Air Data Calibration of a Prototype Aircraft Using GPS

PK Raveendran SC, National Flight Test Centre, Aeronautical Development Agency, Bangalore, India

Abstract

The Indian Light Combat Aircraft (Tejas) has an aerodynamically unstable configuration and a quadruplex digital fly by wire control system which uses air data for gain scheduling and feed back control. Pending in-flight calibration of air data system, the initial block of flights was done with fixed gain control law. Therefore the primary objective of the first block of flights was air data and flow angle sensors calibration so that scheduled gain control law with air data and angle of attack feed backs could be invoked for the second phase of flights. GPS method was used for the first time in the country to establish pressure error correction of the static sources on an airplane. Before using this method on a prototype, as a confidence building measure, the method was validated on a Jaguar aircraft through a lead-in flight test programme. On the Jaguar, both GPS and de-coupled Inertial Navigator methods were tried out. The results clearly brought out the advantages of GPS method. The paper also presents the flight test results from Tejas, which were compared with theoretical estimates. The paper concludes with the 'lessons learnt' from these interesting flight test exercises.