Carbondale: SIU Graduate Student Invents Drone Airbag That Cuts Impact Force by Two-Thirds

A Chemical Reaction That Could Save Lives

When Brady Villiger's dummy drone fell from a fourth-floor balcony on the Southern Illinois University Carbondale campus, nearly a year of research hung in the balance. In the split second before impact, a compact airbag deployed beneath the aircraft and cushioned the fall.

The test proved the concept worked. Villiger, a master's student in SIU's School of Mechanical, Aerospace, and Materials Engineering, designed a self-deploying airbag system that inflates using a chemical reaction. The research was conducted in SIU's Aerospace Controls Research Lab (ACRL), under the guidance of Assistant Professor Hossein Eslamiat.

How Fast Is Fast Enough?

The airbag inflated in as little as 0.033 seconds. Drop tests showed the system reduced impact force by about 66%. According to the researchers, that lowered the impact below the range associated with skull-fracture risk.

The study was published March 12 in Drones, an international peer-reviewed open-access journal focused on unmanned aerial vehicle design. The paper is titled "Development of Chemical Reaction Airbag Safety System for Multi-Rotor UAV to Mitigate Free-Fall Collision Impact."

"Brady has been working on a very special project," Eslamiat said. "It is a chemical-reaction airbag for drones that, to the best of our knowledge, is the first of its kind."

Why Drones Need Airbags

The Federal Aviation Administration held 785,827 total drones registered in the United States as of August 2024, with 390,027 commercially registered. The FAA projected commercial drone use would grow to 373,000 by the end of 2028. That estimate was already surpassed by October 2024, with 396,746 commercial drones registered.

Drones are now used for aerial photography, infrastructure inspection, farming, emergency response and military surveillance. As civilian use expands, so does concern about what happens when a drone fails midair.

A Department of Defense study from 2009 to 2018 found that 64% of UAV failures occur mid-flight. Motor issues account for 27% of those failures. Mechanical issues including propeller or structure damage account for 22%. Loss of connection makes up 15%. Electrical problems make up 13%.

Villiger's system is designed to activate only when onboard sensors detect both freefall and altitude loss. This prevents unnecessary deployment during normal descents. The system had about 1.56 seconds to detect the fall and fully inflate before impact in testing.

From Explosives to Black Powder

Villiger's first approach used explosives to manufacture a detonator. The method fell short. According to the published paper, the explosive compounds did not produce enough gas to fully inflate the airbag. Controlled blasts repeatedly damaged the bag.

"This proved to be much more hassle than it was worth and took many hours before I made the switch to use black powder charges instead," Villiger said.

Black powder burned hot enough to generate the required volume of gas. The heat was too intense for the airbag's Nylon 6 fabric. Villiger solved the problem by containing the reaction in a sealed chamber and using heat-reducing protective materials.

The final design features a 12-inch disc-shaped airbag that covers the underside of the drone. A two-part mounting system allows it to attach to existing drones without structural redesign.

A Student's Path to the Lab

Villiger grew up in Mountain Home, Arkansas. He competed on his high school's Hall of Fame FIRST Robotics team, Team 16 Bomb Squad. He later worked as a U.S. Air Force aircraft mechanic. That experience deepened his interest in aviation hardware and safety systems.

He earned his bachelor's degree from SIU in 2023. He began shaping the airbag concept as part of his master's thesis work in 2024. Full design work began in January 2025.

"It has been a long path to get here," Villiger said. "But seeing the system work and knowing it could help make drone operations safer has made every challenge worth it."

What Comes Next

Villiger earned his Master of Science degree this spring. He is preparing to transition from the Air Force Reserve to active duty.

He envisions his design supporting wider commercial drone use in urban areas. He said mass drone delivery could become viable with a safety system like this in place.

"Ideally, mass drone delivery could be an option with a safety system like this, or multiple safety systems in place, that allows companies to fly UAVs in urban areas without risk of fatality or major injury," Villiger said.

Eslamiat said the project reflects the kind of hands-on research SIU graduate students can accomplish.

"Brady's work shows the kind of hands-on, forward-looking research our graduate students can do here," Eslamiat said. "Chemical-reaction airbags for drones may seem like a niche topic, but they speak directly to how we make future airspace safer. That's the kind of impact we want SIU engineering to have."

All testing took place on SIU's campus using a dummy drone. Villiger gathered detailed measurements of acceleration, rebound height and impact force in both protected and unprotected drops.