FR3159591A1 - INSTRUMENTED AIRCRAFT ENGINE FASTENER AND AIRCRAFT COMPRISING SUCH A FASTENER. - Google Patents

Abstract

The invention relates to a spigot-type fastener (1) for securing an aircraft engine to an element of a primary structure (P) of said aircraft, said fastener extending longitudinally in a first direction (Z) and said fastener comprising: - a first cylindrical portion (1a) having a first diameter (d1), - a second cylindrical portion (1b) having a second diameter (d2), and, said fastener (1) being characterized in that it further comprises a central portion (1c) arranged between said first portion (1a) and said second portion (1b) and having at least one flat (1f) extending substantially parallel to the first direction (Z). Thus, it is advantageously possible to position a strain gauge (100) directly on the spigot fastener (1) and to measure a bending deformation thereof, representative of the engine thrust of the engine supported by this fastener (1). Fig. 1

Description

INSTRUMENTED AIRCRAFT ENGINE FASTENER AND AIRCRAFT COMPRISING SUCH A FASTENER.

The present invention relates to an instrumented aircraft engine attachment intended to be interposed between a primary aircraft structural element and an engine mounting fitting. At least one embodiment relates to a so-called "spigot" type attachment arranged to receive one or more strain gauges configured for measuring engine thrust.

STATE OF THE PRIOR ART

There are various techniques for measuring aircraft engine thrust. Engine thrust can be measured on the ground on dedicated measurement benches, using force balances. In flight, thrust measurement is generally carried out using strain gauges arranged on massive structural interface parts, which allows for direct measurement, or by measuring pressures in the engine veins, which constitutes an indirect measurement. Strain gauge measurements have the advantage of obtaining a good estimate of engine thrust but are accompanied by a margin of error of around a few percent of the measurement range.

In the context of unducted engines, there is a need for increased accuracy, due to a strong influence between engine operation and external conditions, such as strong interactions between the engine and the structure of the aircraft that carries it. The desired level of accuracy is less than 1% of the measuring range, which is not guaranteed by current measuring methods.

Interface parts transmitting forces (for example, engine thrust forces) to the structure of the aircraft that carries it are subject to drastic sizing criteria in relation to all nominal operating conditions as well as failure cases. These constraints imply very large dimensions and stiffnesses of the parts supporting the engine thrust measurement, which results in low measurement sensitivity and significant inaccuracies in the measurement.

The situation can be improved.

An object of the present invention is to provide a mechanical fastener capable of operating both a robust mechanical interface function supporting fastener design loads, and accurate engine thrust measurement when combined with one or more strain gauges.

For this purpose, a spigot-type attachment is proposed for providing a fixing between an aircraft engine and an element of a primary structure of this aircraft, the attachment extending longitudinally in a Z direction and the attachment comprising:

- a first cylindrical part having a first diameter,

- a second cylindrical part having a second diameter.

The attachment being such that it further comprises a central part arranged between the first part and the second part and having at least one flat extending substantially parallel to the Z direction.

The spigot attachment according to the invention may further comprise the optional features, considered alone or in combination:

- The central part of the spigot attachment comprises at least two flats arranged perpendicular to each other and each extending parallel to the Z direction.

- The spigot fastener comprises at least one strain gauge arranged on the flat when the fastener comprises a single flat or on at least one of said flats when the fastener comprises several flats.

- The central part of the spigot attachment has a rectangular or square shaped section.

The invention also relates to a fixing assembly comprising a fitting for the primary structure of an aircraft, a fitting for fixing an aircraft engine and at least one spigot-type fastener as previously described, the fastener being arranged so that its first part is capable of being inserted into a bore of diameter complementary to the first diameter, secured to the primary structure of the aircraft, and so that the second part is capable of being connected to the engine fixing fitting via a ball joint.

The fixing assembly according to the invention may further comprise the optional characteristics considered alone or in combination:

- The fixing assembly further comprises a sleeve, one of whose ends, the first, is assembled between the first part of the spigot-type fastener and the bore of the primary aircraft structure and the other, second, of whose ends forms a stop for the movement of the second part of the spigot-type fastener when a bending deformation of the central part exceeds a predefined threshold level of bending, the central part of the fastener being included inside the sleeve.

