The fuel management system for a fixed-wing aircraft has been developed and
explored with the model-based systems engineering (MBSE) methodology for
maintaining the center of gravity (CoG) and analyzing flight safety. The system
incorporates high-level modeling abstractions that exploit a mix of behaviors
and physical detail resembling real-world components. This approach enables
analysis for a multitude of system requirements, verification, and failure
scenarios at high simulation speed, which is necessary during system definition.
Initially, the CoG is maintained by directly accessing the flight deck valves
and pumps in both wings and controlling them through the bang-bang control law.
In the refinement phase of the fuel system controller, the manual and individual
controls of the valves and pumps are replaced with an autonomous fuel transfer
scheme. The autonomous scheme achieves no more than a 20 kg difference in fuel
between the wings during normal conditions. In the event of failures, the
controller achieves no more than a 100 kg difference in fuel between the wings.
The difference returns to 20 kg within a settling time of 5 sec and a maximum
allowable overshoot safety margin of 10% of the 20 kg difference in normal
conditions (±2 kg). The specification 20 kg/5 sec band varies with pump and
valve parameters. Although this specification is sufficient for a system-level
model, it can be refined with pump and valve parameters and nonlinear effects in
the network. The system identification method is also trialed to control an
individual engine by estimating a proportional integrator derivative (PID)
controller of the engine plant. The safety tests are initiated in a user
interface enabling error detection and injection. The fuel system model is used
for analyzing refueling, defueling, and jettison scenarios with appropriate flow
rates.
Besides the CoG maintenance, several aspects of configurations of the system’s
functional and logical architecture, considering increasing component redundancy
and activities for MBSE framework, have been conducted. The logical and temporal
verification of system requirements is performed in simulation. To ensure
traceability and coverage, the requirements and the associated verification
artifacts are digitally linked to the implementing blocks. Test scenarios are
implemented for investigating resultant and emergent behaviors at various levels
of system hierarchy by isolating either the subsystem or the components that
have been performed. To further check out the MBSE workflow, the fuel system
controller code has been directly emitted from the controller model for DO-178C
objectives. At the mission-level validation, a jettison scenario is developed
for a mission and flight plan in the digital mission engineering and systems
analysis environment of Systems Tool Kit (STK) Aviator. The aircraft fuel system
configuration is set using the fuel system model.
The power of MBSE methodology supported by a modeling and simulation framework
provides plenty of opportunities for through-life analysis in the early design
lifecycle phase.
