Aircraft towing tractor

0001The present invention relates to an aircraft tractor used in airports to tow airplanes, and more specifically relates to a flight tractor having a gripping device, a train gripping process before an aircraft using such a tractor, and a method for towing an aircraft.

0002Are now used tractors are equipped with a gripper for lifting the nosewheel of the airplane to be towed with a train as is known, consists of a pair of wheels each comprising a tire, the pair of wheel being fixed to the end of one leg pointing downwards from the nose of the aircraft.

0003A gripping device known tractor comprises an articulated longitudinal arms extending entry of the gripping system, and which is intended to be placed at the rear of the front axle of the aircraft. This longitudinal arm closes on the wheels so as to clamp the front end. In contrast to the longitudinal arm, a shovel-shaped blade is fixed transversely to the tractor slightly above the ground, and it is pivotable under the action of a jack. The blade makes it possible to lift the front wheels of the aircraft, immobilized against the walls of the longitudinal arm and the scoop-shaped blade. Such a device is used on a tractor tractor type without drawbar (or "tow Barless" in English); for example, a tractor TPX model TLD (TM) brand.

0004Similar arrangements exist. For example, systems are known where the articulated longitudinal arms can be replaced by hinged doors which are intended to be placed on either side of the nosewheel of the airplane. The document<patcit id="pcit0001" dnum="WO2008139437A"><text>WO / 2008/139437</text></patcit> shows such a system.

0005Today we use tractors equipped with such devices to conduct air taxi operations. Two types of rolling operations are commonly carried out. It first is a so-called "push" (or "push-back" in English), which consists of removing planes loaded with passengers (or freight) and fuel bridges and other fixed installations for the purpose of the to autonomous driving position. There then exists an operation known as "Tow maintenance" (or "maintenance towing" in English) of moving empty plane to a hangar that performs maintenance operations and maintenance of the aircraft.

0006In all other cases where the aircraft carries out a rolling operation, it is in autonomous driving position; it moves under its own power, that is to say thanks to the thrust of its reactors. In particular, the plane is autonomous driving position during the phase when it rolls toward the runway (also known phase under the term of "taxiing out") and / or return phase. The operation of the airplane in this case is the responsibility of the driver that adjusts the speed of the aircraft only using the main brakes of the aircraft, the thrust provided by the remaining constant reactors. During this phase where the plane taxiing to the runway, the aircraft speed is about 20 knots, that is to say a speed of about 37 km / h. The average waiting time of an aircraft before it could take off is 20 minutes, but this time may exceed 1 hour. And during all this waiting, the reactors continue to run and fuel consumption.

0007Was devised to substitute the use of reactors by a tractor during this phase called "taxiing out." The operation is then designated English as the "dispatch towing." Tests were carried out in this direction, and it was found that the fuel consumption of the tractor is very much less than might have consumed the reactor had if they had been used.

0008Despite the fuel economy testing was unacceptable for the following reasons. First, the existing tractors have insufficient speed. The airports are overloaded and slow down the delivery of aircraft to the runway is inconceivable. Then the current gripping devices are not suitable for an operational environment where it is important that a problem can be resolved quickly. In particular, current mechanisms do not allow to discharge air rapidly in the case where the tractor fails, resulting in a slowing or blocking of other aircraft. Any delay is extremely costly for airlines. Then loads and fatigue induced on the nose gear of the aircraft are too high during the phase called "dispatch towing." The lifetime of the front landing gear is thus greatly reduced. For this reason, aircraft manufacturers have limited the number of operations that can be performed in this way, others up to prohibit a tractor does this to "dispatch towing." Airlines have therefore abandoned the use of the tractor for a phase of "taxiing". In addition to these economic and technical considerations, there are also legal considerations. The responsibility is being transferred to the pilot at power reactors, and the tractor driver is then discharged from liability. The responsibility of driving a plane on the runway then be up to the driver of the tractor, which is not possible for airlines and airport managers.

0009The document <patcit id="pcit0002" dnum="WO2008139440A"><text>WO / 2008/139440</text></patcit> has an air tractor to realize the taxiing phase by allowing the pilot to control the tractor steering and speed. However, this air tractor comprises a complex gripping system; many actuators are required to install the front of the aircraft on the tractor. loading steps / unloading of the aircraft are too long and complex. Moreover, the large number of actuators makes it difficult and very long unloading of the aircraft in case of failure of the tractor.

0010<patcit id="pcit0003" dnum="US4632625A"><text>US 4632625 (A</text></patcit>) Discloses an aircraft tractor which has an open fork rearwardly within which a frame is mounted to be raised and lowered. telescopically extendable rods of the frame reach the back of the front of a plane so that the front axle is driven towards the opening of the fork and is held there against a front runner.

