Aircraft landing gear assembly

An aircraft landing gear assembly includes a fibre composite leaf spring arranged as a down lock spring to make the lock link.

This application claims priority to and the benefit of European Application 15160005.3, filed on Mar. 20, 2016, which is incorporated herein by reference.

BACKGROUND TO THE INVENTION

An aircraft landing gear assembly is generally movable between a deployed condition, for take-off and landing, and a stowed condition for flight.

An actuator is provided for moving the landing gear between the deployed condition and the stowed condition. This actuator is known in the art as a retraction actuator, and more than one can be provided. A retraction actuator may have one end coupled to the airframe and another end coupled to the main strut such that extension and retraction of the actuator results in movement of the main strut between deployed and stowed conditions.

A brace or stay is generally provided to support the orientation of the main fitting when the landing gear is in the deployed condition. A stay generally includes a two bar linkage that can be unfolded to assume a generally aligned, over centre condition in which the stay is locked to inhibit movement of the main fitting. When the stay is broken, it no longer reacts movement of the main fitting and the main fitting can be moved by the retraction actuator to the stowed condition. Some main landing gear assemblies include a pair of stays coupled to a common main fitting.

A lock link is generally provided in conjunction with each stay to maintain the stay in the locked condition. A lock link generally includes a two bar linkage that can be unfolded to assume a locked over centre condition to inhibit movement of the stay. The lock link must be broken to enable the stay to be folded, thereby permitting the main fitting to be moved by the retraction actuator towards the stowed condition.

It is common for a landing gear assembly to be arranged to move towards the deployed condition in the event of a failure of the retraction actuator. Initially, the landing gear assembly will move by way of gravity, and in doing so the stay is forced to move towards the locked condition. One or more down lock springs are generally provided to assist in moving the landing gear assembly to the deployed condition and locking it in that state by making the lock link. Down lock springs also inhibit the lock link accidentally being unlocked.

A down lock spring is generally a titanium alloy coil spring, which can be coupled between the lock link and another part of the landing gear assembly, such as an arm of the stay assembly.

The present inventor has identified that known down lock springs can be particularly susceptible to impact damage from bird strikes and tyre debris, and can experience early fatigue rupture due to vibratory loading, imparted either from the landing gear operation, aerodynamic affects, or airframe vibrations.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided an aircraft landing gear assembly comprising:

a main shock absorbing strut arranged to be movably coupled to an aircraft so as to be movable between a deployed condition, for take-off and landing, and a stowed condition for flight;

a folding stay having a first stay arm coupled to the main shock absorbing strut and a second stay arm movably coupled to the first arm and being arranged to be coupled to the aircraft, the stay having a generally aligned condition in which it reacts axial loading thereof to maintain the main shock absorbing strut in the deployed condition and a folded condition in which it permits the main shock absorbing strut to be moved from the deployed condition;

a folding lock link having a first link arm coupled to the stay and a second link arm movably coupled to the first link arm and being arranged to be coupled to another part of the landing gear assembly, the lock link having a generally aligned condition in which it reacts axial loading thereof to maintain the stay in the generally aligned condition and a folded condition in which it permits the stay to be folded,

a fibre composite leaf spring rigidly coupled to a part of the landing gear assembly and arranged to urge the lock link to assume the generally aligned condition.

Thus, the landing gear assembly according to the first aspect includes a down lock spring in the form of a fibre composite leaf spring. The present inventor has found that fibre composite leaf springs can deflect sufficiently to accommodate articulation movement of the lock link as the landing gear assembly moves between the deployed and stowed conditions. The fibre composite leaf spring has various advantages over conventional metal coil down lock springs; for example, the leaf spring can have a low profile in comparison to a coil spring, reducing the likelihood of impact damage, in addition to being less susceptible to vibratory loading.

The leaf spring can be elongate and wide in comparison to its thickness, in some cases the leaf spring can be rectangular.

The leaf spring can be formed from fibre reinforced composite material with a nominally organic polymer matrix.

