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Aviation History
1955
1955 - 0351.PDF
FLIGHT, 18 March 1955 351 AGRICULTURAL AIRCRAFT ... equipped airfield up to 40 miles from the dropping site, thus savingtransport of fertilizer and loading crew by road to an outlying air- strip, and in the long run saving the farmer the cost of main-taining the airstrip on his land. The large load would, in theory at least, make repeated sorties unnecessary. This issue of lightversus heavy aeroplanes has recently been clouded, however, by the strenuous opposition, raised before the Air LicensingAuthority in Wellington, to an application by a new company to operate Bristol 170s. This opposition was based on political ratherthan practical issues, since it was feared that the firm in question would be financed by the stock firms controlling the supply ofsuperphosphate—of which there is still an inadequate supply— and would therefore operate at an advantage over its competitors. Aside from the politics of the matter, there are neverthelessdisadvantages in the use of heavy aeroplanes. Such drawbacks include a scarcity of farms large enough to make use of the six-ton load of fertilizer in one drop, and it is not unusual for farmers on adjoining smaller territories to hold opposing views upon theparticular fertilizer mixture that they feel their land requires. Other commercial users of established airfields have, moreover,expressed concern at the possible effect on grass airfields of operating big, heavily loaded aircraft in all weathers. A furtherdisadvantage, so far as the majority of the small operators are concerned, is of course the heavy initial cost of large aeroplanes. Most top-dressing companies throughout the Dominion aretherefore seeking to replace their Tiger Moths with other single- engined aircraft and a number of successors have been suggested.Examples of some of these are already in service and they include the Cessna 180, D.H.C.2 Beaver and Fletcher FU-24. The Cessna 180 (225 h.p. Continental 470-A) was not designedfor agricultural work; so with its rear seats replaced by a large hopper on arrival in New Zealand, it is very much the limousineturned tractor. Nevertheless, this attractive little monoplane has gathered a number of adherents on account of its reasonableprice of £6,450 complete, and its lively performance. There is a body of opinion in the industry which maintains that a highcruising speed such as the Cessna possesses is an advantage in reducing time wasted in reaching and returning from the droppingsites. It will be interesting, therefore, to compare at a later date the relative success of the Cessna 180 and the slower FletcherFU-24 employing the same engine. The D.H.C. 2 Beaver (450 h.p. Pratt and Whitney Wasp Junior),having been designed for bush flying under rugged conditions, adapts itself well to agricultural work. As in the case of theCessna, the rear seats are replaced by a large hopper, in this instance to carry approximately one ton of fertilizer. At the all-up weight of 5,490 lb permitted for agricultural operation in New Zealand the Beaver takes off in 250 yd. Tasks other thantop-dressing are provided for in the Beavers supplied to New Zealand contractors, and a particularly interesting feature is theprovision of electrically operated dropping racks for transporting fence-posts and similar loads to inaccessible sites. It is relevantto mention here that if the materials are brought up by horse transport—usually the only other means possible—a fence inNew Zealand hill country can cost anything from £1,000 to £1,250 per mile to erect. It therefore pays to employ an aerialcontractor to deliver the posts and equipment at strategic points from the air. Compared with the Tiger Moth, the Beaver is a medium;heavy aeroplane and, although the economics of its operation are very sound, it has the disadvantage of being comparativelyexpensive at around £16,000 complete. The Fletcher FU-24 (225 h.p. Continental 470-A) is a com-paratively untried newcomer here in New Zealand, but it has aroused considerable interest within the top-dressing industry bybeing the first aeroplane specially built for fertilizer-dropping. The design, by the Fletcher Aviation Corporation of Pasadena,California, is said to have been inspired by a specification for an agricultural aeroplane issued by the New Zealand Civil AirAuthority in 1951 (though in general arrangement it owes some- thing to earlier Fletcher designs). This specification called for,among other things, a disposable load of 1,000 lb, and a rate of climb of 1,000 ft/min and, although the FU-24 does not quitefulfil the latter requirement, its load-carrying properties exceed the specification. With half-a-ton of fertilizer, the take-off run isapproximately 200 yd. The choice of a nosewheel undercarriage and a high position for the pilot, level with the leading edge of (Above) The de Havilland Company of New Zealand's demonstration Beaver is seen here fitted with the dropping racks for externally carried loads, a feature of its agricultural modification. (Right) The Cessna 180 as a top-dressing monoplane. Loading of the hopper h effected through a circular aperture in the cabin root. The fitting of hoppers and the introduction of other necessary modifications are carried out in New Zealand. the wing, ensure good ground handling and all-round view. Al-though a single-seater, provision can be made for carrying the two loading-crew to and from the airstrip in a compartment aftof the hopper—which, as in the Cessna and Beaver, is behind the pilot. The New Zealand agents for the Fletcher monoplane,a large firm of agricultural-machinery importers, intend it to be the main feature of a top-dressing "system" which is to includeaircraft, trucks and special loaders, and transportable coverings for the superphosphate dumps at the airstrips. The price of theFU-24 in New Zealand is tentatively put at £6,600 [an attractive figure but, surely, a rather optimistic one?—Ed.]. Admirable as are the aircraft previously mentioned, not eventhe best of them is, in New Zealand farming opinion, the ideal machine for the job, since none of them has been designed fromthe beginning for agricultural work alone. In considering the design of an aeroplane of this class, it is necessary to forget muchthat has been commonplace in aeronautical progress since 1934. Aerial top-dressing, as practised at present, requires a long suc-cession of take-offs and landings varied upon the one hand by flights averaging 3^ minutes' duration of which from 8 to 40 secare actually devoted to the release of the load and, upon the other hand, by pauses to recharge the hopper on the airstrip—usually by means of some kind of mechanized conveyor. The breadth of the swath of fertilizer laid is determined by die heightand ground speed of the aircraft, and it is usual to work at 50ft, following the hill contours, at a speed of about 80 m.p.h. Thelaying of anything from two to six hundredweight per acre may be called for. The primary need is thus for an economical load-lifter, capableof carrying one ton of top-dressing and having a low capital cost. High speed being of little significance, a high-lift wing sectioncould be used and flaps omitted from the design to reduce costs, since a wide speed range is not required. A landing speed ofabout 35 m.p.h., with a cruising speed in the eighties, would be adequate. High winds interfere with the accuracy of dropping andthe weather conditions under which aeroplanes are required to fly on this work are not, therefore, exacting. In the interests ofmanoeuvrability, a low wing-loading would be necessary, and there seems no reason why a biplane formula should not beemployed. It used to be held that biplanes could be built more ruggedly than monoplanes of the same structure weight, and
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