Aircraft engine attached to the fuselage

Description

[0001] The present invention relates to a nacelle for an aircraft turbojet engine intended to be connected to the fuselage of an aircraft and a propulsion assembly comprising such a nacelle.

[0002] An aircraft is powered by several propulsion units, each comprising a turbojet engine housed in a nacelle also housing a set of ancillary actuation devices linked to its operation and providing various functions when the turbojet engine is operating or stopped, such as, for example, a thrust reverser device.

[0003] A first type of propulsion unit 101 used to move an aircraft is shown in figure 1 This propulsion unit 101 comprises a turbojet engine 103 and a nacelle 105, which receives the turbojet engine.

[0004] The propulsion unit 101 further comprises a vertical pylon 107 intended to be suspended under a wing (not shown) of the aircraft, in a position called “at 12 o'clock” of the propulsion unit 101.

[0005] The nacelle 105 has a tubular structure comprising an upstream section 109 defining an air inlet 111 upstream of the turbojet engine 103, a middle section 113 intended to surround a fan of the turbojet engine and a downstream section 115 capable of housing a thrust reversal device and intended to surround the combustion chamber of the turbojet engine.

[0006] This type of propulsion unit, designed to be supported by the wings of the aircraft, typically equips long-haul aircraft.

[0007] The middle section 113 of the nacelle 105 comprises, downstream of the air inlet 111, two fan half-cowls 113a, 113b surrounding a fan casing 117 (visible in figure 2 ) of the turbojet engine 103. Each fan half-cowl 113a, 113b is substantially semi-cylindrical. The half-cowls 113a, 113b define, in a closed position as shown, an aerodynamic continuity between the air inlet 111 of the upstream section 109 of the nacelle 105 and the downstream section 115 of the nacelle.

[0008] In this closed position, the two fan half-cowls 113a, 113b are locked to a fixed structure or to each other by a set of locks, along a lower longitudinal locking line, for this use case under-wing power plant.

[0009] As shown in the figure 2 , illustrating the propulsion assembly 101 in the maintenance position, the fan half-cowls 113a, 113b can be opened radially by pivoting around an upper longitudinal hinge line located near an axis of the pylon 107 to which the nacelle 105 is attached, this in order to allow access to certain components of the fan casing 117 during maintenance operations.

[0010] We refer to the figure 3 illustrating a second type of propulsion unit 201, intended to be connected to the fuselage of the aircraft and not to the wings of the aircraft, this type of propulsion unit typically equipping short and medium-haul aircraft.

[0011] This propulsion unit 1 comprises a turbojet engine 203 and a nacelle 205, which receives the turbojet engine.

[0012] The propulsion unit 201 further comprises a lateral pylon 207 intended to be connected directly to the fuselage (not shown) of the aircraft.

[0013] Unlike the vertical pylon 107 referred to in figures 1 et 2 , positioned at 12 o'clock in the propulsion assembly 101 and intended to be suspended under a wing of the aircraft, the pylon 207 is intended to be connected directly to the fuselage of the aircraft. The pylon 207 is for this purpose positioned "at 9 o'clock" in the propulsion assembly or, for a propulsion assembly symmetrical to the propulsion assembly 1 with respect to the fuselage of the aircraft, positioned "at 3 o'clock" in the propulsion assembly.

[0014] The nacelle 25 has a tubular structure comprising an upstream section 209 defining an air inlet 211 upstream of the turbojet engine 203, a middle section 213 intended to surround a fan of the turbojet engine and the external duct of the turbojet engine, a downstream section 215 capable of housing a thrust reverser device, generally of the door type.

[0015] The middle section 213 of the nacelle 205 comprises, downstream of the air inlet 211, two fan half-cowls 213a, 213b surrounding a fan casing of the turbojet engine. Each fan half-cowl 213a, 213b is substantially semi-cylindrical. The half-cowls 213a, 213b define, in a closed position as shown, an aerodynamic continuity between the air inlet 211 of the upstream section 209 of the nacelle 205 and the downstream section 215 of the nacelle.

[0016] In order to be able to carry out maintenance operations on the turbojet engine, one of the two half-cowls 213a, 213b is generally mounted to be able to move between the closed position shown in figure 3 and an opening position shown in figure 4 to which we now refer, allowing access to the turbojet.

