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Adaptive flight control system (AST-FCS) for the ATLANTE UAS

An adaptive flight control system (Adaptive Self-Tuning Flight Control System, AST-FCS) based on ADEX adaptive predictive expert control methodology has been applied in a simulation of the ATLANTE UAS (Unmanned Aircraft System) carried out by the Flight Dynamics and Control Laws Department of Airbus Military. This development corresponds to the first phase of a project to implement an AST-FCS in this UAV (Unmanned Airborne Vehicle).

Atlante is a heavy, tactical, long range, unmanned aircraft financed by the Economic and Competitiveness Ministry of Spain through the Centre of Industrial Technology Development (CDTI). It will be used by the Spanish military to support operations such as Intelligence, Surveillance, Target acquisition, and Reconnaisance (ISTAR).

Using this simulation model, the UAS under AST-FCS control, has been subjected to continuous, severe turbulence, significant measurement errors, and large dynamic changes to the actuators. Under these conditions, performance has achieved levels of stability, robustness and overall precision as would be expected under ideal flight conditions. Under ideal flight conditions, the AST-FCS is capable of guiding the critical variables under control close to the values demanded with great precision and under various flight scenarios within the obvious limits of flight envelopes and physical possibility. The fundamental characteristic of the AST-FCS is its capacity for adaptation which removes the need for precise knowledge of the aircraft dynamics and copes with guaranteed stability and robustness to the operating conditions which are characterised by a high level of uncertainty.

The AST-FCS control strategy consists basically in a longitudinal block and a lateral-directional block whose performance is presented in the following illustrative examples.

Longitudinal control block

The longitudinal block comprises an airspeed control using throttle and an altitude control which a Guidance block generates a desired trajectory based on a current and demand altitude to generate the required climb rate. This value is the set point of a climb rate controller which generates the necessary pitch angle. The value of this required pitch angle is sent to a guidance block which, in turn, outputs a desired pitch rate value based on the current and demanded pitch angle. This output will be the set point of the pitch rate controller which will act on the elevator.

Lateral-directional control block

The lateral-directional block consists of sideslip control in which the objective is to maintain sideslip at zero using the rudder, and heading control where a guidance block generates a heading rate based on a current and desired value for the heading angle. This latter value is the set point of a controller for heading rate and which will generate the roll angle needed to reach it. The desired roll angle will be sent to the guidance block which sends the desired roll rate as an output signal based on the current and required roll angle. This output will be the set point of the roll rate controller which acts on the ailerons.

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