I must admit how surprised I was after finding information linking the famous physicist Albert Einstein to aviation. But before getting into the details, I want to set the stage with some history for those relatively new to the industry. Knowing from whence we came helps us deal with today’s issues and tomorrow’s challenges.
The first known use of aircraft in crop protection was a Curtiss JN4 in 1921 to spread lead arsenate on sphinx moths ravaging catalpa fields in Ohio. The aircraft had a box outfitted on the outside right fuselage, and the pilot had to turn a crank to dispense the product while flying the aircraft at literally treetop level. Yes, it was archaic, but it worked and spawned a new industry to become a front-line fighter in protecting the world’s food resources.
Newer and more capable aircraft were soon added to ‘the Farmers’ Air Force,’ with subsequent additions being stronger and able to carry more payload. In the 1960s, aircraft specifically designed for aerial applications, such as the Cessna AgTruck, Piper Brave, Grumman Ag-Cat, and Thrush S2R, became familiar sights across fields worldwide.
While these new types were a welcome addition to the industry, they faced one primary challenge: ensuring the application was evenly distributed across the field and that the track the aircraft followed on the ground produced an accurate deposition of pesticides across the target area to avoid streaky applications.
Early forays into this navigation challenge were to have ground workers waving flags on long poles to guide the pilot onto successive swaths, trying to be as accurate as possible by taking the precise number of steps corresponding to a specific swath width. That wasn’t too bad, but it was difficult for the field markers to achieve accuracy when walking through dense crop foliage or over undulating terrain. It was also a safety hazard as it was too easy for the field marker to be accidentally sprayed with pesticide by not moving upwind quickly enough to the next successive swath.
There were all sorts of ad-hoc techniques to help. For example, given a swath width of 30 feet and knowing that telephone poles were 150 feet apart, there would be five swaths between each pole, so the pilot could more or less picture where each of the five swaths would be relative to the telephone poles. Talk about a judgment call!
In the early 60s, ‘auto flaggers’ became commonplace, with the pilot able to eject 20-foot-long tissue paper streamers at the beginning of each swath to provide guidance for the following swath. The pilot still had to judge the point to offset the next run from the flag, hopefully as close as possible to a swath width. From one swath to the next, the pilot could use various ground cues – trees, shrubs, or other natural markers – to roughly line up on successive swaths, fine-tuning with the auto flaggers.
To add to the difficulty of lateral spacing, the challenge was to ensure the correct deposition rates were achieved, i.e., a proper number of gallons per acre was applied. The only way to check this was to monitor the hopper levels from swath to swath and make a ‘best guess.’
It took a staggering amount of mental gymnastics; sometimes, it felt like your helmet was on fire. To add to the calculating fun was the wind factor. A ten-mph headwind would decrease the ground speed by ten mph into the wind and increase it by ten mph downwind. That change in ground speed would have to be accounted for as well.
A bit of relief came in the early 1990s with the introduction of flow meter systems that provide direct digital readings of hopper levels on a cockpit display.
But by far, the biggest revolution in ag aviation came with the introduction of GPS systems in the early 90s, which achieved a quantum leap in accuracy and safety virtually overnight. Today’s pilots set the flow rate they want on the dispersal equipment and follow the swath bar guidance to an accuracy of a couple of feet or less. At the same time, the GPS does all the calculations needed to consider changes in ground speed due to wind.
But how is this connected to Dr. Einstein?
GPS starts with your nav unit receiving a signal from any four of 24 satellites: three to determine your position and one to correct that position arising from errors in time and distance. The satellite broadcasts the errors, and the corrections required are calculated using Einstein’s Theory of Special Relativity and General Relativity.
Things get a bit weird here: according to Einstein, time can slow down depending on the satellite’s speed and position relative to Earth, a phenomenon known as time dilation.
If these effects were left unaccounted for, the entire GPS would gradually accumulate timing errors along with subsequent location errors, making it too inaccurate for the precise calculations required to maintain the remarkable accuracy of GPS.
So, the next time you watch the track bar guide you across the fields to an accuracy of a couple of feet or less, appreciate the genius of a messy-haired physicist named Albert, who revolutionized the science of time and distance. Without his insights, we may very well be back in the day and age of flags in the field.
