METHOD AND TRACTOR FOR TOWING AEROPLANES

Abstract: When towing large and heavy aeroplanes at great speed by means of a tractor (1) supporting the nose wheel (6 and 7) of the aeroplane, it may easily happen that the nose wheel (6 and 7) is acted on by impermissable forces, especially in the transverse direction. The tractor according to the invention has means (30, 31, 32) for sensing the transverse force and means for keeping the tranverse force within permissible limits by applying a suitable steering correction to the tractor which correction cannot be changed by either pilot or tractor operator.

Description: METHOD AND TRACTOR FOR TOWING AEROPLANES , The invention relates to a method for towing an aeroplane by means of a tractor where the nose wheel of the aeroplane is supported on and perhaps secured to said tractor and where the tractor is operated by a tractor operator. When towing aeroplanes and particularly large and heavy commercial aeroplanes at great speed safety is a very important factor because of the huge masses being moved. A great part thereof is moreover fuel. It is therefore important to ensure that no damage is done to the aeroplane and in this connection primarily to the nose wheel undercarriage whereto the tractor is usually coupled in some way or other. From the specification to US patent no. 4,113,041 there is known a method whereby the nose wheel is secured against impermissible forces occurring in the longitudinal direction, the force transmitted between tractor and aeroplane being continuously sensed and the sensing signal being applied for continuously controlling the power or braking of the tractor so that the force is constantly being kept within a permissible interval, ie. a force will not occur which the nose wheel structure cannot absorb. This known technique is applicable by a method of the present type as well as by a method where aeroplane and tractor are coupled by means of a towing bar. In both cases the nose wheel steering of the aeroplane has been put out of operation. In the latter case the nose wheel is running on the ground and it has of course been dimensioned so as to absorb the forces that may occur when running on the ground even if due to side wind the wheel should hop and slide sideways. The situation is different when as described by the present method the nose wheel of the aeroplane is secured on the tractor. The frictional force on the nose wheel against the roadway is much larger in this case because the weight of the tractor must be taken into consideration, and therefore much larger trans¬ verse forces on the nose wheel structure may occur. The object of the present invention is therefore to provide a method whereby it is possible to ensure that this structure is not exposed to impermissible transverse forces when being towed. The method according to the invention is characteris- tic in that the sideways force exerted by the nose wheel on the tractor is continuously sensed and that when the sensing signal exceeds a specific permissible value, a steering correction is applied to the tractor said correction being dependent on the excess in such a manner that the excess is at least eliminated independent of the manoeuvers of the tractor operator. It is thereby possible to ensure that no overloading occurs in the lateral direction. It should be noted that a certain amount of transverse forces will naturally in many cases, for example by side wind, be necessary to keep the course just as is the case by ordinary taxiing with the plane. When being towed the nose wheel steering of an aeroplane is generally put out of operation and the nose wheel can be freely turned by the tractor. Should the pilots find when towing that due to the steering described in the present invention - and that is in practice by strong side wind - the aeroplane deviates from the desired course then they will have to make use of two other means for correction, viz. the rudder and the main wheel brakes. As is well known, both these means are pedal controlled, a forward movement of for example the left foot activating the rudder to the left and a tipping of the left foot braking the port main wheel thus making the aeroplane turn aport. Generally, the pilot will first move his foot all the way forwards, ie. swing the rudder as far as possible, * and should this not be sufficient, then tip the foot further, ie. stepping with the toe and braking the main wheels in one side till the desired effect is obtained. At high speeds this is of course a reflex movement made by the pilots. The present invention therefore enables the pilots to steer in quite the same manner as they normally do which is an advantage since they must have the superior responsibility. The nose wheel structure is thus as mentioned above secured against impermissible forces occurring in the transverse direction. In the longitudinal direc¬ tion it is possible to make provisions against imper- missible transverse forces by means of a safety release but a preferred embodiment of the method is disclosed in claim 2. This embodiment is in keeping with the invention because also in this case the pilots will have to concentrate on the same control means, viz. the pedals. They