WO2004103063A1

WO2004103063A1 - Aerial saw

Info

Publication number: WO2004103063A1
Application number: PCT/AU2004/000305
Authority: WO
Inventors: Mark Geoffrey Crumblin; John William Lippitts
Original assignee: Mark Geoffrey Crumblin; John William Lippitts
Priority date: 2003-05-22
Filing date: 2004-03-12
Publication date: 2004-12-02

Abstract

An aerial saw (10) suspended from a helicopter (100) comprising: (a) saw blades (30) offset and overlapped with a small running clearance (b) power source (50), a pump (90) and tank (91) provided in a housing (40) at the lower end of the main beam (40) (c) spray nozzles for spraying tree-treating chemicals onto the blade teeth the aerial saw (10) being suspended from the helicopter (100) by a steerable boom (120) to compensate for yaw and drift of the helicopter (100) in windy operating conditions.

Description

AERIAL SAW

BACKGROUND OF THE INVENTION

1. Field of the Invention

THIS INVENTION relates to an aerial saw. The invention particularly relates, but is not limited to, an aerial saw (or airborne tree trimming apparatus) suitable for trimming trees, where the saw may be suspended from an aircraft, more preferably a helicopter.

2. Prior Art

Public and private utilities, particularly those operating electricity transmission lines and/or pipelines, commonly face difficulties in maintaining a clear, unobstructed path between trees lining the opposite sides of the "rights-of-way" through which the electricity lines, pipelines or other utility installations extend. This problem is particularly exacerbated in rugged, hilly or mountainous regions where access by land-based vehicles is limited or impossible. In addition, while offending branches may be trimmed by operators using "cherry pickers" mounted on land-based vehicles in less- rugged regions, the costs of operating the equipment and the man-power are quite considerable.

The use of aerial saws, or airborne tree trimming apparatus, suspended from helicopters, to trim the branches along the rights-of-way, has been known for approximately 20 years, and examples of known aerial saws or airborne tree trimming apparatus, are disclosed, inter alia, in (i) US 4,554,781 (ROGERS, deceased); (ii) US 4,815,263 (HARTUNG et al); and (iii) US 5,961 ,070 (BRADFORD et al). The respective airborne tree trimming apparatus disclosed in (i) ROGERS and (ii) HARTUNG et al have a plurality of vertically-aligned circular saws, rotatably joumalled on a main beam hanging substantially vertically downwards from the helicopter, (iii) BRADFORD et al discloses an aerial chainsaw suspended from a helicopter by a non-ridged suspension system.

While the respective airborne tree trimming apparatus disclosed in the three US Patents hereinbefore listed above can operate where land-based vehicle access is not possible, they have a number of limitations which adversely affect their performance and/or ease of operation in actual tree trimming operations.

Some of these limitations will be hereinafter described as follows: a) the power supply for the known airborne tree trimming apparatus is a hydraulic motor mounted at the top of the main beam (or at the top of the chainsaw bar), supplied with pressurised hydraulic fluid via hydraulic lines connected to the hydraulic pump in the helicopter. The additional power input, from the helicopter engine(s), required to drive the hydraulic pump may be so high as to make the operation of the helicopter marginal, particularly in mountainous regions, minimising (or even eliminating) any safety operation margins; b) the flexible hydraulic lines required to connect to the hydraulic motor on the tree trimming apparatus to the hydraulic pump in the helicopter are very expensive and are liable to damage from tree strikes; c) the mounting of the hydraulic motor at the top of the main beam raises the centre of gravity of the tree trimming apparatus and tends to make it more unstable in flight, exacerbating any swinging and/or twisting movements applied to the apparatus by contact with the tree(s) being trimmed; d) with the present apparatus, it is not possible to apply chemicals, eg., defoliants/herbicides/fungicides/insecticides to the trimmed branches to reduce any new growth and/or protect the cut branches against fungus and/or other pest attack; e) the adjacent circular saw blades are vertically aligned with a small vertical running clearance - if the main beam does not have sufficient vertical inclination so that the effective cutting paths of adjacent saw blades vertically overlap, then the portion of any branches passing through the clearance will not be effectively cut, and a second pass of the tree trimming apparatus may be required to complete the trimming of these branches; and f) it is difficult to manipulate /control the tree trimming apparatus during the initial landing and take-off procedures.

