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Flight-Path Generation in Inertial Quality

Aerodynamic flight simulation is commonly used for pilot training and for system performance analysis and verification. The former application focuses on creating a piloting experience that is similar to real flight in routine or extreme situations. This includes detailed replication of the cockpit (instruments, controls and functionality) and motion cueing (in a full flight simulator). Aircraft dynamics, control forces and atmospheric effects are modeled with emphasis on similarity in handling characteristics and aircraft performance. Modeling errors, for example in the dynamic response to control inputs, must be small enough so that they are not perceivable by human pilots.

Automated flight-path generation.
Automated flight-path generation.

In the case of aerodynamic flight simulation for system performance analysis and verification, one generic cockpit can be used to control a wide range of aircraft models since the human interface is not of primary interest. The main objective is to replicate the aircrafts true system dynamics as exactly as possible. If the system under test is part of the aircrafts control system, high modeling accuracy of input-output behavior is required (including actuator and engine dynamics, center of gravity movement, performance limits, data latencies and most influential navigation system errors). For testing navigation systems, the simulator should replicate true aircraft flight paths and corresponding navigation sensor measurements as closely as possible.

Convergence of ideal dead-reckoning inertial navigation to reference trajectory [Goercke2013].
Convergence of ideal dead-reckoning inertial navigation to reference trajectory [Goercke2013].

For the detailed analysis of navigation algorithm behavior, e.g. of error generation and propagation, it is essential to be able to control all relevant error sources in simulation. This includes the possibility to simulate the ideal case where all measurements and models used for navigation are free of errors. Therefore, the trajectories produced by an aerodynamic flight simulator should allow ideal simulation of the navigation method with minimal resulting navigation errors. For inertial navigation methods, the trajectories must be consistent with respect to kinematic relationships, meaning that these should be satisfied by the data with negligible error (for example the integral relationship between specific force, angular rate and position over time). This is equivalent to negligible errors when integrating the strapdown inertial navigation equations in time for zero simulated measurement and gravity model errors using the trajectory data. This requirement is called the inertial quality requirement for the generated data, as it is a prerequisite for the assessment of inertial navigation systems in simulation: The navigation error can only be related to the simulated errors in IMU measurements or gravity model, if the remaining error for an ideal simulation of the navigation algorithm is negligible.

Literature

  • L. Goercke, F. Holzapfel, and J. Dambeck, “Aerodynamic Flight Simulation in Inertial Quality,” in Proceedings of the 2013 International Technical Meeting of The Institute of Navigation, 2013, pp. 415–425.

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