Scheme for the Balance Between Stability and Maneuverability of Hypersonic Vehicle

Since the aerodynamic center moving backward sharply in hypersonic flight,the stability margin of the hypersonic vehicle increases largely while the maneuverability decreases.We proposed a novel method to solve this contradiction.We used relaxed static stability(RSS)to improve the maneuverability in hypersonic flight,and designed the stability augmentation system(SAS)to ensure the stability in subsonic flight.Therefore,the relationship between static stability and maneuverability was quantitatively analyzed in the first step,and the numerical value of RSS was obtained on the premise of good maneuverability.Secondly,the relationship between static stability and aerodynamic parameters was quantitatively analyzed.We properly adjusted aerodynamic parameters based on the quantitative relationship to achieve the specific static stability set in the first step,and therefore provided the engineering realization methods.The vehicle will be statically unstable in subsonic flight with the specific static stability.Lastly,SAS was needed to ensure the stability of the vehicle in subsonic flight.Simulation studies were conducted by comparing the linear SAS to the nonlinear SAS,and the results showed that the nonlinear dynamicinversion controller can synthesize with proportional-integrall-derivative(PID)controller robustly and stabilize the hypersonic vehicle.

Stability characteristics and airworthiness requirements of blended wing body aircraft with podded engines

Blended-Wing-Body(BWB)aircraft have a relatively short fuselage and no horizontal tail,and they usually adopt podded engines and a V tail instead of a vertical tail.Generally,BWB aircraft have decreased longitudinal and directional static stability and damping.In this paper,the three-axis static and dynamic stability characteristics of an example BWB aircraft with podded engines are studied.According to the differences in flight characteristics of BWB aircraft and conventional aircraft,the different airworthiness requirements for BWB aircraft are analyzed:first,based on current airworthiness regulations and transport aircraft flying quality specification,the relaxation requirement of longitudinal static stability for BWB aircraft is studied;second,the influences of podded engines on longitudinal trim,attitude and trajectory responses and maximum directional control power requirement of BWB aircraft are analyzed;third,the changes in the proportional relationships between the takeoff characteristic speeds of the example BWB aircraft are analyzed.In view of these variations in directional control power requirement and relationships between takeoff characteristic speeds,new recommendations for airworthiness evaluation are proposed for BWB aircraft.The conclusions of this paper are helpful references for configuration design,flight control law design and airworthiness evaluation of BWB aircraft.