Robust control concept for a hypersonic test vehicle

For an unmanncd hypersonic test vchiclc nit11 ramjct propulsion, pitch control requircmenls and dyiiamics characteristics are considered. Scvcral rcquircmcnts for pitch control powcr are identified and applicd lo the tcst vchiclc. For improving inhcrent damping and stability dcficicncies of longitudinal charactcristics, :I robust control system with fixed gains is considcrcd which fcatures fecdback of pitch ratc and angle of attack. For achieving controller robustness, thc Multi-ModclApproach is applied. The stabilization capability is considered in regard to cxisting control powcr margins and dctrimental effccts of controller timc dcl:i!s and rate limitations of control surface deflcctions. Nomenclature coefficicnt matrix matrix for control input drag cocllicient zcro lift drag lift dcpcndent drag pitch control dcflcction drag accclcration duc to gravity altitude radius of inertia controllcr cocfficicnts Mach number mass pitch ratc time to double controller dcad time thrust components velocity componcnt velocity vector of state variablcs coordinatcs of centcr of gravily rcference coordinatcs (body-lixcd) angle of attack 6 vcctor of control variables <S<, pitch control deflection anglc o'?. thrust setting Y flight path angle (0 n natural frequency i damping cocfficient 0 pitch anglc Introduction Currently, significant efforts in acrospace research arc conccrncd with hypcrsonics technology in order to cslablish a basis for the development of aerospace plancs (c.g., Refs. 1-3). There arc challenging problcms in many tcchnological areas so that a nccd in fundamental rcscarch cxists the goal of which is to provide progrcss i n this highly interesting field. A promising approach for contributing to progrcss is :I dcdicatcd unmanned tcst vehiclc which is aimed at addrcssing key technology issucs. Thc issues ondcr consideration in this papcr relatc to the hypersonic flight regime up to Mach 7. Here, a nccd cxists for sludying and solving problcms which conccrn ramjet engines rcquired for propelling a vchicle, aerothermodynamics for providing lirt and flight dynamics for achieving adcquate stability and control. Thcrc arc slrong interdependcncies bctwccn the addresscd arcas so that a close cooperation of thc various groups involvcd is rcquired. It is the purposc of this paper to consider kcy issues ol hypersonic test vchicle dynamics and its subslantial ititcrdepcndencies with ramjet propulsion and acrothcrmodynamics. L Alternative Concepts for Flying Testbeds In Germany thc Federal Ministry for Rcscarch and Tcchnology (BMFT) iniliated in 1988 the national Hypcrsonics Tcchnology Programmc (HTP) to preparc advanced tcchnologics nccded for thc design and devcl* Prof. Dr.-Ing. Gottfried Sachs, Director, Inslitutc of Flight Mechanics and Flight Control. Associatc Fellow AIAA. t Dipl.-Ing. Wolfgang Schodcr, Rcscarch Assistant, Institutc of Flight Mechanics and Flight Control. Dipl.-Ing. Matthias Heller, Research Assistant. Institutc of Flight Mechanics and Flight Control. 5 Dip1.-Ing. Pcter W. Sachcr, Manager Hypcrsonics Tcchnology Programmes. Member AIAA. Copyright