Flying Quality Analysis And Gust Alleviation System Design Of Elastic Vehicles

In this paper, flying quality and gust alleviation system of elastic vehicles are discussed. Today,more and more lightweight composite materials have been used by advanced aircrafts in order toreduce the weight and improve the flight performance. As a result, the flexibility of aircrafts,especially wings, is increased. That makes the modal frequency of structure reduced, which causes thedynamic coupling between the body movement and the structure movement. For these advancedaircrafts, on one hand, flying quality analysis is different from conventional aircrafts; on the otherhand, gust alleviation system will be more complicated. The research in this paper could be dividedinto four parts. First, two criteria, which could reflect the influences of flexible deformation on flyingquality, are selected and campared by simulating, they are respectively the CAP and the time-domainNeal-Smith. Second, one kind of elastic aircraft is used as an example, by which three longitudinalflight dynamic models are established. They are rigid body model ignoring flexible structure,quasi-static model based on quasi-static approximation, and elastic body model including elasticmodes. The CAP and the TDNS are used to contrast the differences on flying quality among thosemodels above, and flying quality of closed-loop systems with preliminary control laws is alsoanalyzed here. Third, the gust response analysis and gust load calculation are discussed. Finally,according to H2/H∞state feedback controller and H∞output feedback controller based on LMI,gust allivation systems are designed for rigid body model and elastic body model.The research results show that the CAP can reflect the influence of quasi-static deformation onflying quality, while the TDNS can evaluate the flying quality of elastic aircraft morecomprehensively and more accurately. Because there is no limit to the wind models, the H∞outputfeedback controller has more advantages than the H2/H∞state feedback controller. For elasticvehicles, the dynamic effects of flexible deformation must be considered in flying quality analysis, atthe same time, it is necessary to design gust alleviation system based on elastic body model.