Browsing by Author "Nalbantoğlu, Volkan"

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Citation - Scopus: 0
Control of a Helicopter During Autorotation
(Vertical Flight Society, 2019) Sansal,K.; Ilhan Konukseven,E.; Nalbantoglu,V.; Airframe and Powerplant Maintenance
This paper demonstrates an autonomous autorotation controller, which is developed and implemented to a real-time high-fidelity mathematical model of a full-scale light utility helicopter. For developing the autonomous autorotation controller that consists of a standard inner-outer loop architecture, full linear and reduced order linear models, which are obtained around different trim points, are utilized. Inner loops are used for stabilizing the helicopter as well as for holding attitude, heading and speed of the helicopter. While designing the outermost loop, autorotation maneuver is divided into five different phases (steady state descent, preflare, flare, landing and touchdown) and different controllers are developed for each of these phases. Collective commands generated from these controllers are blended using fuzzy transitions. Comparison results of non-linear and linearized models are presented together with details of control law formation. For assessing performance of the autorotation controller, real-time simulation results of integrated high-fidelity model are provided. Results demonstrate the capability of the proposed controller for achieving safe power-off landings. © 2019 The Vertical Flight Society. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 4
Multiloop State-Dependent Nonlinear Time-Varying Sliding Mode Control of Unmanned Small-Scale Helicopter
(Sage Publications Ltd, 2020) Ozcan, Sinan; Salamci, Metin U.; Nalbantoglu, Volkan; Airframe and Powerplant Maintenance
Time delays, parameter uncertainties, and disturbances are the fundamental problems that hinder the stability and reduce dramatically the tracking performance of dynamical systems. In this paper, a new state-dependent nonlinear time-varying sliding mode control autopilot structure is proposed to cope with these dynamical and environmental complexities for an unmanned helicopter. The presented technique is based on freezing the nonlinear system equations on each time step and designing a controller using the frozen system model at this time step. The proposed method offers an improved performance in the presence of major disturbances and parameter uncertainties by adapting itself to possible dynamical varieties without a need of trimming the system on different operating conditions. Unlike the existing linear cascade autopilot structure, this study also proposes a nonlinear cascade state-dependent coefficient helicopter autopilot structure consisting of four separate nonlinear sub-systems. The proposed method is tested through the real time and PC-based simulations. To show the performance of the proposed robust method, it is also bench-marked against a linear sliding control control in PC-based simulations.
Citation - WoS: 8
Citation - Scopus: 9
Nonlinear Sliding Sector Design for Multi-Input Systems With Application To Helicopter Control
(Wiley, 2020) Ozcan, S.; Salamci, M. U.; Nalbantoglu, V.; Airframe and Powerplant Maintenance
The ability of helicopters to hover and land vertically has spurred an interesting field of research on the development of autonomous flight for these rotatory wing aircrafts. Linear control theory with gain scheduling, which is based on linearizing the system at the equilibrium points, dominated the helicopter autopilot design. Unlike the linear cascaded autopilot structure used in the existing literature, this paper uses state-dependent linear like structure, including rate-limited actuator dynamics, with cascaded autopilot topology. This approach allows nonlinear control laws to be implemented throughout the entire flight envelope, providing satisfactory robustness and stability over the various parameter uncertainties and time delays. The cascaded autopilot topology with nonlinear dynamical equations contains a new sliding sector control (SSC) mechanism which is derived for multi-input nonlinear dynamical systems. The proposed SSC structure for multi-input nonlinear systems is used in the inner loop of the cascaded autopilot system where the fastest dynamics are required to be controlled for rapid changes in the helicopter dynamical characteristics which enables one to stabilize the helicopter over a wide range of flight conditions. The proposed cascaded autopilot topology with the new SSC mechanism is tested in simulations to assess its robustness and stability properties. To establish its feasibility, the proposed control method is replaced with a suboptimal control method, namely state-dependent differential Riccati equation (SDDRE) method, for the inner loop and the results of the proposed control architecture are compared with those of SDDRE method.