Original scientific paper Hydraulic simulators are extremely important in the flight control actuator system's verification process. Flexible nozzle has a number of specifics, comparing to other flight controls, because the load cannot be described, classically, by the hinge moment. Additionally, classical hydraulic simulator, in which the cylinder simulates the load, is not sufficient for performing a complete simulation of the real load. Building a mechanical pendulum, to which a hydraulic cylinder acts, and that rests on two elastic supports, enables simulation of additional phenomena that exist in flexible nozzle, but not in other control surfaces. Force from impulse that exists in reality, and which is impossible to be generated by standard hydraulic simulator, can be realized through the pendulum. This paper demonstrates that a simulator can be designed through modelling of the elastic load using bond graph, without a precise elaboration of direction of forces in elastic structure, just by observing, on energy level, the input of force in flexible structure over the point in which actuator force acts. Simulator with hydraulic cylinder is convenient to be used when there is a need for considering the risk of self-oscillation of flexible joint and nozzle, i.e. for defining the so-called notch filter. Then, the hydraulic cylinder of load simulator can generate the oscillation, frequency and amplitude that match this dynamic case of flexible nozzle actuator's load that is being reduced to its piston rod, without a risk of damaging the flexible structure that exists in the construction of a simulator with pendulum. Keywords: bond graph modelling; electro-hydraulic actuator; flexible nozzle; load simulator; servo-distributor Različite tehnologije modeliranja hidrauličkog simulatora opterećenja aktuatora za upravljanje vektorom potiskaIzvorni znanstveni članak Hidraulički simulatori su posebice važni u procesu verifikacije aktuacijskog sustava za kontrolu leta. Fleksibilni mlaznik ima niz specifičnosti u odnosu na druge komande leta, jer se opterećenje ne može opisati na klasičan način preko zglobnog momenta. Pored toga, klasičan hidraulički simulator, na bazi cilindra koji simulira opterećenje, nije dovoljan za potpunu simulaciju realnog opterećenja. Potrebno je napraviti mehaničko njihalo na koje deluje hidraulički cilindar i koje se oslanja na dva elastična oslonca kako bi se mogle simulirati i dopunske pojave koje postoje kod fleksibilnog mlaznika, a koji ne postoje kod drugih upravljačkih površina. Preko njihala se može zadati impulsna sila koja postoji u realnosti, a koju nije moguće generirati standardnim hidrauličkim simulatorom. U članku se pokazuje da se modeliranjem elastičnog opterećenja preko bond grafova simulator može projektirati bez preciznog razmatranja smjerova i pravaca sila u elastičnoj strukturi, već se samo energetski promatra unošenje sile u fleksibilnu strukturu preko mjesta djelovanja aktuacijske sile. Simulator s hidrauličkim cilindrom je pogodan u slučaju kad treba razmotriti rizik od ...

This paper presents all the significant nonlinearities that exist in the description of an electro hydraulic actuator for flexible nozzle thrust vector control. Starting from practical possibilities of the theory of a nonlinear system (which are based on the analyses of one nonlinearity or one equivalent nonlinearity in the proximity of the linear description of an actuator), this paper explores the possibilities of additional analyses of a nonlinear electro hydraulic actuator for flexible nozzle thrust vector control. These explored possibilities can provide information that is useful for the design of the control algorithm, as well as for the general design of a flexible nozzle and actuator system.

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The hydraulic cylinder is dimensioned based on a static or dynamic criterion, assuming the desired operating pressure. The paper further analyzes the dimensioning of cylinders according to different load categories. The sizing of the hydraulic cylinder affects the choice of control algorithm parameters but also the stability of the system. How the cylinder dimension and the gain of the distributor affect the choice of the integral constant in the control algorithm in the case when we have the PI control law is especially considered. Then we have by definition an unsTable system 1 / s2 to which we provide stability through feedback.