[0017] To the figure 4 is shown the middle section 213 of the nacelle 205 of the figure 3 . We removed some of the figure 4 the upstream section 209 and the downstream section 215 of the nacelle 205, as well as the turbojet 203 and the pylon 207, for better visibility.

[0018] On the figure 4 , the half-cowl 213a is in the closed position and the half-cowl 13b, also called “maintenance half-cowl 213b”, is in the open position allowing access to the turbojet engine (not shown) to carry out maintenance operations there.

[0019] In the example illustrated, only the half-cover 213b is mounted to move between the closed position and the open position. According to an alternative embodiment not shown, the two half-covers 213a, 213b can be mounted to move between the closed position and the open position.

[0020] The fan half-cowl 213b is kept closed on the pylon 207 (visible at figure 3 ) by means of a set of tension locks 219, 221, 223, arranged along the half-hood 213b.

[0021] A fire seal 225 is further positioned between the half-cowls 213a, 213b and the pylon, in order to prevent a fire started in the propulsion unit from spreading in the aircraft.

[0022] Furthermore, a first shear lock 227 is generally arranged at the front of the movable half-cowl 13b. The shear lock 227 is designed to fix the half-cowl 213b on the upstream section 209 of the nacelle.

[0023] A second shear lock 229, designed to secure the half-cowl 213b to the downstream section 215 of the nacelle, is also generally disposed at the rear of the movable half-cowl 213b.

[0024] These shear locks 227, 229 are provided to provide a force path in the event of breakage of one of the tension locks 219, 221, 223, in order to avoid scooping of the fan half-cowl in flight, this situation being catastrophic.

[0025] The fan half-cowl 213b can be opened radially by pivoting around a hinge line 231, positioned “at 3 o’clock”, a position diametrically opposite that of the pylon 207.

[0026] Thus, when one wishes to carry out maintenance operations on the turbojet engine, it is necessary to open the fan half-cowl 213b, in order to access the turbojet engine, then to close this half-cowl once the maintenance is finished.

[0027] The maintenance half-cover 213b is opened as follows.

[0028] A first operator unlocks the tension locks 219, 221, 223 and the shear locks 227, 229, which hold the half-hood 13b in the closed position on the pylon.

[0029] Meanwhile, a second operator holds the half-hood 213b in the closed position, in order to prevent the half-hood 213b from falling by gravity, under the effect of its weight.

[0030] The maintenance half-hood 213b is closed as follows.

[0031] The first operator moves the half-hood 213b from its open position to its closed position on the pylon.

[0032] The operator exerts a high force on the half-hood 213b, in order to firmly compress the fire seal 225 onto the pylon.

[0033] The first operator forcibly holds the half-hood 213b in this position while the second operator closes the tension locks 219, 221, 223 on the pylon, then the shear locks 227, 229, respectively on the upstream and downstream sections of the nacelle.

[0034] These phases of opening and closing the maintenance half-hood 13b have several drawbacks.

[0035] First of all, these operations are tedious and at least two operators are required, both to open the maintenance half-hood 13b and to close it.

[0036] In fact, during an opening phase of the maintenance half-hood, the first operator unlocks the tension and shear locks, which hold the maintenance half-hood in the closed position, while the second operator holds the half-hood, in order to prevent it from falling by gravity.

[0037] During the closing phase of the maintenance half-hood, the first operator moves this half-hood from its open position to its closed position.

[0038] When the maintenance half-hood is in its closed position, this operator must exert significant pressure to ensure good compression of the fire seal located between the pylon and the maintenance half-hood, making it even more difficult to close the half-hood, which tends to fall under the effect of its weight, while the second operator closes the tension locks.

[0039] Then, these operations of opening and closing the maintenance half-hood prove to be particularly dangerous for the operators.

[0040] In fact, the propulsion unit in question in the figures 3 et 4 is intended to be mounted directly on the aircraft fuselage.

[0041] Thus, operators work at great height, on ladders (whereas when the propulsion unit is suspended under the wing of the aircraft, operators can access it without a ladder), making handling the very heavy maintenance half-cowls extremely dangerous.

[0042] Document FR3012114 concerns an aircraft propulsion unit equipped with a cowl locking and closing mechanism.

[0043] Document FR3025548 concerns a mechanism for locking a rod to hold it in the open position.

[0044] Document EP0596070 relates to a hood closure fault indicator.

[0045] Document FR2926285 relates to a nacelle with simplified cowling. This nacelle further comprises an intermediate cowl fixed to a first cowl so as to sandwich a support mast of a turbojet engine. A second cowl is attached to said intermediate cowl by removable fixing means.

