AIRCRAFT LANDING GEAR PROVIDED WITH AT LEAST ONE MOTORIZED WHEEL

An aircraft has an upper portion and a lower portion provided with a first and second axle. The first axle is provided with a braked wheel and the second axle is provided with a motorized wheel. A landing gear of the aircraft includes a main arm pivoting with respect to the strut on which the first axle is fixed. The second axle is fixed on the strut, and a main actuator moves the first axle between a remote position and a close position with respect to the upper portion. In the close position, the braked and motorized wheels are simultaneously in contact against a running plane, and in the remote position, the braked wheels are in contact against the running plane while the motorized wheel is at a distance from the running plane.

The present invention relates to the field of aircraft landing gears provided with at least one motorised wheel and at least one braked wheel.

BACKGROUND OF THE INVENTION

Patent document FR3072943A1 describes a landing gear provided with an upper portion intended to be joined to a structure of the aircraft and a lower portion equipped with a bogie forming a beam and two axles carried at the ends of this bogie.

This landing gear comprises a strut connecting the upper portion and the lower portion. The two axles of the landing gear are perpendicular to the bogie.

The front axle is equipped with a plurality of braked wheels and the rear axle is equipped with at least one motorised wheel to enable the progression of the aircraft on the ground (taxiing).

Each motorised wheel is thus arranged to transmit moving forces to the ground and each braked wheel is arranged to transmit the braking forces to the ground.

A damper is connected on the one hand to the bogie and on the other hand to the strut to damp a pitching movement of the bogie with respect to the leg, the braked and motorised wheels being simultaneously moved during the pitching movement of the bogie with respect to the strut.

The distribution of ground forces between the braked wheels at the front and the motorised wheels at the rear is difficult to control with this single damper coupled to the bogie. As a result, each motorised wheel is likely to undergo significant accelerations/shocks during the take-off and landing phases, which requires taking significant margins relative to the dimensioning of the motorised wheels.1Translation of the title as established ex officio.

AIM OF THE INVENTION

An object of the present invention is to propose a landing gear making it possible to limit the risk of damaging a motorised wheel at the time of the take-off and landing phases.

SUMMARY OF THE INVENTION

To this end, the invention relates to an aircraft landing gear having an upper portion intended to be joined to a structure of the aircraft and a lower portion provided with first and second axles, the first axle being equipped with at least one braked wheel and the second axle being equipped with at least one motorised wheel, the landing gear comprising a strut having a upper end belonging to the upper portion of the landing gear and a lower portion belonging to the lower portion of the landing gear.

The landing gear according to the invention is essentially characterised in that it comprises a main arm mounted so as to pivot with respect to the strut via a pivot connection, said first axle being fixed to this main arm at a distance from the strut and the second axle being fixedly connected to the leg, the landing gear comprises a main actuator arranged to act on the main arm so as to move the first axle between a position remote with respect to the upper portion and a position close with respect to the lower portion, in the close position the braked and motorised wheels are arranged so as to be able to be simultaneously in contact with a running surface and in the remote position the braked and motorised wheels are arranged so that each braked wheel equipping the first axle can be in contact with the running surface while each motorised wheel equipping the second axle remains at a distance from this running surface.

For the understanding of the invention:a braked wheel is a wheel mechanically coupled with a brake to apply a torque opposing the rotation of this braked wheel with respect to the axle equipped with this braked wheel (in this case, the first axle); anda motorised wheel is a wheel mechanically coupled with an engine intended to selectively apply an engine torque rotating this motorised wheel with respect to the axle equipped with this motorised wheel (in this case, the second axle).

With the landing gear according to the invention, the first axle equipped with one or more braked wheels is carried by the main arm which pivots relative to the landing gear strut under the effect of the main actuator.

Depending on the movement of the main arm with respect to the strut, one can simply either bring the braked and motorised wheels into contact with the ground running surface or move the motorised wheel away from this running surface so that only the braked wheel(s) is/are in contact with the running surface.

Thus, the main mechanical forces transmitted, via the strut, from the aircraft to the ground, pass via the only braked wheels carried by the first axle.

In addition, as long as the motorised wheel is not brought into contact with the ground, it belongs to a suspended part of the landing gear that is carried via the main arm.

