The Agribotix journey towards selecting an airframe
Interest in agricultural drones has exploded even since Agribotix was founded 15 months ago. Many growers, agronomists, and entrepreneurs are interested in the space and their question is almost always, “Which airframe to use?” While there are proponents for every type of multirotor and fixed wing imaginable, Agribotix and our customers have been logging hundreds of hours on 5 different airframes. We feel we are in a strong position to provide our commentary and help educate those considering this endeavor.
The first decision one must make is fixed wing versus multirotor. The origins of Agribotix lie in developing a multirotor for wildlife observation and capture, so initially we were inclined to continue with that type of airframe. After all, a multirotor has many advantages conducive to farming. Vertical takeoff and landing eliminates the need for a runway, multirotors are generally easier for the layman to operate, and airframe characteristics to do need to be taken into account when programming flight paths. However, for the row crops (corn, wheat, soy, milo, etc.) that Agribotix has been focusing on, all of these potential advantages are outweighed by the range problem inherent in multirotor design. It is simply much more efficient to use a wing to generate lift rather than multiple constantly spinning propellers. Most of our customers farm quarter or half section plots (160 or 320 acres), which require tens of kilometers of linear flight to accurately map. The roughly five times greater efficiency afforded by a fixed wing aircraft over a multirotors proved essential for covering these large areas.
The quadcopter that started it all in action in Mongolia. The spars below the frame are part of the net dropping apparatus designed to aid in the tagging and observation of Cenarius Vultures in Ikh Nart Nature Reserve.
After recognizing we would need a fixed wing design, we had to identify a suitable airframe. We could have built a custom frame to our exact specifications, splurged on a high end carbon fiber or fiberglass design, or used one of any dozen or so foam airframes available. This decision was an easy one. At Agribotix, we believe the hardware side of this business will rapidly become commoditized and we agreed that it made no business sense to design a custom airframe, despite the strong temptation to do so by the engineers on our team. The high-end airframes certainly perform nicely, but we were looking for a Camry, rather than a Ferrari. The foam designs are cheap, tough, easy to assemble, and get the job done.
Agribotix began with the Finwing Penguin, a traditional foam airframe and, despite the superb autonomous flight characteristics, we quickly identified two major problems with this type of airframe. First was the setup time. A traditional airframe is too large to transport assembled and took 5-10 minutes to set up and another 5-10 minutes to tear down. This substantially impacted the time it took to map each field and we sought an airframe that could be either transported assembled or assembled very quickly. The second issue was the durability. Rough landings are par for the course with autonomous fixed wing flight and they certainly took their toll on the tail of the Penguin. After repairing or replacing several airframes due to failures related to the tail boom and struggling to speed up the setup time, we decided we needed to move to a flying wing.
The original Agribotix airframe was the Finwing Penguin. It handled autonomous flight beautifully, but the dangling tail proved to be its undoing as it required repairs after every few hard landings.
The flying wing design is perfect for an agricultural UAV. Flying wings are relatively compact and easy to transport, extremely tough with no dangling pieces, and have large bodies capable of easily carrying a range of cameras. Furthermore, they are available with shorter wingspans, decreasing wind sensitivity and increasing efficiency at the expense of maneuverability. After experimenting with several flying wings, Agribotix selected the RV Jet as the ultimate agricultural UAV airframe.
However, the RV Jet comes in both a long and a short wing configuration. Shorter wings are better for ease of transportation, improved efficiency, and decreased wind sensitivity, but less wing area means more difficult take offs, landings, and tight maneuvers. To determine whether Agribotix could get away with the short wings, we conducted a number of experiments in different wind conditions. Not surprisingly, the long winged RV Jet handled much better than the short winged version at the edge of the comfort zone. While the long winged version flew 100’s of kilometers without mishap, the short winged version suffered 3 horrific tip stalls (the airframe was undamaged after all three, another testament to its toughness). This was enough to push Agribotix towards the long wings, but we also measured the efficiency of each configuration to ensure we weren’t dramatically reducing our range. Surprisingly, the efficiencies were nearly identical (1.55 Wh/km for short wings and 1.53 Wh/km for long wings at 14 m/s) and both allowed the surveying for more than 350 acres as configured. Given the reduced chance of mishaps and the identical real world efficiencies, the only real drawback to the large wings was a larger footprint when transporting the drone. This was strongly outweighed by the advantages conferred by the long wings and in the past several months Agribotix and our customers have put thousands of miles of the long wing RV Jet without a single failure in winds up to 30 mph.
When selecting a UAV for agricultural applications, range, toughness, and ease-of-use are paramount, in roughly that order. Only a fixed wing platform offers to range required for large farms that are most likely to invest in UAV technology and a flying wing design is both tough and easy to transport and assemble. There are a number of nice flying wing designs available, but Agribotix has identified the RV Jet as the best out there. Check out our Services page for leasing information.
The RV Jet represents the ultimate agricultural UAV. It is tough, flies well in strong winds, has a large bay for cameras and other instruments, and can be assembled in less than a minute.