Autonomous drone landings have long been constrained by a simple physical problem: most unmanned aircraft can only touch down safely on flat, calm surfaces at very slow speeds. A research team at the University of Sherbrooke's 3IIT institute is working to change that, with field results showing reliable landings on slopes of up to 60 degrees at descent speeds reaching 2.75 metres per second.
The implications extend well beyond academic curiosity. As sUAS News reports, unmanned aerial systems have already become essential tools in environmental monitoring, industrial inspection and emergency response. The single factor holding them back is the landing envelope, and the 3IIT team is tackling that constraint directly.
The Research Team and Its Facilities
The work is led by professor Alex Debier, who directs research across aerial robotics and sports engineering at the 3IIT institute. Working alongside him are post-doctoral researcher Isaac, who completed a PhD in mechanical engineering before specialising in robotics, and doctoral candidate John, who is nearing completion of his own mechanical engineering PhD.
The institute sits four hours east of the university's main campus and operates within uncontrolled airspace, which gives the team the ability to fly and iterate experimental aircraft directly on site. Supporting that work are motor test benches, fabrication laboratories, a closed-loop wind tunnel and an indoor flight room fitted with a wind generator. The team also has access to a local airport runway, closeable on demand, 30 minutes away for high-speed trials.
Why Conventional Landing Gear Falls Short
According to sUAS News, traditional rigid landing gear behaves like an undamped spring. It forces pilots and autopilots alike to limit descent rates to approximately 0.5 metres per second, prolonging the exposure of the aircraft to wind gusts and aerodynamic disturbances. When impact speeds rise, rigid structures generate violent rebounds and extreme forces that destabilise the craft.
The problem is compounded by standard flight controllers, which delay motor thrust cutoff until state stability is confirmed. During that latency window, residual thrust actively pushes the drone off the landing surface rather than holding it in place.
Overcoming the 0.5 metres per second constraint is therefore not a marginal refinement. It shifts unmanned aircraft from fragile laboratory instruments into robust, all-weather field tools capable of aggressive touchdowns across terrain that is currently off-limits.
Autonomous Drone Landings on Steep Slopes: Friction and Reverse Thrust
To tackle inclines of up to 60 degrees, the 3IIT team engineered a dissipative suspension system built around a stacked friction disc shock absorber mechanism. An integrated 10 gram DC motor adjusts the compression force on the disc stack, allowing researchers to tune the energy dissipation rate to match expected impact velocities without heavy real-time active control feedback loops during the impact itself. Internal torsion springs then reset the leg geometry once joint friction is relieved.
On the software side, the team modified the ArduPilot landing mode to trigger motor reverse thrust the moment contact is detected. When onboard inertial measurement unit accelerometers register the impact, the flight controller scales motor PWM output across a 1500 to 2000 range within a custom landing mode flag, generating reverse thrust that pushes the aircraft against the slope.
The two elements work together in a precise sequence. The dissipative friction joints extend the total impact duration, creating the time window the reverse thrust command needs to spool up and generate firm surface adhesion. In field tests, as reported by sUAS News, this dual strategy delivered reliable touchdowns on slopes up to 60 degrees at impact descent speeds of 2.75 metres per second, representing an eightfold expansion of the landing envelope compared with conventional rigid gear.
The team also confirmed that this automated capability allows drones to land, reconfigure leg geometry and re-take off autonomously across sloped rooftops in North America, providing a foundation for repeatable urban deployment and emergency touchdowns.
High-Speed Vehicle Landings: The Next Frontier
Transferring those kinetic absorption principles from a stationary slope to a fast-moving ground vehicle introduces a further layer of complexity. At high forward velocities, the drone must maintain a steep forward pitch angle to overcome aerodynamic drag, which creates a risk that propellers or landing gear will strike the vehicle surface unevenly on descent. The drone must also descend through the turbulent airflow boundary layer generated by the moving target.
To address these challenges, sUAS News reports that the team developed the Dart UAV platform alongside an ultra-low-latency telemetry system designed to reduce the tracking lag that makes precise touchdown on a moving vehicle so difficult. The combination aims to give the aircraft enough positional accuracy to meet a fast-moving surface cleanly, rather than glancing off it.
Readers with an interest in unmanned and experimental aircraft developments can explore further using the Aircraft Search tool on The Aviation Hub.
The Bottom Line
The 3IIT team's results represent a concrete step toward autonomous drone landings that work in the real world rather than only on prepared flat pads. An eightfold improvement in permissible descent speed, combined with demonstrated performance on 60-degree inclines, removes barriers that have limited UAV deployment in search and rescue, infrastructure inspection on difficult terrain and glacier monitoring.
The move toward high-speed vehicle integration suggests the research programme has further ambitions beyond fixed landing sites. The work described by sUAS News is ongoing, and the progression from slopes to moving platforms points to a systematic effort to eliminate landing constraints one environment at a time.
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