Upon landing, the braked wheel is in contact with the ground and the motorised wheel is away from the ground, the main shocks and forces transmitted via the strut thus transiting via the first axle and the braked wheel(s) without ever passing through the second axle and the motorised wheel.

The motorised wheel is thus protected from many risks of failure and it can be dimensioned as accurately as possible to be able to transmit a predefined maximum motor torque within a predefined speed range.

It is thus possible to limit the mass of the motorised wheel to that which is just necessary.

Moreover, during all the taxi phases of the aircraft, the aircraft is at least carried by the braked wheel(s) equipping the first axle while each motorised wheel on the second axle can be selectively moved with respect to the running surface by moving the main arm under the effect of the main actuator.

As long as the taxiing conditions do not enable a contact of the motorised wheel on the running surface (for example, because the aircraft moves at a to high speed), a distance can be kept between the motorised wheel and the running surface, so that only one braked wheel stay into contact with the running surface.

When the taxiing conditions so allow, it can be decided to control the main actuator to put the running surface in contact with the motorised wheel(s) equipping the second axle in addition to the braked wheel(s) equipping the first axle.

The control delivered to the main actuator makes it possible to adjust the distribution of the forces applied to the ground via the strut between the portion of forces transiting via the first axle and the braked wheel(s) and the portion of forces transiting via the second axle and the motorised wheel(s) equipping this second axle.

Thus, by means of the invention, the forces applied to the motorised wheel can be adjusted via a control delivered to the main actuator.

Typically, during the landing, take-off or high-speed taxiing phases, each motorised wheel of the landing gear is kept away from the running plane to preserve these motorised wheels.

By means of the invention, the motorised wheel is then protected against accelerations or impacts of too high strength.

The invention also makes it possible to dispense with disengagement means of the motorised wheel with respect to the engine, since aircraft speed conditions can be chosen, required to bring the motorised wheel into contact with the ground.

The size of the motorised wheel can be adapted to the sole need of moving the aircraft (pulling or pushing the aircraft).

The motorised wheel/tyre assembly and the whole kinetic chain between this wheel and the engine is subjected to speeds and forces which are a lot lower than the braked wheels, which makes it possible to reduce the risks of damaging the motorised wheel.

Being able to distance the motorised wheel with respect to the running surface during braking phases, makes it possible to not degrade the braking performance.

It can also be considered that the movement of each at least one motorised wheel by the main actuator is synchronised with the aircraft speed, this synchronisation being able to occur with a relaxed precision with respect to the synchronisation precision normally required to manage a motorised wheel clutching with its engine.

The synchronisation/transmission error can be recovered by the flexibility and the sliding of the motorised wheel tyre.

Another advantage of the landing gear according to the invention is that it can be optionally installed on an existing aircraft landing gear that would have a first axle carried by a main arm that pivots relative to the strut.

In this case, it is sufficient to fix on a lower portion of the strut, a second axle equipped with a motorised wheel so that this motorised wheel can be selectively moved away from the running surface by varying, under the effect of the main actuator, the orientation of the main arm with respect to the strut.

To this end, a fastening interface of the second axle that is removable with respect to the strut could be used.

An fastening interface could, for example, take the form of a flange tightening a lower portion of the strut, this strap being able to come into contact and possibly be fixed against a pivot pin serving as a pivot connection between the main arm and the strut.

Alternatively, the strut may include a forged portion in a structural part of the strut to form a radial protrusion of the strut arranged to assemble the second axle thereto.

Preferably, the first axle is exclusively equipped with braked wheel and does not support any motorised wheel.

Preferably, the second axle is exclusively equipped with a motorised wheel and does not support any braked wheel.

According to a second aspect, the invention also relates to an aircraft comprising at least one landing gear according to any one of the landing gear embodiments according to the invention.

This aircraft is arranged to selectively adopt first and second aircraft configurations, distinct from one another.

In the first aircraft configuration, said at least one braked wheel on the first axle and said at least one motorised wheel on said second axle are simultaneously in contact with a running surface to enable the taxiing of the aircraft.

In the second aircraft configuration, said at least one braked wheel on the first axle is in contact with the running surface while said at least one motorised wheel on said second axle is away from this running surface, the passage of one of these aircraft configurations to the other of these aircraft configurations being done by actuation of said main actuator.

