Ultra-reliable and low-latency transmission will be a key feature of the next generation of wireless communications and will be based on the transmission of short packets. To model short packets transmission in mobile relay systems using Unmanned Aerial Vehicles (UAVs), a two-way channel with peer-to-peer protocol is considered. Using mobile relay to transmit data requires reliable communication. For this, it is necessary to explore the possibilities of combining the Ground Control Station (GCS) with a UAV for effective interaction with intensive data traffic. This work focuses on modelling information transmission, estimating packet latency and communication channel throughput for different packet sizes, data rates and Bit Error Rates (BERs). UAV short packets transmission via a mobile drone was first simulated using NetCracker software. The practical value of the data obtained is the ability to estimate the functioning of the communication channel, detect problems at the beginning of designing reliable mobile relay channels, which will reduce time, capital investments and provide scalability for new projects. The results obtained allow us to predict the exchange of information in mobile relay systems using UAVs.