GB2261640A

GB2261640A - Tractor for towing aircraft

Info

Publication number: GB2261640A
Application number: GB9124864A
Authority: GB
Inventors: Irving Melnick; Bo Elfstrom
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-11-22
Filing date: 1991-11-22
Publication date: 1993-05-26
Anticipated expiration: 2011-11-22
Also published as: GB9124864D0; GB2261640B

Abstract

The tractor has a main frame (104) carrying drive wheels (102), and supporting a pivotable beam (10). One end of the beam (10) carries a replaceable tool (20) for engaging an aircraft nose wheel assembly, and the other end is pivoted (12) to the frame (104). A piston and cylinder unit (14) is connected to the beam (10) and the frame (104). In use, the tool (20) engages the nose wheel assembly and then a lifting force is applied by way of the piston and cylinder unit (14) to pivot the beam (10) upwardly relative to the frame whereby a lifting force is applied to the nose wheel assembly just sufficient to lift the aircraft nose wheel assembly such that a proportion of the aircraft nose wheel weight is transferred to the driving wheels of the tractor whereby the effective weight of the tractor is increased enough to move the aircraft. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO THE TOWING OF AIRCRAFT The present invention relates to a method of towing an aircraft, and to a tractor for towing an aircraft.

It is becoming increasingly popular to tow aircraft when on the ground at airports as a fuel economy measure.

Because of this, a number of towing devices have been proposed or are in operation.

Until recently the common method of moving aircraft when on the ground has been to use heavy tractors, for example, weighing 20-60 tonnes, and to connect the tractor to the nosegear of the aircraft by way of a long tow bar.

Sometimes the tow bar has needed to be many metres long.

In such an arrangement, all the traction weight is supplied by the tractor's tare weight, and this therefore has to be kept high.

Lately, however, many tractor designs have been tested and proposed in which the nose wheel assembly of the aircraft is arranged to be captured and lifted prior to towing. With this arrangement, part of the weight of the aircraft, perhaps 10-15%, is transferred onto the tractor thus contributing considerably to its traction weight.

This, in turn, means that the tare weight of the tractor can be reduced. Such arrangements also have other advantages as compared to the use of a conventional tractor and tow bar, for example, fewer tow bars are needed, there is better stability of the resultant aircraft-tractor combination, and less personnel are needed for coupling the combination together.

However, these recently proposed towbarless tractors still have to be rather large, especially for aircraft having heavy loads on their nosegear, both relatively, perhaps 15% of total weight, and absolutely, perhaps 43 tonnes or more. The nosegear weight of such aircraft is also generally heavier than that needed for traction purposes.

It is an object of the present invention to provide a method of towing an aircraft which does not require the large tractor arrangements which are currently utilised.

According to a first aspect of the present invention there is provided a method of towing an aircraft in which a tractor is connected to the nose wheel assembly of the aircraft,- the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, the method comprising the steps of coupling said pivotable beam to the nose wheel assembly, actuating said lifting means to apply a lifting force to said beam and hence to said nose wheel assembly, the arrangement being such that the application of said lifting force to said nose wheel assembly applies a reaction force to said drive wheels, and then driving said drive wheels such that said tractor pushes or pulls the nose wheel assembly, and hence the aircraft, wherein said lifting force is arranged to be just sufficient to lift the aircraft nose wheel assembly.

The lifting force is arranged to put enough weight on the drive wheels to move the aircraft, without necessarily lifting the nose wheel assembly from the ground.

A method of the invention utilises a towbarless arrangement, the pivotable beam provided within the structure of the tractor being directly connected to the nose wheel assembly. Thus, the weight of the aircraft at the nose wheel assembly is applied to the tractor and thereby provides some of the weight needed in order to move the aircraft. However, because the lifting force is just sufficient to lift the nose wheel assembly of the aircraft only part of the weight of the aircraft at the nose wheel assembly is applied to the tractor. In this respect, it is generally sufficient to transfer just part of the weight to the tractor to provide sufficient traction wieght. The method has the advantage that it needs a much smaller relative lifting capacity than existing towbarless methods, and this means that the weight and complexity of a tractor to be employed in this method can be kept low.