Other limitations will become apparent to the skilled addressee in the following description.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an aerial saw

(or airborne tree trimming apparatus) which does not derive its power input from the helicopter (or supporting aircraft).

It is a preferred object of the present invention to provide an aerial saw which has an internal power source. It is a further preferred object to provide an aerial saw where the power source and associated equipment are provided in al least one housing at the base of the main beam to improve the stability of the main beam. It is a further preferred object of the present invention to provide an aerial saw where the housing is operable to co-operate with a landing/take-off base unit.

It is a still further preferred object to provide a steering mechanism which enables the aerial saw to be selectively rotated relative to the longitudinal axis of the helicopter.

It is a still further preferred object of the present invention to provide an aerial saw where the circular saw blades are horizontally- displaced, but vertically overlapping to ensure complete cutting of the tree branches. It is a still further preferred object of the present invention to provide an aerial saw having a plurality of spray nozzles operable to spray chemicals, such as growth retardant chemicals and fungicides onto the trimmed branches.

Other preferred objects of the present invention shall become apparent from the following description.

In one aspect, the present invention resides in an aerial saw (or airborne tree trimming apparatus) including: an elongate main beam, operable to be suspended substantially vertically below a helicopter (or other supporting aircraft); a plurality of circular saw blades mounted on respective axles rotatably joumalled in or on the main beam; at least one housing at the lower end of the main beam; a power source in the housing; and a transmission system operable to transfer drive from the power source to the axles to rotatably drive the circular saw blade.

In a second aspect, the present invention reside in an aerial saw (or airborne tree-trimming apparatus) including: an elongate main beam operable to be suspended substantially vertically below a helicopter (or other supporting aircraft); a plurality of circular blades mounted on axles rotatably joumalled on or in the main beam; a power source mounted in a housing on the main beam; and a transmission system operable to transfer drive from the power source to the axles to drive the circular saw blades wherein: adjacent circular saw blades are horizontally displaced, with a small running clearance, and are vertically overlapping.

Preferably, the power source is an internal combustion engine which drives the transmission system. While the transmission system may comprise a hydraulic pump interconnected to one or more hydraulic motors driving the axles, it is preferred that the transmission system comprises a plurality of belt and pulley drives, preferably where the axle of a first circular saw blade operably drives the axle of a second saw blade immediately above it, and the axle of the second saw blade drives the axle of the third saw blade immediately above it. The circular saw blades may all be driven in the same rotational direction. However, the transmission system may incorporate a reversing mechanism so that the circular saw blades are alternately driven in opposite rotational directions. Preferably, in addition to containing the power source, the housing also contains a fuel tank for the engine and any cooling system therefor.

Preferably, the housing also contains one or more tanks containing chemicals (eg., growth retardant / fungicides / herbicides / insecticides), the tank being connected to a pump driven by the engine, the pump being operably connected to a plurality of spray nozzles where each spray nozzle directs chemicals onto the overlapping teeth of a pair of the circular saw blades.

Preferably, the lower portion of the housing is shaped, eg., in an inverted pyramid or inverted cone shape (or inverted frusto-pyramid, or inverted frusto-cone shape) to co-operate with a complementary shaped hopper hingedly mounted on a landing base. Preferably, the landing base also has at least one main beam engaging support, spaced from the hopper, and operable to receive and support the main beam when the housing is engaged in the hopper and the main beam is lowered to a substantially horizontal position, eg., on landing. Preferably, the or each support has roller means operable to engage the main beam to enable the main beam to be moved away from the hopper, to release the housing from the hopper during a take-off operations. Preferably, the circular saw blades are horizontally-spaced with a small running clearance (eg., 5-10mm) (allowing for any flexure of the circular saw blades during the cutting of the branches) and are vertically overlapped by a distance, preferably at least equal to the depth of the saw teeth on the periphery of the circular saw blades.

