Turbojets require variable exhaust nozzles to fit high-demanding applications; however, few reports on nozzle control are available. The purpose of this paper is to investigate the possible advantages of an exhaust gas control through a variable exhaust nozzle. The control design method combines successful linear active disturbance rejection control ($LADRC$) capabilities with a loop shaping controller ($LSC$) to: (i) allow designing the closed-loop characteristics in terms of gain margin, phase margin and bandwidth, and (ii) increase the LSC disturbance rejection capabilities with an extended state observer. A representation of the nozzle dynamics is obtained from first principles and adapted to achieve a stream-velocity-based control loop. The results show that the resulting controller allows improving the expansion of the exhaust gas to the ambient pressure for the whole operating range of the turbojet, increasing the estimated thrust by 14.23% during the tests with experimental data.

The autonomous operation of turbojets requires reliable, accurate, and manageable dynamical models for several key processes. This article describes a practical robust method for obtaining turbojet thrust and shaft speed models from experimental data. The proposed methodology combines several data mining tools with the intention of handling typical difficulties present during experimental turbojet modeling, such as high noise levels and uncertainty in the plant dynamics. The resulting shaft speed and thrust models achieved a percentage error of 0.8561% and 3.3081%, respectively, for the whole operating range. The predictive power of the resulting models is also assessed in the frequency domain. The turbojet cut frequencies are experimentally determined and were found to match those predicted by the identified models. Finally, the proposed strategy is systematically tested with respect to popular aeroengine models, outperforming them both in the time and frequency domains. These results allow us to conclude that the proposed modeling method improves current modeling approaches in both manageability and predictive power.

Microturbojets are one of the main thrust sources in several high-performance unmanned aerial vehicles (UAVs). In many applications these vehicles operate in conditions that may demand performance at the limits of microturbojets’ capabilities. These conditions can eventually result in component degradation and engine malfunction. Safety and reliability demand to monitor and diagnose the health of the motor during the operation of the vehicle. One of the main microturbojet health indicators is the exhaust gas temperature (EGT). The scope of this article is to evaluate the estimation accuracy and computational cost of several EGT models through extensive experimental data. The evaluated models include classical, data-based, and novel approaches: an adiabatic nozzle representation, a nozzle model with a lineal correction, a nozzle model including heat transfer, a genetic programming model, a feed-forward neural network, a polynomic approximation and a multiphysics model. This evaluation provides information regarding the advantages and disadvantages of each model. The results show that the best-suited model depends mainly on the application and available identification data.

Purpose: Aircraft pitch control is fundamental for the performance of micro aerial vehicles (MAVs). The purpose of this paper is to establish a simple experimental procedure to calibrate pitch instrumentation and classical control algorithms. This includes developing an efficient pitch angle observer with optimal estimation and evaluating controllers under uncertainty and external disturbances. Design/methodology/approach: A wind tunnel test bench is designed to simulate fixed-wing aircraft dynamics. Key elements of the instrumentation commonly found in MAVs are characterized in a gyroscopic test bench. A data fusion algorithm is calibrated to match the gyroscopic test bench measurements and is then integrated into the autopilot platform. The elevator-angle to pitch-angle dynamic model is obtained experimentally. Two different control algorithms, based on model-free and model-based approaches, are designed. These controllers are analyzed in terms of parametric uncertainties due to wind speed variations and external perturbation because of sudden weight distribution changes. A series of experimental tests is performed in wind-tunnel facilities to highlight the main features of each control approach. Findings: With regard to the instrumentation algorithms, a simple experimental methodology for the design of optimal pitch angle observer is presented and validated experimentally. In the context of the platform design and identification, the similitude among the theoretical and experimental responses shows that the platform is suitable for typical pitch control assessment. The wind tunnel experiments show that a fixed linear controller, designed using classical frequency domain concepts, is able to provide adequate responses in scenarios that approximate the operation of MAVs. Research limitations/implications: The aircraft orientation observer can be used for both pitch and roll angles. However, for simultaneousyaw angle estimation the proposed design method requires further research. The model analysis considers a wind speed range of 6-18 m/s, with a nominal operation of 12 m/s. The maximum experimentally tested reference for the pitch angle controller was 20°. Further operating conditions may require more complex control approaches (e.g. scheduling, non-linear, etc.). However, this operating range is enough for typical MAV missions. Originality/value: The study shows the design of an effective pitch angle observer, based on a simple experimental approach, which achieved locally optimum estimates at the test conditions. Additionally, the instrumentation and design of a test bench for typical pitch control assessment in wind tunnel facilities is presented. Finally, the study presents the development of a simple controller that provides adequate responses in scenarios that approximate the operation of MAVs, including perturbations that resemble package delivery and parametric uncertainty due to wind speed variations.

Aircraft pitch control is fundamental to improve the performance of unmanned aerial vehicles. This paper presents the instrumentation and modeling process of an experimental platform for aircraft pitch control. A complementary filter is designed to improve the angular position estimation based on inertial measurements. The platform was used for the implementation of different controllers in a wind tunnel facility: a Ziegler-Nichols PID and a loop shaping compensator. The test bench allows the implementation of typical continuous-time linear and non-linear controllers. The plant identification process is designed to compute the parameters that meet the open loop time domain characteristics and the closed loop frequency characteristics. The time delay in the control loop is computed through an experiment and used for the loop shaping design process. The controllers are implemented and compared according to its time domain performance. The best suited control is then analyzed in terms of perturbation rejection and more demanding tests. The article shows that the resulting test bench is suitable for the experimental evaluation of typical pitch angle control strategies. Due to the integration with a wind tunnel, the test bench is able to simulate a wide range of flight conditions. Including extreme conditions that would not be safe in real flight experiments.