[0046] Document EP1493664 relates to a device for locking the nacelle cowls of a turbojet engine.

[0047] The present invention aims to overcome the aforementioned drawbacks, and to this end relates to an aircraft propulsion unit, comprising: a turbojet engine; a lateral pylon, intended to be directly connected to the fuselage of said aircraft, said lateral pylon being positioned at approximately 90° or approximately 270° relative to a substantially vertical median plane of said propulsion unit when said propulsion unit is connected to the fuselage of the aircraft, a nacelle mounted on said lateral pylon and surrounding said turbojet engine, comprising: an upstream section, comprising an air inlet of the nacelle; a downstream section, capable of housing a thrust reverser device;a median section, downstream of said upstream section and upstream of said downstream section, comprising two fan half-cowls, surrounding a fan casing of said turbojet engine and being provided, when said half-cowls are in a closed position, to define an aerodynamic continuity between said upstream and downstream sections of the nacelle, said fan half-cowls comprising at least one maintenance half-cowl positioned under the substantially horizontal median plane of the nacelle, movable between said closed position and an open position allowing access to the turbojet engine for turbojet engine maintenance operations; ; said propulsion assembly being remarkable in that said nacelle comprises at least one waiting lock, designed to hold said maintenance half-cowl in a position intermediate to said closing and opening positions.

[0048] Thus, by equipping the nacelle of the propulsion unit with a holding lock designed to hold the maintenance half-cowl in a position intermediate the closed and open positions, holding the maintenance half-cowl in a position intermediate the closed position and the open position makes it possible to prevent the maintenance half-cowl from falling by gravity, under the effect of its weight.

[0049] When an operator wishes to open the maintenance half-cowl in order to carry out maintenance operations on the turbojet engine, this operator positions the maintenance half-cowl in a waiting position, intermediate between the closed position and the open position.

[0050] He can then unlock the tension and shear locks himself, the half-hood being held in the waiting position by the waiting lock.

[0051] Thus, thanks to the present invention, a single operator can safely open such a maintenance half-hood.

[0052] When an operator wishes to close the maintenance half-cowl once the turbojet engine maintenance has been carried out, this operator moves the half-cowl from its open position to its waiting position, intermediate to its final closed position.

[0053] Maintaining the maintenance half-hood in this waiting position, obtained using the waiting lock, makes it possible, on the one hand, to prevent the hood from falling by gravity under the effect of its weight during the closing phase.

[0054] Thus, the operator who moved the hood from its open position to its waiting position can himself close the tension locks, then the shear locks and, on the other hand, firmly compress the fire seal present between the pylon and the maintenance half-hood.

[0055] Thus, thanks to the present invention, a single operator can manage to close such a maintenance half-hood, in complete safety.

[0056] According to the invention, the nacelle comprises a device for locking said half-covers in the closed position, said locking device comprising: at least one tension lock, designed to fix said half-cowls on said lateral pylon; at least one shear lock, designed to fix said half-cowls on at least one of the upstream and downstream sections of the nacelle and provided to ensure a force path in the event of breakage of said at least one tension lock, said shear lock comprising: a shear bolt, and a shear receptacle, mounted on at least one of the upstream and downstream sections of the nacelle, comprising a shear striker cooperating with the shear striker when said half-cowls are in the closed position; said propulsion assembly being remarkable in that the standby lock of the nacelle comprises: a standby bolt, and a standby striker, mounted on the shear receptacle, designed to cooperate with said standby bolt.

[0057] Thus, by providing for mounting the holding latch of the holding lock on the shear receptacle of the shear lock, it is possible to limit the space required for integration of the holding lock of the invention into the nacelle. This arrangement is particularly advantageous in the context of the present invention where the nacelles are intended to be connected directly to the fuselage of an aircraft and not suspended under the wings of the aircraft, these nacelles being of greatly reduced dimensions compared to the nacelles suspended under the wings of the aircraft.

[0058] According to another advantageous arrangement of the propulsion assembly of the invention, the holding bolt of the holding lock is constituted by the shear bolt of the shear lock.

[0059] It is thus possible to obtain, thanks to the present invention, a complete mutualization of the waiting lock and the shear lock. This arrangement is very interesting in terms of reducing the space requirement inside the nacelle.

