Flying Ad hoc Network (FANET) is the result of Unmanned Aerial Vehicles (UAVs) that collaborate to perform tasks in several applications such as rescue, military, and others. The unmanned aerial vehicle which is also known as a drone improves routing as the line-of-sight probability is increased due to its three-dimensional movement capability. Drones can be used as aerial relays in complex communication scenarios. Routing protocols are necessary for FANETs to establish communication between UAVs. Various routing protocols have been reported for FANETs targeting to find the routing protocol with minimal overhead while establishing a reliable end-to-end transmission. Wireless Sensor Network (WSN) consists of sensor nodes and base stations. The wireless sensors collect different types of information for their surroundings. Then, this information is uploaded to the internet through the base station. In a crisis case scenario, the base station might be nonfunctional resulting in a data upload failure. This paper proposes to use the UAV as an aerial base station to compensate for the nonfunctional terrestrial base station. As delay is one of the major metrics in routing protocols this paper targets to study theoretically the transmission time of packets traveling from the sensors in the WSN to the UAV. Besides, a simulation had been carried using MATLAB to study the total transfer time with respect to several network variables such as the coverage radius, the number of levels in WSN, the angle of propagation of the UAV, and the UAV's speed.