Control and Guidance of Low Altitude Stationary Flight Test Vehicle

Abstract

The flight control and guidance technology to keep the airship around the preset target point against the wind stream in the stratosphere is one of the key technologies of the stratospheric platforms airship system. The stratospheric airships should be an unmanned vehicle and so must be controlled remotely or autonomously. And its air speed is limited to be lower than conventional airships because it must be much lighter than them. So, appropriate flight control and guidance system of the airship is necessary to keep its position around the target point. And the airship must be guided along the predetermined route when it climbs and descends. It is also necessary to control the pressure difference between the gas in the envelope and the atmosphere within the certain range and to keep the moderate rate of climb to enable the pressure control. The Low Altitude Stationary Flight Test was conducted to prove and demonstrate the flight control technology of stratospheric airships. Low Altitude Stationary Flight Test Vehicle that is a 60 m-class unmanned airship and able to reach 4 km altitude was developed for the flight test. The test vehicle has two ducted thrusters and two elevators and two rudders attached to the tail stabilizers and for the flight control. It also has three air ballonets inside its envelope and controls the pressure and buoyancy by changing the mass of the air in each ballonet. These ballonets are also used for the pitch control by modifying the position of the center of the gravity. The control effecters are driven both remotely by the ground operator and autonomously from the FCC (Flight Control Computer) on the test vehicle. Along with the development of the test vehicle, a numerical simulation system for the airship has also been developed. The characteristics of the airships, such as deviation of the mass and the center of gravity, effects of the superheat/supercool, virtual mass, are considered in the simulation model. FLOPS (FLight and OPeration Simulator) was developed for the flight test by NICT. It was a flight simulation system using the same human interface that is used at the actual flight test. It was used for the pilot training, tuning of the control parameters and checking the flight plan. The flight test was conducted from May to November in 2004. It was conducted step by step proving the function of the control systems. Eight flights were conducted and the target of the flight test that is the geo-stationary flight at the 4 km altitude was achieved. The control and guidance system has functioned as expected and enabled the test vehicle to climb to the expected altitude and to perform the geo-stationary flight within the prescribed flight area. The flight tracks of the actual test flight were agreed to the result of the simulation very well.