[0060] According to other advantageous arrangements of the propulsion unit of the invention: the distance between a substantially horizontal median plane of said nacelle when said nacelle is mounted on the lateral pylon and the standby latch is less than the distance between said substantially horizontal median plane and the shear latch; the shear receptacle comprises a ramp provided for constraining the standby bolt between a deployed position and a retracted position during a movement of the maintenance half-hood from said open position to said closed position; the standby latch comprises a groove defining a half-cylinder; the standby bolt comprises a longitudinal axis substantially parallel to a longitudinal axis of the nacelle; the shear receptacle is fixed on a rear frame of the air intake of the nacelle; the maintenance half-hood is positioned under the substantially horizontal median plane of said nacelle when said nacelle is mounted on the lateral pylon.

[0061] Other characteristics and advantages of the invention will appear on reading the detailed description which follows, for the understanding of which reference will be made to the appended drawings in which: there figure 1 illustrates in isometric view a propulsion assembly of the prior art, in operating position, intended to be suspended from a wing of an aircraft; the figure 2 represents the propulsion system of the figure 1 , in maintenance position; the figure 3 illustrates in isometric view a propulsion assembly of the prior art, in operating position, intended to be connected to the fuselage of an aircraft; the figure 4 partially represents the propulsion system of the figure 3 , in maintenance position; the figure 5 illustrates in isometric view a propulsion assembly according to the invention, in operating position, intended to be connected to the fuselage of an aircraft; the figure 6 partially represents the propulsion system of the figure 5 , in maintenance position; the figure 7 is a detail view of zone VII of the figure 5 , and illustrates the nacelle according to the invention seen from the inside, in the open maintenance position, the view being centered on the junction between the middle section and the upstream section of the nacelle; the figure 8 is a view similar to that of the figure 7 , the nacelle being shown in the waiting position; the figure 9 is a view similar to those of the figures 7 et 8 , the nacelle being shown in the closed operating position.

[0062] In the description and in the claims, the terms "upstream" and "downstream" must be understood in relation to the circulation of the air flow inside the propulsion unit formed by the nacelle and the turbojet.

[0063] Furthermore, throughout the figures, identical or similar references represent identical or similar organs or sets of organs.

[0064] We refer to the figure 5 , illustrating the propulsion assembly 1 according to the invention, of identical design to the propulsion assembly 201 referred to in figures 3 et 4 , that is to say, it is a propulsion unit intended to be connected directly to the fuselage of an aircraft, generally used to equip short and medium-haul aircraft.

[0065] The propulsion unit 1 comprises a turbojet engine 3 and a nacelle 5, which receives the turbojet engine.

[0066] The propulsion unit 1 further comprises a lateral pylon 7 intended to be connected directly to the fuselage (not shown) of the aircraft.

[0067] Unlike the vertical pylon 107 referred to in figures 1 et 2 , positioned at 12 o'clock in the propulsion assembly 101 and intended to be suspended under a wing of the aircraft, the lateral pylon 7 is intended to be connected directly to the fuselage of the aircraft. The pylon 7 is for this purpose positioned "at 9 o'clock" in the propulsion assembly or, for a propulsion assembly symmetrical to the propulsion assembly 1 with respect to the fuselage of the aircraft, positioned "at 3 o'clock" in the propulsion assembly.

[0068] In other words, the lateral pylon 7 is positioned at approximately 90° or approximately 270° relative to a substantially vertical median plane 8 of the propulsion unit 1 when the propulsion unit 1 is connected to the fuselage of the aircraft.

[0069] The nacelle 5 has a tubular structure comprising an upstream section 9 defining an air inlet 11 upstream of the turbojet engine 3, a middle section 13 intended to surround a fan of the turbojet engine, a downstream section 15 capable of housing a thrust reversal device, generally of the door type, and intended to surround the combustion chamber of the turbojet engine.

[0070] The middle section 13 of the nacelle 5 comprises, downstream of the air inlet 11, two fan half-cowls 13a, 13b surrounding a fan casing of the turbojet engine. Each fan half-cowl 13a, 13b is substantially semi-cylindrical. The half-cowls 13a, 13b define, in a closed position as shown, an aerodynamic continuity between the air inlet 11 of the upstream section 9 of the nacelle 5 and the downstream section 15 of the nacelle.

[0071] In order to be able to carry out maintenance operations on the turbojet engine, one of the two half-cowls 13a, 13b is generally mounted to be able to move between the closed position shown in figure 5 and an opening position shown in figure 6 to which we now refer, allowing access to the turbojet.