0011The invention aims to avoid these disadvantages by providing an air tractor comprising a gripping device to improve the loading and unloading of the aircraft on the tractor, and in particular a gripping device adapted to tow a plane to a runway.

0012For this, it is proposed an air tractor type gripping nose wheel of the aircraft, according to claim 1.

0013The tractor of the invention may further comprise at least one of the following characteristics:<ul><li>at least one door for opposing a force on at least one nose wheel of the aircraft in the grip platform;</li><li>the platform comprises a gripping device for locking at least one nosewheel of the airplane;</li><li>the said locking device comprises at least one nose wheel is installed on a turret disposed on the gripper platform, the turret being free to rotate about a substantially vertical axis relative to the gripper platform;</li><li>the locking device of said at least one wheel comprises:<ul><li>a wheel to stop the train before the aircraft;</li><li>a clamping device for holding the nose wheel of the aircraft against the stop;</li></ul></li><li>the clamping device comprises a clamping plate connected to a triangle actuated by a jack;</li><li>the clamping plate is retractable in the absence of an aircraft wheel on the platform;</li><li>the stop has an adjustable location;</li><li>the actuator of each wheel module is a hydraulic cylinder;</li><li>the clamping device of the actuator is a hydraulic cylinder;</li><li>the damping and actuating means is a movement sensor of relative movement between the platform and the frame;</li><li>the platform has a base connected to the chassis by vertical tie rods;</li><li>an actuator for inducing an inclination of the base of the platform relative to a horizontal plane;</li><li>the vertical tie rods have adjustable lengths and / or for attaching to the chassis adjustable items;</li><li>each gear module has a respective rotation angle relative to a longitudinal axis of the tractor and about a substantially vertical axis of rotation to the tractor frame;</li><li>the turret includes at least one sensor measuring an angular displacement of the turret with respect to the gripper platform, and each respective angle of rotation is determined based on the measured angular displacement of the turret;</li></ul>

0014There is also provided a method of gripping the front end of an airplane using a flight vehicle according to claim 10.

0015The gripping method of the nosewheel of an airplane using a flight tractor may further comprise at least one of the following characteristics:<ul><li>a step of closing a door of the tractor when the gripper platform is in contact with said at least one nose wheel of the aircraft;</li><li>a step of opening the door of the tractor when the frame back;</li><li>when the gripper platform was slid under the wheel, the method further comprises a step of moving the tractor to cause said at least one wheel on a locking device;</li><li>the steps of:<ul><li>adjust the location of a stop depending on the aircraft type and / or type of wheel;</li><li>causing said at least one wheel on the locking device against the abutment;</li><li>bring a clamping plate against the wheel to hold it against the stop;</li></ul></li><li>a step of tilting the platform relative to a horizontal plane.</li></ul>

0016It is also proposed a method for towing an aircraft comprising the steps of:<ul><li>load the aircraft on a tractor following the gripping process of the front of an airplane using an air tractor;</li><li>roll the tractor at a constant speed;</li><li>regulate the speed of the tractor as a function of the force measured by the damping means and actuating.</li></ul>

0017The process to tow an aircraft may further comprise at least one of the following:<ul><li>tractor speed is controlled when the measured force exceeds a dynamically determined threshold level;</li><li>the tractor platform includes a turret receiving said at least one nosewheel of the airplane, the turret being free to rotate about a substantially vertical axis relative to the gripper platform, the direction of the tractor being modified according rotation of the turret with respect to the gripper platform;</li></ul><ul><li>rotation of the turret is driven by a rotational movement of the front axle;</li><li>the tractor comprising in association gear modules to the chassis, each wheel module being rotatable along a substantially vertical axis of rotation to the tractor frame, wherein each wheel module has its own rotation and the longitudinal axis of the plane is coincident with the longitudinal axis of the tractor.</li></ul>

0018Other characteristics and advantages of the invention will appear on reading the following detailed description of the invention embodiments, given by way of example only and with reference to drawings which show:<ul><li><figref idrefs="f0001">FIG. 1</figref>A schematic side view of an aircraft tractor according to the invention;</li><li><figref idrefs="f0001">FIG. 2</figref>A schematic side view of the gripping system according to the invention;</li><li><figref idrefs="f0001">FIG. 3</figref>Is a diagrammatic perspective view of the rear of an aircraft tractor according to the invention;</li><li><figref idrefs="f0002">FIG. 4</figref>Is a diagrammatic perspective view of the gripping system according to the invention;</li><li><figref idrefs="f0002">FIG. 5</figref>Is a diagrammatic top view of the gripping system according to the invention;</li><li><figref idrefs="f0003 f0004 f0005 f0006 f0007 f0008 f0009">FIG. 6-23</figref>, The steps of a grasping method of the front of an aircraft according to the invention;</li><li><figref idrefs="f0009">FIG. 24</figref>A diagrammatic view of an aircraft tractor towing an aircraft according to the invention;</li><li><figref idrefs="f0010">FIG. 25</figref>, A flowchart of a method for towing an aircraft.</li></ul>