The leaf spring can be mounted in a cantilevered manner so as to define a free end which contacts the lock link to urge the lock link to assume the generally aligned condition.

Alternatively, the leaf spring can be rigidly coupled at a first anchor point to a part of the lock link and rigidly coupled at a second anchor point to another part of the landing gear assembly, the leaf spring including a kinked region arranged to enable the effective length of the spring to increase and decrease relative to a default length in order to accommodate articulation movement of the lock link as the landing gear assembly moves between the deployed and stowed conditions.

The landing gear assembly can include a second leaf spring arranged to provide redundancy should the first spring fail.

The second spring can be identical to the first spring.

The second spring can be arranged in parallel with the leaf spring and mounted in the same manner.

The second spring can be mounted on a different part or surface of the landing gear assembly in comparison to the first spring. For example, the first spring can be rigidly mounted in a cantilevered manner on the stay arm which is arranged to be coupled to the aircraft and the second spring can be rigidly mounted in a cantilevered manner on a cardan joint via which the lock link is coupled to a part of the landing gear assembly other than the stay. Alternatively, the first and second springs can be rigidly mounted on opposite sides of the stay arm which is arranged to be coupled to the aircraft, the distal end of each spring being coupled to a bell crack or pivot pin arranged to pivot with the lock link.

According to a second aspect of the invention, there is provided an aircraft including one or more landing gear according to earlier aspects of the invention.

DESCRIPTION OF THE EMBODIMENTS

As an overview, embodiments of the invention relate to a landing gear assembly having a conventional stay and lock link, but having a fibre composite leaf spring arranged to urge the lock link to assume a locked state, so as to serve as a down lock spring.

Referring first toFIGS. 1aand 1b, part of an aircraft, namely an aircraft landing gear assembly is shown generally at10. The landing gear assembly10includes a conventional foldable stay12and a conventional lock link14. In addition, the landing gear assembly10includes a fibre composite leaf down lock spring30mounted to the stay12and arranged to urge the lock link14to assume a locked state.

The stay12is arranged to be moved between a folded condition, in which the landing gear assembly10is stowed for flight, and a generally straight or aligned condition, in which the landing gear assembly10is deployed for take-off and landing.

The stay12has an elongate upper stay arm12ahaving a lower end defining a pair of lugs pivotally coupled via a pivot pin16to a pair of lugs defined at an upper end of an elongate lower stay arm12b. The stay arms12a,12bmay therefore pivotally move relative to one another about the pivot pin16. The upper end of the upper stay arm12adefines a pair of lugs that are pivotally coupled to a lug of a connector18which in turn is pivotally coupled to the airframe19. The lower end of the lower stay arm12bdefines a pair of lugs that are pivotally coupled to a lug of a connector20which in turn is pivotally coupled to the main strut21.

The lock link14has an elongate upper link arm14ahaving a lower end pivotally coupled to an upper end of an elongate lower link arm14bvia a pivot pin22. The link arms14a,14bmay therefore pivotally move relative to one another about the pivot pin22. An upper end of the upper link arm14adefines a pair of lugs that are pivotally coupled to a lug of a connector24which in turn is pivotally coupled to the main strut21. A lower end of the lower link arm14bdefines a lug that is pivotally coupled to lugs of the stay arms12a,12bvia the pivot pin16. Lugs of the upper stay arm12aare disposed between the lugs of the lower stay arm12band the lugs of the lower link arm14b.

A lock stay actuator (not shown) can be coupled between the upper stay arm12aand lower link arm14band arranged to pivotally move the link arms14a,14bto ‘unlock’ the lock link14.

As will be appreciated, when the lock link14is in the locked condition, as illustrated inFIG. 1a, the upper and lower link arms14a,14bare generally longitudinally aligned or coaxial, and can be ‘over-centre’, such that the lock link14is arranged to oppose a force attempting to fold the stay12, so as to move the landing gear assembly from the deployed condition towards the stowed condition.

