In recent times, the widespread adoption of smart devices has made smart flying devices increasingly common. These devices, organized into flying ad-hoc networks (FANETs), have seen a surge in popularity. FANETs, essentially networks of drones or similar flying smart devices, serve various purposes such as traffic monitoring, fire surveillance, filmmaking, border monitoring, forest monitoring and etc. By connecting these flying devices, FANETs streamline tasks, saving both time and human effort. FANETs belong to the broader category of Vehicular ad-hoc networks (VANETs), which, in turn, are a subset of mobile ad-hoc networks (MANETs). Navigating through a three-dimensional physical world and characterized by highly dynamic nature, FANETs pose distinct challenges. This paper focuses on comparing the behavior of well-known MANET routing protocols AODV, OLSR, DSDV, and DSR when applied to FANETs using the Gauss Markov 3D mobility model in the NS3 simulator. The comparison evaluates various parameters including throughput, packet delivery ratio, average end-to-end delay, average jitter, and routing overhead, while considering different speeds of the flying devices and varying numbers of devices in the network. Through simulation and performance analysis across various parameters, it is determined that AODV demonstrates the highest throughput, packet delivery ratio, and lowest routing overhead compared to DSR, OLSR, and DSDV, regardless of varying speed and the changing number of devices. Although AODV performs better than DSR and DSDV in terms of average end-to-end delay and jitter, it slightly lags behind OLSR in these aspects. Overall, except for average end-to-end delay and jitter, AODV shows the most optimal performance in the 3D mobility model when compared to OLSR, DSDV, and DSR.