0019It is proposed an air tractor type by gripping the front end of the plane. The tractor comprises a frame, and the link wheel module with the frame. Each gear module comprises at least one actuator to induce a vertical movement of the module relative to the chassis. Thus, it is possible to raise or lower the chassis relative to a rolling plan. The tractor also comprises a gripper platform nosewheel of an airplane which has a chassis with the freedom (substantially circular translation, that is to say that all points of the platform have trajectories which are circles same radius but different centers). Thus, with this freedom by approximately circular translation of the platform relative to the frame, the platform maintains a substantially constant angle to the tractor frame. Thus, the gripper platform can move in a reciprocating motion relative to the tractor frame. In other words, the platform may remain substantially parallel with a horizontal plane of the tractor or be inclined relative to the horizontal and retain substantially the same inclination during its movement relative to the tractor. The tractor includes a damping and actuation means connecting the platform and chassis. In particular, the actuating means is a damping means of the free circular translation movement of the gripper platform relative to the chassis. This damping means and actuating advantageously used to modify the positioning of the platform relative to the chassis, but also to capture a relative movement of said platform relative to the chassis.

0020The <figref idrefs="f0001">FIG. 1</figref> is a diagram of a side view of an aircraft tractor according to the invention. The flight tractor 1 comprises a chassis 5 which is connected with four wheels 3. Only modules are visible in FIG both wheels of the modules located on one side of the vehicle.

0021The wheel modules can rotate in one direction or the other along a substantially vertical axis of rotation to the tractor frame.

0022Each gear module comprises at least one actuator to induce a vertical movement of the module relative to the chassis. In practice, the actuator is an actuator, eg a hydraulic cylinder, disposed on either side of two arms articulated with respect to one another which provide the connection of the wheel module to the chassis. The whole articulated arm, actuator, and wheels form a wheel unit. The actuator provides the force necessary to finely adjust the angle between the two articulated arms. The vertical movement of each wheel unit relative to the chassis can be done independently with respect to other gear modules.

0023The number of gear modules that includes a tractor may vary. Preferably, the number of gear modules is an even number; for example the flight tractor may have 4 or 6 wheel modules. In addition, each wheel module may include one or more wheels. For example, each wheel module 3 shown in<figref idrefs="f0001">FIG. 3</figref> comprise two wheels.

0024The aircraft tractor 1 shown <figref idrefs="f0001">FIG. 1</figref> also includes a gripping system 2 of the front of a plane 4 which is detailed in <figref idrefs="f0001">FIG. 2</figref>.

0025The <figref idrefs="f0001">FIG. 2</figref> shows a gripping system according to an embodiment of the invention. The gripping system of the front axle 4 of an aircraft comprises a gripper platform 20 that has a substantially circular freedom in translation with the chassis, that is to say that all points of the platform have trajectories which are circles with the same radius but different centers. Thus, because of the freedom in substantially circular translation of the platform relative to the chassis, the platform maintains a substantially constant angle with a horizontal plane formed by the chassis of the tractor.

0026In practice, the gripper platform 20 is in relation to the chassis 1 of the tractor by means of vertical tie rods 21 connected to the frame. The tie rods are fastened respectively to the platform and the chassis in a ball joint so that the platform has a substantially circular translatory freedom in the chassis. Four vertical tie rods are used for example in the<figref idrefs="f0001">FIG. 3</figref>. The number of drawing may be more important or less important; eg 6 ties. Preferably, the number of tie rods is an even number. In the figures, the vertical tie rods are substantially the same length, and their attachment point to the frame located at the same height, which ensures that the gripping plane and the frame are substantially parallel.

0027According to one embodiment, the base of the gripper platform 20 may be inclined relative to a horizontal plane, for example when the tractor is used for an aircraft having a front end with an inclined leg with respect to a vertical axis - case Airbus A320 for example. The grip platform can be tilted 20 per share on the vertical tie rods 21. For example, the tie length can be adjusted to raise or lower the front or rear of the platform 20 and thus give it the necessary angle with the horizontal plane. For this purpose, at least some of the vertical tie rods 21 may be made of ball screw, hydraulic cylinder or associated with a rack. Rather than adjust the length of the vertical ties, it is also possible to adjust the height of their base chassis 5 of the tractor in order to create the angle of inclination, for example by fixing one end of the tie rod a cam or a cylinder. A combination of these two embodiments may also be considered.

