Today, it is hard to assume the difficulties of providing network communication over environments that include changeable and mobile nodes. In that kind of situation, traditional applications of cellular networks do not keep up with this unpredictable and mobile environment. Drones are the most preferred technologies that are useful with their characteristic features for that kind of environment. Our goal is to provide network connectivity by placing drones without including any terrestrial base stations in this paper. To set and optimize the number of used drones in related environments, we propose a heuristic method. Finding 3-D placement with the optimum number of used drones, we aim to serve and cover the target percentage of users. And to verify our optimization algorithm, which provides the 3-D placements of drones, we use a simulation tool ns-3 to create network environments that include mobile users and aerial base stations. Our simulation results are based on users' network requirements. We verify that our optimization approach with the heuristic method satisfies the users according to their QoS needs.