A METHOD OF PREVENTING OVERLOAD OF THE NOSE WHEEL OF AN AEROPLANE DURING TOWING AND AN AEROPLANE TRACTOR

Abstract: A method and an aeroplane tractor for preventing overload of the nose wheel of an aeroplane comprising a platform intended for receiving and securing the nose wheel of an aeroplane, and where the platform is anchored to be displaceable in the longitudinal direction of the tractor away from a predetermined reference position along a path having a lowermost point relative to the aeroplane tractor, and having forwards as well as backwards as seen in the longitudinal direction of the aeroplane a gradient which increases progressively relative to the horizontal plane with the distance from the lowermost point, and that means are provided for measuring the displacement reference position, and in that means for limiting the engine output and/or the braking effect transmitted to the tractor wheels as a function of the displacement distance measured for the platform whereby the transmission of force between the tractor and the nose wheel of the aeroplane is maintained within a predetermined accepted range.

Description: A method of preventing overload of the nose wheel of an aeroplane during towing and an aeroplane tractor The present invention relates to a method of preventing overload of the nose wheel of an aeroplane, wherein the nose wheel of the aeroplane is positioned on and secured to a platform arranged on an aeroplane tractor intended therefor, and wherein the aeroplane tractor comprises means for limiting the engine output or the braking effect transmitted to the wheels of the aeroplane tractor with a view to regulating the force transmitted from the aeroplane tractor to the nose wheel of the aeroplane. The invention further relates to an aeroplane tractor of the type that comprises a platform arranged for receiving and securing the nose wheel of an aeroplane, and means for limiting the engine output and/or the braking effect transmitted to the tractor wheels with a view to regulating the force transmitted from the tractor to the nose wheel positioned on the tractor. Today, many different embodiments are known of aeroplane tractors provided with means for limiting the force transmitted to the nose wheel of the aeroplane, and wherein the nose wheel of the aeroplane is positioned on a platform on the tractor, or is towed by the tractor by means of a towing rod or the like device. In the known tractors e.g. force sensors may be used whereby the force which is transmitted to the nose wheel of the aeroplane is measured directly, or alternatively an indirect measurement is carried out e.g. by measurement of the acceleration of the tractor or the momentum transmitted to the tractor wheel. Examples of such tractors are described in e.g. US patent No. 4,113,041. However, in particular in case of high-speed towing where the importance of the dynamic load of the nose wheel of the aeroplane will increase as the towing speed increases, the known tractors are associated with the problem that the automatic regulation of the engine output and/or the braking effect to the wheels of the aeroplane wheel cannot timely compensate for an excessive force transmitted to the nose wheel of the aeroplane whereby the frame or other suspensions of the nose wheel may be damaged. At the same time the known tractors and methods presuppose that the operating system of the tractor for regulating the engine output and/or the braking effect is fed with data which are specific to the individual type of aeroplane to be towed since, of course, the maximum transmission of force to the nose wheel in the horizontal direction depends of the relevant aeroplane type. For instance, the towing by mistake of a given aeroplane which does not correspond to the data on which the tractor's regulation of the engine output and/or the braking effect is based, may result in damage to the aeroplane . In the light of this, it is the object of the present invention to provide a method for the towing of aeroplanes, and an aeroplane tractor whereby the adverse effect of the transmission of dynamic forces to the nose wheel of the aeroplane is reduced while simultaneously ensuring a high degree of security that no mistakes occur during the aeroplane towing procedures. This is obtained with the method given in claim 1 and the use of an aeroplane tractor according to claim 2, respectively. Thereby the nose wheel of the aeroplane is anchored in such a manner relative to the aeroplane tractor that the nose wheel of the aeroplane relative to the aeroplane tractor may be displaced along a path extending in the longitudinal direction of the tractor, said path having such configuration that it has a lowermost point relative to the plane tractor and has a gradient that increases progressively relative to the horizontal plane with the distance from the lowermost point, forwards as well as backwards seen from the lowermost point and in the longitudinal orientation of the aeroplane, whereby a force is caused to act upon the nose wheel via the platform in the longitudinal direction of the tractor when the nose wheel moves away from a predetermined reference position, said force increasing with the distance of the nose wheel from the predetermined reference distance, and that the distance to the predetermined reference position is measured, and that the engine output and/or the braking effect transmitted to the tractor wheels are limited as a function of the distance measured in such a manner that the transmission of force between the aeroplane tractor and the nose wheel of the aeroplane is maintained within a predetermined accepted range. Hereby it is obtained that, in case of a given displacement of the nose wheel of the aeroplane relative to the