Project Overview
The Piecewise Linear Control Algorithm Development Project, conducted at ARBON – ARI Technopark, is an R&D initiative focused on developing an advanced control architecture for medium-sized single-spool turbojet engines.
The primary objective is to develop a control algorithm capable of maintaining stable and accurate engine speed regulation across a wide flight envelope, taking into account changing altitude, Mach number, atmospheric conditions, fuel flow requirements, and engine temperature limits.
Unlike conventional fixed-gain control approaches, the project adopts a piecewise linear control architecture in which individual control parameters are optimized for different engine operating regions.
The developed approach aims to improve engine response, RPM tracking accuracy, transition stability, and thermal protection while maintaining compatibility with real-time embedded control systems.
The project combines nonlinear engine modeling, flight envelope segmentation, local linear model development, gain scheduling, control algorithm optimization, and Model-in-the-Loop (MIL) and Software-in-the-Loop (SIL) simulation and verification.
Initiated in May 2026, the project is planned to progress through January 2027, covering the complete development cycle from system requirements and mathematical modeling to control design, simulation, performance evaluation, and technical documentation.
Project Development Timeline
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May 2026
1. System Requirements, Technical Planning and Control Architecture Research
The initial phase focused on technical planning, system requirements analysis, and defining the overall project development strategy. A project kick-off meeting was conducted to establish the work packages, technical objectives, engineering responsibilities, and project schedule.
A comprehensive literature review was carried out covering existing turbojet engine control technologies, including:
- Conventional engine control methods.
- Gain-scheduling control architectures.
- Piecewise linear control approaches.
- Real-time engine control system architectures.
Fundamental turbojet engine operating parameters were also identified, including RPM operating ranges, fuel flow requirements, and engine temperature limits. Altitude and Mach number ranges representing the intended flight envelope were defined.
In parallel, the development of a Model-in-the-Loop (MIL) based modeling and simulation infrastructure was initiated.
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June 2026
2. Nonlinear Turbojet Engine Modeling and Dynamic System Analysis
This phase focused on developing mathematical models representing the nonlinear dynamic behavior of the turbojet engine. Models were established to describe the dynamic relationships between:
- Engine rotational speed (RPM).
- Fuel flow rate.
- Engine inlet temperature.
- Exhaust gas temperature.
The effects of atmospheric operating conditions on engine performance were also investigated. Key atmospheric parameters, including air density, ambient temperature, pressure, and Mach number, were incorporated into the engine modeling framework.
Initial MIL simulations were conducted to evaluate the fundamental operating characteristics of the developed models. In addition, simulation models for thermocouple-based temperature sensors and RPM sensors were developed. Preliminary analyses for flight envelope segmentation were also completed.
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July 2026
3. Flight Envelope Segmentation and Local Linear Model Development
The July phase focused on defining the engine operating regions across the intended flight envelope. Different operating regions were identified, including:
- Low-altitude and low-Mach conditions.
- Medium-altitude and medium-Mach conditions.
- High-altitude and high-Mach conditions.
Local linear engine models were developed to represent the engine dynamics within these individual operating regions.
The development of the Software-in-the-Loop (SIL) simulation infrastructure was also initiated, with sensor and actuator models integrated into the simulation architecture.
MIL verification tests were performed to evaluate how accurately the developed models represented the physical engine behavior. Initial performance analyses were conducted to assess model accuracy and system stability.
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August 2026
4. Piecewise Linear Control Architecture and Initial RPM Tracking Development
During this phase, the design of the piecewise linear control architecture was initiated. Individual controller parameters were defined for different engine operating regions within the flight envelope.
The first version of the RPM tracking algorithm was developed, together with the associated fuel flow control structure. The control algorithms were implemented and tested within the MIL simulation environment.
Simulation results were analyzed using key control performance indicators, including:
- Overshoot.
- Settling time.
- RPM tracking accuracy.
- Overall controller response.
In addition, the fundamental design of safety-oriented protection mechanisms was established, including engine temperature limits and maximum RPM protection.
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September 2026
5. Controller Optimization and Transition Management Between Operating Regions
The September phase focused on improving regional controller parameters and enhancing the stability of the overall control architecture. Controller optimization activities were carried out to improve performance across different flight envelope regions.
A hysteresis-based transition mechanism was developed to minimize potential control oscillations when switching between operating regions. Particular attention was given to RPM stability and fuel flow variations during transitions.
Thermal protection mechanisms considering exhaust gas temperature and engine inlet temperature limits were also integrated into the control architecture.