The present invention also relates to a tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, wherein the tractor is arranged for use in a method as defined above.

In a further aspect, the invention relates to a tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor further comprising a tool carried by said pivotable beam for engagement with a nose wheel assembly of the aircraft, said tool comprising support means arranged, in use, to extend substantially horizontally and beneath a portion of said nose wheel assembly.

In a preferred embodiment said support means comprises a support block having an elongate groove or recess extending therein.

For example, said support means may comprise a support block arranged on said beam for reciprocable movement along at least one dimension of said support block. Preferably, said support block is reciprocable in a direction substantially prependicular to a pivot axis of said pivotable beam.

In an embodiment said support block is reciprocable in a direction substantially towards and away from a pivot axis of said pivotable beam.

Said support block may be arranged between at least two spaced, upstanding guide walls, and resilient material is provided between each side of said support block and an adjacent upstanding guide wall.

Preferably, said beam is connected to said frame by pivot means arranged at or near the centre of gravity of said tractor.

In an embodiment, said beam is elongate, having first and second spaced ends, and extends generally beneath said frame between said drive wheels, said tool being carried at or near said first end of the beam, and said beam being pivoted to said frame at or near its second end, and wherein said first and second ends of said beam are arranged on opposite sides of said drive wheels, and said lifting means act on said beam at or near said first end thereof.

The present invention also extends to a tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor further comprising a replaceable locking tool carried by said beam for engagement with a nose wheel assembly of an aircraft, said replacement locking tool comprising means for engaging said nose wheel assembly, and means for applying a lifting force to said nose wheel assembly.

Preferably, said replaceable locking tool comprises a body member carrying said lifting force applying means, and wherein said engaging means comprises a connector pivotably connected to said body member.

In an embodiment, said replaceable locking tool comprises a pair of rollers arranged to engage and lift said nose wheel assembly.

For example, said beam is elongate, having first and second spaced ends, and extends generally beneath said frame between said drive wheels, said tool being carried at or near said first end of the beam, and said beam being pivoted to said frame at or near its second end, and wherein said first and second ends of said beam are arranged on opposite sides of said drive wheels, and said lifting means act on said beam at or near said first end thereof.

The invention also extends to a tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor further comprising a tool carried by said pivotable beam for engagement with a nose wheel assembly of the aircraft, wherein said beam is elongate, having first and second spaced ends, and extends generally beneath said frame between said drive wheels, said tool being carried at or near said first end of the beam, and said beam being pivoted to said frame at or near its second end, and wherein said first and second ends of said beam are arranged on opposite sides of said drive wheels, and said lifting means act on said beam at or near said first end thereof.

In an embodiment, said beam is connected to said frame by pivot means arranged at or near the centre of gravity of said tractor.

Preferably, said tool carried by said beam is replaceable.

In an embodiment, said lifting means comprises a piston and cylinder unit pivotably connected to said beam at or near its first end, and pivotably connected to said frame.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a side elevation of a tractor for towing an aircraft using a method of the invention, Figure 2 shows a plan view of the tractor of Figure 1, Figure 3 shows on a larger scale a detail of the view of Figure 1, Figures 4 and 5 show a plan view from above and a side elevation of a pivotable beam arrangement provided in the tractor of Figure 1, Figure 6 shows a replaceable locking tool of the beam arrangement of Figures 4 and 5 in a non-connected condition, and Figure 7 shows an enlarged detail of the replaceable tool.

The tractor 100 shown in the drawings is to be connected to the nose wheel assembly of an aircraft to tow the aircraft. In this respect, it is intended that the tractor be directly coupled to the aircraft, rather than byway of a tow bar. The use of direct coupling enables the weight of the aircraft to be applied to the tractor and thereby provide effective weight for the tractor. This means that the tractor can be made relatively small and light, and yet be able to produce traction forces which are sufficient to move the aircraft.