tractor, the nose wheel of the aeroplane is influenced by a horizontally acting force which is a fixed percentage of the vertical load on the nose wheel, irrespective of the magnitude of the vertical load. Hereby an upper limit is defined for the horizontal load on the nose wheel of the aeroplane as a percentage of the vertical load on the nose wheel whereby e.g. the same percentage may be used for all aeroplane types to be towed thereby reducing the risk of mistakes substantially. Simultaneously the displaceable platforms permits that some allowance is made for the influence of the dynamic force without presupposing a quickly reacting operating system for regulating the engine output and/or the braking effects transmitted to the tractor's wheels. According to a preferred embodiment the platform is suspended like a pendulum relative to the tractor' s frame. Hereby a substantially circular path is obtained for the platform movement relative to the aeroplane tractor. Thereby, the suspension may be established exclusively by means of swivel joints and bearings which are particularly preferred from a maintenance point of view. Alternatively, the platform may be provided with abutment means which are arranged for displaceable abutment on at least a support ramp secured relative to the aeroplane tractor, said support ramp having a lowermost point relative to the aeroplane tractor, and forwards as well as backwards from the lowermost point and in the longitudinal direction of the aeroplane tractor it has a gradient that increases progressively with the distance from the lowermost point relative to the horizontal plane. Hereby it is possible that the ramp may be designed to define a ' path for the movement and displacement of the ramp, said path having a configuration which varies from e.g. circular. Moreover, it is also possible in a simple manner to provide different ramps for one and the same platform, and which have different embodiments corresponding to any actual need. The means for the measurement of the displacement of the platform away from the predetermined reference position may in a simple manner consist of a position transducer or an angle position transducer. According to further preferred embodiment, the upper side of the platform is provided with a swivel disc with means for supporting and securing the nose wheel of the aeroplane in such a manner that the swivel disc allows turning of the aeroplane's nose wheel relative to the longitudinal direction of the aeroplane. Thereby the tractor may advantageously be provided with means for measuring the angular rotation of the swivel disc relative to the longitudinal direction of the tractor, and the tractor has pivotable guide wheels and means for turning the guide wheels of the tractor relative to the longitudinal direction of the tractor substantially proportionally with the angular rotation measured for the swivel disc. Thereby the tractor may easily be operated from the aeroplane cockpit by usual turning of the nose wheel of the aeroplane. In this context, it is a further advantage that means are provided for remote-controlling the engine output transmitted to the tractor wheel from the aeroplane cockpit. Hereby the braking effect as well as the engine output may be controlled from the aeroplane cockpit, since the braking effect on the tractor wheels may by activated by activation of the aeroplane's own braking system. The invention will now be described in further detail with reference to the drawings, wherein: Figure 1 is a side view of an embodiment of an aeroplane tractor according to the invention, Figure 2 is a perspective principle sketch of an embodiment of a platform for an aeroplane tractor according to the present invention, Figure 3 is a perspective principle sketch of an alternative embodiment of a platform for an aeroplane tractor according to the present invention, and Figure 4 outlines the relation between vertical and horizontal forces at a platform according to any one of Figures 1, 2 or 3 with a circular path course. Thus, Figure 1 is a partially sectional side view outlining an aeroplane tractor according to the invention where the tractor is provided with a set of front wheels 2 and a set of rear wheels 3, at least one of these sets of wheels being controllable in a commonly known manner for turning the tractor. Between the frontmost set of wheels 2 and the rearmost set of wheels 3, the tractor 1 is provided with a platform 4 that supports the nose wheel 5 of an aeroplane as outlined. In a manner known per se the tractor is provided with an access ramp 6 for the nose wheel 5 of the aeroplane, said access ramp 6 being optionally elevated or lowered. Moreover, the tractor has a driver's cab 7. The platform 4 for receiving the nose wheel 5 of the aeroplane is suspended like a pendulum from the frame of the aeroplane by means of two sets of supporting joints 8,9, each of which has an upper securing point 10, whereby the supporting joints 8,9 are pivotally secured to the platform 4. Thereby the platform 4 may swing like a pendulum relative to the frame of the tractor 1 and in the longitudinal direction of the tractor 1, and according to the invention a position transducer 12 is provided which may record the degree of swinging of the platform 4 relative to the frame of the tractor 1. Here, a linear position transducer which may be used according to the present invention is shown, but the invention will be described in further detail below in connection with an angle transducer instead of the position transducer shown here. Moreover, Figure 1 illustrates that the platform may be provided with a rotation disc 13 that allows the nose wheel 5 of the aeroplane to turn relative to the platform 4. Now reference is made to Figure 2 