The aircraft according to the invention benefits from the advantages associated with the landing gear according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The landing gear according to the invention is substantially illustrated byFIGS.1a,1b,1c,2a,2b,2cwhich show different configurations adopted by the landing gear1during its use.

The landing gear1of the aircraft2comprises an upper portion1aintended to be joined to a structure2aof the aircraft2and a lower portion1bprovided with first and second axles3,4.

As illustrated inFIGS.1ato2c, the landing gear1according to the invention is preferably a main landing gear of the aircraft.

Such a landing gear is arranged to selectively adopt a retracted configuration, wherein it is placed in a zone of the structure2aof the aircraft2and a deployed configuration, where it extends under the aircraft2in order to be able to support it and enables it to taxi over the running surface P.

For this end, the landing gear may be connected to the structure2aof the aircraft via a main pivot axis X-X of the landing gear, substantially parallel to the usual movement direction S of the aircraft.

Alternatively, the landing gear according to the invention could be connected to the structure2aof the aircraft2via any other connection mechanism conventionally used.

The landing gear also comprises an operating cylinder (not shown) to control the passage of the landing gear (in this case, by pivoting the landing gear about the axis X-X) between its retracted configuration and its deployed configuration.

The first axle3is, in this case, a rear axle and the second axle4is, in this case, a front axle with respect to a usual movement direction S of the aircraft2.

The first axle3is always equipped with two braked wheels3aand the second axle4is always equipped with one motorised wheel4a.

Each braked wheel3ais adapted to taxi over the running surface P and thus, on the one hand, support a portion of the weight of the aircraft2during landing, during the taxiing of the aircraft and during the take-off and, on the other hand, transmit a braking force of the aircraft when a brake associated with a braked wheel is actuated.

Each motorised is adapted to transmit a moving force of the aircraft (force causing the movement of the aircraft) when the motorised wheel is put in contact with the surface P and when the engine associated with this motorised wheel4ais activated.

These first and second axles3,4are parallel to one another, such that each wheel3aon the first axle can rotated about a main axis of the first axle3and that each wheel4aon the second axle4can rotate about a main axis of the second axle, these main axes of the first and second axles3,4being parallel to one another.

The landing gear1comprises a strut10, an upper end of which belongs to the upper portion1aof the landing gear1and a lower end of which belongs to the lower portion1bof the landing gear.

The landing gear1also comprises a main arm30which is pivotably mounted with respect to the strut10via a pivot41which is in this case located close to the lower end of the strut10.

This main arm30is pivotably mounted with respect to the strut10to only enable a pitching movement of this main arm30.

It should be noted that a pitching movement is a movement of rotation about a transverse axis of the landing gear.

The first axle3is fixed to the main arm30, at a distance from the strut10.

The landing gear2comprises a main actuator50arranged to move the second axle3between a remote position and a close position with respect to said upper portion1awhile the second axle stay stationary with respect to the upper portion of the landing gear.

In the remote position shown inFIG.1a, each wheel3aon the first axle3is positioned to be able to be in contact with the running surface P while each wheel4aon the second axle4is positioned to remain at a distance from this surface P.

In the close position shown inFIG.1b, the wheels3a,4awhich equip the first and second axles3,4are positioned to be simultaneously in contact with the running surface P.

In other words:when the first axle is in the remote position, the distance between the first axle and the upper portion of the landing gear is greater than the distance between the second axle4and the upper portion1a, in contrast;when the first axle is in the close position, the distance between the first axle and the upper portion of the landing gear is less than the distance between the second axle4and the upper portion1a.

The main actuator50is, on the one hand connected (via a first pivot connection Pvt1) to the strut10and on the other hand, connected (via a second pivot connection) to said main arm30to, on the one hand control the orientation of the main arm30with respect to the strut10and on the other hand, dampen the pivot movement of this main arm30with respect to the strut10and thus dampen movements of the first axle3with respect to the strut10.

Thus, the movement of the first axle3with respect to the strut10is damped by the damper51of the main actuator50.

Therefore, as long as the first axle is in its remote position with respect to the upper portion of the landing gear1a, the strut10, the second axle4and the motorised wheel4aequipping this second axle4belong to a suspended and damped part of the landing gear.

The equipment which is fixed to the suspended portion is thus protected from vibrations/shocks caused during the landing.

