By Jonny Lupsha, Wondrium Staff Writer
Over the last 10 years, the prominence of small-scale drones has skyrocketed. From hobbyists to delivery services, the skies are becoming increasingly populated. Why do drones seem to be everywhere these days?
Once thought to be exclusively the stuff of military use, drones have worked their way into the public sphere. The model airplane has, to an extent, been replaced by camera-equipped drones flown via smartphone by aviation enthusiasts. Companies like Zipline and Wing are preparing autonomous drone delivery systems to launch as soon as 2024. Filmmakers are getting once pricey aerial footage at a fraction of the price.
On May 3, Russia alleged that two explosions over the Kremlin were drones on an assassination mission with Vladimir Putin as their intended target. Putin was unharmed, but Russia has placed blame on Ukraine and the United States, both of which have denied involvement.
Regardless of their promises and perils, how did drones become so widespread in the 21st century? In his video series The Science of Flight, Dr. James Gregory, Professor of Mechanical and Aerospace Engineering at The Ohio State University, explains the rise of small-scale drones.
How Did Smartphones Lead to Drones?
“The development of small-scale drones such as quadcopters has largely been enabled by the revolution of smartphone technology of the late 2000s,” Dr. Gregory said. “Three key technological developments for smartphones have been leveraged for drones.”
The first is battery capacity, which grew rapidly. According to Dr. Gregory, the energy density of lithium ion batteries and similar devices doubled from 100 watt-hours per kilogram in the mid-1990s to 200 watt-hours in the mid 2000s. Meanwhile, the cost came down by 75% in the same time period.
“Second, the cost and performance of inertial measurement units, or IMUs, have dramatically improved in the same time period,” he said. “These IMUs are the same devices used in the glass-panel avionics for manned aircraft. However, the smartphone revolution pushed the development of miniaturized electromechanical technology, driving down the cost of IMU technology.”
IMU sensor suites contain three-axis accelerometers, three-axis gyroscopes, three-axis magnetometers, and pressure transducers—all of which facilitate stable flight.
Finally, smartphones have led to low-cost chipsets with low power consumption for global navigational satellite systems such as GPS. This technology is also used in drones.
What are the Pros and Cons of Small-Scale Drones?
“Small-scale drones are much more maneuverable than large, manned aircraft,” Dr. Gregory said. “The reasons are that they are much lighter and have much lower moment of inertia. Now, whenever mass is concentrated closer to the axis of rotation, the moment of inertia about that axis decreases, and bodies with a lower moment of inertia can rotate much more rapidly.”
However, maneuverability comes at a price: The smaller the drone, the more susceptible it is to gusts of wind. This can lead to turbulent flight or a total loss of flight stability. The lift produced by rotors such as those on small drones is related to the wake development underneath the rotor. A strong gust can disrupt the configuration of the wake, causing unexpected drops in the drone’s flight.
“The impact of wind gusts is one of the key challenges to operating small drones in an urban environment,” Dr. Gregory said. “When multiple tall buildings are present, an urban canyon effect can be present, where wind flowing over and around the buildings results in strongly gusting conditions within the canyon corridor between them.
“This can lead to unsteady downdraft gusts that have a speed several times that of the average wind speed.”
The Science of Flight is now available to stream on Wondrium.