Delivery systems for aerial vehicles may provide a passive automatic delivery system that is automatically triggered during landing of the aerial vehicle. One or more arm assemblies of the delivery system may include a respective landing arm, resilient member, and package guide. The landing arm is configured to rotate in response to an applied external force, with the resilient member being operatively coupled to the landing arm and configured to bias the landing arm towards a resting position. The package delivery system automatically releases the package when a delivery condition is met, such as the landing arms of the delivery system being rotated past a threshold position. Delivery systems can thus passively and automatically ensure that all landing arms are on a landing surface before the package is released. Related methods include approaching and contacting a landing surface, and releasing the package at the landing surface of the delivery location.