only have to apply both pedals at one and the same time should they find the speed too high or otherwise find any cause for braking to a stop. It should be noted, moreover, that not only does it make it possible to correct the course by a gust of side wind but the invention will of course also make it possible for the pilots to actively perform the steering. The invention moreover relates to a tractor for performing the method and which is of the kind provi¬ ded with a platform for supporting and perhaps secur- ing the nose wheel. This tractor is characteristic in having force sensing means arranged in or by the platform or by its sides for sensing the sideways thrust against the nose wheel, and a calculator and control unit that on the basis of the sensing is adapted to act on the steering wheels of the tractor with a steering correction when the force exceeds a specific value so that the excess is at least eliminated. One embodiment is characteristic in that the platform is mounted on a transverse slide. It is thereby possible by suitably lubricating the guides or bear¬ ings of the slide to obtain a good measuring basis for the transverse force. An improvement of this embodiment is characteristic in that at its sides the slide is provided with vertical plates for abutting the sides of the nose wheel and the mutual distance thereof being adjust- 1_ΛJ EΛ OMPI able, the means for measuring the transverse force being constituted by one or more hydraulic piston cylinders that are connected to the slide and substan¬ tially retaining same and there being means for measuring the pressure in the cylinders.lt is thereby possible in a simple manner to perform the desired continuous measuring at the same time as the nose wheel can be retained in a firm position. An improvement of this construction is characteristic in that at its rear end the slide is provided with a leaf hinged at the bottom said leaf in its raised position being adapted to abut the rear of the nose wheel and being retained and controlled by a pressure cylinder. It is thereby possible to measure the transverse force quite correctly. Should one think of the hinged leaf or back plate being secured to the tractor, then consideration would have to be taken to the friction between the plate and the nose wheel when there is a pull between tractor and aeroplane and so the measuring of the transverse force would never be correct. If the tractor is of the type which can steer on all four wheels with steering deflection in the same direction, ie. with so-called crab steering, it may be characteristic in that the calculator and control unit is adapted to give steering correc¬ tion to all the tractor wheels. It is thereby possible to obtain a quicker control, ie. swinging in of the tractor to the desired position, particularly at low speed in sharp curves where the pilots might -BUREA OMPI wish to take a course different from that chosen by the tractor operator. Furthermore, the tractor according to the invention can be provided with a tableau indicating the type of aeroplane for which the calculator and control unit is set. In connection with such a tableau the tractor accord- ing to the invention may on the outside at a visible place be provided with means for programming the type of aeroplane over and above corresponding means in the cab of the tractor, and that the calculator and control unit can be adapted to lock the drive means of the tractor as long as the two programmings are not identital. It is thereby possible to obtain double security that the tractor is programmed for the correct type of aeroplane. It is for example possible to let another person than the tractor operator perform the adjustment on the outside. Finally, the tractor according to the invention may be provided with means for measuring a torque or the reaction stemming from such torque around the axis of the nose wheel leg and means for releasing the connections between aeroplane and tractor and/or to block any further motion of the tractor should such torque occur. As mentioned above, the nose wheel steering of an aeroplane is not operative when towing with a tractor, ie. the nose wheel can be freely turned within its OMPI turning angle. This measure serves the purpose of securing the nose wheel structure against overloading should the tractor operator when manoeuvering the plane happen to turn the nose wheel past the permissi¬ ble limit, ie. having the effect that it hits a stop. The invention will be further explained with refer¬ ence to the drawing wherein: Fig. 1 is a side view of an embodiment of a tractor according to the invention, Fig. 2 is a top view of the tractor, Fig. 3 is an enlarged top view being to some extent schematic of the central part of the tractor, and Fig. 4 is a chart illustrating socalled input and output of a possible calculator and control unit for a tractor according to the invention. Figs. 1 and 2 can be seen together and show a tractor 1 having four steerable wheels 2, 3, 4, 5. There is moreover shown a set of wheels 6, 7 being the set of nose wheels of an aeroplane. For practical reasons the aeroplane itself is not shown. This set of wheels 6 and 7 is supported on a slide 8 that in its turn rests