A hovercraft sprayer

Philips tech. Rev. 38, No. 1

It may happen that crops have to be sprayed ata time when the ground is so wet that conventionalsprayers, which are drawn by tractors, would causetoo much damage to soil and crops. It occurred to PaulBrown and Alistair Wolf (Newcastle upon Tyne, Eng-land) that a small hovercraft, which they had builttogether with some fellow pupils as a practical exer-cise in mechanical engineering, would be much bettersuited for this purpose. The total weight of a hover-craft, a vehicle which can tra vel over land just as easilyas over water, is distributed by an air cushion over aso much larger surface than in the case of vehicles onwheels that damage to soil or crops in wet periodswould be ruled out. To be used as a sprayer the hover-craft, which was originally built to take part in races,had to be modified in some points. The modificationinvolved a number of problems, and the jury was mostimpressed by the manner in which Brown and Wolfsucceeded in solving them with the means they had attheir disposal. The result of this work is described intheir entry entitled 'The hovercraft sprayer' . In itsfirst trials their hovercraft fully proved its usefulnessas an agricultural spraying machine.

11

A hovercraft in its present form can only be usedas a light transport vehicle and for racing. Its load-carrying capacity is relatively small. At first sight,therefore, a hovercraft would not seem to be sosuitable as a spraying machine, because in order tospread pesticides homogeneously it is necessary tospray large quantities of dilute solutions. Moreovera hovercraft is not sufficiently manoeuvrable to beable to reach all corners of a field with the same ease.The great advantage of the hovercraft, however, isthat, even in adverse conditions, it can still travelover crops without causing any appreciable damage.

Nowadays there are atomizing installations avail-able that need much less liquid per hectare than con-ventional sprayers - about 10 litres of liquid per'hectare against several hundred litres. The use ofsuch atomizers enabled Brown and Wolf to over-come the difficulties presented by the load-carryingcapacity of the hovercraft.

A hovercraft is normally steered with the aid ofrudders that are fitted behind the propellors. Sincethere is no direct contact with the ground, however,it tends to drift sideways in the bends, like a-sailingship without a keel, and there is also the risk that itmay spin around on its axis. The young scientistsovercame this steering disability by providing the

Front wheel of the hovercraft sprayer showing the extended spokes that grip the ground.

12 Philips tech. Rev. 38, No. 1

hovercraft with three light wheels with extendedspokes which grip the ground and thus give thenecessary stability. Two of these wheels are steer-able. They are coupled with the rudders in such away as to minimize the lateral forces on the wheels.There is one front wheel, which is provided with atachometer so that the driver, by selecting speed,spray-fluid pressure and atomizer setting, can givethe correct dosage of pesticide. All wheels are free tomove vertically, and they are held on the ground byslight spring pressure.Trials were set up to check the evenness of atom-

ization. This was necessary because there was a pos-sibility that air escaping from the air cushion coulddisturb the uniformity of atomization.At a later stage, to ensure proper dosage of the

atomized liquid, a peristaltic pump was used, coup-led to the front wheel, so that the stream of liquid isdirectly affected by the forward speed. The frontwheel was also fitted with a brake, to keep the hover-craft under better control on slopes.

Minor improvement of some features, togetherwith various other planned improvements, mean thatthis hovercraft may be regarded as a prototype of anew sprayer, which has distinct advantages over con-ventional sprayers in difficult conditions.

The hovercraft sprayer.

Test plots laid out to check the evenness of atomization.Marker poles at the edges of the field and moles buried inthe ground are used to mark the position of the plots.

j~Edge .r cultivated

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I 3 met~e/

PosLtion in which hovercraft travelled

Each plot900 mms sq.

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~GT,950

I"~ I- - - - - - - --"2,. metres 1/' ----1',/ 5 metres

Mole buried 1 metre out ineach direction frem outsidecorner of each square

NOT 'IQ SCALE

/ ~~C~:~c:a6~~r,:as;rom/ edge of sprayed field.

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Marker post in Fence

15,. metres