- The second part of the spigot-type fastener comprises a shoulder having a recess hollowed out in the Z direction (for example a groove) in which the second end of the sleeve is housed, which is arranged on the one hand at a first predetermined distance from an inner wall of the recess and is arranged on the other hand at a second predetermined distance from an outer wall of the recess.

- The sleeve of the fixing assembly is an assembly of a first so-called inner sleeve arranged in a bore of a second so-called outer sleeve, said inner and outer sleeves having the same central longitudinal axis and the outer surface of the inner sleeve being arranged to bear against the inner surface of the outer sleeve.

- One or more strain gauges are arranged and oriented to measure a force recovery in at least one direction perpendicular to the Z direction.

Another object of the invention is an aircraft comprising at least one fixing assembly as mentioned above.

The above-mentioned and other features of the invention will become more clearly apparent from the following description of an exemplary embodiment, said description being made in conjunction with the accompanying drawings:

FIG. 1 is a section of a spigot fastener, adapted to operate an interface between a primary aircraft structure and an aircraft engine mounting fitting and arranged to carry one or more strain gauges, according to one embodiment;

FIG. 2 is a top view of the spigot attachment already shown in section on the FIG. 1 ;

FIG. 3 is a section of a spigot attachment, adapted to operate an interface between a primary aircraft structure and an aircraft engine mounting fitting and arranged to carry one or more strain gauges, according to an alternative embodiment;

FIG. 4 illustrates a fixing assembly between a primary aircraft structure and an engine attachment fitting, comprising a spigot attachment as already shown in the FIG. 3 , according to one embodiment;

FIG. 5 illustrates an alternative embodiment of the fixing assembly already shown in the FIG. 4 ; And,

FIG. 6 illustrates an aircraft comprising a spigot attachment or attachment assembly as already shown in the FIG. 1 has FIG. 5 .

DETAILED PRESENTATION OF EMBODIMENT METHODS

There FIG. 1 is a schematic representation of a spigot fastener 1 according to one embodiment. The FIG. 1 is more precisely a section of the spigot attachment 1 according to the section plane AA visible on the FIG. 2 . The spigot attachment 1 is designed and intended to operate a fixing of an aircraft engine, or more precisely of a fixing fitting of an aircraft engine to an element of a primary structure of this aircraft. To do this, the spigot attachment extends longitudinally in a Z direction and comprises:

- a first cylindrical part 1a having a first diameter, d1, which first part 1a is intended to be fixed integrally to an element of the primary structure of the aircraft, for example a fitting of an engine mast or a fitting of a wing or fuselage,

- a second cylindrical part 1b having a second diameter, d2, which second part 1b is intended to be fixed integrally to a mounting fitting of an aircraft engine.

The spigot attachment 1 further comprises, cleverly, a central part 1c arranged between said first part and said second part and having at least one flat extending substantially parallel to the Z direction. The flat is configured to affix a strain gauge there to carry out a deformation measurement in a direction X perpendicular to the Z direction.

According to one embodiment, the spigot attachment 1 further comprises a central bore 1h machined in the Z direction passing through the parts 1a, 1b and 1c, useful for fixing the spigot attachment 1 to elements external to the spigot attachment 1, such as the primary structure of the aircraft and a fitting for fixing an engine.

ThereFIG. 2 is a top view of the spigot attachment 1 defining the section plane A-A used on theFIG. 1and on which appears more legibly the flat 1f of the central part 1c which also comprises three other flats including a flat 1t, perpendicular to the flat 1f, since according to the example described, the central part 1c has a rectangular section. According to a variant, the central part 1c has a square section. According to another variant, the part 1c has a circular section and two pairs of flats perpendicular to each other.FIG. 2defines a Y direction, perpendicular to each of the X and Z directions, which X and Z directions are perpendicular to each other. Thus, the X, Y and Z directions form a reference trihedron.

