When a large military helicopter collided midair with a small quadcopter in 2017, the helicopter sustained only minor damage and returned safely home; the drone was destroyed. But tests performed at the University of Dayton Research Institute show that outcome may not always be the case.
In a test designed to mimic a midair collision at 238 miles per hour, researchers in UDRI's Impact Physics group launched a 2.1-pound DJI Phantom 2 quadcopter at the wing of a Mooney M20 aircraft. The drone did not shatter on impact. Rather, it tore open the leading edge of the wing as it bore into the structure, damaging its main spar.
"While the quadcopter broke apart, its energy and mass hung together to create significant damage to the wing," said Kevin Poormon, group leader for impact physics at UDRI.
As the number of hobby drones in the air dramatically increases, so does the risk of a catastrophic event, Poormon said. "We've performed bird-strike testing for 40 years, and we’ve seen the kind of damage birds can do. Drones are similar in weight to some birds, and so we've watched with growing concern as reports of near collisions have increased, and even more so after the collision last year between an Army Black Hawk helicopter and a hobby drone that the operator flew beyond his line of sight."
Although the helicopter returned home with only minor damage to a rotor, Poormon said it is only a matter of time before a drone strike causes more significant damage to a manned aircraft. To educate the community, Poormon presented test results and video of the drone shot at the fourth annual Unmanned Systems Academic Summit.
"We wanted to help the aviation community and the drone industry understand the dangers that even recreational drones can pose to manned aircraft before a significant event occurs. But there is little to no data about the type of damage UAVs can do, and the information that is available has come only from modeling and simulations," said Poormon. "We knew the only way to really study and understand the problem was to create an actual collision."
Poormon and his team collaborated with the Sinclair College National UAS Training and Certification Center, whose experts provided guidance on unmanned aerial systems. "We're fortunate to be in close proximity to Sinclair's nationally renowned UAS Center,” Poormon said. "We're experts on bird strikes, but Sinclair’s team provided valuable insight on how these systems are being used and helped us determine the best models for testing."
After calibration work to ensure they could control the speed, orientation and trajectory of a drone, researchers fired a successful shot at the Mooney wing. The researchers then fired a similarly weighted gel "bird" into a different part of the wing to compare results. "The bird did more apparent damage to the leading edge of the wing, but the Phantom penetrated deeper into the wing and damaged the main spar, which the bird did not do."
Poormon said additional tests using similar and larger drones on other aerospace structures, such as windscreens and engines, would provide critical information about how catastrophic a collision would be. He and his team are hoping even this first test result will help bring awareness to the manned and unmanned aviation communities about the importance of regulations related to safe drone operating.
In addition to the FAA regulations already in place for drone operators, Poormon noted other factors that could help enhance safety, such as building drones to be more frangible — meaning they'll shatter more easily on impact — or keeping them under a certain weight limit.