An alternative approach for determining the Position Error Corrections (PEC) in static pressure measurement at altitude

Thomas Dumoulin, Royal Netherlands Aerospace Centre, NLR, The Netherlands

Abstract

Currently, flight tests are still required in determining the Position Error Correction (PEC) in static pressure measurement for qualification requirements. The alternative approach described in this paper makes use of different types of flight tests and a computational analysis. Computational Fluid Dynamics (CFD) is used with a highly accurate 3D scan of the aircraft to provide an a priori model for the PEC as a function of the inherent variables.

This a priori model is validated and delicately tuned by means of flight tests. At first the conventional tower fly by method is used to measure the PEC at sea level conditions. Thereafter, extrapolation flights at altitude are performed. Traditionally, this is accomplished by measuring the atmospheric static pressure inflight by means of a trailing cone or static bomb. This requires comprehensive engineering work to design and manufacture the device as well as install the device on smaller pressurised aircraft.

The alternative approach does not require this modification to the aircraft or the use of additional devices on the aircraft. Acceleration-Deceleration manoeuvres are executed at altitude parallel to straight and aligned isohypses in the atmospheric pressure field. In addition, the Global Positioning System (GPS) altitude differences are translated into ambient static pressure differences to correct for the relatively small change in altitude during these runs. In this manner the so-called “delta mode” is used to determine the PEC at altitude and further tune the a priori model.

The resulting 3sigma accuracy of the PEC for the aircraft used in this study is 35 Pa, much less than the strictest Reduced Vertical Separation Minima (RVSM) requirements of 68 Pa.