Preferably, the circular saw blades are releasably mountable on hubs on the respective axles to enable easy removal of the circular saw blades, eg., for re-sharpening of the teeth or replacement of damaged saw blades. Preferably, spacers or fingers, eg., of plastics- or other low- friction material, are provided between the overlapping saw blades, and between the main beam and the saw blades, to limit flexing of the saw blades when cutting the branches, to prevent interference between the blades and/or the main beam. The spray nozzles for the chemicals may be mounted in the spacers or fingers to direct the chemicals onto the saw teeth.

Preferably, recesses or notches are provided in the main beam, aligned with the overlap between adjacent pairs of the circular saw blades to provide additional clearance between the main beam and any tree branches being trimmed by the blades.

In a third aspect, the present invention resides in a steerable suspension system for an aerial saw (or airborne tree trimming apparatus) including: a boom; a first attachment member rotatably joumalled at an upper end of the boom, operable to releasably engage a cargo hook or load support member on the helicopter (or other supporting aircraft); and drive means on the boom or on the first attachment member operable to rotate the first attachment assembly relative to the boom to selectively steer an aerial saw, attached to the boom, relative to the helicopter.

Preferably, the first attachment assembly includes a clevis member with a shaft rotatably joumalled in the upper end of the boom; and the drive means is an hydraulic or electric motor mounted on the clevis member with a pinion gear operable to drive a sun gear provided about the upper end of the boom.

Preferably, the clevis member is arranged for hinged, non- rotational, connection to the cargo hook or load support member. Preferably, the boom incorporates two or more telescopic stages of a torque tube; and stop means on the telescopic stages prevent relative rotation between the telescopic stages when the torque tube is in an extended configuration. Preferably, a second attachment assembly is provided at a lower end of the boom to connect the boom to a main beam of the aerial saw.

Preferably, the second attachment assembly includes a second clevis member, connected or integral with a lower end of the boom, with vertically spaced upper and lower pins interconnecting spaced legs of the second clevis member; and a mounting flange, receivable in the second clevis member, having a vertical lower slot and a curved upper slot with an apex, the upper and lower pins being received in the upper and lower slots and operable, in a first position, to form a rigid connection between the second clevis member and the mounting flange and in a second position, forming a hinged connection between the second clevis member and the mounting flange.

Preferably, in the first position, the upper pin is engaged in the apex of the upper slot and the lower pin is engaged in an upper end of the lower slot; while in a second position, the upper pin is engaged in a curved portion of the upper slot and the lower pin is engaged at a lower end of the lower slot.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic side view of the aerial saw, suspended from a helicopter prior to engagement with the landing base; FIG. 2 is a similar view showing the aerial saw during the takeoff procedure;

FIGS. 3 and 4 are respective schematic front and side views of the aerial saw;

FIG. 5 is a side view of the lower portion of the aerial saw on a larger scale;

FIG. 6 is a sectional side view of the lower portion of the aerial saw;

FIG. 7 is a schematic perspective view showing a portion of the drive between adjacent circular saws;

FIG. 8 is a sectional view showing the mounting of the circular saw on the main beam;

FIG. 9 is a perspective view showing an internal view of the main beam; FIG. 10 is a perspective view showing operating of a spray nozzle adjacent a pair of the circular saw blades;

FIG. 11 is a perspective view of a blade spacer finger and spray nozzle of a second embodiment;

FIG. 12 is a schematic side view showing the aerial saw mounted on an alternative landing base;

FIG. 13 is a schematic side view showing the attachment of an alternative embodiment of the suspension unit to a helicopter;

FIG. 14 is a schematic side view showing an alternative saw embodiment of the aerial saw during the take-off procedure; FIGS. 15 and 16 show schematic side and top plan views of a drive mechanism for rotatable feet for the aerial saw;

FIGS. 17 and 18 are top plan views of alternative drive mechanisms for the feet;

FIG. 19 is a sectional side view of a torque tube for the suspension system of FIGS. 13 and 14;

FIGS. 20 and 21 are respective side and end (part-sectional) views of the connection of the torque tube to the cargo hook on the helicopter; FIG. 22 is a part-sectional view of the upper end of the torque tube;

FIG. 22A is a side view of an alternative top mounting for the boom;

FIG. 23 is a perspective view of the lower end of the torque tube; and

FIG. 24 is a side view corresponding to FIG. 23.