Referring additionally toFIGS. 1cto 1e, when in the unlocked condition, the link arms14a,14bare not aligned, meaning that folding of the stay12results in folding the lock link14. Thus, when in the unlocked condition, a retraction actuator (not shown) coupled between to the main strut21and the airframe19can move the landing gear assembly10between the deployed and stowed conditions.

A fibre composite leaf spring30is mounted on the upper stay arm12ain a cantilevered fashion and arranged in a laterally deflected state such that a free end30aof the spring30presses against the lower lock link14bto force or bias the lock link14to assume the locked condition when the stay12is in the generally aligned condition or near the generally aligned condition. Thus, the spring30serves as a down lock spring. The spring30can be arranged to be generally straight when in an unloaded state and assumes an arcuate shape when holding the lock link14in the locked condition as illustrated inFIG. 1a. The spring30can be rigidly mounted by any suitable means; for example, mechanical fixings29such as bolts or the like, or the spring can be strapped or bonded in place.

As illustrated inFIG. 1c, an actuator (not shown) can break the lock link14against the down lock spring bias. The spring30flexes laterally and the free end30amoves along an outer surface of the lower lock link14btowards the pivot22.

As illustrated inFIG. 1d, the stay12can then be folded as main strut21is drawn towards the airframe19. Folding articulation of the stay12causes folding articulation of the lock link14, which in the illustrated geometry reduces the angle α between the upper stay arm12aand the lower link arm14b, causing the spring30to flex further and the free end30ato move closer to the pivot22.

As illustrated inFIG. 1e, as the stay12approaches a folded condition, the angle α between the upper stay arm12aand the lower link arm14bincreases beyond that of when the landing gear assembly is in the deployed condition ofFIG. 1a, such that the spring30adopts a relatively straight configuration and the free end30afurther from the pivot22. In some embodiments the angle α may exceed 180°, in which case the spring30can move out of contact with the lower link arm14b.

Referring now toFIGS. 2ato 2e, a landing gear assembly according to a further embodiment of the invention is shown generally at40. The landing gear assembly is similar to the assembly10ofFIG. 1and like parts have been given the same reference numerals. However, the landing gear assembly40ofFIG. 2includes a fibre composite leaf spring42which is mounted on the upper stay arm12avia a first end fitting F1and the distal end42aof which is coupled to the lower link arm14bvia a second end fitting F2. The end fittings can comprise any suitable means for rigidly coupling the ends of the spring42to appropriate parts of the landing gear assembly, such as mechanical fixings. The landing gear assembly ofFIG. 2can reduce component wear in comparison to the assembly10ofFIG. 1by reducing or in some cases eliminating relative motion between the distal end42aof the spring42and the lower link arm14b.

In order to provide a biasing force when the stay12is approaching the generally aligned condition, as illustrated inFIGS. 2aand 2b, yet permit free articulation of the landing gear assembly40as it moves towards the stowed condition, as illustrated inFIGS. 2cto 2e, the spring42includes a kinked region42bwhich enables the spring42to extend as the assembly40articulates towards the stowed condition. The kinked region42btherefore permits a greater amount of deflection of the spring at one end in comparison to the other. The kinked region42bcauses the leaf spring42to assume a default shape when unloaded in which the effective length defined by the distance between the ends of the spring42is an intermediate length. The spring42will flex laterally when the effective length is increased or decreased, or when the ends of the spring otherwise move relative to one another, and the spring42will attempt to assume the default position.

As illustrated inFIG. 2a, the spring42biases the lock link14towards the locked condition by having an effective length L which is decreased in comparison to the default length. In some embodiments the effective length L can be equal to the default value but the spring42is configured and mounted so as to be in a deflected position such that the distal end42aof the spring42attempts to move to a default position that is within or beyond the lower lock link14b.

As illustrated inFIGS. 2cand 2d, retraction of the landing gear assembly40causes the gap defined by the kinked region to reduce in size such that the effective length L of the spring42decreases.

As illustrated inFIG. 2e, as the stay12approaches the folded condition kinked region flexes such that the effective length L of the spring42increases relative to its effectively length when the lock link14is made.

