Effects of the Wind Field on the Synthetic Measurement of the Aerodynamic Angles of an Aerial Vehicle

The estimation of the angle of attack and sideslip angle is of fundamental importance for the situational awareness of an aerial vehicle. Historically, several accidents occurred due to failures of the traditional protruding probes applied to measure these two angles. The MIDAS project aims to design and develop a certifiable Air Data System capable of providing the entire set of Air Data, integrating a synthetic estimation of the aerodynamic angles. All operating conditions shall be taken into account, even those related to atmospheric phenomena. The wind effects (both steady and unsteady) represent a very challenging topic when design a synthetic sensor because of its intrinsic nature. In fact, the airflow surrounding the AC can be affected by several phenomena with a very wide range of characteristics (e.g. speed and direction range) that can be hardly simulated during the design stage. It is clear that the atmosphere condition (both steady and unsteady) can affect this particular kind of sensor, and it must be analysed the error in the presence of the wind. The paper shows the estimation error due to the steady wind field and correction to be applied to previous synthetic sensors design in order to be reliable both in still air and in presence of the wind.

I. Introduction

During flight, the measurement of the Air Data set is crucial. Basically, there are 2 main reasons. First of all, the forces and moments acting on the aircraft are generated depending on the reciprocal relationship between the aircraft itself and the control volume where the aircraft is flying. Second, Air Data are used as basis to understand the flight condition. For instance, the barometric altitude or the various airspeed definitions. The system applied to measure the air data is composed by a set of external and, generally, protruding probes. Each of them has different requirements in terms of position and power supply and a triplex redundancy is a standard in commercial aviation to deal with the level of criticality of the system.