Abstract: A modular VTOL drone aircraft can include a primary processor, a plurality of propellers, one or more line replacement modules (“LRMs”) and one or more line replacement units (“LRUs”). LRMs can include a fuselage, a center wing, two booms, two outer wings, two vertical tails, a horizontal tail, and/or an engine. LRUs can include an avionics module, a radio communications assembly, a sensor package assembly, an ISR assembly, and/or a deployable payload assembly. Each LRM and LRU can be self-contained and removably attached to the remainder of the VTOL drone. Each LRM can be readily interchanged with another similar LRM, which can be of a different size. LRM interfaces can include a blind mate electric connector and/or a floating connector.