[0072] To the figure 6 is represented the middle section 13 of the nacelle 5 of the figure 5 . We removed some of the figure 4 the upstream section 9 and the downstream section 15 of nacelle 5, as well as turbojet 3 and pylon 7, for better visibility.

[0073] On the figure 6 , the half-cowl 13a is in the closed position and the half-cowl 13b, also called “maintenance half-cowl 13b”, is in the open position allowing access to the turbojet engine (not shown) to carry out maintenance operations there. The maintenance half-cowl 13b is positioned under a substantially horizontal median plane of the nacelle 5, when the nacelle is mounted on the lateral pylon.

[0074] In the example illustrated, only the half-cover 13b is mounted to move between the closed position and the open position. According to an alternative embodiment not shown, the two half-covers 13a, 13b can be mounted to move between the closed position and the open position.

[0075] The fan half-cowl 13b is kept closed on pylon 7 (visible at figure 3 ) by means of a set of tension locks 19, 21, 23, arranged along the half-hood 13b.

[0076] A fire seal 25 is further positioned between the half-cowls 13a, 13b and the pylon, in order to prevent a fire started in the propulsion unit from spreading in the aircraft.

[0077] Furthermore, a first shear lock 27 is generally arranged at the front of the movable half-cowl 13b. The shear lock 27 is designed to fix the half-cowl 13b on the upstream section 9 of the nacelle.

[0078] A second shear lock 29, designed to secure the half-cowl 13b to the downstream section 15 of the nacelle, is also generally arranged at the rear of the movable half-cowl 13b.

[0079] These shear locks 27, 29 are provided to provide a force path in the event of breakage of one of the tension locks 19, 21, 23, in order to avoid scooping of the fan half-cowl in flight, this situation being catastrophic.

[0080] The fan half-cowl 13b can be opened radially by pivoting around a hinge line 31, positioned “at 3 o’clock”, a position diametrically opposite that of the pylon 7.

[0081] We refer to the figure 7 , detailed view of zone VII of the figure 5 and illustrating the nacelle 5 of the invention seen from its interior, in the open maintenance position, the view being centered on the junction between the middle section 13 and the upstream section 9 of the nacelle 5.

[0082] The maintenance half-cowl 13b receives at its internal face, that is to say the face intended to come opposite the fan casing of the turbojet, the tension locks 19, 21, 23, arranged along the half-cowl 13b (only the tension lock 23 being visible at the figure 7 ), as well as the shear locks 27, 29 (only the shear lock 27 being visible at the figure 7 ).

[0083] The tension lock 23 is mounted on a support fitting 33 fixed on the internal face of the maintenance half-hood 13b.

[0084] The tension lock 23 comprises a tension bolt 35, cooperating with a tension striker (not shown) which can be supported by the pylon when the maintenance half-hood is in the closed position.

[0085] The arrangement of the tension locks 19 and 21 are identical to that just described for the tension lock 23.

[0086] The shear lock 27 provides a lock between the maintenance half-hood 13b and the upstream section of the nacelle. The shear lock 27 is positioned upstream of the tension lock 23 and close to the latter.

[0087] The shear lock 27 comprises a shear bolt 37 and a shear receptacle 39.

[0088] As regards the shear bolt 37, this is mounted on a support fitting 41 fixed on the internal face of the maintenance half-cover 13b.

[0089] The support fitting 41 comprises a first fixing plate 41a, and a second fixing plate 41b.

[0090] The second fixing plate 41b is offset relative to the first fixing plate 41a, on the one hand in order to allow good integration of the shear lock 27 in the nacelle, and on the other hand in order to take up the forces of the shear lock 27.

[0091] The shear bolt 37 comprises a portion 37a, movable between a deployed position and a retracted position. The movable portion 37a adopts for example a generally cylindrical shape. The longitudinal axis 38 of the shear bolt 37 is substantially parallel to a longitudinal axis 40 of the nacelle (shown in figure 5 ).

[0092] As regards the shear receptacle 39, this is mounted on a rear frame 43 of the air inlet 11 of the upstream section 9 of the nacelle.

[0093] The shear receptacle comprises a shear striker 45 which is intended to cooperate with the shear bolt 37 when the maintenance half-cover 13b is in the closed position (position shown in figure 9 ).