on a platform 9 on three transverse guides or bearers 10, 11 and 12. The slide 8 is flush with a chute 13 with a part 14 that can be raised and which is provided with a roller 15 so that the nose wheels 6 and 7 of the aeroplane can be wheeled up onto the platform 9 of the tractor by backing the tractor under the nose wheels 6 and 7. In front the nose wheels 6 and 7 abut a vertical front plate and at the back they are retained by a pivotable back plate 17. On the side of the tractor there is a tableau 40 showing the type of aeroplane which the tractor is presently programmed to tow. Furthermore, there is an outside panel 41 for the programming. On the other side of the tractor there may be provided similar arrangements. Fig. 2 only shows the parts securing the set of nose wheels 6 and 7 in the longitudinal direction or in the direction of travel. Fig. 3 shows the parts retaining the set of nose wheels 6 and 7 in greater detail and therefore also the parts retaining the set of nose wheels 6 and 7 in the transverse direction and which are decisive of the present invention. The port nose wheel abuts on its outside a plate 19 secured to a vertical hinge 18, said plate 19 being fastened on the slide 8 that is movably mounted on the guides or bearers 10, 11 and 12. The starboard nose wheel 7 abuts on its outside a forwardly mounted plate 20 and a rearwardly mounted plate 21 which are both movably mounted in the transverse direction in piston cylinders 22 and 23 complete with pres¬ sure pipes 24 and 25. These plates 20 and 21 are also mounted on the slide 8. Finally, the back plate 17 is mounted on the slide 8 and its tipping action and the retaining thereof in the substantially vertical position is provided for by two piston cylinders 26 and 27 arranged in parallel having a common pressure pipe 28. - UREA OMPI Moreover, by the action of a piston cylinder 29 the plate 19 can be moved to the position shown in dotted lines where the nose wheels 6 and 7 are to be pressed up onto the slide and so ensure that the nose wheels 6 and 7 are correctly arranged. Finally, the slide 8 is secured in a position around the centre of a double-acting piston cylinder 30 complete with closed pressure pipes 31 and 32 for sensing the transverse force. The pulling force can be sensed through the pressure pipe 28 which is of course also closed when towing. The pressure pipes 24 and 25 are activated when the nose wheels are in place in the longitudinal direction thereby pushing the nose wheels against the plate 19 where¬ after the pressure pipes 24 and 25 are closed. Should a difference in pressure between these two pressure pipes then occur, it means that a torque around a vertical axis is applied to the nose wheel. In this connection it is assumed that friction between nose wheels and slide 8 is eliminated, for example by greasing the surface of the slide or by designing it with a smooth surface. This is also advantageous when locking or fixing the nose wheels by activating the piston cylinders 22 and 23. Fig. 3 schematically shows input and output of the calculator and control unit. The input is as shown the column to the left, whereas the output is the right column of the Figure. A speedometer is required for the input because 1_ΛJR£Ac OMPI Λ,^ WIPO the steering correction for neutralising a given force will depend on the speed. Furthermore, signals are given from pulling force and transverse force sensors, respectively, and from a torque sensor. The signal from the driving controls of the tractor will likewise have to pass the calculator and control unit because this is the signal which according to the invention may require correction. Finally, the calculator and control unit must have a signal for the type of aeroplane to be towed and perhaps also with an indication of the gross weight. For ensuring that this information is correct it may be programmed two places by two different persons each one of them having a key, if so desired. One place may be by the panel 41 and the other in the cab of the tractor. For further security the programming is shown on the tableau 40. The calculator and control unit can then give a primary steering signal without correction corres¬ ponding to the steering manoeuver made by the tractor operator. Should this manoeuver, however, prove to be such that it overloads the nose wheel undercar¬ riage with an impermissible transverse force, the calculator and control unit will give a steering correction on which the tractor operator will have no influence and which will cause the transverse force on the undercarriage of the nose wheel to be reset within the permissible limit. In practice measures are of course taken so that this limit is never exceeded. The calculator and control unit can moreover be designed in such a manner that it will effect an emergency release of the nose wheel of the aeroplane should the pulling force exceed the permissible limit. Furthermore, it may be designed so as to block the tractor movement and perhaps effect an emergency release should there occur a torque on the nose wheel undercarriage. Finally, the calculator and control unit will control the tableau indicating the type of aeroplane which the tractor is set to tow.