The second axle4is rigidly fixed to the strut10in greater proximity to the lower end of the strut than to the upper end of the strut10.

In the present example, the lower end of the strut has a portion10cradially offset from a longitudinal axis z-z of the strut10.

This radially offset part10cextends on the front side of the strut in the direction S of movement of the aircraft and the second axle4is fixedly mounted on this radially offset part of the strut10.

In this way, the motorised wheel4ais offset towards the front of the landing gear while the braked wheels3aare offset towards the rear of the landing gear.

The part10cof the strut10is preferably a forged part of the strut10and the second axle4is rigidly fixed to this part10cof the strut10to guarantee its parallelism between the axles3and4.

Preferably, these braked wheels3aare arranged on either side of the main arm30.

To simplify the side views of the landing gear according to the invention illustrated inFIGS.1a,1b,1c,2a,2b,2c, the braked wheel3anormally concealing the main arm30has been omitted.

It must be noted that the number of braked wheels3aand their arrangements on the first axle3could vary without moving away from the scope of the present invention.

In the embodiment shown inFIGS.1ato2c, the second axle4is equipped with a single motorised wheel4a.

It can however be considered that this second axle4is equipped with several motorised wheels, the number and the arrangement of which could vary without moving away from the scope of the invention.

In particular, there could be two motorised wheels respectively placed on either side of the strut10.

The strut10, the main arm30and the main actuator50may each extend along axes which may be longitudinal and which are specific to them.

These axes may be coplanar with each other and lie in a main plane of symmetry Px of the landing gear (this plane Px is illustrated inFIGS.3and4). Alternatively, these axes may be parallel to the main plane of symmetry Px of the landing gear without being coplanar.

The pivot connections30a, Pvt1and Pvt2form simple (non-slip) pivots along respective pivot directions that are parallel to each other and perpendicular to said main plane of symmetry Px.

To improve running stability and avoid the risk of interaction between the braked wheels3aand the motorised wheels4a, the motorised wheel(s)4acarried by the second axle4are preferably positioned between and at a distance from planes, parallel to one another, in which the braked wheels3aextend.

In the embodiment ofFIGS.3and4, in which the landing gear comprises a single motorised wheel4a, the latter is offset with respect to the main plane of symmetry Px of the landing gear.

Preferably, each motorised wheel4ais on the outer side of the aircraft with respect to the main plane of symmetry Px of the landing gear1.

Each motorised wheel4ais generally associated with an engine M which corresponds to it and which enables its drive, but it can also be considered that a motorised wheel is driven by several engines or conversely, that one same engine drives several motorised wheels.

Preferably, the engine for driving a motorised wheel4ais an electric engine M powered by an electric power unit belonging to the aircraft.

As illustrated inFIG.3, an engine M can be mounted outside of the motorised wheel4awith a kinetic chain between the engine M and the wheel4awhich is fully supported by the second axle4, the engine M being located at a distance from the wheel4a, between the moving arm40and the wheel4a.

Alternatively, as illustrated inFIG.4, the engine can be integrated with the wheel. In this embodiment, the engine belongs to a propeller system assembly M1mainly placed in the wheel4a, at a distance from the tyre4a1.

As shown inFIGS.2ato2c, the main actuator50comprises a first damper51interposed between the main arm30and to the strut10so as to dampen a pivot movement of the main arm30with respect to the strut10.

As is understood fromFIGS.2ato2c, this first damper51is provided with first and second parts511,512slidingly mounted against one another and together defining first and second damper chambers513,514which are separated from one another by a movable wall515of the first damper51.

This movable wall515is, in this case, defined by a portion of the first sliding part511which forms a piston sealingly sliding in a cylinder512adefined in the second part512.

A peripheral seal of this piston515can be in contact all around this piston in the cylinder512adefined in the second part512.

These first and second chambers513,514of the first damper51have respective internal volumes which vary according to a sliding position of the movable wall515of the damper with respect to the second sliding parts512of the first damper51.

Alternatively, the movable wall515which delimits the two chambers513,514could be defined by a portion of the second sliding part512which would form a piston sealingly sliding in a cylinder defined in the first part511.

The movable wall515is equipped with at least one fitted passage connecting the chambers513,514together to enable a passage of fluid from one of these chambers to the other of these chambers in order to dampen the movement of the first and second parts511,512against one another).

