Dynamic modelling of a compact EHSA for the Stabilization and Command Augmentation System of rotary wing aircraft

Rotary-wing aircrafts, under critical operating conditions, generally use the Stability Control Augmentation Systems (SCAS) to improve stability and manoeuvrability. While fixed-wing aircraft commonly use fly-by-wire systems as the basis for primary flight control, rotary-wing aircraft still primarily rely on hydraulic servosystems to control collective and cyclic pitch of the main rotor and the collective of the tail rotor. As technology has improved, the use of fly-by-wire systems in rotary-wing aircraft has spread to provide more efficient and safer aircraft that require less effort from the pilot to complete their missions. Briefly, the SCAS system is a circuit parallel to the hydraulic-mechanical system that provides the pilot assistance in manoeuvring the machine through electrical signals. This system acts via a limited authority actuator on the aircraft's main control linkage, imitating the pilot-induced command into the movement of the helicopter's main flight actuator. SCAS are system that, in the majority of applications, uses an electro-hydraulic servo actuator position controlled EHSA. The main component of this system is the servo-valve, that functions as an interface between an electrical (or mechanical) input signal and the hydraulic power represented by the flow and pressure output. In this thesis, a dynamic model is developed to simulate, in a MATLAB - Simulink environment, the behaviour of the electro-hydraulic servomechanism used in SCAS. Hence, the system will test only the use of the first stage for servo valve for reasons of compactness, weight, and reduced wear. The purpose of this discussion is to produce an accurate model of the first stage of a jet-pipe servo-valve, and after the aims is to dimensioning and model a compact actuator. Finally, all the tests that were performed necessary to demonstrate the validity, and therefore the usefulness, of the model created will be shown and properly commented on.