Advantageously, when the direction X, perpendicular to a plane comprising the flat 1f is oriented in the direction of movement in flight of an aircraft comprising the spigot attachment 1, one or more strain gauges affixed to the flat 1f makes it possible to measure the force absorption between a primary structural element of the aircraft, fixed integrally to the part 1a of the spigot attachment 1 and an engine mounting fitting fixed integrally to the part 1b of the spigot attachment 1. The force absorption thus measured due to the bending of the spigot attachment under the effect of the engine thrust is representative of the intensity of the engine thrust. Thus, when a calibration has been carried out in the laboratory and/or during calibration tests, a measurement using a strain gauge placed on the flat 1f of the spigot attachment 1 advantageously makes it possible to obtain information representative of the engine thrust generated by the engine fixed by means of the spigot attachment 1.

According to one embodiment, the central part of the spigot attachment 1 comprises a second strain gauge affixed to the second flat 1t, which is arranged perpendicular to the first flat 1f in the central part 1c of the spigot attachment 1, which makes it possible to characterize effects induced by a transverse force in the direction of the engine thrust force to be measured and to correct the measurement, while respecting the measurement precision objectives.

According to one embodiment, the strain gauges are connected to one or more computers on board the aircraft comprising electronic circuitry configured to determine engine thrust values from signals (voltages and/or currents) from the gauges. These onboard computers are not described here further since their description does not contribute to the understanding of the present invention.

There FIG. 3 schematically illustrates an alternative embodiment of the spigot attachment 1 according to which the second part 1b of the spigot attachment 1 takes the form of a shoulder in which a recess 1g here taking the form of a circular groove is hollowed out in the Z direction. The recess 1g cleverly makes it possible to receive one end of a sleeve inside which the parts 1a and 1c of the spigot attachment 1 are inserted and of which a part of the inner surface is fixed in abutment against the periphery of the part 1a of the spigot attachment 1 which has the diameter d1. Such an assembly makes it possible to operate a stop for the part 1b of the spigot attachment 1 when the spigot attachment 1 is deformed in bending under the effect of an engine thrust in the X direction.

There FIG. 4 schematically illustrates a fixing assembly 10 comprising the spigot fastener 1 configured to connect an aircraft engine fixing fitting E to a fitting P of the primary structure of the same aircraft. According to one embodiment, the engine mounting bracket E is connected to the spigot attachment 1 of the mounting assembly 10 via a ball joint B. According to one embodiment, a sleeve 11 is inserted between the spigot attachment 1 and the primary structure bracket P, with a tight fit, which sleeve 11 extends to the inside of the circular recess 1g of the spigot attachment 1. According to one embodiment, a first space (or first functional clearance) J1 separates the outer surface of the sleeve 11 and the outer surface of the circular recess 11g and a second space (or second functional clearance) J2 separates the inner surface of the sleeve 11 and the inner surface of the circular recess 1g. Thus, the end of the sleeve 11 positioned in the circular recess 1g is capable of operating a stop function when the spigot attachment 1 is deformed in bending in the direction under the effect of forces exerted, in particular in the X direction. An inequality of the spaces J1 and J2 makes it possible to operate a stop for different bendings, for the two directions of application of forces in the X direction. Following the same principle applied to the Y direction, the force leading to contact may be different there depending on the direction considered, and different from the values retained in the X direction. FIG. 4 further illustrates a positioning of a strain gauge 100 on the flat of the central part 1c of the spigot attachment 1. According to one embodiment, an upper plate 10e on which the primary structure fitting P, the sleeve 11 and the spigot attachment 1 rest is used to operate a solid fixing of these elements, for example using screws or bolts (not shown in the figure).

There FIG. 5 schematically illustrates an alternative embodiment of the fixing assembly 10 already shown in the FIG. 4 , according to which the sleeve 11 is a tightly mounted assembly of an inner sleeve 11i and an outer sleeve 11o, to increase the strength of the assembly and secure the mechanical connection by doubling .

There FIG. 6 illustrates an aircraft 6 advantageously comprising a fixing assembly such as the fixing assembly 10, which comprises a spigot attachment similar to the spigot attachment 1, making it possible to operate a mechanical engine fixing interface and to precisely measure the engine thrust using at least one strain gauge affixed to a zone in the central part of the spigot attachment 1, then instrumented, when the latter is arranged in a plane perpendicular to the direction in which the thrust of the engines is exerted.

