[Paper Review] Towards a New Paradigm of UAV Safety

Juan-Pablo Afman, Laurent Ciarletta+4 more|arXiv (Cornell University)|Mar 24, 2018

Fault Detection and Control Systems15 references18 citations

TL;DR

This paper proposes a mechanical Active Cutting System (OABBS) that safely terminates runaway multi-rotor UAVs by instantly severing propellers to reduce lift and enable controlled descent. The system ensures a deterministic, non-recoverable landing, minimizing impact energy and collateral damage, with experimental validation showing effective crash mitigation in real-world run-away drone incidents.

ABSTRACT

With the rising popularity of UAVs in the civilian world, we are currently witnessing and paradim shift in terms of operational safety of flying vehicles. Safe and ubiquitous human-system interaction shall remain the core requirement but those prescribed in general aviation are not adapted for UAVs. Yet we believe it is possible to leverage the specific aspects of unmanned aviation to meet acceptable safety requirements. We start this paper with by discussing the new operational context of civilian UAVs and investigate the meaning of safety in light of this new context. Next, we explore the different approaches to ensuring system safety from an avionics point of view. Subsets of operational requirements such as geofencing or mechanical systems for termination or impact limitation can easily be implemented. These are presented with the goal of limiting the collateral damages of a system failure. We then present some experimental results regarding two of the major problems with UAVs. With actual impacts, we demonstrate how dangerous uncontrolled crashes can be. Furthermore, with the large number of runaway drone experiences during civilian operations, the risk is even higher as they can travel a long way before crashing. We provide data on such a case where the software controller is working, keeping the UAV in the air, but the operator is unable to actually control the system. It should be terminated! Finally, after having analyzed the context and some actual solutions, based on a minimal set of requirement and our own experience, we are proposing a simple mechanical based safety system. It unequivocally terminates the flight in the most efficient way by instantly removing parts of the propellers leaving a minimal lifting surface. It takes advantage of what controllability may remain but with a deterministic ending: a definite landing.

Motivation & Objective

• To address the growing safety risks posed by civilian UAVs, especially in cases of uncontrolled flight or 'run-away' drones.
• To shift the safety paradigm from crash-free operations (as in general aviation) to safe-to-crash design for cost-effective UAV deployment.
• To develop a low-cost, mechanically robust solution that ensures flight termination without relying on expensive software validation or complex avionics.
• To demonstrate through real flight data and prototyping that mechanical systems can effectively mitigate crash risks in civilian UAVs.

Proposed method

• Design and prototype an Optimal Active Breaking Braking System (OABBS) using servomotors to rapidly deploy blades that cut propellers to a controlled length.
• Integrate the OABBS into quadcopter arms so that activation severs propellers cleanly, reducing lift while preserving some controllability for descent guidance.
• Ensure the system is non-recoverable: once activated, the UAV cannot be restored to normal flight without replacing propellers.
• Use real flight data from the Afman Aeromechanics Lab at Georgia Tech to analyze runaway drone incidents and validate the need for such a system.
• Combine the OABBS with potential future systems like smart parachutes to enhance descent control and impact safety.
• Evaluate the system against key safety criteria: speed of activation, irreversibility, and ability to limit descent speed and impact energy.

Experimental results

Research questions

• RQ1 How can UAV safety be redefined to prioritize ground safety over crash-free operations in civilian applications?
• RQ2 What mechanical design enables rapid, irreversible flight termination that minimizes impact energy and collateral damage?
• RQ3 Can a low-cost, hardware-based system outperform software-centric safety solutions in terms of reliability and cost-effectiveness?
• RQ4 How do real-world runaway drone incidents demonstrate the need for deterministic, non-recoverable termination mechanisms?
• RQ5 To what extent can residual controllability after propeller severance be leveraged to guide the UAV away from people and structures?

Key findings

• Real flight data from a runaway quadcopter showed uncommanded throttle inputs due to electromagnetic interference, causing the drone to ascend uncontrollably and drift 100 yards away before crashing.
• The OABBS system successfully cuts propellers to a length that reduces lift, enabling a controlled descent even at full throttle, thus minimizing kinetic energy on impact.
• The system is irreversible: once activated, the UAV cannot be restored to flight without replacing the propellers, ensuring no false recovery.
• Clean cuts were achieved on various propeller types, confirming mechanical feasibility and consistency of the severing mechanism.
• The system allows for some degree of controlled descent, enabling potential avoidance of people and structures during the final phase of flight.
• The OABBS provides a deterministic, hardware-based solution that avoids the high costs of software verification and certification required in traditional aviation.