Chapter 12. Other Equipment

12.3. Hydraulic system

The capacity of the control computer, engine and other major units provided with the help of different kinds of moving mechanical forces. According to the type of the moving forces, there are hydraulic, pneumatic and electrical systems. Each of these systems are characterized by some specific features that contribute to its use for the specific needs of aircraft.

The hydraulic system provides control of aircraft and certainly influences on flight safety. Reliability is achieved by multiple redundant hydraulic system.

Using of the hydraulic system on the modern aircraft is predetermined relatively low weight and size, high speed response and low inertia of moving mechanisms then in the electric motors. Devices of the hydraulic systems can provide high values of pressure in a short time and provide easy fixation position of the moving mechanisms.

The main disadvantages of hydraulic system:

  • large mass;
  • dependence the devices operetion of the enviroment temperature;
  • damage of components of the hydraulic system, which can lead to system malfunction.

On modern aircraft the main working fluid is hydraulic oil jet.

Hydraulic system of every modern aircraft is used to perform many different functions. Each function has a direct impact on flight safety. Accordingly, it should be done properly and in time, that is marketed under the command of its execution, if it present.

The hydraulic system consists of two parts: a network of pressure sources and users network . The main functions of a network of pressure sources are creating pressure in the network, energy storage, pressure regulation in system, distribution of the working fluid between users and store it. Useres network consists of separate parts, each of which is required for actuation of a particular mechanism. In particular hydraulic system provides the driving force for such systems:

  • Control of aircraft and wings mechanization : ailerons, slats, flaps, intertseptory, air brakes and others.;
  • landing gears extantion;
  • turn of nose landing gear;
  • Landing gears break;
  • Windshield cleaning ;
  • engine reverse;
  • opening-closing of hatches and doors.

To achieve the maximum reliability of some systems operation some users use the moving force of several hydraulic systems. Thus, in case of failure of one system user can enforce its functions by another one. Accordingly, each function of aircraft control is performed using the maximum number of hydraulic systems available on this aircraft, and other critical systems are at least two.

Simplified scheme of the hydraulic system shown in Fig. 186.The main source that creates pressure in the hydraulic system is hydraulic pumps powerplant. Using a special mechanical mechanism engine of aircraft we switche hydraulic pumps. In order to create pressure (as a backup power system) electric pumps,gas turbines and accumulators can be used .

Fig. 186 . A simplified structure of the hydraulic system

Various hydraulic systems interconnected via torques whicht transmit power without controlling fluid exchange.

The hydraulic system consists of long pipelines and a large number of different devices and subsystems; control and manage are implemented using avionics equipment.

The structure of the construction of the hydraulic system and manage of it depends on the type and design of aircraft.

Hydraulic system of A-320. The aircraft has three full-scale hydraulic systems, "blue", "green" and "yellow". Each of these systems is connected to a separate hydraulic fluid reservoir and a separate pump device (Fig.187).

"Green" hydraulic system pump is powered by a single engine, "blue" - from the electric pump and pump air turbine and is used as a backup, and "yellow" - from the second pump hydraulic system and electric pump motor . The main purpose of this system is to create pressure in the system on the ground with the purpode of cargo loading /unloading . When the engine is off and no external power supply "yellow" system contains hand pump that is used to create pressure in the opening and closing hatches.

Fig. 187 . Hydraulic system of A-320

Each system includes a hydraulic accumulator and creates pressure in the system from ground sources.To control the hydraulic system hydraulic system monitoring unit is used (Hydraulic Systems Monitoring Unit - HSMU). Control and signaling modes of the hydraulic system is indicated by ECAM.

AVIONICS training course materials represented only in demonstrative mode. If it useful, all grammar mistakes will be corrected and more documents will be added. Let me know if you interest in avionics.
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Avionics training in details by
Ostroumov IvanOSTROUMOV Ivan, PhD
Associate Professor, www.ostroumov.sciary.com