The tractor has a main frame 104 which carries drive wheels 102, and which also supports a pivotable beam assembly, generally indicated 10, which can be seen more clearly in Figures 4 and 5. In the embodiment illustrated, the beam assembly 10 has a generally triangular configuration and is mounted at its apex to the frame 104 by way of a universal joint 12. This universal joint 12 enables pivoting movement of the beam assembly 10 substantially vertically and laterally. Towards its base, the beam assembly 10 carries an hydraulic piston and cylinder unit 14 which, as can be seen most clearly in Figure 3, is supported by and pivotably connected to the main frame 104 of the tractor 100. It will be appreciated that this piston and cylinder unit 14 can be actuated to pivot the beam assembly 10 vertically.The piston and cylinder unit 14 is connected to the beam 10 by way of a bearing 16 which enables the beam assembly 10 to be pivoted with respect to the piston and cylinder unit 14 when required. This enables the accommodation of lateral forces applied to the beam assembly 10 by steering the drive wheels 102 of the tractor.

At its base, the beam assembly 10 carries a replaceable locking tool generally indicated at 20. This locking tool 20 is arranged to couple the beam assembly 10, and hence the tractor, to an aircraft nose wheel assembly, and accordingly the locking tool 20 is sized and configured to conform to the particular type of aircraft to be towed.

It will be appreciated that the replaceable tool 20 may be exchanged when a different aircraft type is to be towed.

The replaceable locking tool 20 is supported on a longitudinal bar 22 which extends from the base of the beam assembly 10 substantially along the central longitudinal axis thereof. The bar 22 is preferably welded to the base of the beam assembly 10. The replaceable locking tool 20 comprises a support 24 which is affixed on the bar 22 and comprises a base plate 26 and spaced upstanding walls 28.

Preferably the plate 26 and the walls 28 of the support 24 are formed in one piece, and the support 24 is releasably connected to the beam assembly 10 and the bar 22 by any suitable means. A connector 30 is pivotably supported by the upstanding walls 28 of the support 24. In addition, a support block 32 is carried on the base plate 26. The connector 30 is arranged to engage the aircraft nose wheel assembly, whilst the support block 32 is arranged to apply lifting force thereto.

Figure 6 shows the replaceable locking tool 20 in its unengaged condition. It will be seen that the connector 30 comprises at least one lower jaw 34 with which one or more upper jaws may engage. The jaws 34 are arranged to engage around, and enclose a substantially horizontal bar 38 of the nose wheel assembly. The jaws 34 may be operated by hydraulic power, as is well known. Thus, it will be appreciated that the connector 30 may be selectively engaged and disengaged with the nose wheel assembly horizontal bar 38. The horizontal bar 38 is carried by a substantially vertical nose wheel strut 36 which extends between two nose wheels 40 of the assembly.

At its base, the strut 36 has a conventional jacking nipple 42. The support block 32 is provided with a transversely extending groove 44 into which the nipple 42 can engage. Thus, in the connected position of the locking tool 20, which is shown in Figure 3 and 5, the support block 32 engages the base of the strut 36, whilst the connector 30 is locked onto the horizontal bar 38 carried thereby. It will be appreciated that in this position the beam assembly 10 can be pivoted upwardly to apply lifting forces to the nose wheel assembly. It will also be appreciated that during the application of lifting forces, or during the subsequent movement of the aircraft the connector 30 is able to pivot relative to the upstanding walls 28 and hence to the beam assembly, by way of the pivoted connection to the walls 28.In this way, the nose wheel assembly is protected from the application of inappropriate forces. Similarly, relative movement of the nose wheel assembly longitudinally of the beam assembly 10 is enabled by the resilient coupling of the base of the strut 36 to the support block 32. In this respect, and as is most clearly seen in Figure 7, the support block 32 is positioned on the bar 22 between upstanding walls 46. A resilient material 48, such as rubber, is positioned between the support block 32 and the walls 46. In the illustrated embodiment, this arrangement allows reciprocable movement of the support block 32 longitudinally of the beam assembly 10, towards and away from the universal joint 12 at which the beam assembly 10 is pivoted. If required, it is possible to provide opposed upstanding walls extending transversely to the walls 46, and extending substantially longitudinally of the beam assembly 10, and to similarly interpose resilient material between the support block 32 and the transverse walls. In this manner, reciprocable movement of the support block 32 substantially transverse to the longitudinal axis of the beam assembly 10 is enabled.