Initial integration tests of the control algorithm were completed in the SIL environment, followed by preliminary assessments of real-time execution performance.
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October 2026
6. Real-Time Control Software Development and Performance Optimization
The October phase focused on developing a control software architecture suitable for real-time execution. An embedded-system-compatible software architecture was established, and the control algorithm was executed in real time within the SIL environment.
Controller gain optimization activities were completed, and performance analyses were conducted under different flight scenarios. The evaluated scenarios included:
- Rapid engine acceleration.
- Sudden load variations.
- High-temperature operating conditions.
Safety limit mechanisms were also subjected to verification testing. Furthermore, computational load and processing performance analyses were performed to assess the algorithm's suitability for implementation on embedded control hardware.
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November 2026 · In progress
7. System Testing, Performance Benchmarking and Comparative Evaluation
The November phase marks the beginning of comprehensive testing and verification activities.
Performance tests are planned under different altitude and Mach number conditions, with RPM tracking accuracy and fuel flow control performance as the main evaluation criteria. Additional transition stability tests will be carried out to minimize abrupt variations in control signals when moving between different operating regions.
The developed piecewise linear control algorithm will also be evaluated against conventional benchmark control approaches, including:
- PID control.
- Fixed-gain control.
Comparative performance analyses will identify the advantages and limitations of the developed control architecture, and additional controller parameter improvements will be implemented based on the evaluation results.
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December 2026 · Planned
8. Comprehensive MIL/SIL Verification and Final Controller Optimization
This phase is planned to focus on comprehensive verification of the developed control architecture within both MIL and SIL simulation environments, including completion of temperature limit protection analyses and detailed evaluation of transient response performance.
Particular attention will be given to the following performance criteria:
- Overshoot and settling time.
- Dynamic response and stability.
- Engine temperature management.
- Acceleration response.
- High-altitude operating performance.
The controller will also be evaluated under rapid acceleration and high-altitude operating scenarios. Final controller parameter optimization is planned, together with the start of technical reporting and documentation activities.
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January 2027 · Planned project completion
9. Final Verification, Technical Documentation and Project Closure
The final project phase is planned to focus on completing the remaining verification activities and consolidating the engineering outputs. The performance of the developed piecewise linear control algorithm is scheduled to be evaluated across the full defined flight envelope.
Final assessments will cover:
- RPM tracking performance.
- Engine temperature management.
- Transient response characteristics.
- Operating region transition stability.
- Safety limit and protection performance.
- Comparative benchmark analysis.
The final benchmark results will be documented, and the technical documentation package will be completed. Project closure evaluation meetings are also planned to review the engineering outputs and overall project achievements.
Potential future development opportunities, including adaptation and expansion of the control architecture for different turbojet engine platforms, will also be evaluated.
Engineering Capabilities and Technical Scope
This project brings together several advanced engineering disciplines within a unified turbojet engine control development framework. The main engineering capabilities addressed throughout the project include:
- Nonlinear turbojet engine dynamic modeling
- Mathematical system modeling and simulation
- Flight envelope analysis and segmentation
- Piecewise linear control architecture development
- Gain-scheduling and regional controller optimization
- RPM tracking and fuel flow control algorithms
- Temperature monitoring and thermal protection
- Hysteresis-based operating region transition management
- MIL-based control algorithm development and verification
- SIL-based software integration and real-time simulation
- Sensor and actuator modeling
- PID and fixed-gain controller benchmarking
- Transient response and system stability analysis
- Embedded control software architecture
- Computational load and real-time execution analysis
- Technical reporting and engineering documentation
Conclusion
The Piecewise Linear Control Algorithm Development Project represents an advanced R&D initiative addressing the challenges of turbojet engine control across a wide range of operating and flight conditions.
By combining nonlinear engine modeling with flight envelope segmentation and region-specific linear control algorithms, the project aims to establish a flexible and adaptable control architecture.
The integration of hysteresis-based transition management, RPM tracking, fuel flow regulation, and thermal protection mechanisms provides a comprehensive framework for evaluating engine control performance and operational stability.
Through MIL and SIL simulation environments, the developed algorithms are being progressively evaluated under different operating conditions, including rapid acceleration, changing loads, and high-altitude scenarios.
The project also includes comparative benchmarking against conventional PID and fixed-gain control approaches to assess the performance of the proposed architecture.
This project reflects ARBON's engineering capabilities in advanced control systems, nonlinear dynamic modeling, real-time embedded software, simulation-based verification, and aerospace-oriented control technology development.