which is a perspective view outlining a platform 14 with a suspension which in principle corresponds to the platform shown in Figure 1 but without the swivel disc 13. Like in the platform 4 shown in Figure 1, this platform 14 is suspended in the supporting joints 15,16 which are at the bottom connected by joints to the platform 14 and at the top via the studs 17,18, and may be embedded in the frame of an aeroplane tractor. One of the supporting joints 15 is indicated by a dashed line in two further positions where the carrier joint 15 has been pivoted out around the stud 17 which may be secured to an aeroplane frame. In this way the entire platform which is suspended from such supporting joints may swing like a pendulum whereby a nose wheel arranged on the platform may be moved in a substantially circular arch relative to a tractor frame. An alternative embodiment of a suspension for a platform is now described with reference to figure 3 which is a perspective view outlining how a platform 19 is provided with wheels or rolls 20 each of which is arranged in a guideway 21 which is secured relative to the tractor and which forms a driveway or a rolling path 22 for each wheel or roll 20. In the embodiment shown, the driveway or rolling path 22 is a circular path, but it is within the scope of the invention for the path to have other shapes, e.g. parabolic paths, elliptic paths or path courses with variable gradients, and without eliminating the advantages associated with the present invention, the paths may be partially interrupted by plane sections, where required by circumstances. In certain cases, it may even be desirable that the tractor is provided with several curve paths which are interchangeable thereby providing one set of curves for one group of aeroplanes and another set of curves for another group of aeroplanes . Figure 3 further illustrates that the platform 19 is provided with a swivel disc 23 embedded into the top surface of the platform 19, where the swivel disc 23 is provided with a guide 24 for receiving the nose wheel of an aeroplane whereby the swivel disc 23 is caused to rotate relative to the platform 19 upon turning of the nose wheel of the aeroplane. According to a preferred embodiment, a transducer is arranged between the swivel disc 23 and the platform, which transducer is capable of recording the mutual angular setting between the swivel disc and the platform. This measured value may subsequently be used as input for a servocontrol system provided for the tractor wheel whereby the wheels on the tractor are caused to turn proportionally with the said angle measurement value. This is not shown in details in the drawings as it is obvious to the skilled person to provide practical solutions thereto on the basis of the above specifications. Reference is now made to Figure 4 which illustrates the relation between the vertical force F v with which the nose wheel of an aeroplane is influenced relative to the corresponding horizontal transmission of force F H as a function of the gradient θ for a rolling path 25 on which a roll 26 rests. The total reaction force R is, as shown in the drawings, the sum of the vertical force F v and Fn, and the angle between vertical and the reaction force R corresponds to the gradient of the rolling path 25 in the abutment point between the roll 26 and the rolling path 25, which again corresponds to the angle with which the roll is displaced outwards relative to the lowermost point on the circular rolling path and the centre for the circular arch of the rolling path. Consequently, the relation between the vertical force and the horizontal transmission of force is as follows: F H = F v *tanθ In this context F 7 is given by the weight imposed by the nose wheel when resting on the support and is thus comparatively constant, dynamic loads disregarded. Thus, F H depends on the angle θ. It follows that where a maximum accepted value for F H = F HHAX is given, and for F = FVMA a maximum accepted value for may be calculated using the formula: FHMAX = FVMAX * anσ A and it follows that noMAX = FHMAX/ VMAX • Thus, the use of an angle position transducer makes it easy to record whether Θ HA approaches a critical point where F HM AX exceeds the accepted value during towing. If it is desired to tow more types of aeroplanes with the same tractor, Θ,IA may either be selected as a constant which should consequently correspond to the smallest value for Θ HAX for the aeroplane types used. However, it may also be chosen to use a new Θ HAX each time another aeroplane or a different type of aeroplane is to be towed even though this may cause mistakes with ensuing damage to the planes . As stated, the calculation mode takes its starting point in the fact that the nose wheel of the aeroplane is conveyed along a circular path. Corresponding calculations may also readily be made for paths with other courses. Moreover, corresponding calculations may be carried out on the embodiments shown in Figures 1 and 2 which in a similar manner cause the nose wheel of an aeroplane to be displaced along a circular path relative to the aeroplane tractor. It is obvious that in the light of the present description, the skilled person may provide a number of different embodiments without eliminating the advantages of the present invention. Thus, as mentioned before it is possible to establish different path courses for the nose wheel of the aeroplane, and more or less complex suspensions for anchoring the nose wheel relative to the tractor are possible whereby the nose wheel may rock comparatively freely in the anchoring. As to the means necessary to realise the conceptual idea of the invention, they will be obvious to the person skilled in the art in the light of the above description.