DETAILED DESCRIPTION OF THE

PREFERRED EMBODIMENTS

Referring to FIGS 1 to 6, the aerial saw 10 is arranged to be suspended from a helicopter 100 via a suspension apparatus 120 to be hereinafter described.

On the ground, the aerial saw 10 is supported by a base unit 150 also to be hereinafter described.

The aerial saw 10 has an elongate main beam 20 formed of substantially C-channel aluminium - see FIG.9 - to which is fitted a cover plate (not illustrated).

A plurality of circular saw blades 30 with saw teeth 31 about their periphery (see FIG. 7) are provided along the main beam 20 in an alternating horizontally-displaced, vertically-over-lapping arrangement illustrated more clearly in FIGS. 3, 4 and 5. A running clearance 32 (eg., 5mm wide) is provided between the adjacent overlapping teeth 31 to accommodate any flexing of the circular saw blades 30 whilst trimming the tree branches. The vertical overlap between the blades 30 is preferably equal to, or greater than, the depth of the saw teeth 31.

The suspension system 120 is operable to enable the main beam 20 to be suspended substantially vertical below the helicopter 100 allowing movement of the main beam along an axis substantially parallel to the longitudinal axis of the helicopter but limiting any rotational movement of the main beam 20 about its longitudinal axis, relative to the helicopter 100.

A housing 40 is provided atthe lower end of the main beam 20 and has a lower portion 41 substantially inverted pyramid or inverted conical shape which is complementary to a hopper 151 hingedly mounted on a support post 152 at one end of the landing base 150. The landing base 150 may be supported by two or more ground engaging wheels and may be provided with a draw bar (not shown) for towing from location to location.

A pair of main beam support posts 153 are provided at spaced locations along the chassis 154 of the landing base 150 and each support post 153 is provided with a yoke provided with roller(s) to operably receive and support the main beam 20 when the aerial saw is in the landed position shown in FIG.2. The roller(s) on the support posts 153 allow the main beam 20 to be pulled forwardly of the landing base 150 to release the housing 40 from the hopper 151. At the end of a tree trimming operation, the helicopter pilot locates the housing 40 co-axially with the hopper 151 and then lowers the housing 40 into engagement thereto. As the helicopter 100 moves forwardly relative to the landing base 150, the hopper 151 tilts from the position shown in FIG. 1 to the position shown in FIG. 2 until the main beam 20 is supported by the yokes on the support posts 153.

For take-off, the helicopter 100 moves forwardly to pull the main beam 20 forwardly a short distance relative to the landing base 150 to release the housing 40 from the hopper 151. As the helicopter 100 pulls the top of the main beam 20 upwardly, the hopper 151 is raised to locate the housing 40 until the main beam 20 is substantially vertical and the helicopter pilot then gains altitude to fully release the housing 40 from the hopper 151.

As shown schematically in FIG. 6, the housing 40 contains an internal combustion engine 50 which is provided with a fuel tank 51 and a cooling system 52.

The engine 50 drives a transmission system 60, to be hereinafter described in more detail, which drives the circular saw blades 30.

The engine 50 also selectively drives a pump 90 which draws chemicals from a chemical tank 91 and pumps the chemicals, eg., fungicides/growth retardant chemicals, under pressure, via a pipe system 92, connected to respective spray nozzles 93 - see FIG. 10 - which spray the chemicals onto the overlapping teeth 31 of each pair of circular saw blades 30. The sprayed chemicals are distributed by the saw blades 30 onto the trimmed tree branches, eg., to deter future growth/prevent fungal attack on the cut branch ends and/or deter insects, etc.

The operation of the engine 50, transmission 60 and the pump 90 may be controlled by a control system 95 which receives control signals from a control unit 101 mounted in the helicopter - see FIG. 6. As illustrated more particularly in FIG. 5, both the leading and trailing edges of the main beam 20 may be provided with recesses or notches 21 substantially aligned with the overlap of the adjacent pairs of saw blades 30 to provide additional clearance between the main beam 20 and the tree branches 30 to provide additional clearance between the main beam 20 and the tree branches as they are trimmed in the region of the overlap of the saw blades 30.

