Unmanned Aerial Vehicles (UAVs) are used in numerous applications ranging from defense, law enforcement, environmental monitoring, disaster recovery, aerial photography, and delivering consumer packages. Securing wireless communication between drones in-flight is critical to ensure safe operation during flight and avoid multiple types of attacks, e.g., eavesdropping, spoofing, jamming, etc. Quantum communication protocols offer enhancements over classical approaches. In this effort, we present progress towards demonstrating Quantum Key Distribution (QKD) between two drones in flight. A significant challenge includes achieving system performance using compact Size, Weight, and Power (SWaP) constraints of the drone vehicle. We introduce and evaluate critical subsystems including the QKD source, which is based on resonant-cavity Light Emitting Diodes (LED) controlled by an FPGA, and we discuss a secondary QKD source based on a fiber-coupled polarization modulator. The Pointing, Acquisition and Tracking (PAT) system is comprised of several cascading subsystems, which provide course alignment using based on Infrared (IR) beacons/cameras with gimbals, and fine alignment using Fast Steering Mirrors (FSM) with absolute encoders and feedback position sensors. We discuss both transmit and receive optics including custom designed 3D-printed optical benches. Finally, we introduce single-photon detectors, FPGA-based time-tagger, and a novel statistical post-processing synchronization algorithm. Establishing a quantum communications link between drones in-flight is an important prerequisite for future drone-based quantum applications such as entanglement distribution, distributed quantum sensing, and Quantum Positional Verification (QPV).