How big can a drone get and still be operational? That’s what the Army Research Laboratory (ARL) wants to know. In late March 2019, they awarded a grant of more than $130,000 to Blake Stringer, PhD, assistant professor of aerospace engineering in Kent State’s College of Aeronautics and Engineering, to study propulsion systems for a new generation of intermediate-sized unmanned aircraft systems (UAS), commonly known as drones.
“I would say that UAS are becoming the disruptive tech of the 21st century in the aerospace and aviation industries,” says Stringer, who retired as a lieutenant colonel after serving 20 years in the Army and is the founding faculty member of Kent State’s aerospace engineering program.
“This technology is changing the way we function as a society. So how do we control them? How do we implement them? How do we use them? How big can they be?”
Small consumer-grade quadcopters have been a favorite holiday present in recent years, while companies like Amazon.com, Inc. want to use them for package delivery. The military’s options for moving people and supplies through the air, however, remain limited to airplanes and helicopters.
“This [drone] technology is changing the way we function as a society.”
In a collaborative effort with ARL consultants and researchers at the University of Tennessee, Stringer will assess the feasibility of creating a drone that is sized somewhere in between.
“We’re taking something between zero and 55 pounds, and trying to make it 1,000 pounds,” Stringer says. “We want to make it able to drop off supplies or perform some mission.” He says the drone needs to serve a wide variety of functions: “Maybe soldiers in an urban area need to be extracted from a top floor of a high-rise building, or you’re looking to send supplies to a more remote area.”
His project involves building an experimental test stand. “We’ll put different sized electric motors and different sized rotors on it, and measure things like thrust, speed, thermal efficiency, acceleration, deceleration and vibration data,” Stringer says. “From that, we’ll be able to determine how big is too big before we have to change the way we’re constructing things. When you scale these things from small to big, the dynamics of the rotor change.”
One of the main challenges for designing such aircraft is meeting the power requirements. “How do we efficiently produce power that’s not around a gas turbine or a piston engine? Is it going to be some kind of hybrid propulsion system? Will you have a fuel cell that feeds into a battery and uses the battery for surge moments? There are a lot of different questions.”
The grant is for a one-year project, but Stringer hopes the research will be successful enough to take the group project to a second phase.