The main actuator50also includes a linear telescopic actuator52of variable length to vary the orientation of the main arm30relative to the strut10by rotating the main arm30about the pivot connection30arelative to the strut10.

The telescopic actuator52of the main actuator50is a hydraulic actuator provided with a first port521for the passage of hydraulic fluid.

The length of this actuator52is variable according to a volume of hydraulic fluid taken into this actuator52via this first port521for the passage of hydraulic fluid.

The telescopic actuator52of the main actuator50comprises a first actuator rod52aand a first cylinder52b.

The first actuator rod52ais sealingly slidingly mounted in this first cylinder52bso as to define a main chamber523in which said port521for the passage of hydraulic fluid leads.

This sealing is achieved by means of an annular seal J1extending all around the first cylinder rod52a, in a groove of this first rod in order to achieve sliding sealing against an internal surface of the first cylinder52b.

The first actuator rod52aand the first cylinder52btogether defining a secondary chamber524in which a second port for the passage522of hydraulic fluid leads.

The actuator has a passage formed between the secondary chamber524and a zone external to the actuator52through which the first rod52aslides.

A second annular seal J2can be fixed in an internal groove formed in this passage to seal against an annular surface of the first rod52ato oppose the passage of fluid between the secondary chamber524and the zone external to the actuator via the passage through which the rod52apasses and slides.

This telescopic hydraulic actuator52is a double-acting actuator of variable length between a minimum length and a maximum length.

The maximum length of the cylinder is determined in such a way that, even if the braked wheel is deflated, the motorised wheel always remains away from the running plane as long as the current length of the cylinder is maximum.

The first damper51is interposed between the rod of the telescopic actuator52aand said main arm30in order to damp the displacement of the main arm30relative to the rod52aof the actuator and thus damp the pivoting of this arm30relative to the strut10about the pivot30a.

To this end, the rod52aand said second part512of the damper may constitute a single part, thereby facilitating the connection between the actuator52and the damper51.

The minimum length of the telescopic hydraulic actuator52is reached when the main actuator rod52is abutted against a first abutment formed inside the main chamber523.

The maximum length telescopic hydraulic actuator52is reached when the main actuator rod is abutted against a second abutment formed inside the secondary chamber524.

The increase in the length of this actuator52is achieved by intaking fluid to the main chamber523via the first port521and by backflow of fluid outside of the secondary chamber524via the second port522.

The decrease in the length of this actuator52is achieved by intaking fluid to the secondary chamber524via the second port522by backflow of fluid outside of the main chamber523via the first port521.

The aircraft2comprises a hydraulic circuit (not represented) provided with a conduit for supplying highly pressurised hydraulic fluid connected to a hydraulic pump and a conduit for returning low pressure fluid relative to said high pressure.

The aircraft2also comprises a hydraulic distribution system Dis connected to the first and second ports of the actuator521,522and to the supply and return conduits to selectively adopt:at least one configuration for extending the length of the actuator52wherein the first port521is connected to the supply conduit and the second port522is either preferably connected to the return conduit, or connected to the first port521; andat least one configuration for reducing the length of the actuator wherein the second port is connected to the supply conduit and the first port is connected to the return conduit.

According to a particular embodiment, it could be provided that the hydraulic distribution system Dis can adopt a configuration for immobilising the actuator, wherein the circulation of fluid via the first and second ports521,522would be inhibited so as to prevent any length variation of the actuator52.

When the actuator is controlled to prevent any length variation of the actuator52, then the pivoting of the main arm30with respect to the strut is allowed only within a predefined damping stroke allowed by the damper51.

This actuator52could also be a monostable actuator which, in the event of a hydraulic supply fault, for example in the event of a drop in hydraulic pressure in at least one of its chambers below a predefined minimum value, would force the passage of the first axle to its remote position relative to the upper portion1aof the landing gear. In this way, in the event of a hydraulic failure, only the braked wheel could come into contact against the running surface, the motorised wheel being moved away from this surface and thus preserved.

To this end, the actuator ofFIGS.2a,2b,2ccould be equipped with an elastic return means (not shown) exerting an elastic force forcing the extension of the actuator52.