The invention is not limited to the examples and embodiments described above and more generally relates to any spigot fastener comprising a central portion having one or more flats each configured to affix thereto a strain gauge capable of measuring a bending deformation of the spigot fastener, as well as a fastening assembly comprising such a fastener and optionally configured to comprise stops delimiting the bending deformations of the spigot fastener. For example, the stops can be implemented in various ways, by the arrangement of mechanical parts other than one or more sleeves.

The invention is not limited to the examples and embodiments described but relates more broadly to a spigot-type mechanical fastener extending longitudinally in a first direction Z and comprising a central part, which central part comprises at least one flat extending parallel or substantially parallel to the first direction Z. For example, the first diameter d1 and the second diameter d2 may be equal so that the spigot-type fastener is elongated and has a flat in the central part which may be arranged to receive at least one strain gauge configured to measure a strain exerted in a direction perpendicular to the first direction Z.

Claims (10)

Spigot-type fastener (1) for providing a fastening between an aircraft engine and an element of a primary structure (P) of said aircraft, said fastener extending longitudinally in a first direction (Z) and said fastener comprising:
- a first cylindrical part (1a) having a first diameter (d1),
- a second cylindrical part (1b) having a second diameter (d2), and,
said attachment (1) being characterized in that it further comprises a central part (1c) arranged between said first part (1a) and said second part (1b) and having at least one flat (1f) extending substantially parallel to the first direction (Z). Spigot-type fastener (1) according to claim 1, wherein said central portion (1c) comprises at least two flats (1f, 1t) arranged perpendicular to each other and each extending parallel to the first direction (Z). Spigot-type fastener (1) according to one of claims 1 and 2, comprising at least one strain gauge (100) arranged on said flat (1f) when the fastener (1) comprises only one flat (1f) or one of said flats when the fastener comprises a plurality of flats. Spigot-type fastener (1) according to claim 3, wherein said central portion (1c) has a rectangular or square-shaped section. Fastening assembly (10) comprising a primary structure fitting (P) of an aircraft, a fastening fitting (E) of an aircraft engine and at least one spigot-type fastener (1) according to one of claims 3 to 4, said fastener (1) being arranged so that its first part (1a) is capable of being inserted into a bore of diameter complementary to said first diameter (d1) and so that said second part (1b) is capable of being connected to said fastening fitting (E) of an engine by means of a ball joint (B). Fastening assembly (10) according to claim 5, further comprising a sleeve (11) one of whose ends, first, is assembled between said first part (1a) of said spigot-type fastener and said bore of said primary structure (P) of aircraft and the other, second, of whose ends forms a stop for the movement of said second part (1b) of said spigot-type fastener (1) when a bending deformation of said central part exceeds a predefined threshold level of bending, said central part (1c) of said fastener (1) being included inside said sleeve (11). Fastening assembly (10) according to claim 6, wherein said second part (1b) of said spigot-type fastener (1) comprises a shoulder having a recess (1g) hollowed out in the first direction (Z) in which said second end of said sleeve (11) is inserted, which is arranged on the one hand at a first predetermined distance (J1) from an outer wall of the recess (1g) and is arranged on the other hand at a second predetermined distance (J2) from an inner wall of said recess (1g). Fastening assembly (10) according to one of claims 5 to 7, in which said sleeve is an assembly of a first sleeve (11i) called inner sleeve arranged in a bore of a second sleeve (11o) called outer sleeve, said inner (11i) and outer (11o) sleeves having the same central longitudinal axis and the outer surface of said inner sleeve (11i) being arranged to bear against the inner surface of said outer sleeve (11o). Fastening assembly (10) according to one of claims 5 to 8, wherein said strain gauge (100) is arranged and oriented to measure a force recovery in at least a second direction (X) perpendicular to the first direction (Z). Aircraft (6) comprising at least one fixing assembly (10) according to one of claims 5 to 9.