In any of the aforementioned embodiments the landing gear assembly can include a pair of fibre composite leaf springs to provide redundancy should one spring fail. The springs can be mounted in parallel, or the second spring can be provided on a different part of the landing gear while being arranged to press against part of the lock link14to force or bias the lock link14to assume the locked condition; for example, a spring could be mounted on a cardan joint provided at connector24and arranged to press against the upper lock link14a.

Referring now toFIG. 3, a landing gear assembly according to a further embodiment of the invention is shown generally at50. The landing gear assembly50is similar to the assembly10ofFIG. 1and like parts have been given the same reference numerals. However, the landing gear assembly50ofFIG. 3includes a pair of leaf springs52,53which govern the rotational position of a bell crank pivot pin56. The first spring52is mounted on a first side12aaof the upper stay arm12aand has a distal end52acoupled to a first projection56aon a first side of the bell crank56. The second spring53is mounted on a second side12abof the upper stay arm12a, opposite to the first side12aa, and has a distal end53acoupled to a second projection56bof the bell crank56which is diametrically opposite to the first protection56a. The lower link arm14bis pivotally coupled to the stay12via the bell crank pivot pin56such that the lower lock link14band bell crank56pivot together. Both springs52,53include kinked regions52b,53bwhich are similar to the kinked region42bdescribed with reference toFIG. 2.

Thus, the springs52,53can be arranged to balance when the lock link14is in the locked condition. Pivotal movement of the lower link arm14bfrom the locked condition causes the effective length of one spring52to reduce and the effective length of the other spring53to increase, creating a reactive torque on the bell crank56which urges the lock link14to assume the locked condition. In some embodiments the springs52,53can be arranged to be unbalanced when the lock link14is in the locked condition so as to continue to load the lock link14. In other embodiments the bell crank56can be coupled to just a single spring, for weight saving purposes, or a pair of springs mounted in parallel on the same side of the stay arm and coupled to the same side of the bell crank56, for redundancy.

In any embodiment of the invention each leaf spring can be provided with end fittings to couple it to parts of the landing gear assembly. In embodiments where the spring is cantilevered, the end fitting provided at the free end of the spring can comprise a roller or polished surface arranged to reduce wear due to friction. The end fittings can be rigid. In some embodiments the end fittings can each be longer than the spring, such that the spring defines a flexible elbow region in an otherwise rigid linkage, which can be advantageous when the spring is formed from a fibre composite material; in such embodiments the fittings and spring can be integrally formed with the spring, with the fibre layup in the fittings being arranged to define rigid portions and the layup in the spring portion being arranged to define a leaf spring. Alternatively, the fittings can each be shorter than the spring, or the spring can be directly coupled to the landing gear assembly, which can advantageously increase the amount of spring deflection for unit load in comparison to an embodiment where the spring defines a relatively short flexible elbow region, meaning that the spring can accommodate a greater range of relative movement between the stay and lock link during landing gear retraction; such spring arrangements are particularly suitable for landing gear assembly geometries which require a greater net travel of the spring from unloaded to fully loaded.

In any embodiment of the invention the leaf spring can be formed from any suitable fibre composite material; for example, a carbon fibre reinforced composite material with a nominally organic polymer matrix, a glass fibre such as S-glass or E-glass, or an aramid fibre reinforced plastic.

As will be appreciated by the skilled person, the down locking force required to make a lock link varies. The skilled person will however be capable of determining a required down locking force for a given landing gear assembly and designing a suitable fibre composite spring without undue burden.

Thus, a landing gear assembly according to embodiments of the invention includes a down lock spring in the form of a fibre composite leaf spring. The present inventor has found that fibre composite leaf springs can deflect sufficiently to accommodate articulation movement of the lock link as the landing gear assembly moves between the deployed and stowed conditions. The fibre composite leaf spring has various advantages over conventional metal coil down lock springs; for example, the leaf spring can have a low profile in comparison to a coil spring, reducing the likelihood of impact damage, in addition to being less susceptible to vibratory loading.