[0094] The arrangement of the shear lock 29, arranged in the downstream part of the maintenance half-cowl 13b and ensuring the locking between the maintenance half-cowl 13b and the downstream section of the nacelle, is identical to that which has just been described for the shear lock 27. The shear lock 29 comprises a shear bolt mounted on a support fitting of similar design to the support fitting 41, and the arrangement of which with respect to the maintenance half-cowl is identical to that described for the shear lock 27.

[0095] According to the invention, the nacelle 5 comprises a waiting lock 47. The waiting lock 47 comprises a waiting striker 49, designed to cooperate with a waiting bolt 51 of the waiting lock 47 when the maintenance half-hood is in a waiting position shown in figure 8 , intermediate position to the opening positions of the figure 7 and closing of the figure 9 .

[0096] According to one embodiment of the invention, the waiting latch 49 is mounted on the shear receptacle 39. The waiting latch 49 comprises a groove, defining a half-cylinder.

[0097] It may however be envisaged to dissociate the waiting latch 49 from the shear receptacle 39, that is to say to offset the waiting latch relative to the shear receptacle 39.

[0098] In any case, the distance between a median plane 53 (visible at the figure 5 ) substantially horizontal of the nacelle 5 when said nacelle is mounted on the lateral pylon 7 (visible in the figure 5 ) and the waiting latch 49 is less than the distance between said substantially horizontal median plane and the shear latch 45.

[0099] According to an advantageous arrangement of the invention, the holding bolt 51 is constituted by the shear bolt 37. However, it may also be envisaged to dissociate the holding bolt 51 from the shear bolt 37, that is to say to offset the holding bolt 51 relative to the shear bolt 37.

[0100] The shear receptacle 39 comprises a ramp 55, provided to constrain the waiting bolt 51 between a deployed position and a retracted position, during a movement of the maintenance half-cover 13b from its open position shown in figure 7 towards its closed position shown in figure 9 .

[0101] The operation of the invention is now described, with reference to figures 7 à 9 .

[0102] When the nacelle is in operation, the maintenance half-hood 13b is in the closed position shown in figure 9 .

[0103] In this position, the tension locks are locked on the pylon and the shear locks are locked on the upstream and downstream sections of the nacelle.

[0104] Regarding the shear lock 27 visible at the figure 9 , this cooperates with the shear catch 45 of the shear receptacle 39.

[0105] When an operator wishes to carry out maintenance operations on the turbojet, the first step is to unlock the tension locks.

[0106] The half-hood 13b is held in the position shown in figure 9 thanks to the shear lock 27, the shear bolt 37 of which continues to cooperate with the shear strike 45.

[0107] During a second stage illustrated in the figure 8 , it unlocks the shear lock 27 (as well as the one located downstream of the maintenance half-cover), and it positions the shear bolt 37 (waiting bolt 51 when said bolts are identical), so that it cooperates with the waiting latch 49.

[0108] The maintenance half-hood 13b is then neither in the closed position shown in figure 9 , nor in the opening position shown in the figure 7 , but it is in an intermediate position to these positions, a position also called a waiting position.

[0109] The center distance between the longitudinal axis of the shear catch 45 and the longitudinal axis of the waiting catch 49 is very small. It can be between 10 millimeters and 20 millimeters, preferably 15 millimeters, which makes it possible to limit the retaining force that the operator must exert on the maintenance half-cover 13b when he has released the shear bolt 37 from its shear catch 45.

[0110] At this stage, the maintenance half-hood is then only supported thanks to the cooperation of the waiting bolt 51 and the waiting strike 49.

[0111] When the operator is ready to move the maintenance half-hood from its standby position shown in figure 8 to its opening position shown in figure 7 , it releases the holding bolt 51 from the holding latch 49.

[0112] At the end of the maintenance operations carried out on the turbojet, when an operator wishes to close the maintenance half-cowl, he proceeds, during a first step, to move the maintenance half-cowl from its open position shown in figure 7 towards its closed position shown in figure 9 .

[0113] During this movement, the ramp 55 of the shear receptacle 39 causes the movement of the waiting bolt 51, from its deployed position shown in figure 7 to its retracted position, until the waiting bolt cooperates with its waiting strike 49, position shown in figure 8 .

[0114] The maintenance half-cover 13b is then neither in the open position shown in figure 7 nor in the closed position shown in the figure 9 , but it is in its waiting position, an intermediate position to these positions.

