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Aviation History
1985
1985 - 0037.PDF
Does it pay to spray? Agricultural aviation is more than "crop-spraying" and "crop-dusting". '•It covers the use of aircraft for assessment and development of natural resources, for forestry work, disease vector control, and the control of pollution. Types range from single-engined, single- seaters (fixed or rotary-wing), to con verted airliners. Pawnee, Agtruck, and Ag-Cat typify "ag" aircraft, and it is this class of aircraft that is considered here. Crop losses due to pests are believed to amount to about 10 per cent, ranging from about 5 per cent in Europe to maybe 20 per cent in parts of Asia. Africa loses about 5 per cent. These figures account for exist ing pest-control methods where they are already applied, but ignore losses due to poor soil condition, lack of irrigation, the use of low-yielding varieties, or similar causes. There is considerable scope for improvement. Ag aviation has a further role in securing these improvements. The aviation industry would like this role to be extensive. Specialist ag aircraft manufacturers are having as lean a time as the other general-aviation companies. Factory shipments of ag aircraft similar to those mentioned fell from 355 in 1980 to 72 in 1983. Although the fleets only partly comprise new or nearly new aircraft, the non-replacement of some means that the fleet does not represent properly the more capable and economic types available. Current utilisation is much less than optimal; budgetary constraints affect the amount of activity. For the small com panies that predominate the Western industry this is little short of disastrous. Profitability is marginal at the best of times. Ag aircraft operators need to utilise their resources fully to derive benefit from them, while their customers require value for money; it is the chicken and egg prob lem faced by operators the world over. Any method of treatment which is significantly more expensive than practical alterna- Agricultural aviation is more than just crop spraying. John Trevett, who has lectured at the International Centre for the Application of Pesticides, considers the economics of aerial application. fives is unlikely to find favour. Thus the choice is largely an issue of cost effectiveness. How good is aerial application compared with ground methods, and what is its relative cost? There can be circum stances where only one application method is possible. The site may be inac cessible to surface vehicles, it might be too remote to make it practical, or the time available to deal with a sudden crop infestation might be critical. In these examples, aerial application has real and substantial advantages. The prime feature of aerial application lies in its high productivity. This is regard less of whether labour manhours or elapsed time are considered. The problem with high productivity is the high total cost, including recovery of the high capital cost of the aircraft and its support equip ment, the relatively high energy cost of fuel (compared with other methods) and the cost of meeting safety regulations. Agricultural aviation is recognised as being the most dangerous form of general aviation, involving continuous manoeuvr ing close to the ground, and the applica tion of highly toxic and highly corrosive chemicals. Despite their high pro ductivity, there is the problem of the high cost of skilled aviation personnel com pared with general farm labouring. The economics involve a number of considerations—volume and cost of appli cants and how well they are applied; amount and cost of the flying required. The question of what quantity of which agent to apply is for the agronomists, while how to apply it requires decisions on how each sortie is to be flown. It is common practice to split the costing of operations into two main elements: one involving the work per formance of the aircraft operation (the so- called logistic formula) and another concerning the cost of the aircraft opera tion. Ag aircraft work performance is usually measured in minutes flown per hectare treated or similar units (or by its reciprocal: aircraft productivity in hectares per hour flown). Daily work performance in the field has to take account of several time elements —aircraft turnround time (to replenish the hopper or fuel tank), downtime for maintenance, and pilot duty-time. Limitations have been set by safety regulators as a condition of the aerial application certificate. The operation cost is a multiple of the appropriate aircraft productivity for the site to be treated, site area, and the average hourly operating cost. Considerable scientific effort has gone into developing "logistic" formulae. There are at least seven recognised methods! Perhaps the best-known is that of two UN Food and Agriculture Organisation researchers, Akesson and Yates. Each method divides the sortie into distinct elements. Four are common to all the formulae: ground time between spraying operations, ferry to/from the forward base to the spraying site, actual productive spraying time, and turning time between successive passes over the crop. Four of the seven researchers consider the interfield ferry between two or more spraying sites. Two add take-off and land ing phases, and one considers the time FLIGHT International, 5 January 1985 35
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