Control of a helicopter during autorotation

Download
2018
Şansal, Kaan
Autorotation is a maneuver that requires no power and it is used in rotorcrafts when last operating engine is lost. It is an extremely complex state of flight and landing successfully after total power loss requires considerable skill. Main idea behind autorotation is that, by descending with a controlled rate, available potential energy is used as a source that turns main rotor at desired speed for providing thrust and flight control. Just before touchdown, ground speed and descent rate must be reduced for safe landing which can only be possible by managing available energy effectively. In this study, an autonomous autorotation controller is developed and implemented to a real-time high fidelity mathematical model of a full-scale light utility helicopter. For developing autorotation controller that consists of a standard inner-outer loop architecture, full linear and reduced order linear models are used which are obtained by linearizing and reducing the order of non-linear helicopter model around different trim points. 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. These outer-loop controllers also generate references for velocity tracking controllers which provides attitude references to the inner loop attitude hold controllers. While designing attitude and heading hold controllers, Aeronautical Design Standard 33E-PRF (ADS-33EPRF) specifications are used as a guideline for evaluation of helicopter handling qualities. Details of linearization and model order reduction techniques that are used during the study are expressed. 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 from different initial flight conditions. Results demonstrate the capability of the proposed controller for achieving safe power-off landings.

Suggestions

Design and analysis of fixed load crushable column type energy absorbing mechanism for a helicopter seat
Öztürk, Gülce; Kayran, Altan; Department of Aerospace Engineering (2018)
Crashworthiness is the survivability of occupants inside a vehicle during a crash. In helicopters, crashworthiness is ensured by three subsystems; the landing gear, floor structure and the seats. Because of the critical role of the seats in helicopter crashworthiness evaluation, dynamic performance of the seat has to be studied in depth. There are different regulations in which requirements of survivable loads and crash conditions are defined. In this respect, a seat that is used in helicopter should be cer...
Separation simulation for helicopter external stores and generation of safe separation envelopes
Kapulu, Özge; Şahin, Melin; Department of Aerospace Engineering (2015)
In many aerospace applications, simulations are used to predict the behavior of the flight vehicle and reduce the number of flight tests required. In this thesis modeling and development of separation simulation tool for helicopter external stores is carried out. Detailed explanations of mathematical modeling, procedure of store separation analysis and collision detection approach from flight dynamics point of view are presented. The nonlinear mathematical model of armed configuration of Black Hawk helicopt...
Shape optimization of helicopter subfloor intersection element under crash loading
Türe, Mustafa Okan; Dağ, Serkan; Department of Mechanical Engineering (2017)
The aim of the crashworthiness is maintaining a survivable space for occupants and absorb crash energy as much as possible. The statistics showed that 85% of all rotorcraft accidents can be survivable. Thus, crashworthy design has direct effect on occupants' survival. This thesis analyses a longitudinal beam and lateral frame intersection point on helicopter subloor. Analysis is performed on ABAQUS Dynamic/Explicit solver. Analysis includes high deformation levels, self-contact and nonlinearities. 110 kg ma...
A New method for the calculation of static flight loads of rigid fuselage of rotorcraft
Gül, Seyhan; Yaman, Yavuz; Department of Aerospace Engineering (2016)
The loads acting on a rotorcraft fuselage in pull-up, push-over, and yaw maneuvers and gust conditions are required to be calculated by civil and military standards. For each maneuver and the gust condition, different flight and rotor speeds, mass states, altitudes, and temperatures are required to be analyzed. This may add up to thousands of conditions. Calculation of fuselage loads for all these conditions with transient analysis is not only computationally expensive but it also requires a lot of engineer...
A Comparison of model following control systems for helicopter flight control near hover
Okçu, Ilgaz Doğa; Kutay, Ali Türker; Department of Aerospace Engineering (2015)
Helicopters are complex, coupled dynamic systems with unstable behavior. Countless studies have shown that decoupling the helicopter flight dynamics greatly reduces pilot work load and increases the handling qualities. Design guidelines such as Aeronautical Design Standard 33E-PRF (ADS-33E), which are developed as a means of measuring the handling qualities of a given helicopter, emphasizes that coupling between pitch, roll, yaw and heave degrees of freedom are undesired. ADS-33E also gives flight dynamics ...
Citation Formats
K. Şansal, “Control of a helicopter during autorotation,” M.S. - Master of Science, Middle East Technical University, 2018.