Said elastic return means could comprise a spring arranged in the secondary chamber524to be elastically compressed therein in response to an extension of the actuator52.

The telescopic jack52of the main actuator50may also comprise a locking system53shown schematically inFIGS.2ato2c.

The locking system53could comprise one or more locking segments or one or more locking claws.

This locking system53is arranged to selectively take a locked configuration and an unlocked configuration.

In its locked configuration, the telescopic actuator52of the main actuator50is blocked to keep the first axle3in its remote position with respect to said upper portion1aof the landing gear.

In its unlocked configuration, the telescopic actuator52is released to be able to move the first axle3between its remote position with respect to the upper portion1aof the landing gear and its close position with respect to said upper portion1aof the landing gear.

This locking system53is arranged to pass from its locked configuration to its unlocked configuration in response to an unlocking control.

In the present case, the unlocking control consists of an increase in pressure of the hydraulic fluid taken in via the second port522for the passage of hydraulic fluid.

The locking system53is preferably arranged so that the passage from the unlocked configuration to the locked configuration takes place automatically during the extension of the telescopic actuator52when the actuator52has a running length equal to its maximum length.

The damper51of the main actuator50is shaped to exert a return force, forcing this damper51to return to an extended configuration of the damper51. Thus, as soon as the braked wheel comes into contact against the running surface, the damper is compressed under the effect of the pivoting of the main arm and the movement of this arm is then damped.

The main actuator50is arranged so that when the motorised wheel4ais in contact against the running plane, the damper51exerts an elastic force opposing the compression of the motorised wheel4aagainst the running plane.

Thus, in order to increase the compression force of the motorised wheel4aagainst the running plane P and thus increase the motor force that can be transmitted via the motorised wheel4a, it suffices to retract the actuator52in order to reduce the damping force applied via the damper51to the main arm30.

Conversely, in order to reduce the compression force of the motorised wheel4aagainst the running surface P and thus preserve the motorised wheel4aagainst a risk of overload, it suffices to extend the actuator52in order to increase the damping force applied by the damper51to the main arm30.

The distribution of the forces supported by the strut10occurs between the braked wheel(s) equipping the first axle3and the motorised wheel(s) equipping the second axle4as a function of the force applied by the main actuator50on the main arm30, this force itself being a function of the hydraulic pressure inside the main chamber523of the actuator52.

The aircraft can also comprise a control unit UC of the landing gear which is connected to said hydraulic distribution system Dis to transmit a control Cd of the main actuator50.

The main actuator50is preferably controlled via the control unit UC such that as long as the speed of the aircraft2is greater than a predetermined speed threshold, this main actuator50applies a force tending to keep the second axle3in its remote position with respect to said upper portion1aof the landing gear1.

Thus, as long as the speed of the aircraft is greater than the predetermined speed threshold, the motorised wheels4aare necessarily away from the running surface P (ground) and only the braked wheel(s)3acarried by the first axle3can come into contact with the running surface P.

The main actuator50is preferably controlled by the control unit UC so that when the speed of the aircraft is less than the predetermined speed threshold, the actuator50then applies a force tending to hold the first axle3in an intermediate position between its remote and close positions with respect to said upper portion1aof the landing gear1so that the braked and motorised wheels can be simultaneously in contact against the running surface P to thus distribute forces transmitted via the strut to the motorised and braked wheels.

To this end, the control unit UC of the landing gear which is connected to said hydraulic distribution system Dis can be adapted to control the main actuator50, in this case to control said actuator52, so as to maintain it in a predetermined intermediate position in which the actuator52has a predetermined length in a range from said minimum length to said maximum length.

This predetermined intermediate length is calculated by a computer in order to limit the load applied via the strut to the motorised wheel below a predetermined maximum load value.

To this end, the control unit UC may be adapted to control a variation in the length of the telescopic actuator52and/or a variation in the damping coefficient of the damper51as a function of a measured value representative of a load applied by the main actuator50to the main arm30and/or as a function of a measured value representative of a current length of the damper51and/or as a function of a measured value representative of a current pressure in the motorised wheel and/or as a function of a measured value representative of a current pressure in the braked wheel and/or as a function of a current mass value of the aircraft to be supported by the landing gear.