[0115] In such an intermediate position, the hood is pre-stressed by the cooperation of the holding bolt 51 with the holding striker 49. The maintenance half-hood is then supported only by the cooperation of the holding bolt and the holding striker.

[0116] The operator can thus exercise in complete safety, that is to say without fear that the maintenance half-hood 13b will fall by gravity under the effect of its weight, exert a force on the maintenance half-hood 13b, in order to firmly compress the fire seal 25 on the pylon.

[0117] The operator then closes the tension locks during this second stage, so as to fix the maintenance half-hood on the side pylon.

[0118] In a third step, the operator moves the shear bolt 37 so that it cooperates with the shear striker 45.

[0119] The maintenance half-hood is then in its closed position. In this position, the nacelle is operational, i.e. it is no longer in the maintenance phase.

Claims

1. An aircraft propulsion unit (1), comprising: - a turbojet engine (3); - a lateral mast (7), intended to be directly connected to the fuselage of said aircraft, said lateral mast being positioned at about 90° or at about 270° with respect to a substantially vertical midplane (8) of said propulsion unit when said propulsion unit is connected to the fuselage of the aircraft, - a nacelle (5) mounted on said lateral mast (7) and surrounding said turbojet engine (3), comprising: • an upstream section (9), comprising an air inlet (11) of the nacelle; • a downstream section (15), which can accommodate a thrust reverser device; • a middle section (13), downstream of said upstream section and upstream of said downstream section, comprising two fan half-cowls (13a, 13b), surrounding a fan casing of said turbojet engine and being intended, when said half-cowls are in a closure position, to define an aerodynamic continuity between said upstream and downstream sections of the nacelle, said fan half-cowls including at least one maintenance half-cowl (13b) positioned under the substantially horizontal midplane (53) of the nacelle, movable between said closure position and an opening position enabling access to the turbojet engine for maintenance operations on the turbojet engine; said propulsion unit includes at least one standby lock (47), designed to hold said maintenance half-cowl (13b) in an intermediate position between said closure and opening positions, wherein the nacelle (5) comprises a device for locking the half-cowls (13a, 13b) in the closure position, said locking device comprising: - at least one tension lock (19, 21, 23), designed to fasten said half-cowls (13a, 13b) on said lateral mast (7); - at least one shear lock (27, 29), designed to fasten said half-cowls (13a, 13b) on at least one of the upstream (9) and downstream (15) sections of the nacelle and intended to ensure a force path in case of breakage of said at least one tension lock (19, 21, 23), said shear lock comprising: • a shear pin (37), and • a shear receptacle (39), mounted on at least one of the upstream (9) and downstream (15) sections of the nacelle, comprising a shear latch (45) cooperating with the shear pin (37) when said half-cowls (13a, 13b) are in the closure position; the standby lock (47) of said nacelle (5) includes: • a standby pin (51), and • a standby latch (49), mounted on the shear receptacle (39), designed to cooperate with said standby pin.

2. The propulsion unit (1) according to claim 1, wherein the standby pin (51) of the standby lock (47) is constituted by the shear pin (37) of the shear lock (27, 29).

3. The propulsion unit (1) according to any of claims 1 or 2, wherein the distance between a substantially horizontal midplane (53) of said nacelle when said nacelle is mounted on the lateral mast (7) and the standby latch (49) is smaller than the distance between said substantially horizontal midplane (53) and the shear latch (45).

4. The propulsion unit (1) according to any one of claims 1 to 3, wherein the shear receptacle (39) includes a ramp (55) intended to constrain the standby pin (51) between a deployed position and a retracted position during a displacement of the maintenance half-cowl (13b) from said opening position towards said closure position.

5. The propulsion unit (1) according to any one of claims 1 to 4, wherein the standby latch (49) includes a groove defining a hemicylinder.

6. The propulsion unit (1) according to any one of claims 1 to 5, wherein the standby pin (51) includes a longitudinal axis (38) substantially parallel to a longitudinal axis (40) of the nacelle.

7. The propulsion unit (1) according to any one of claims 1 to 6, wherein the shear receptacle (39) is fastened on a rear frame (43) of the air inlet (11) of the nacelle.

8. The propulsion unit (1) according to any one of claims 1 to 7, wherein the maintenance half-cowl (13b) is positioned under the substantially horizontal midplane (53) of said nacelle when said nacelle is mounted on the lateral mast (7).