Uncertainty in the sky

Service drones are increasingly expected to operate in public spaces, assisting in tasks such as package delivery. Drones will interact with the public, including recipients who engage with the drone and bystanders who pass by. The majority of public users are novice users, defined as those who currently have little prior experience in interacting with drones. This can lead to feelings of uncertainty (also referred to as psychological uncertainty), for instance, about drone intentions and may raise concerns about trust and safety during Human-Drone Interaction (HDI). To address these challenges, this dissertation aims to investigate the factors contributing to psychological uncertainty during HDI and develop design strategies for service drones to manage the psychological uncertainty of novice users. The research follows a threefold approach: (1) exploring needs for HDI in public spaces; (2) designing HDI with multiple human roles; and (3) investigating solutions for HDI. Semi-structured interviews with domain experts and public users revealed that managing psychological uncertainty is a critical human factors challenge. Based on expert suggestions, package delivery was selected as the primary use case due to its societal and commercial relevance. The user interview study identified human, drone, and environmental factors contributing to uncertainty, as well as the user requirements. While recipients primarily need to track and identify their service drone, bystanders are likely to experience greater uncertainty and require information about the drone’s purpose and the space the drone occupies in the vicinity. Focus groups were implemented to generate stage-specific design recommendations, ranging from the pre-arrival stage to the retraction stage, for HDI with recipients and bystanders in public spaces. Some of the recommendations included indicating the drop-off or landing location during the delivery and retraction stages. Visual cues, such as drone behavior and interfaces, were recommended to communicate the drone’s intentions. Six interface concepts combining on-board lights, displays, and ground projections were developed to communicate drone intentions during critical stages, providing cues for vertical movement, proximity warnings, state progression, and spatial guidance. An online study confirmed the effectiveness of the concepts by demonstrating improved clarity of drone intentions, intuitiveness, and social acceptability of the cues. A virtual reality experiment and two online studies evaluated the effects of drone behavior and interfaces on psychological uncertainty in HDI. Curved approach paths and cable-based hovering deliveries were perceived as safer and more predictable, reducing psychological uncertainty, whereas orthogonal paths and drone landing increased uncertainty. Users highlighted the need for explicit interfaces to clarify drone intentions. Directional displays and helipad-like ground projections effectively communicated delivery intentions and vertical motion, improving trust and reducing uncertainty for both recipients and bystanders, while indicator lights were less effective due to limited visual clarity. Bystanders emphasised the importance of explicit approach cues to maintain safe distances and prevent premature interaction, and interfaces should not only communicate intentions but also when not to approach. Practical considerations, including visibility and safety, are discussed to support real-world implementation. This research highlights the uncertainties and needs of two distinct roles of novice users in public-space HDI and provides design recommendations to reduce psychological uncertainty and improve trust, supporting the societal integration of drones.