Referring to FIGS. 7 and 8, each saw blade 30 is releasably mounted on a hub 32 at one end of an axle 33 rotatably joumalled in bearings 34, 35 mounted on the main beam 20. Each saw blade 30 is positively located on its hub 32 by a plurality of studs 36 and a locking plate 37.

Each axle 33 is provided with a pair of pulleys 38, 39 operable to engage respective drive belts (eg., of the Gilmer-type) 61 which operably connect the axle 33 of one circular saw blade 30 with the axles 33 of the saw blades 30 immediately above and below it. The series of belts 61 provide a cascade drive in the transmission system 60 to enable the engine 50 to drive the circular saw blades 30. In the embodiment shown in FIGS. 6 and 7, all of the saw blades 30 are driven in the same rotational direction. In an alternative embodiment shown in FIG. 9, alternative saw blades 30 may be driven in the opposite rotational direction by providing a further pulley 62 so that the pulley 38, 39 on the axle 33 is driven by the outer face of the return run of the drive belt 61 to rotate the axle 33 in the opposite direction to the driving pulley 38, 39 of the preceding saw blades 30. The tension in the drive belt 61 may be maintained by a spring- loaded turk-arm assembly 63 illustrated in FIG. 7.

Referring to FIG. 11 , a plurality of main beam spacers 70 are provided at intervals along the main beam 20 and the spray nozzles 92 may be mounted in the main beam spacers 70 to direct the spray chemicals onto the teeth 31 of the saw blades 30. The main beam spacers 70 have an inner finger 71 , eg., of urethane- or like plastics material, to prevent any flexing of the saw blades 30 adjacent the main beam 20 from coming into contact with the main beam 20. An outer finger 32, of similar material, is interposed between the overlapping adjacent saw blades 30 to prevent them from coming into contact due to blade flexing.,

It will be readily apparent to the skilled addressee that the provision of the engine 50 on the aerial saw 10, to drive the circular saw blades 30, avoids the power-sapping drive, from the hydraulic pump on the helicopter motor, to drive the hydraulic pump on the saw, as has been previously used, and so the operational performance of the helicopter 100 is not compromised (or a smaller helicopter can be used).

Furthermore, the provision of the engine 50, its ancillaries 51 , 52, the chemical pump 90 and chemical tank 91 in a housing 40, at the base of the main beam 20, lowers the effective centre of gravity of the aerial saw 10 to increase its stability markedly over known saws (where a significant portion of the weight is provided at the top of the main beam).

In addition, the provision of the housing 40 at the lower end of the main beam 20 enables it to be configured to engage the hinged hopper 151 on the landing base 150 for safe landing and take-off operations.

Referring to FIG. 12, the landing base 150 may be modified by mounting it on a skid frame 159 which may be transported from site to site via a vehicle such as a tilt tray truck 160.

In certain locations, or in emergency situations, it may not always be possible to provide the landing base 150 for the aerial saw 10.

As shown in FIGS.4, 5 and 14, inverted T-shaped landing feet 154 may be provided at spaced intervals along the main beam 20, each foot 154 having a shaft 155 rotatably joumalled in the main beam 20.

When flying, the feet 154 are aligned with the main beam 20, but for landing, the shafts 155 are rotated through 90° so that the feet 154 are transverse to the main beam 20. FIGS. 15 and 16 show a first embodiment of a mechanism for rotating the shafts 155, where a hydraulic ram 156 (or electric solenoid) moves a rod 157 in a reciprocating motion. A lever arm 158 on each shaft 155 has a pin 159 received in a slot 160 in a link 161 on the rod 157 to form a "lost-motion" connection.

In the alternative embodiment in FIG. 17, the rod 157 is provided with racks 162 which engage pinions 163 on the shafts 155; while in FIG. 18, a respective electric or hydraulic motor 164 has a drive gear 165 engaged with a pinion 163 to rotate the shaft 155. In the embodiment of the aerial saw 10 shown in FIGS. 1 , 2, 3 and 6, the saw 10 is suspended from the helicopter 100 by a suspension system 120, generally comprising a cable or boom which enables the main beam 20 of the aerial saw 10 to be suspended substantially vertically, for movement parallel to the longitudinal axis of the helicopter 100 but limiting any rotational movement of the main beam 20 about its longitudinal axis, relative to the helicopter 100.