0028The <figref idrefs="f0001">FIG. 2</figref> also shows a damping means and actuating 8 connecting the platform and the chassis. This damping means and actuating 8 advantageously allows to control the relative position of the platform relative to the frame during operations of loading and unloading of the aircraft. In particular, the average amortization and operating 8 to control and order translation grip platform position, so it is possible to cause slippage of the platform 20 under the wheels of the train before the aircraft during a loading operation. Conversely, during an unloading operation, it is possible to cause a withdrawal of the platform 20 in order to free the nose wheels of the plane of the platform. In addition, the damping and actuation means 8 serves to damp relative movement of the aircraft relative to the tractor, when the aircraft is loaded on the tractor, and more specifically on the grip platform 20 tractor . In particular, the damping and actuation means 8 serves to damp the free circular translation movement of the grip platform 20 with the tractor frame; ie the free pendulum movement of the grip platform is damped by the damping means and actuator 8.

0029The amortization of this relative movement has the advantage of limiting the forces on the front wheels of the aircraft, particularly when a deceleration of the convoy of the plane and the tractor towing the aircraft occurs following a braking force induced by the aircraft. Decelerations are then transmitted from the aircraft to the tractor through the front end of the plane that is integral with the grip platform. The damping means and actuating 8 dampens efforts on the front end of the plane, and thus increase the average running speed of the tractor when the towing aircraft. Thus, the damping and actuation means 8 helps improve and accelerate the transport aircraft to its runway, while limiting the forces on the front end of the plane and premature fatigue of the train before.

0030In practice, the damping means and actuating 8 may be a hydraulic cylinder.

0031The <figref idrefs="f0001">FIG. 2</figref> also shows that the tractor comprises at least one door 6 intended to oppose a force exerted on at least one nosewheel of the airplane by the gripper platform. Indeed, during the loading operation of the front axle of the aircraft on the platform, the platform 20 is slid under the wheels of the aircraft. And despite the fact that the wheels can rotate freely, the friction induced by the sliding of the platform gripping under the wheels are important, and a substantial force is exerted on the front wheels of the aircraft. Thus, under the effect of the displacement of the platform gripping and its contact with the wheels of the front axle, the latter is pushed in a direction similar to that of the movement of the platform, which induces efforts leading to a early tiredness nosewheel of the aircraft. To limit the effects on the nose, wickets 6, articulated around a vertical axis of rotation, close behind the wheels of the front so as to provide support to oppose the movement of the latter. The wheels are thus in contact on one side with the gates 6 and on the other side in contact with the platform 20 that slides under them.

0032Grip platform 20 may further have a locking device of at least one nosewheel of the airplane. Such a device is intended to prevent detaching of the front of the plane load on the tractor and to transmit tensile forces. The said wheel locking device comprises in particular a wheel stop 26 of the nosewheel of the airplane and a clamping device (22, 23, 24) for maintaining the nosewheel of the airplane against the stop.

0033The locking device of said nosewheel can be installed on a turret disposed on the gripper platform. The turret may be free in rotation with respect to the gripper platform about an axis of rotation substantially perpendicular to the platform gripping and substantially vertical. The<figref idrefs="f0002">FIG. 5</figref> shows the locking device which is arranged on a turret 52 which is freely rotatable about an axis of rotation 50 substantially vertical to the platform 20.

0034The wheel stop 26 of the nose gear of the aircraft is designed to stop the progression of the aircraft gear wheel when the gripper platform is slid under the wheel. The stop can have various shapes. It can for instance have the general form of a plate large enough to be in contact with both wheels of the front axle 4, as shown in<figref idrefs="f0001">FIG. 3</figref>. Other shapes are envisaged: the stop 26 may have the general form of a shovel, thereby increasing the contact surface with the nosewheel of the airplane.

0035The stop has an adjustable location so that its position is adapted depending on the aircraft type and / or type of wheel. Indeed, the diameter of the nose wheels of an aircraft can vary from one aircraft model to another, so that the wheel contact area on the platform gripping varies depending on the diameter of the wheel and the location of the stop. Advantageously, the location of the abutment can be adjusted in order to position correctly on the wheel locking device of the front axle of the aircraft. Further, correct adjustment of the location of the stop adjusts the coincidence between the axis of rotation of the nosewheel of the aircraft and the rotation axis of the turret. This greatly improves the transmission of the rotation of the front axle to the turret.