Claims: C l a i m s 1. A method of preventing overload of the nose wheel of an aeroplane where the nose wheel of the aeroplane is arranged on and secured to a platform on an aeroplane tractor intended therefor, and wherein means are provided on the aeroplane tractor for regulating the engine output and/or the braking effect transmitted to the tractor wheel with a view to limiting the influence of the force transmitted from the tractor to the nose wheel of the aeroplane, c h a r a c t e r i z e d in that the nose wheel of the aeroplane is anchored in such a manner relative to the tractor that the nose wheel of the aeroplane may be displaced along a path that extends in the longitudinal direction of the tractor, said path having such configuration that it has a lowermost point relative to the aeroplane tractor and has, forwards as well as backwards seen from said lowermost point and in the longitudinal direction of the aeroplane, a gradient that increases progressively relative to the horizontal plane with the distance from the lowermost point, whereby the nose wheel is influenced via the platform with a force in a longitudinal direction of the tractor when the nose wheel moves away from a predetermined reference position, said force being increased with the distance from the predetermined reference position, and in that the distance to the predetermined reference position is measured, and that the engine output and/or the braking effect transmitted to the tractor wheels (is) are limited as a function of the measured distance in such a manner that the transmission of force between the tractor and the nose wheel of the aeroplane is kept within a predetermined accepted range. 2. An aeroplane tractor of the type that comprises a platform intended for receiving and securing the nose wheel of an aeroplane, and means for regulating the engine output and/or the braking effect transmitted to the tractor wheel with a view to regulating the force transmitted from the tractor to the nose wheel positioned on the tractor, c h a r a c t e r i z e d in the platform is anchored to be displaceable in the longitudinal direction of the tractor away from a predetermined reference position along a path having a lowermost point relative to the aeroplane tractor, and having forwards as well as backwards as seen in the longitudinal direction of the aeroplane a gradient which increases progressively relative to the horizontal plane with the distance from the lowermost point, and that means are provided for measuring the displacement distance of the platform away from the predetermined reference position, and in that means for limiting the engine output and/or the braking effect transmitted to the tractor wheels as a function of the displacement distance measured for the platform whereby the transmission of force between the tractor and the nose wheel of the aeroplane is maintained within a predetermined accepted range. 3. A tractor according to claim 2, c h a r a c t e r i z e d in that the platform is suspended in a pendulum-like manner relative to the tractor frame. 4. A tractor according to claim 2, c h a r a c t e r i z e d in that the platform is provided with abutment means which are arranged for displaceable abutment on at least one support ramp secured relative to the aeroplane tractor, the gradient of said support ramp having a lowermost point relative to the aeroplane tractor, and forwards as well as backwards seen from said lowermost point and in the longitudinal direction of the aeroplane tractor, it has a gradient that increases progressively relative to the horizontal plane with the distance from the lowermost point. 5. A tractor according to any one of claims 2 through 4, c h a r a c t e r i z e d that the means for measuring the displacement of the platform away from the predetermined reference position consists of an electrical position transducer. 6. A tractor according to any one of claims 2 through 4, c h a r a c t e r i z e d that the means for measuring the displacement of the platform away from the predetermined reference position consists of an angle position transducer. 7. A tractor according to any one of claims 2 through 6, c h a r a c t e r i z e d in that the top surface of the platform is provided with a swivel disc arranged for supporting and securing the nose wheel of the aeroplane in such a manner that said swivel disc allows turning of the nose wheel of the aeroplane relative to the longitudinal direction of the tractor. 8. A tractor according to claim 7, c h a r a c t e r i z e d in that means are provided for measuring the angle rotation of the swivel disc relative to the longitudinal direction of the tractor, and wherein the tractor is provided with turnable guide wheels, and means for turning the guide wheels of the tractor at an angle relative to the longitudinal direction of the tractor, substantially proportional with the measured angular rotation of the swivel disc. 9- A tractor according to any one of claims 2 through 8, c h a r a c t e r i z e d in that means are provided for remote-controlling the engine output transmitted to the tractor wheels from the cockpit of the aeroplane .

Inventors: BRUUN SVEND AAGE JOHAN, BRUUN, SVEND, AAGE, JOHAN
Applicants: BRUUN SVEND AAGE JOHAN, BRUUN, SVEND, AAGE, JOHAN
Application year: 1997
Main classification: B64F1
IPC codes: B64F1