The helicopter 100 can be subject to cross wind situations, when trying to maintain a constant cutting direction parallel to the utility (ie., power lines) and the tendency is for the helicopter 100 to drift in the direction of the wind, or crab or yaw into the wind.

This can be corrected by the pilot applying directional or yaw control with the anti-torque pedals in the aircraft or helicopter, but there is a limited amount of input available before the pilot reaches the anti-torque or yaw control limit of the aircraft or helicopter.

The present invention provides a steerable suspension system

220 which enables the pilot to steer the aerial saw 10 straight in the direction of cutting, while the aircraft or helicopter 100 crabs into the wind. This steerable suspension system 220 will now be described with reference to FIGS. 13, 14 and 19 to 24.

The steerable suspension system 220 employs a boom comprising a telescopic torque tube 230 which has two or three telescopic stages 231 which non-rotatably interlock when the torque tube 230 is fully extended. At the upper end of the torque tube 230, a clevis 232 is releasably connected to a cargo hook 105 hingedly connected to a supporting spindle 106 extending below the helicopter 100, the cargo hook 105 being allowed to non-rotatably move in a plane parallel to the longitudinal axis of the helicopter 100. As the helicopter 100 takes off, or lands, the torque tube 230 can swing upwardly or downwardly relative to the helicopter 100.

As shown in more detail in FIGS. 19 to 22, the uppermost telescope stage 231 of the torque tube 230 has a hub 236 rotatably joumalled, via bearings 233, about a shaft 234 on the clevis 232. A sun gear

235 is connected to the hub 236 by studs 237, which also secure the hub

236 to the uppermost stage 231 of the torque tube 230.

As shown in FIG. 21 , a pinion gear 237 on an hydraulic motor 238, mounted on one side of the clevis 232, is operable to drive the sun gear 235 to rotate the torque tube 230 relative to the clevis 232, and thereby relative to the cargo hook 105 (and the helicopter 100).

By operation of the motor 238, which is controlled by the pilot, eg., via radio control through control system 95, the pilot can "steer" the aerial saw 10 along a line parallel to the utility to compensate for varying degrees of yaw or drift of the helicopter due to different wind strengths, air currents, etc.

It will be readily apparent to the skilled addressee that the steering of the torque tube could be effected by rotation of the spindle 106, supporting the cargo hook 105, relative to the helicopter 100. FIG. 22A illustrates an alternative embodiment of the cargo hook 105a, where a flange 105b secures the cargo hook 105a to a plate 106b at the lower end of spindle 106a on the helicopter. If the spindle 106a is joumalled relative to the helicopter, a hydraulic motor (not shown) mounted to the underside of the helicopter can operably drive a sun gear 106c about the plate 106b.

Diagonally arranged stops 239 within the torque tube 230 prevent relative rotation of the torque tube stages 231 when the torque tube 230 is fully extended, but allow at least some relative rotation therebetween when the torque tube 230 is at least partially collapsed, as in FIG. 23.

The torque tube 230 has a releasably lockable connection to the upper end of the main beam 20 of the saw 10, so that the torque tube

230 and main beam 20 are rigidly interconnected where the aerial saw 10 is operational, but are hingedly connected during take-off and landing, as per FIG. 14.

The lowermost stage 231 of the torque tube 230 has a clevis assembly 240, where the respective legs of the clevis assembly 240 are connected by vertically spaced pins 241 , 242.

A mounting flange 243 is secured to the upper end of the main beam 20, by suitable fasteners not shown.

A vertical lower slot 244 is provided intermediate the mounting flange 243 and operably receives the lower slot 242 of the clevis assembly 240.

An upper slot 245 in the mounting flange 243 has a lower curved portion 246 connected to an upper portion 247 with an apex 248.

The upper slot 245 receives the upper pin 241 of the clevis assembly 240.

When the main beam 20 is suspended from the torque tube 230 for operational use of the aerial saw 30, the upper pin 241 is engaged in the apex 248 of the upper slot 245 and the lower pin 242 is engaged at the upper end of lower slot 244 to provide a rigid connection between the main beam 20 and torque tube 230.

