Abstract-Unmanned aerial vehicles are specialized robots. Recently they were used in many civil applications such as patrolling, firefighting, rescuing tasks and being the shadow cinematographer in many movie-making companies. The new developments in material technology led to new sophisticated, miniature range of sensors and actuators, which are able to substitute gyroscopes and accelerometers. In light of this, new miniature aerial vehicles appeared in the market. Micro-UAV (MUAV) is able to infiltrate sites, where the bigger aerial robots could not. It is more maneuverable and recently is becoming able to fly to new altitudes. This allow the MUAV to be used for site scanning, to perform or assist in photogrammetry procedures in light to create 3D building models and maps. The future of the MUAV seems to be existing: In relation to medical field, the aerial robot is being used to perform radiation leakage test that, is done manually in most of the hospitals. It is also planned to be used to deliver lightweight goods within the city.The versatility and adaptability of the miniature aerial robot creates new requirements for stability, maneuverability and speed. In this paper, we offer to study the quadrotor while inspecting high-rise structures using simulations. As the quadrotor is vertical take-off and landing vehicle, it is very important to analyze the effect of the altitude on the stability of in order to create control algorithm able to maintain the necessary hovering position of the quadrotor. A better stabilization leads to better scanning results and high quality captured images.

Unmanned Aerial Vehicle (UAV) is a military product used extensively in the last decade. The successful outcome has expedited the migration of this technology to the civil market. Nowadays, UAVs can perform photogrammetry, inspection of civil buildings, delivering goods and assisting in rescue missions. The results depend on multiple factors, such as identification of flight mission, choice of UAV type and control algorithms. There are various types and sizes of UAV. The quadrotor is the one of most affordable and manoeuvrable system but it lacks stability. Therefore, we are discussing in this paper how to improve the stability of the quadrotor, while performing routine bridge inspections.