Aeronautics and astronautics – Aircraft power plants
Reexamination Certificate
1998-08-13
2001-01-30
Poon, Peter M. (Department: 3644)
Aeronautics and astronautics
Aircraft power plants
C244S13400A, C244S129400
Reexamination Certificate
active
06179249
ABSTRACT:
DESCRIPTION
1. Technical Field
The invention relates to a jet engine bay, whose architecture is optimized, so as to ensure a laminar air flow around the bay up to the vicinity of the thrust reversers. The invention more particularly applies to turbofan engine bay equipping aircraft.
2. Prior Art
In a turbofan engine, the bay channels around a core engine the secondary air flow produced by a fan, which is driven by a low pressure turbine forming part of the core engine.
The mechanical connection between the jet engine and the aircraft wings is ensured by a structure known as a pylon. This complex structure ensures the transmission of forces and permits the passages of various circuits, particularly hydraulic circuits, linking the jet engine with the aircraft.
Starting from the front of the engine in the air flow direction, the bay generally incorporates an air intake box, pivoting cowls giving access to an accessory box housed in the bay, thrust reversers and articulated cowls for the maintenance of the core engine.
In this conventional architecture, the mobile elements constituted more particularly by the pivoting cowls positioned immediately behind the air intake box create significant discontinuities, which greatly disturb the aerodynamic air flow along the outer surface of the bay. Thus, although this shape is optimized so that the theoretical air flow is laminar, at least around the front half of the bay, it is impossible to obtain such a flow in practice. This leads to an undesired increase in drag compared with the theoretical value thereof.
Moreover, articulated cowls are thin and not very stiff structures. Thus, in flight, they are subject to significant deformations, which does not permit the maintenance of their aerodynamic shape. When the aircraft is flying, these deformations increase the distortion between the theoretical, laminar air flow around the front half of the bay and the true value of said flow. This further prejudices the drag.
With reference to
FIGS. 8 and 9
, FR-A-2 732 074 envisages the replacement of the pivoting cowls normally positioned behind the air intake box of the bay by an external envelope fixed to the pylon and rearwardly extending said box.
Compared with a conventional bay architecture, this arrangement makes it possible to eliminate the surface discontinuities around all the front part of the bay, with the exception of the area where it is connected to the pylon.
However, the fixed, external envelope extending the air intake box in
FIGS. 8 and 9
of FR-A-2 732 074 remains a thin metal sheet having no maintaining means over most of its length and circumference. Thus, in flight, said envelope is inevitably subject to sensitive deformations, which do not make it possible to maintain an optimum aerodynamic shape adapted to obtaining a laminar air flow around the bay.
Moreover, the fixing of the front part of the bay to the pylon constitutes a supplementary, external envelope deformation source, which contributes to the illusion of obtaining a laminar flow in flight.
The architecture described in the above document also makes it virtually impossible to install an accessory gearbox in the region of the bay positioned around the fan. Thus, the non-dismantlable character of the external envelope fixed to the pylon prevents any intervention in this region.
DESCRIPTION OF THE INVENTION
The invention relates to a jet engine bay, whose original architecture makes it possible to eliminate any discontinuity, at least over the front half of the external surface thereof, thus controlling both on the ground and in flight, the aerodynamic shape of said surface, so as to ensure there a laminar air flow, whilst rendering possible access to the region of the bay located around the jet engine fan.
According to the invention, this result is obtained by means of a jet engine bay, characterized in that it comprises:
a rear structural element,
a front structural element, integrating an air intake box and an external shell extending rearwards and without any discontinuity, an external surface of the air intake box, so that the front structural element has a continuous, external surface extending over at least 50% of the geometrical chord of the bay,
maintenance and guidance means, interposed between the front structural element and a jet engine fan case, so as to allow a limited sliding forwards of the front structural element parallel to a longitudinal axis of the bay and
locking means normally opposing said sliding.
The expression “geometrical chord” here designates the right-hand segment linking the leading edge of the bay to its trailing edge, when the bay is observed in longitudinal section.
In the bay architecture according to the invention, the continuous, external surface of the front structural element is given an optimum aerodynamic shape, so as to obtain a laminar air flow around the front part of the bay. The presence of maintenance and guidance means between said front structural element and the fan case ensures both the maintenance of the aerodynamic shape of the continuous, external surface, when the aircraft is flying, whilst giving access to the bay region surrounding the fan, when the aircraft is on the ground. The locking means prevent any sliding of the front structural element when the aircraft is flying.
In a preferred embodiment of the invention, the air flow is also improved in the region of the pylon, by implementing the front structural element in such a way that it surrounds and shrouds the front part of the suspended pylon of the jet engine.
In order to take account of certain technical and industrial constraints and to make it possible to replace the front lip of the air intake box when said lip has become damaged, the front structural element incorporates a main structure, made in one piece, as well as an interchangeable, front lip, mounted on the front end of the main structure by dismantlable fixing means. The junction is made in such a way that no discontinuity is created on the external surface of the front structural element.
In the preferred embodiment of the invention, the locking means comprise latches oriented substantially parallel to the longitudinal axis of the bay, so as to ensure under optimum conditions, the transmission of forces between the two structural elements forming the bay. For this purpose, the latches are interposed between the rear end of the front structural element and the front end of the rear structural element.
In order to ensure the transmission of forces between the front structural element and the fan case, the front structural element has a front abutment surface and a rear abutment surface, which normally bear against bearing surfaces formed on the fan case.
The substantially non-deformable character of the continuous, outer surface of the front structural element can be further improved by equipping said element with shear pins, which project rearwards along the longitudinal axis of the bay, from the aforementioned abutment surfaces, so as to penetrate in clearance-free manner into holes formed in the bearing surfaces. This arrangement can be reversed, i.e. the holes can be formed in the abutment surfaces and the shear pins installed on the bearing surfaces.
In the preferred embodiment of the invention, the maintenance and guidance means comprise slides carried by the blower case and on which can slide the front structural element. These slides are spaced from the blower case by a distance exceeding the maximum deformation of the latter, which is liable to be produced by a breaking or fracture of the fan blade.
To take account of the sliding character of the front structural element of the bay, different arrangements can be provided for the lines, which are at least partly placed in said element.
Thus, the bay can have one or more rigid lines, such as the deicing line, formed by a front section installed in the front structural element and a fixed, rear section. These two sections are then aligned parallel to the longitudinal axis of the bay, so as to normally bear by their ends, under the effec
Aerospatiale - Societe Nationale Industrielle
Burns Doane , Swecker, Mathis LLP
Dinh Tien
Poon Peter M.
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