Different Methods Preventing Interactions Problems in Hydraulic Systems

The design of an airplane hydraulic system concerns the sizing of pipes, pumps and related supply pressure regulation devices. The design of system and subsystems must be performed in an integrated form: in fact different configuration choices regarding each subsystem can appreciably affect the pumps sizing and the system stability. The work highlights the interactions between the design choices concerning both the generation/power regulation and the users in all the aspects important for the operation of the complete system outlining the design of a defined hydraulic system of an airplane. To this end the dynamic simulation models (with associated calculation programs) capable of analyzing the behavior of the complete system have been made; employing it a series of investigations was carried out, aiming to analyze the dynamic behavior of different configurations of the system in similar operating conditions. Particularly, the present work regards the comparison between two different methods/devices capable of preventing major interactions by limiting the actuation speed in aiding load conditions. The above mentioned methods concerns the implementation of a ramp generator in the control law of the critical users or the employment of control servovalves having a reduced spool stroke acting in the aiding load conditions. In conclusion, the paper compares the advantages and shortcomings of the two solutions (reduced spool stroke and ramp generator); as it is usual in these cases, the cheaper solution is not necessarily the best one, in terms of actuation rate control capability. The present work focuses all the considerations regarding the design activities.