Typically, the control for varying the length of the actuator52delivered by the control unit UC is such that when the braked and motorised wheels are simultaneously in contact with the running surface (during taxiing), then the vertical force applied to the running surface via the motorised wheel(s)4arepresents approximately 20%, within plus or minus 5%, of the total vertical force applied to the running surface via the braked wheel(s)3a.

To do this, the length variation control of the actuator52can be calculated as a function of:a vertical stiffness Kactof the motorised wheel4a;
andan overall vertical suspension stiffness of the landing gear Ksusp(including the respective stiffnesses of the tires of the braked wheels3a, of the damper51and of the actuator52, all in series), taking into account the geometry of the landing gear and a current mass of the aircraft.

By virtue of this control of the main actuator50by the control unit UC:when the aircraft is under a minimum static load (seeFIG.2b), the predetermined intermediate length of the actuator52is small so that the force applied by the damper51on the main arm30and consequently on the braked wheel is sufficiently small to ensure that the motorised wheel receives a sufficient load to ensure minimum adhesion to the ground; andwhen the aircraft is under maximum static load (seeFIG.2c), the predetermined intermediate length of the actuator52is large so that the force applied by the damper51on the main arm30and consequently on the braked wheel is sufficiently strong to ensure that the motorised wheel receives sufficient load to ensure minimum adhesion to the ground while ensuring that this load remains below a maximum load value tolerable by the motorised wheel.

As a result, when the aircraft is at minimum static load (OEW for Operating Empty Weight), as shown inFIG.2b, the actuator52is maintained at an intermediate length/stroke necessary to place the motorised wheel4aon the ground with a minimum force necessary for the adhesion of the tire.

The aircraft hydraulic pressure is used to retract the actuator. This minimum pressure level of pressure in the actuator must be maintained throughout taxiing.

This aircraft configuration corresponds for the actuator to a predetermined maximum depression, i.e. a minimum predetermined intermediate length value.

When the aircraft is at maximum static load (MTOW for Maximum Take-Off Weight), as shown inFIG.2c, the actuator is controlled by the control unit UC to have a maximum predetermined intermediate length value so that the damper is in the compressed position at about 85% of its stroke under maximum load.

In this aircraft configuration, the necessary taxiing effort is significant. If necessary, the cylinder52is controlled in pressure to be in an intermediate position between the maximum stroke (at minimum aircraft load) and the locked position by the locking system53(the locked position is used during the landing phase in particular to ensure that when the braked wheel is in contact on the ground, the motorised wheel is then away from the ground).

The current length of the actuator is always chosen to ensure that sufficient adhesion of the motorised wheel4ato the ground is maintained while avoiding overloading of this motorised wheel4a.

It should be noted that the main actuator50could also comprise controlled adjustment means for varying the characteristics of the damper51, such as its length and/or its stiffness, i.e. the characteristics of the damper.

For example, the variation in length and/or stiffness and/or damping of the main damper could vary according to the speed of the aircraft.

Thus, as long as the speed of the aircraft is greater than the predetermined speed threshold, this main actuator50could be controlled to apply a force on the main arm30tending to flatten the braked wheel3aagainst the running surface P and to keep the strut10at a distance sufficiently away from the running surface P to guarantee that no motorised wheel4acarried by the second axle4comes into contact with the running surface P.

However, when the speed of the aircraft2is less than the predetermined speed threshold, this main actuator50is controlled to flatten the motorised and braked wheels on the running surface P and thus adjust the distribution of the bearing forces of the aircraft, between the braked and motorised wheel(s).

In this manner, it can be guaranteed that at any moment during the taxiing of the motorised and braked wheels, each motorised wheel can transmit effective traction forces of the aircraft and that each braked wheel can support the aircraft, while transmitting effective braking forces.

Generally, thanks to the invention, during taxiing, each braked wheel3on the first axle remains in contact with the running surface, while said at least one motorised wheel on the second axle is selectively put into contact with the running surface P or away from this running surface P according to which the running taxiing speed is adapted, or not, to the operation of the motorised wheel.

Thanks to the invention:the tyre of each braked wheel and the diameter of each braked wheel can be adapted to meet the needs associated with the landing, braking, and take-off phases; andthe tyre of each motorised wheel and the diameter of each motorised wheel can be adapted to meet the sole needs of moving the aircraft, during taxiing ranges outside of the landing, high-power braking, and take-off phases.