On landing, the pins 241 , 242 move downwardly relative to the slots 244, 245, the lower pin 242 is engaged at the lower end of the lower slots 244 and the upper pin 241 can move to the curved lower portion 246 of upper slot 245 to allow hinged connection between the clevis assembly 240 and mounting flange 243, and thereby between the torque tube 230 and main beam 20. The operation is reversed on take-off.

The releasably lockable connection between the torque tube 230 (which forms part of the suspension system 220) and the main beam 20 of the aerial saw 10 simplifies the take-off/landing procedure, which enables the aerial saw 10 to be steered, as hereinbefore described. The specific arrangement of the circular saws 30 on the main beam 20 ensures a clean, accurate cut of the trimmed branches; and the ability to apply chemicals to the trimmed branches ensures that future growth of the trimmed trees may be retarded and the branches may be protected from fungal or insecticide or other pest attack. With the improved overall stability of the aerial saw 10, and the improved individual cutting of the tree branches where any pair of saw blades 30 overlap, an operator can ensure a clean, accurate trimming operation in a single pass, avoiding the need for secondary passes to cut any trimmed branches not cleanly cut in the first pass.

In addition, the ability to "steer" the aerial saw relative to the helicopter enables the saw to be operated in conditions not possible with existing saws.

It will be readily apparent to the skilled addressee that various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.

Claims

CLAIMS:

1. An aerial saw (or airborne tree trimming apparatus) including: an elongate main beam, operable to be suspended substantially vertically below a helicopter (or other supporting aircraft); a plurality of circular saw blades mounted on respective axles rotatably joumalled in or on the main beam; at least one housing at the lower end of the main beam; a power source in the housing; and a transmission system operable to transfer drive from the power source to the axles to rotatably drive the circular saw blade.

2. An aerial saw as clamed in Claim 1 , wherein: the power source is an internal combustion engine which drives the transmission system; and the transmission system comprises a hydraulic pump interconnected to one or more hydraulic motors driving the axles, or a plurality of belt and pulley drives, where the axle of a first circular saw blade operably drives the axle of a second saw blade immediately above it, and the axle of the second saw blade drives the axle of the third saw blade immediately above it.

3. An aerial saw as claimed in Claim 2 wherein: the circular saw blades are all driven in the same rotational direction or where the transmission system incorporates a reversing mechanism so that the circular saw blades are alternately driven in opposite rotational directions.

4. An aerial saw as claimed in any one of Claims 1 to 3, wherein: in addition to containing the power source, the housing also contains a fuel tank for the engine and any cooling system therefor.

5. An aerial saw as claimed in Claim 4 wherein: the housing also contains one or more tanks containing chemicals, such as growth retardant / fungicides / herbicides / insecticides, the tank being connected to a pump driven by the engine, the pump being operably connected to a plurality of spray nozzles where each spray nozzle directs chemicals onto the teeth of a pair of the circular saw blades.

6. An aerial saw as claimed in any one Claims 1 to 5, wherein: the lower portion of the housing is shaped of an inverted pyramid, inverted cone shape, inverted frusto-pyramid, or inverted frusto- cone shape, to co-operate with a complementary shaped hopper hingedly mounted on a landing base; and the landing base has at least one main beam engaging support, spaced from the hopper, and operable to receive and support the main beam when the housing is engaged in the hopper and the main beam is lowered to a substantially horizontal position.

7. An aerial saw as claimed in Claim 6 wherein: the or each support has roller means operable to engage the main beam to enable the main beam to be moved away from the hopper, to release the housing from the hopper during a take-off operations.

8. An aerial saw (or airborne tree-trimming apparatus) including: an elongate main beam operable to be suspended substantally vertically below a helicopter (or other support aircraft); a plurality of circular blades mounted on axles rotatably joumalled on or in the main beam; a power source mounted in a housing on the main beam; and a transmission system operable to transfer drive from the power source to the axles to drive the circular saw blades wherein: adjacent circular saw blades are horizontally displaced, with a small running clearance, and are vertically overlapping.