In use, the tractor 100 is positioned around the nose wheel assembly of an aircraft to be towed so that the replaceable tool 20 can be engaged with the nose wheel assembly. In this respect, the particular design of the tractor can be chosen as is required and accordingly will not be described in detail herein. The particular tractor illustrated is a self-powered, self-contained arrangement having an engine, indicated at 106 for powering the drive wheels 102 by way of a gear box 108. In the embodiment illustrated the universal joint 12, forming the pivot point of the beam assembly 10 is sighted beneath the gear box 108 at or about the centre of gravity of the tractor.

At its rear, the tractor is provided with accommodation indicated at 114 for a driver, and as its front the frame 104 of the tractor is extended by two spaced beams 110, each supported by a respective steerable guide wheel 112. The beams 110 are provided to give stability to the tractor and to enclose the aircraft nose wheel assembly. In place of steerable guide wheels 112 it would be possible to use castors or other freely rotatable wheels.

When an aircraft is to be lifted the tractor is driven towards the front of the aircraft so that the beams 110 are positioned to either side of the nose wheel assembly.

Movement of the tractor underneath the aircraft body is continued until the tractor is located such that the replaceable tool 20 can be engaged with the nose wheel assembly as described above. Once the replaceable tool 20 has been so engaged, a lifting force is applied to the nose wheel assembly by way of the hydraulic piston and cylinder unit 14. For example, the piston and cylinder unit 14 may be connected to an hydraulic accumulator (not shown) carried by the tractor. Actuation of the piston and cylinder unit 14 causes the beam assembly 10 to be pivoted upwardly relative to the main frame 104 and applies a lifting force to the nose wheel assembly. This lifting force is arranged to be just sufficient to lift the aircraft nose wheel assembly, that is, to oppose the weight forces at the strut 36. However, it is not necessary to lift the wheels 40 clear of the ground. The arrangement of forces applied to the beam assembly 10 is such that the aircraft weight at the nose wheel assembly is transferred to the driving wheels 102 carried by the frame 104 of the tractor whereby the effective weight of the tractor is increased.

The hydraulic piston and cylinder unit 14 is controlled to maintain the appropriate lifting force to the nose wheel assembly irrespective of any forces applied thereto by movement over the ground.

The replaceable locking tool 20 as illustrated may be replaced by other arrangements for engaging and applying a lifting force to the nose wheel assembly. For example cooperating rollers may be utilised to grip and then lift the wheels.

It will be appreciated that variations in and modifications to the embodiments as described and illustrated may be made within the scope of the present invention.

Claims

1. A method of towing an aircraft in which a tractor is connected to the nose wheel assembly of the aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, the method comprising the steps of coupling said pivotable beam to the nose wheel assembly, actuating said lifting means to apply a lifting force to said beam and hence to said nose wheel assembly, the arrangement being such that the application of said lifting force to said nose wheel assembly applies a reaction force to said drive wheels, and then driving said drive wheels such that said tractor pushes or pulls the nose wheel assembly, and hence the aircraft, wherein said lifting force is arranged to be just sufficient to put enough weight on the drive wheels to move the aircraft without necessarily lifting the nose wheel assembly.

2. A tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor being arranged for use in the method as claimed in Claim 1.

3. A tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor further comprising a tool carried by said pivotable beam for engagement with a nose wheel assembly of the aircraft, said tool comprising support means arranged, in use, to extend substantially horizontally and beneath a portion of said nose wheel assembly.

