Fundamental to the derivation of a performance model from flight testing is the determination of the incidence angles of the aircraft in flight. Knowledge of the effective angle of attack at the aircraft centre of gravity is of primary concern. An indication of the angle of sideslip may also be used to ensure there is no significant motion normal to the plane of symmetry or to account for any motion if appropriate.

This Data Item comprises procedures that are used to derive these angles from flight test data.

The flow angle measured by a sensor generally corresponds to the local flow angle at the location of the sensor rather than the true angle. Procedures are listed in this document for determining the true angles of attack and sideslip which take sensor location into consideration.

Calibration procedures for flow angle sensors are also described in detail. Methods discussed include the following.

• Equating angle of attack to pitch angle

• Determining the angle of attack using the energy height method

• Determining the angle of attack using an accelerometer

• Determining the angles of attack and sideslip using INS/GPS

The different forms of sensor that are used to measure the angles of attack and sideslip are also described.

The Data Item forms part of a series of documents devoted to the prediction of aircraft performance from flight test analysis, and should be read in conjunction with ESDU 15001, Aircraft performance from flight test. Part 1: derivation of a mathematical model.