0036The clamping device holds the wheel 4 of the front undercarriage of the airplane against the stop, as shown in <figref idrefs="f0001">FIG. 2</figref>. It is held in place by a clamping plate 22 connected a triangle 24 actuated by a jack 23. In practice, the clamping device comprises two triangles, two cylinders, which are arranged either side of the clamping plate 22. in the following description, only one side of the clamping device is disclosed.

0037The clamping plate 22, when actuated by the jack 23 comes into contact against the nosewheel of the airplane, which itself is in contact with the abutment 26. The cylinder 23 connects elements positioned on the platform without any connection to the chassis. The clamping plate 22 is therefore grip the wheel by applying a force mainly directed towards the stop. This force applied by the clamping plate 22 can also be directed substantially towards the platform.

0038The clamping device may comprise, besides the clamping plate 22 connected to the triangle 24 actuated by the actuator 23, a connecting rod 25. In practice, the device comprises two connecting rods; one for each cylinder torque / triangle.

0039All these elements 22, 23, 24, 25 is arranged as shown in <figref idrefs="f0001">FIG. 2</figref>. A first apex 240 of the triangle 24 is connected to the platform by a pivot connection. When the locking device is installed on a turret, the triangle 24 may be connected to the turret so as not to impede its rotation. The jack 23 is connected to a second apex 242 of the triangle 24 by a ball joint. The third summit of the triangle 244 24 joins clamping plate 22 via a pivot connection. Preferably, the pivot connection between the third corner 244 and the clamping plate 22 is in a median position on one side of the plate 22, while the connecting rod 25 is connected to one end 220 side of the plate 22 on one side, and to the platform on the other side. When the actuator 23 retracts, the triangle 24 pivots about its first vertex 240, so that the third vertex of the triangle 24 rises carrying with it the plate 22. Simultaneously, the rod 25 acts on the end 220 of the clamping plate 22, which causes rotation of the clamping plate 22. this rotation allows the passage of a substantially horizontal position of the clamping plate with at least one vertical position in which the largest surface of the plate 22 is in contact with the nosewheel of the aircraft. Advantageously, the clamping plate engages the wheels 4 regardless of the diameter of the wheel of the aircraft load.

0040The clamping plate 22 may be retractable into the platform by rotation of the clamping plate 22 driven by the connecting rod 25. The clamping plate 22 is then placed in a housing provided in the platform for this purpose. Alternatively, the clamping plate 22 can constitute an access to the platform ramp. The clamping plate 22 is then sufficiently long to engage the ground when the rod is rotated by 25. In other words, the clamping plate 22 is adapted to pivot from an upper position wherein the plate clamping is in contact with the wheels 4 to a low position in which one end of the clamping plate is in contact with the ground. In another alternative, the clamping plate 22 can be both retractable and form an access to the platform ramp. The clamping plate, whether removable and / or that it constitutes a ramp, offers the advantage of facilitating the rolling of the wheel 4 in the direction of the stop 26 as the clamping plate is not a obstacle to be crossed by the wheel.

0041In practice, the actuator 23, which actuates the clamping device is a hydraulic cylinder. Indeed, the use of a hydraulic cylinder has the advantage of freeing the plane quickly when the tractor is broken. In particular, the clamping device can easily switch between a clamped position (that is to say, the clamping plate has a coercive force against the plane of the wheel) to a released position. Simply drain the cylinder which relaxes, whereby the clamping plate retracts into the platform, which makes it easy to identify the nosewheel of the aircraft.

0042The <figref idrefs="f0001">FIGS. 3</figref> and <figref idrefs="f0002">4</figref> respectively show the locking device according to one embodiment of the invention in the clamped and unclamped position. The<figref idrefs="f0002">FIG. 4</figref> particularly shows the clamping plate 22 which is retracted into the platform 20.

0043The <figref idrefs="f0002">FIG. 5</figref> shows the same locking mechanism to that of <figref idrefs="f0001">FIGS. 3</figref> and <figref idrefs="f0002">4</figref>But is that once installed on a turret 52 provided on the grip platform 20.

0044The <figref idrefs="f0003 f0004 f0005 f0006 f0007 f0008 f0009">FIGS. 6-23</figref> show the successive steps of a grasping method of the front of an aircraft according to an embodiment of the invention.

