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UNMANNED AIR VEHICLE home > Research > Unmanned Air Vehicle
1. Introduction
 
Single-antenna GPS provides position and velocity measurements, from which pseudo-attitudes can be synthesized for a fixed wing aircraft. This suggests the potential of single-antenna GPS receiver as the sole sensor of the aircraft. Based on the previous works (Fig.1,2), we developed the flight control system for a small endurance UAV only using a low cost single-antenna GPS receiver that provides navigation solution at 4 Hz.
 
Figure 1. UAV of GNSS Lab.
 
 
2. Flight Control System Design
 
2.1 Aircraft Feature
 

The small endurance UAV (Fig.3) developed by KARI is the traditional tailless aircraft with horizontal control surfaces on its main wing surface. It has rudders at the wing tips for vertical stabilization. 


 

2.2 Controller Design
 

We selected the linear quadratic regulator (LQR) control law based on full states feedback. For longitudinal control, altitude and airspeed hold controller was designed. For lateral control, bank hold, heading hold, line and circle following controllers were designed. Integral-error feedback was added by applying LQR control laws to the dynamic system augmented with integral-error state, to remove the steady state error due to external disturbance and inaccurate model information.

 

 
 
3. Flight Test
 

The U-blox 4 module GPS receiver was used as the main sensor. Flight modes consist of manual, stick auto, hold mode, waypoint navigation, pre-program and emergency modes such as return home. Each controller of hold mode was tested. As a result, the error of airspeed and altitude converged within 1 m/s and 1 m in the steady state (Fig.7, 8). Due to the limitation of linear controller, the error of bank hold controller increased in proportion to bank command (Fig.11). Heading hold controller converged within 2 degree (Fig.12). In the waypoint navigation mode, circle following and path following controller was tested. The cross track error was kept within 10 m (Fig.9, 10, 13, 14).


 
 
 

4. UAV's future and Works in SNU GNSS Lab.
 
GPS keeps being modernized and other satellite navigation systems such as GALILEO and GLONASS are under development. Accuracy, integrity, availability and continuity of satellite navigation systems will be more improved. Thus the role of developed system will be able to be expanded further as a main control system of a low-cost UAV.
 
Seoul National University GNSS Lab (SNUGL) developed an automatic flight control system of UAV based on a single-antenna GPS. In 2003, SNUGL succeeded in waypoint path following control. In 2007, we successfully demonstrated fully automatic control of the UAV from takeoff to landing only using single antenna GPS. After that we applied single-antenna GPS based automatic flight control system to flying wing platform, small endurance UAV of KARI (Korea Aerospace Research Institute). In 2009 winter, automatic flight of small endurance UAV of KARI using single antenna GPS only was successfully demonstrated.

 

 
IEEE AES Magazine 2009.05
 
Inside GNSS Magazine 2010.04




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