Technical Research Of Initial State To Level Flight Control For Parachute-type Small Aircraft

This paper has focused on a specific stage during the delivery process of a parachute-typesmall aircraft, i.e. parachuting–diving–level flight stage. The article gives a definition ofsuch a stage, and names it as ‘initial-level flight procedures’(or I-LF procedures). Thecorresponding technology directing the aircraft to complete the stage is defined as ‘initial-level flight control’. Referring to general flight control technologies and similar controlprocesses, the paper later summarizes and analyzes the basic research content and keytechnologies contained in the ‘initial-level flight control’.And then the main purposes of thestudy include: establishing a mathematical model for the initial-level flight, giving an in-depth analysis of the law of movement during the stage, deducing the ‘initial-level flightcontrol’ process model, designing a control system which can meet requirements of themission, setting up a controller to conduct experiments for verification, and hence providinga strong theoretical basis for the project implementation of a parachute-type small aircraft.To begin with, this paper gives a mathematical account of the I-LF procedures. Based on theoperational features of a parachute-type small aircraft, four initial phases of I-LF proceduresare introduced as parachuting phase, unfolding phase, initial-level flight phase, and missionflight phase. Then use the state space method to provide a formalized description of the fourphases. On the other hand, according to different states, the I-LF procedure can be dividedinto three stages: parachuting stage, unfolding stage and I-LF stage.And set up mathematicalmodels for every stage respectively. Finally, four characteristics of I-LF procedures areanalyzed based on model derivation.With regard to the four characteristic of I-LF procedures, post-parachuting stability of a smallaircraft hasbeen researched andanalyzed,andthroughtheoretical derivation, the relationshipbetween stability and design parameters of aircraft and parachute has been clarified.Furthermore, simulate the shock that wing unfolding brings and the impact resulting fromwind gusts in real circumstances, and then analyze their influence over post-parachutestability. Based on the analysis above, a complete model of the delivery process of aparachute-type small aircraft has been established. Finally, the features related to controlduring the I-FL procedures are verified by simulation. Based on the verification outcome, this paper designs two different control structures according to different feedback, i.e. pitchangle feedback control structure and tri-magnetometers control structure.Next, the paper focuses on the key technologies related to feedback in the two controlstructures. Since environmental factors during launch can cause unavailability of initialattitude data in the parachuting process, a method using three-axis accelerometer and three-axis magnetometer is designed to solve this problem. Such method is based on the featurethat vectors of geomagnetic and acceleration remain constant throughout parachuting.Another problem arises when using three-axis magnetometer in the initial-level flight controlcannot accurately determine the change of aircraft attitude. To work this out, the paperdesigns a new method where we use the measurement of geomagnetic vector duringparachuting to estimate baseline vector for level flight, so as to determine the attitude change.The breakthroughs in key technologies demonstrate the effectiveness of the two controlstructures, and the scopes of application between the two methods are compared accordingto their characteristics.Finally, the control system using pitch angle feedback is built in this article. During thisprocess, the modeling of a control object with respect to a parachute-type small aircraft hasbeen studied. We propose a method to improve the ability to predict identification resultsthrough changing the form of test data. This method can reduce the risk of early flightexperiment for parachute-type small aircraft. Based on the object model, the control law andcontroller’s hardware have been designed, finally completing the setup of control system.Then apply the system, an I-LF control experiment is successfully conducted. Derivedexperiment data has proved the theoretical analysis to be correct, the design method to befeasible, and the ideas of this paper to be effective.