9. An aerial saw as claimed in Claim 8 wherein: the power source is an internal combustion engine which drives the transmission system; and the transmission system comprises a hydraulic pump interconnected to one or more hydraulic motors driving the axles, or a plurality of belt and pulley drives, where the axle of a first circular saw blade operably drives the axle of a second saw blade immediately above it, and the axle of a second saw blade drives the axle of the third saw blade immediate above.

10. An aerial saw as claimed in Claim 9 wherein: the circular saw blades are all driven in the same rotational direction, or the transmission system incorporates a reversing mechanism so that the circular saw blades are alternately driven in opposite rotational directions.

11. An aerial saw as claimed in any one of Claims 8 to 10 wherein: the housing also contains one or more tanks containing chemicals such as growth retardant / fungicides / herbicides / insecticides, the tank being connected to a plurality of spray nozzles where each spray nozzle directs chemicals onto the overlapping teeth of a pair of the circular saw blades.

12. An aerial saw as claimed in any one of Claims 7 to 11 , wherein: the circular saw blades are horizontally-spaced with a small running clearance, to allow for any flexure of the circular saw blades during the cutting of the branches and are vertically overlapped by a distance, at least equal to the depth of the sawteeth on the periphery of the circular saw blades.

13. An aerial saw as claimed in Claim 12 wherein: the running clearance is 5-10mm.

14. An aerial saw as claimed in any one of Claims 8 to 13 wherein: the circular saw blades are releasably mountable on hubs on the respective axles to enable easy removal of the circular saw blades, for re-sharpening of the teeth or replacement of damaged saw blades.

15. An aerial saw as claimed in any one of Claims 8 to 14 wherein : spacers or fingers, of plastics- or other low-friction material, are provided between the overlapping saw blades, and between the main beam and the saw blades, to limit flexing of the saw blades when cutting the branches, to prevent interference between the blades and/or the main beam.

16. An aerial saw as claimed in Claim 10 wherein: the spray nozzles for the chemicals are mounted in the spacers or fingers to direct the chemicals onto the saw teeth.

17. An aerial saw as claimed in any one of Claims 8 to 16 wherein: recesses or notches are provided in the main beam, aligned with the overlap between adjacent pairs of the circular saw blades to provide additional clearance between the main beam and any tree branches being trimmed by the blades.

18. A steerable suspension system for an aerial saw (or airborne tree trimming apparatus) including: a boom; a first attachment member rotatably joumalled at an upper end of the boom, operable to releasably engage a cargo hook or load support member on the helicopter (or other supporting aircraft); and drive means or on the boom or on the first attachment member operable to rotate the first attachment assembly relative to the boom to selectively steer an aerial saw, attached to the boom, relative to the helicopter.

19. A system as claimed in Claim 18 wherein: the first attachment assembly includes a clevis member with a shaft rotatably joumalled in the upper end of the boom; and the drive means is an hydraulic or electric motor mounted on the clevis member with a pinion gear operable to drive a sun gear provided about the upper end of the boom.

20. A system as claimed in Claim 19 wherein: the clevis member is arranged for hinged, non-rotational, connection to the cargo hook or load support member.

21. A system as claimed in any one of Claims 17 to 20, wherein: the boom incorporates two or more telescopic stages of a torque tube; and stop means on the telescopic stages prevent relative rotation between the telescopic stages when the torque tube is in an extended configuration.

22. A system as claimed in any one of Claims 17 to 21 wherein: a second attachment assembly is provided at a lower end of the boom to connect the boom to a main beam of the aerial saw.

23. A system as claimed in Claim 22 wherein: the second attachment assembly includes a second clevis member, connected, or integral with, a lower end of the boom, with vertically spaced upper and lower pins interconnecting spaced legs of the second clevis member; and a mounting flange, receivable in the second clevis member, having a vertical lower slot and a curved upper slot with an apex, the upper and lower pins being received in the upper and lower slots and operable, in a first position, to form a rigid connection between the second clevis member and the mounting flange and in a second position, forming a hinged connection between the second clevis member and the mounting flange.

24. A system as claimed in Claim 23, wherein: in the first position, the upper pin is engaged in the apex of the upper slot and the lower pin is engaged in an upper end of the lower slot; while in a second position, the upper pin is engaged in a curved portion of the upper slot and the lower pin is engaged at a lower end of the lower slot.