
3
′ of the air inlet
1
′. Largely due to the 180° curve of the airflow pattern of the outside air
5
′ flowing directly over the nose portion
6
′ of the inlet lip
3
′, a flow separation bubble B′ is formed directly downstream from the upper nose edge
61
′ of the nose portion
6
′ within the air guide channel C′. This separation bubble B′ extends into or is sucked into the air intake system connected to the downstream end of the air guide channel C′. This leads to high inlet losses, which in turn reduce the theoretically obtainable air flow and air power that would be achieved without such inlet losses.
A thesis by Michael Klas (Matr. No. 041101, “Theoretische Untersuchung zur Erhöhung des Durchsatzes am Staulufkanal der Klimaanlage am Beispiel des Airbus A330/A340” (“Theoretical Investigation for Increasing the Throughput at the Ram Air Channel of the Air Conditioning Plant in the Exampl

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