0045The <figref idrefs="f0003">FIG. 6</figref> shows a starting configuration, <figref idrefs="f0003">FIG. 7</figref> shows a top view of the <figref idrefs="f0003">FIG. 6</figref>. The plane is parked and the engines are off. Its main brakes engaged, that is to say that the brakes of its rear axle are applied while the wheels of the front axle are free. The tractor is near the aircraft. The tractor gripper platform is in an equilibrium position. The equilibrium position of the gripper platform corresponds to the lowest position thereof relative to the frame. In practice, the damping and actuation means 8 which connects the platform and gripping the frame exerts no force on the platform. The<figref idrefs="f0003">FIG. 7</figref> shows in particular that the gates 6, arranged on either side of the opening 9 permitting the passage of the front undercarriage of the airplane, in the open position. In this initial configuration, the stop 26 is positioned based on the aircraft type and / or type of tire that the tractor will have to load. Alternatively, the positioning stop 26 may be performed in step shown in<figref idrefs="f0006">FIGS. 14 and 16</figref>.

0046Then the tractor grip platform moves from one equilibrium position to a retracted position. The gripper platform pass into the retracted position upon actuation of the damping means and actuating platform which connects the gripping member and the frame. The retracted position is the position in which is located the gripping platform after being translated in the opposite direction to the opening 9 for passage of the nose gear of the aircraft. Once the gripper platform has reached its retracted position, or simultaneously, the tractor frame descends in response to actuation of the actuators of each wheel module. In the<figref idrefs="f0004">FIG. 8</figref>All wheel modules have contributed to lowering the chassis, but we might consider not get off the back of the tractor. The descent of the frame is stopped when the gripper platform reaches a predetermined distance from the ground potential to the ground contact. The tractor is then driven so that the platform gripper comes into contact of the nose wheels of the aircraft, as shown in<figref idrefs="f0004">FIG. 9</figref> which corresponds to a top view of the <figref idrefs="f0004">FIG. 8</figref>.

0047The next step is shown in <figref idrefs="f0004">FIGS. 10</figref> and <figref idrefs="f0005">11</figref>, the <figref idrefs="f0005">FIG. 11</figref> being a top view of the <figref idrefs="f0004">FIG. 10</figref>. This step is to close the doors 6 so that they are positioned either side of the front end of the plane, away from the platform.

0048The next step is shown in <figref idrefs="f0005">FIGS. 12 and 13</figref>, the <figref idrefs="f0005">FIG. 13</figref> being a top view of the <figref idrefs="f0005">FIG. 12</figref>. The damping means and actuating platform which connects the gripping member and the frame is actuated to move the platform to a gripping position. The gripping position is the position in which is located the gripping platform after being translated in the direction of opening for the passage of the front end of the plane. During movement of the gripper platform from its retracted position to its deployed position, the chassis height is adjusted by at least two wheel units to allow the passage from one position to another. Indeed, the gripper platform is movable substantially in circular translation relative to the frame, implying that it passes through its equilibrium position which is the lowest position. On the<figref idrefs="f0005">FIG. 12</figref>All wheel module involved in the height adjustment of the chassis. During this step, the gripper platform slides under the nose wheels of the aircraft. The gates have been closed in the previous step, the nose wheels are in contact on one side with the doors, and the other side in contact with the platform that slides under them, the tires rolling on the platform . To limit friction of the wheels against the gates, they may have arranged horizontally rollers are free to rotate.

0049The <figref idrefs="f0006">FIGS. 14 and 15</figref> show that the aircraft wheels began to rise on the platform for gripping during the displacement of the platform from the retracted position to the gripping position.

0050The <figref idrefs="f0006">FIGS. 16</figref> and <figref idrefs="f0007">17</figref> show the aircraft wheels which are arranged against the stop and the locking device. If needed, the tractor retreats to allow the train front wheels of the aircraft to be effectively placed against the abutment and the locking device. The platform is horizontal, that is to say parallel to the ground, there is no effort on the front end of the plane taxiing on the platform, which is beneficial and preserves the front.

0051The <figref idrefs="f0007">FIGS. 18 and 19</figref> show the next step which is to lock the lock of the wheels of the aircraft, as described above with reference to <figref idrefs="f0001">FIG. 2</figref>.

0052Then, the frame of the tractor is raised in response to actuation of the actuators of each wheel module. On the<figref idrefs="f0008">FIGS. 20 and 21</figref>All wheel modules mounted. At this stage, the gripper platform is always in gripping position.

0053Finally, as shown in <figref idrefs="f0008">FIGS. 22</figref> and <figref idrefs="f0009">23</figref>, The gripper platform is in an equilibrium position and the doors are open. The tractor can now tow the aircraft.

