Spraying, seeding and fertilising crops and pastures involves operating heavily loaded aircraft from runways which may be of marginal length and surface; finding the correct paddock to treat, manoeuvring the aircraft at very low altitude amongst many obstacles whilst applying materials. The agricultural pilot is expected to do this in a manner which is safe to themselves, the general public and the environment. The job must also be done effectively and efficiently.
The aircraft with which the pilot has to do this job have shown dramatic improvement in performance and safety over a period of 50 years. The first aircraft used in Australia for dusting in 1947, spraying in 1948 and spreading the following year were DH 82 Tiger Moths. They were not, of course, designed as agricultural aircraft, but as two-seater trainers. Modifications to them were many but basically involved removing the front cockpit and replacing it with a hopper. The Tiger Moth was powered by a 130hp engine and had a payload of 33 gallons of spray or 330 lb. of super-phosphate. The DH82 was phased out by 1965 following agreement between the Department of Civil Aviation and the industry owing to its high accident rate and the availability of other more suitable alternatives.
The DH82 Tiger Moths were replaced in the 1960s by such aircraft as the locally assembled CA28 Ceres and Transavia PL12 Airtruck and the imported Cessna 188, Piper PA 25 Pawnee, DHC-2 Beaver, G-164 Ag Cat, and the Snow Commander S-2D, to name the most numerous.
The Cessna 188 Ag Wagon (230hp), Ag Truck (300hp) or Ag Husky (310hp), became the leading models by the mid 1970s followed by the Piper PA 25 Pawnee (235hp) and PA 36 Pawnee Brave (285 & 300hp). The DHC-2 Beaver (450hp) and PAC Fletcher FU 24 dominated the fertiliser spreading business.
The hopper size varied from 750L on the Ag Wagon to 1000L on the Ag Husky and from 550L on the PA-25 to 850L on the PA36. These were specialised agricultural aircraft with greater attention paid to pilot safety. The FU24 has a dry solids capacity of just over 1000 kg.
By the late 1970s the US manufactured Air Tractor and Ayres Thrush models were being introduced into Australia. The Air Tractor AT301/2, 401/2, 501/s and 802 model numbering system followed the hopper size in US gallons. The first turbine engined model was the 400, powered by a Pratt and Whitney Canada PT6A-15 Ag engine with a reversible pitch propeller. A P&WC PT 6A-35 Ag turboprop engine of 750hp powers the AT-502 introduced in the late 1980s. The first AT 802 was delivered to an Australian operator in 1995. By the end of 1997 there were 12 on the register. This is the largest production ag plane in the world. A PT 6A-45 or 65 engine powers it
The Ayres Thrush models are descended from the Rockwell Thrush Commander and consist of the Thrush S2R-600 (1340) powered by a P & WR-1340 radial engine; the Bull Thrush S2R-1820 and the Turbo Thrush S2R with options of a P&WC PT 6A-15, -34 and-65 turboprop engines or Garrett TPE 331-10.
Another imported aircraft is the Dromader (Melex M-18) manufactured in Poland by PZL-Miele. The latest Australian ag aircraft is the GA-200 "Fatman" produced by Gippsland Aeronautics at Morwell, Victoria.
There are several makes and models of helicopters, all imported, used for spraying, spreading and stock mustering. They include the Bell 47 and 206, Hiller 12 E, Hughes 269 and Robinson R-22.
In their 50-year history, Australian aerial agriculture operators have constantly improved their technology and management systems to become a highly efficient industry. Largely through the innovations created by members from within the industry, aerial agriculture now enjoys the reputation of a modern, safe and environmentaly friendly industry.
Aerial agriculture has benefited greatly from improved aircraft performance and safety over the years. The first aircraft used in Australia for dusting in 1947, spraying in 1948 and spreading the following year were DH 82 Tiger Moths. Originally designed as two-seater military aircraft, the planes had to be modified by removing the front cockpit and replacing it with a hopper. These bi-planes were slow, powered by a 130hp engine, and had a limited payload of 33 gallons of spray or 330lb of super-phosphate. They were phased out by 1965 because of their high accident rate and the availability of safer, more suitable alternatives. In the 1960s, purpose-built aircraft were introduced to the market, allowing for a larger hopper size and greater pilot safety.