4. A tractor as claimed in Claim 3, wherein said support means comprises a support block having an elongate groove or recess extending therein.

5. A tractor as claimed in Claim 3 or 4, wherein said support means comprises a support block arranged on said beam for reciprocable movement along at least one dimension of said support block.

6. A tractor as claimed in Claim 5, wherein said support block is reciprocable in a direction substantially prependicular to a pivot axis of said pivotable beam.

7. A tractor as claimed in Claim 5 or 6, wherein said support block is reciprocable in a direction substantially towards and away from a pivot axis of said pivotable beam.

8. A tractor as claimed in any of Claims 5 to 7, wherein said support block is arranged between at least two spaced, upstanding guide walls, and resilient material is provided between each side of said support block and an adjacent upstanding guide wall.

9. A tractor as claimed in any of Claims 3 to 8, wherein said beam is connected to said frame by pivot means arranged at or near the centre of gravity of said tractor.

10. A tractor as claimed in any of Claims 3 to 9, wherein said beam is elongate, having first and second spaced ends, and extends generally beneath said frame between said drive wheels, said tool being carried at or near said first end of the beam, and said beam being pivoted to said frame at or near its second end, and wherein said first and second ends of said beam are arranged on opposite sides of said drive wheels, and said lifting means act on said beam at or near said first end thereof.

11. A tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor further comprising a replaceable locking tool carried by said beam for engagement with a nose wheel assembly of an aircraft, said replaceable locking tool comprising means for engaging said nose wheel assembly, and means for applying a lifting force to said nose wheel assembly.

12. A tractor as claimed in Claim 11, wherein said replaceable locking tool comprises a body member carrying said lifting force applying means, and wherein said engaging means comprises a connector pivotably connected to said body member.

13. A tractor as claimeda in Claim 11, wherein said replaceable locking tool comprises a pair of rollers arranged to engage and lift said nose wheel assembly.

14. A tractor as claimed in any of Claims 11 to 13, wherein said beam is connected to said frame by pivot means arranged at or near the centre of gravity of said tractor.

15. A tractor as claimed in any of Claims 11 to 14, wherein said beam is elongate, having first and second spaced ends, and extends generally beneath said frame between said drive wheels, said tool being carried at or near said first end of the beam, and said beam being pivoted to said frame at or near its second end, and wherein said first and second ends of said beam are arranged on opposite sides of said drive wheels, and said lifting means act on said beam at or near said first end thereof.

16. A tractor as claimed in any of Claims 11 to 15, wherein said means of the replaceable locking tool for applying a lifting force to said nose wheel assembly comprise support means arranged, in use, to extend substantially horizontally and beneath a portion of said nose wheel assembly, and wherein said tractor is as claimed in any of Claims 4 to 8.

17. A tractor for towing an aircraft, the tractor comprising a frame carrying drive wheels, a beam pivotable with respect to said frame, and lifting means for pivoting said beam, and the tractor further comprising a tool carried by said pivotable beam for engagement with a nose wheel assembly of the aircraft, wherein said beam is elongate, having first and second spaced ends, and extends generally beneath said frame between said drive wheels, said tool being carried at or near said first end of the beam, and said beam being pivoted to said frame at or near its second end, and wherein said first and second ends of said beam are arranged on opposite sides of said drive wheels, and said lifting means act on said beam at or near said first end thereof.

18. A tractor as claimed in Claim 18, wherein said beam is connected to said frame by pivot means arranged at or near the centre of gravity of said tractor.

19. A tractor as claimed in Claim 17 or 18, wherein said tool carried by said beam is replaceable.

20. A tractor as claimed in any of Claims 17 to 19, wherein said lifting means comprises a piston and cylinder unit pivotably connected to said beam at or near its first end, and pivotably connected to said frame.

21. A method of towing an aircraft in which a tractor is connected to the nose wheel assembly of the aircraft, substantially as hereinbefore described with reference to the accompanying drawings.

22. A tractor for towing an aircraft, substantially as hereinbefore described with reference to the accompanying drawings.