Aerial Fire-fighting Trials

New Zealand Journal of Agriculture, Volume 94, Issue 1, 15 January 1957, Page 9

Aerial Fire-fighting Trials

By

D. A. CAMPBELL,

Superintendent of Soil Conservation, Department of Agriculture Wellington

ERIAL fire-fighting trials organised by the Soil Conservation and Rivers Control Council ** and carried out by the James Aviation Company and the Aircraft Engineering Company at Rotorua and Rongotai respectively are as promising as the aerial topdressing and aerial fencing trials were at a comparable stage of development. Two hundred gallons of water is "bombed" at a fire in 2 seconds, compared with a delivery of 6| gallons per second from a big fire engine. This instantaneous effect of 100 gallons delivered per second on the target is overwhelming and can be delivered as frequently as the number of aircraft in the organisation permits and its intensity varied according to the height flown.

THE need for modernising firefighting methods in country areas arose from the restrictions placed on the burning of tussock grasslands and scrub lands by the Soil Conservation Act and the Forest and Rural Fires Act. To conserve soil and water more protective, absorptive, and erosionresistant vegetative cover is essential on farmed and unfarmed land, but such cover creates an increasing fire hazard, which must be matched by developing modern control techniques. The potentialities of aircraft have been confirmed by their efficacy in

mechanising hill country farming; aerial topdressing, seeding, weed spraying, fence dropping, and rabbit poisoning have revolutionised it and laid the foundations of a conservation farming system. The fleet of over 300 agricultural aircraft fitted with hoppers to distribute fertiliser constituted a potential quick-acting aerial fire brigade if techniques were developed for effective dropping of water on tussock, scrub, and even forest fires. Accordingly the author prepared proposals for trials in August 1955 and

these were supported by the Soil Conservation and Rivers Control Council’s Advisory Committee on Agricultural Aviation. The council made a grant to finance investigative and development trials. Rongotai Trials Arrangements were made with the Aircraft Engineering Company to use a Tiger Moth aircraft fitted with a spray tank and jettison equipment for the preliminary trials. The first runs to determine the pattern and density of spread in relation to the height flown revealed that the slipstream had a paramount influence on spread, even when the water was jettisoned. Several flights at heights of 15ft. to 50ft. were made across 2 rows of 15 rain gauges sft. apart. Though the rain gauges proved unsatisfactory, owing to the angle at which the “rain” fell, they did confirm the pattern of spread seen on a thoroughly saturated strip of grass some 20ft. . wide and 200 ft. long.

When the pattern and density of application had been determined straw spread generously on a strip 12ft wide and 20yds. long and ignited was used to simulate tussock fires. In successive trial flights across the fire the flames were replaced by a cloud of steam in the 22ft. wide strip on which water was dropped from the aircraft. Except where there were dense heaps of straw the fire was put out, but it rekindled slowly from the dense heaps which were not thoroughly wetted by the light “rain” from the aircraft. The rate of application of water was estimated at 400 gallons per acre, so that this light application of the equivalent of l/56in. of rain was effective on a simulated tussock fire. This information indicated the potentialities of a new practical method of attacking tussock fires and further field trials on tussock grassland and trials with scrub and simulated forest fires were arranged. Rotorua Trials In support of this programme the Soil Conservation Council approved of the expenditure of a further £250 to cover the cost of a more advanced trial in collaboration with the James Aviation Company at Rotorua on 21 November 1956. The company was prepared to adapt the fertiliser hoppers of 3 Beaver aircraft for rapid jettisoning of water in a . manner calculated to be suitable for fighting fires likely to occur in scrub and in cut-over forests. A fire area (50yds. x 12yds.) was created by burning bales ‘of hay and heaps of light branches saturated with diesel fuel on the edge of a rubbish tip. The first flight made at 40ft. above this flaming mass completely doused the flames and, except along one edge, replaced them with a cloud of steam. The second plane doused this flaming edge 1 minute later, and the third

dropped its load on the reviving flames created by the diesel fuel and embers of the logs. This quick, continuous attack ; was most effective and impressive, and was marred only by the fact that one aircraft had to be withdrawn owing to leakage from the hopper. The next target area, of 1 square chain, consisted of several heaps of dead branches about 3ft. high sprayed with diesel fuel. The first flight doused a swath very effectively through the fire area and the second enlarged the swath. Unfortunately another aircraft had to be withdrawn owing to faulty sealing of the hopper. As a result the embers on the under side of the small logs rekindled in the longer interval between water-spray-ing flights (6 minutes). Standard rain gauges were placed at intervals through the fire area and four water-bombing flights were made over rain gauges at heights ranging from 30ft. to 150 ft. to define the pattern of water spread. The jettisoning of 200 gallons of water from the aircraft at heights of from 20ft. to 50ft. in 2 to 3 seconds creates an advancing curtain of water most of which is spread and dissipated into large “raindrops” which fall in a swath that saturates clothing and burning material over a width of about 22ft. to 33ft., according to the height from which it is released. The release of this volume of water in such a short time creates the effect of a rapidly moving inverted geyser with its characteristic “shots” or “bolts” of water interspersed with the dissipated “raindrops”. The result is a curtain of water. At the lowest height the bolts of water not completely dissipated struck with force sufficient to overturn rain gauges set in the pumice sand and to scour holes 4in. deep in the sand. The rate of discharge in 2 seconds from an aircraft flying at 100 m.p.h. was

such that water was spread over an ■area 1/3 chain wide and. 2 chains long. The heaviest density of application was naturally in the middle of the swath, but the over-all rate of application was equivalent to 0.15 in. of rain, which was undoubtedly very effective in extinguishing a scrub fire. However, it was not sufficient to douse the embers on the under sides of thick branches, though burning was reduced to smouldering. Rain gauge measurements showed the width of spread to vary according to the height flown (from 22ft. to over 50ft. at altitudes ranging from 25ft. to 150 ft). Owing to the 45 degree angle at which the driving “rain” fell, the rain gauges recorded only about half of the total fall. Evaluation Senior officers of the New Zealand Forest Service and several private forest companies in the area saw the trials and were impressed with the potentialities of using aircraft in fire fighting. Further trials and collaboration between the Soil Conservation Council, Forest Service, catchment boards, the aviation industry, and Civil Aviation Administration should indicate the possibilities of using this new technique. There are millions of acres of fireprone tussock grassland in the South Island and large exotic forests in the centre of the North Island that are subject to disastrous fire damage and where ground fire control has presented problems which the use of aircraft could answer.

Proceedings of Weed Control Conference

PROCEEDINGS of the 9th New Zealand Weed Control Conference, held at Timaru in July 1956, are now available.

The publication gives much up-to-date information on weed control problems in New Zealand, including papers on the difficult-to-kill weeds hawthorn, barberry, and sweet brier. New uses of chemicals as crop desiccants for lucerne and red clover seed production, the scope of chemicals for soil sterilisation, and the new grasskilling chemicals and their uses for weed control in lucerne and brassica crops are described. The publication can be obtained for 15s. a copy from the secretary, Weed Control Conference, P.O. Box 1500, Wellington. Those interested are invited to join the society that organises the conference, the New Zealand Weed Control Conference (Inc.). The annual subscription of 15s. will procure a copy of the Proceedings. The society has the support of the Department of Agriculture.