It was not until the 1980s that heavy piston engine aircraft were supplemented with the lighter turbine engines that doubled the aircraft's power and decreased its weight. This development vastly improved the reliability, safety and productivity of the aircraft.
Unfortunately, the level of sophistication required in the manufacture of turbine engines makes them significantly more expensive than piston engines. With all turbine engines being manufactured outside of Australia, mainly in the USA, the dollar exchange rate also has a dramatic effect on cost. The cost of a brand new turbine engine ranges easily between AUS$490,000 and AUS$900,000, with the engine's cost comprising at least half of the total aircraft cost.
Global Positioning System (GPS)
In the early days of air ag, human markers had to run with flags to direct ag pilots across crops and fields. Two markers, or people, were placed at opposite sides of the field and moved across at regular intervals to guide the planes accurately. Naturally, the method was somewhat inaccurate and proved problematic with occasional overlaps or gaps in spray patterns across odd shaped fields.
With the advent of the Global Positioning System (GPS), a free service inaugurated by the United States department of defence, sub meter guidance for aerial applications became a reality in the early 1990s and eliminated the need for human ground markers. Based on references transferred by a series of satellites orbiting the earth on a 24-hour basis, the GPS allows ag pilots to calculate their exact position through an on-board computer. Using a minimum of four satellites, the computer can be used for pre-flight planning, in-flight guidance and recording flight path data for later evaluation (Source: Aerial Agriculture in Australia, Derrick Rolland).
However, the GPS satellite constellation, on its own, could not provide sufficiently accurate guidance to ag aircraft due to various errors in accuracy that could vary from 20 to 100 metres. To overcome these errors, differential correction came into being. This system uses a fixed reference point to compare the computed GPS position with a fixed reference station and then calculates the actual error in the GPS system. Once this is calculated, it is transmitted to the aircraft via a separate satellite to the aircraft onboard computer and applied to the aircraft position, updated at 5 times per second.
One of the major advantages of GPS differential correction was that the pilot could now change his application pattern or direction at any time, dictated by wind shifts or other reasons, without wasting valuable flying time waiting for ground markers to be repositioned. Pilots can punch in the key points of the field's layout and the swath width required and leave it to the computer to indicate when the pilot should position the aircraft to carry out the spraying within centimetre accuracy. The same course can be flown over and over again with sub-metre accuracy - that is, less than one metre's difference in the flying course no matter how much time passes between flights.
GPS also allowed for accurate mapping of paddock shapes, hugely improving the accuracy of spraying and therefore the productivity of the crop involved. Furthermore, data logging through GPS has allowed pilots to prove what was sprayed, where it was distributed and what the prevailing wind conditions were at the time of spraying. This allows for greater accountability and transparency in the industry.
Future developments for GPS include its use in combination with Geographic Information Systems (GIS) to match the aircraft position with the amount of fertiliser required in a particular area. Eventually, pesticide application will also benefit from this cross-fertilisation of technology.
Better management systems
With improved aircraft in the industry came better management systems. This change incorporated computer programs to improve flying safety and chemical management. Air ag businesses are taking seriously their management systems, with Queensland company Jones Air gaining what may be the world's first ISO14001 certification to improve the company's communications and standard procedures. Air ag operators and pilots have developed a greater understanding of how droplet size, wind and weather can affect drift, and they implement a Pesticide Application Management Plan (PAMP) on any property before spraying to prevent drift.
Better control of drift and increasing spray efficacy has been the industry's focus for more than a decade. Managing droplet behaviour is now a significant part of an ag pilot's education. Ag pilots require a detailed knowledge of the variables that affect spraying such as changing meteorological conditions including atmospheric stability and the effect of water added to the chemical, the number of droplets required and the droplet size.