Error Induced at Installed Air Data Sensors due to Extra-Design Variation in Local Flow Field

Abstract

*† In this paper the computed error in pressure and local flow orientation at installed air data sensors of a modern fighter aircraft is presented. The source of this error is a proposed aerial refueling probe modification in the vicinity of air data sensors. This modification was not part of basic design (i.e. is extra-design) and therefore causes errors in addition to those normally present (and catered for in system design) due to variation of flow conditions such as angle-of-attack (AOA) and sideslip angle (β). These errors adversely affect critical aircraft systems like the fly-by-wire flight control system. It is, therefore, necessary to quantify these additional errors for subsequent correction. In the present study the errors are computationally evaluated near M=0.6 at low-to-moderate AOA and β, which are the conditions of interest to designers. Since the proposed modification is major and has other aerodynamic repercussions as well, therefore the complete aircraft with and without the modification was computationally evaluated. Thus, quantifying the air data errors is a by product of this comprehensive study. The results of this study indicate significant induced errors in terms of variation in static pressure and flow orientation at the location of the air data probes. This error reduces for the air data probe located farthest from the proposed aerial refueling probe. In this study the computed induced error has been characterized as function of angle-of-attack and sideslip angle for all the affected air data sensors.