Longitudinal Control of Hypersonic Aircraft: an Alpha Follow-Up Scheme

A longitudinal control scheme is presented that is applicable to hypersonic flight vehicles (HSV). It addresses the unique control issues of hypersonic flight, namely the long path-mode time constant and the requirement for precise angle-of-attack control at the engine inlet. HSV's low C/sub L/ characteristic, if conventional elevator pitch control is used, would result in a very large T/sub /spl theta/2/ (the flight-path to attitude lag). A "g" command, "alpha follow-up" (GAF) scheme is presented that is designed using successive loop closures and by applying a conceptual "pseudo-system" where needed. The final design was implemented on the Generic Hypersonic Aerodynamic Model Example (GHAME) model at NASA Dryden, and evaluated by a NASA test pilot familiar with the SR-71. The vehicle was found to have acceptable flying qualities. The "alpha follow-up" scheme offers an interesting solution to the hypersonic flight control problem and would require some accommodations to the present GHAME design (such as high authority body-flaps).