0054When the gripper platform is in its equilibrium position, it can also be inclined relative to the horizontal plane if necessary, before the tractor starts rolling. This function is particularly useful in the case of airplanes having a landing gear leg back 4 inclined with respect to the vertical. The axis of the front axle is not perpendicular to the horizontal plane. But during an action of the pilot of the plane on his leadership, the tires should ideally rotate on a plane perpendicular to the axis of the landing gear leg 4. The inclination of the grip platform 20 may be provided by any means described above, by acting either on the length of some vertical tie rods either on their attachment to the chassis of the towing points.

0055Unloading is the reverse manner of the loading operation. the aircraft's brakes are applied and the aircraft is stationary.

0056Firstly, the gripper platform pass through the gripping position. Then the tractor frame descends. Then, the locking system of the aircraft wheel is unlocked. Then, the gripper platform is brought from the grasping position to the retracted position. The platform retires to progressively so that the nose wheels of the aircraft are heading out of the grip platform. The tractor advance to totally disengage the wheels of the plane is unloaded.

0057It appears that the aircraft tractor according to the invention has many advantages. First, the operation of the gripper tractor is simple and requires only a limited number of actuators. In particular, the average damping and actuation facilitates the loading of the aircraft, but it also allows the traction of the aircraft at high speed as it dampens the tractor speed variations relative to plane, the latter having to brake its own weight.

0058Then the tractor is fault tolerant in the sense that a failure of the tractor does not stop to unload the aircraft. Indeed, the actuators are arranged so that there is no obstacle to the withdrawal of the front of the plane of the platform. In particular, the actuators can be hydraulic cylinders, which facilitates the movement of elements in case of failure of the tractor. For example, the gripper platform can be lowered to ground level by draining the compression chambers of the jacks. By gravity, the tractor frame drops. Similarly, the wheel of the front axle can be taken out of the locking device by emptying the rooms cuts hydraulic cylinders of the locking device. Moreover, the clamping plate can be retracted into the platform, which facilitates even more the rolling of the front out of the gripper platform. Thus, the tractor according to the invention allows to discharge the air in a period of the order of several minutes, even in case of failure, without any energy input other than that required for the translation; for example, another vehicle may come tow the failed tractor.

0059An object of the invention is also to provide a method for towing an aircraft. The document<patcit id="pcit0004" dnum="WO2008139440A"><text>WO / 2008/139440</text></patcit>, Mentioned above, has an air tractor for operations of "taxiing". This document describes a system wherein a transfer signal is supplied to the tractor in response to a movement of an aircraft control component. Including the system described in this document comprises a pivoting support (turret) to receive the nose gear of the aircraft and for transferring pilot steering commands to the tractor. The system described in this document also includes a shock absorber for transferring driver braking commands to the tractor. However, the system described in this document comprises a gripping system of the train before the complex plane, as for the loading of the train on the tractor for unloading. The method of the invention proposes to use such a tractor as described with reference to<figref idrefs="f0001 f0002">Figures 1 to 5</figref> to tow the aircraft. The tractor of the invention comprises a platform having gripper with the frame a freedom in translation substantially circular and connected thereto by a damper - actuator. The tractor of the invention allows both loading and unloading fast nosewheel of the aircraft, as has been described above, and also allows to tow the aircraft to the runway.

0060The steps of this taxiing process are shown in <figref idrefs="f0010">FIG. 25</figref>. During the phase where the tractor towing the aircraft, ie after loading the aircraft on the tractor, the plane's pilot controls the braking of the convoy of the plane and the tractor towing the aircraft. For this, the driver can reduce the speed of the convoy with the braking of the aircraft, and increase the speed of the train by reducing the braking of the aircraft; Manager tractor accelerating the convoy. In addition, the pilot controls the direction of the convoy.

0061The first step is to load the aircraft on the tractor (S100).

0062After the plane has been loaded, the tractor began to roll. For the tractor to begin to roll, the pilot releases the main brakes of the aircraft. The airplane resistance force is then less than the tractor pulling force which can then roll. The tractor exerts sufficient tensile force which allows to move the aircraft. The tractor accelerates until it reaches a constant cruising speed (S110). For example, when the aircraft must be transported to the runway, the cruising speed can be 20 knots, about 37 km / h.

0063The speed of the tractor must however be regulated; for example, the driver must stop the tractor at a crossing. For this, the method for towing an airplane control the tractor speed based on the tensile force measured by the damping and actuating means (S140). Indeed, the damping means and actuating connects the gripping platform with the chassis, so that the tensile force occurring during the aircraft traction can be measured by the damping means and actuation. Thus, when the pilot of the aircraft brakes, it has the consequence that the tensile force measured increases.

