Determination of X-36 stability margins using real-time frequency response techniques

Abstract

The NASA/Boeing X-36 remotely-piloted aircraft was designed to demonstrate key technologies for a tailless agile fighter configuration. The X-36 completed a highly successful 31-mission flight test program at the Dryden Flight Research Center, Edwards AFB, CA in November, 1997. The X-36 flight control system architecture included a single control path in each axis to allow estimation of open-loop transfer functions. Real-time estimation of single-input, single-output open-loop transfer functions using frequency response techniques allowed rapid and safe expansion of the X-36 flight envelope. Flight data obtained using real-time stability margin (RTSM) methods provided insight to control law performance and indicated changes required for stability margin improvement. The RTSM capability also greatly increased hardware-in-the-loop simulation productivity, significantly reducing control law development time. It was demonstrated that RTSM frequency response techniques can be applied from a remote site, provided voice and data communication are available. This paper presents the real-time stability margin measurement techniques developed for the X-36 flight test program along with results from simulation and flight test. Real-time application of multi-input, multi-output singular value analysis to the X-36 lateraldirectional controls is also addressed.