Claims: PATENT CLAIMS 1. Method for towing an aeroplane by means of a tractor where the nose wheel of the aeroplane is supported on and perhaps secured to said tractor and where the tractor is operated by a tractor operator, c h a r a c t e r i s e d in that the sideways force exerted by the nose wheel on the tractor is continuously sensed and that when the sensing signal exceeds a specific permissible value, a steering correction is applied to the tractor said correction being dependent on the excess in such a manner that the excess is at least eliminated, independent of the manoeuvers of the tractor opera- tor. 2. Method according to claim 1, c h a r a c t e r ¬ i s d in that in a manner known per se the trans¬ mitted force between tractor and aeroplane in the longitudinal direction is continuously sensed and that on the basis thereof the engine and the brakes of the tractor are controlled in such a manner that the force is kept within a permissible interval, preferably within the traction area. 3. Tractor for performing the method according to claim 1 and which is provided with a platform for supporting and perhaps securing the nose wheel, c h a r a c t e r i s e d by force sensing means arranged in or by the platform or by its sides for sensing the sideways thrust against the nose wheel, and a calculator and control unit that on the basis of the sensing is adapted to act on the steering wheels of the tractor with a steering correction when the force exceeds a specific value so that the excess is at least eliminated. 4. Tractor according to claim 3, c h a r a c t e r - i s e d in that the platform is mounted on a trans¬ verse slide. 5. Tractor according to claim 4, c h a r a c t e r ¬ i s e d in that at its sides the slide is provided with vertical plates for abutting the sides of the nose wheel and the mutual distance thereof being adjustable, the means for measuring the trans¬ verse force being constituted by one or more hydraul¬ ic piston cylinders that are connected to the slide and substantially retaining same and there being means for measuring the pressure in the cylinders. 6. Tractor according to claim 5, c h a r a c t e r ¬ i s e d in that at its rear end the slide is provid- ed with a leaf hinged at the bottom said leaf in its raised position being adapted to abut the rear of the nose wheel and being retained and controlled by a pressure cylinder. 7. Tractor according to claims 3, 4, 5 and 6 and which is of the type which can steer on all four wheels with steering deflection in the same direc¬ tion, ie. with so-called crab steering, c h a r a c ¬ t e r i s e d in that the calculator and control unit is adapted to give steering correction to all the tractor wheels. 8. Tractor according to claims 3, 4, 5, 6 or 7, c h a r a c t e r i s e d in that on its outside it is provided with one or more tableaux indicating the type of aeroplane for which the calculator and control unit is set. 9. Tractor according to claim 8, c h a r a c t e r ¬ i s e d in that on the outside of the tractor at a place where a tableau is visible there are arranged means for programming the type of aeroplane over and above corresponding means in the cab of the tractor and that the calculator and control unit is adapted to lock the drive means of the tractor as long as the two programmings are not identical. 10. Tractor according to one or more of the preceed- ing claims, c h a r a c t e r i s e * d in means for measuring a torque or the reaction stemming from such torque around the axis of the nose wheel leg and means for releasing the connections between aeroplane and tractor and/or to block any further motion of the tractor should such torque occur. -fUREA

Inventors: BIRKEHOLM MOGENS, BIRKEHOLM, MOGENS
Applicants: BIRKEHOLM MOGENS, BRUUN SVEND AAGE JOHAN, BIRKEHOLM, MOGENS, BRUUN, SVEND, AAGE, JOHAN
Application year: 1984
Main classification: B64F1
IPC codes: B64F1