0064The force measured is compared to a dynamically determined threshold level so as to test whether or not the threshold level is exceeded (S 150). The threshold level is determined in real time based on extrinsic parameters convoy such as wind speed, the slope of the rolling plane, and parameters intrinsic to the convoy as the type of aircraft or the aircraft model is towed. Other parameters may intervene in determining in real time the threshold level. As this level of dynamically determined threshold is not exceeded, the continuous tractor from rolling. On the contrary, if this level of dynamically determined threshold is exceeded, then the tractor speed is reduced (S 160). Tractor speed is reduced as the force measured by the damping means and actuating the level of dynamically determined threshold. On the contrary, the tractor speed increases to cruising speed when the force measured by the damping means and actuating is again below the threshold level. Thus, the front axle undergoes only a unidirectional tractive force and no thrust force during braking. The aircraft manufacturers consider that the efforts are sufficiently controlled to allow towing the aircraft without damaging the nose gear of the aircraft.

0065In practice, the damping and actuating means may be a hydraulic cylinder which comprises at least one adapted to measure a force sensor.

0066In parallel with the control of the tractor speed, its direction is changed by the driver based on the rotation of the turret with respect to the gripper platform. Rotation of the turret can indeed be induced by a rotational movement of the nose gear of the aircraft. Indeed, any rotational movement issued by the nose gear of the aircraft may be accompanied and transcribed by the turret, as shown in<figref idrefs="f0009">FIG. 24</figref>.

0067The <figref idrefs="f0009">FIG. 24</figref> shows a convoy formed of the tractor 1 and the plane 9. The aircraft 9 is loaded on the tractor 1. The stop has been adjusted so that the axis of rotation of the nosewheel of the airplane and the turret axis of rotation coincide and define a common axis of rotation 90 of the noted <figref idrefs="f0009">FIG. 24</figref> The turret is rotated about the axis of rotation 90 in a clockwise direction by an angle θ shown in <figref idrefs="f0009">FIG. 24</figref>. The turret includes means capable of measuring the rotation angle between two successive positions of the turret with respect to the gripper platform. It may for example comprise at least one sensor measuring an angular displacement of the turret with respect to the gripper platform. These measures can be used to change the direction of the tractor. The direction of the tractor is changed by rotating the modules following tractor wheels of a substantially vertical axis of rotation at the tractor frame. In particular, the rotation of each gear module of its own.

0068The tractor 1 shown in <figref idrefs="f0009">FIG. 24</figref> comprises six wheel units (3a, 3b, 3c, 3d, 3e, 3f) and each wheel module has a respective rotation angle. The front end of the plane 9 has rotated through an angle θ on the turret of the tractor grip platform, so that the nose wheels of the aircraft, if they were not loaded on the tractor, follow the rolling plane a circle with center and radius 94 whose length the distance in the center 94 and item 92 on the plane. Each wheel module (3a, 3b, 3c, 3d, 3e, 3f) has a rotation of its own and that allows him to tractor to follow the same direction would have followed the nose wheels of the aircraft.

0069It is particularly advantageous that each gear module has a rotation of its own. Indeed, the tractor changes direction while limiting the risk of understeer and oversteer parasites, avoiding serious incidents where the tractor would be left in the portfolio relative to the plane. The longitudinal axis of the plane is coincident with the longitudinal axis of the tractor, and so there is no relative angle between the aircraft and the tractor during a change of direction.

0070In addition, the driver retains steering sensations since the aircraft behaves as if the front of the aircraft was traveling. In particular, if the airplane has a landing gear leg back 4 inclined with respect to the vertical, the gripper platform 20 has been inclined as described above and the tires run on a plane perpendicular to the axis of the landing gear leg 4.

0071Advantageously, the rotation command of the front axle of the plane given by the pilot can be executed while keeping the wheels of the secure front end on the locking device and without this requiring any action on the locking device .

0072The angle of rotation between two successive positions of the turret with respect to the gripper platform is measured (S120). The rotation angle measured to estimate the direction the driver wishes to apply to the aircraft. tractor wheel modules then have their respective orientations are changed (S130) so as to transcribe the angle measured in the previous step.

0073During the phase where the aircraft is taken to the runway, the pilot steers the tractor in the same way as if the plane was powered by its engines. Advantageously, the method for towing an aircraft according to the invention requires no modification of the aircraft. In addition, such operations that are performed when the aircraft moves through its engines are not changed. Finally, the driver remains responsible to bring the aircraft to the runway.

0074The invention is not limited to the embodiments described by way of example. In particular, the contraction and relaxation of the cylinders can be reversed if the cylinders are positioned differently. In addition, the actuators may be electric actuators controlled electronically. The locking device may include other elements as a plate, rod, triangle and, as the tightening of the nose wheels of the aircraft is insured.