Aircraft System

• Manual or mechanical methods of operation


  • Had several limitations
  • Involved huge man power and long working hours for a particular job
• Smaller aircraft have relatively low flight control surface loads, and the pilot can operate the flight controls by hand
• Hydraulic systems were utilized for brake systems on early aircraft
• Hydraulic system


  Uses a fluid under pressure to drive machinery or move mechanical components
• Components of a hydraulic system


  • Hydraulic fluid
  • Pressure generator or hydraulic pump
  • Hydraulically powered "motor"
  • System "plumbing"
• Components that a hydraulic system might power


  • Wheel brakes
  • Nose wheel steering
  • Landing gear retraction/extension
  • Flaps and slats
  • Thrust reversers
  • Spoilers/speed brakes
  • Flight control surfaces
  • Cargo doors/loading ramps
  • Windshield wipers
  • Propeller pitch control
• Overview of how a hydraulic system works


  1. Hydraulic fluid is pumped from the reservoir into the rest of the system, creating hydraulic power

  2. The pressurized fluid then passes through valves and flows to the actuator where hydraulic power is converted to mechanical energy to achieve the desired function
• Reservoir


  Holds the fluid, usually hydraulic oil, and protects it from contamination
• Piping


  Hollow structures that carry the hydraulic fluid from one location to another within the system
• Hydraulic pumps


  Force the hydraulic fluid from the reservoir to the rest of the circuit
• Fixed displacement pumps


  • Have an unchangeable flow rate, good for jobs with a single action that are repeated for long periods
  • Examples include gear, gerotor and screw pumps
• Variable displacement pumps


  • Can change the flow rate of the fluid and outlet pressure, can power a variety of complex equipment but are more expensive and require more attention than fixed displacement pumps
  • Examples include piston pumps and vane pumps
• Hand or manual hydraulic pumps


  Operated manually by the hand and foot
• Hydraulic actuator


  • Changes the hydraulic power in the fluid into mechanical power to achieve the desired action
  • Can be a hydraulic cylinder which creates linear movement or a hydraulic motor which creates torque and rotation
• Accumulator


  Can be used during emergencies such as Pump failure and supply line drop
• Types of valves


  • Pressure control valves
  • Flow control valves
  • Direction control valves
• Pressure control valves


  Limit the pressure within the system to protect all the components from damage
• Flow control valves


  Influence the rate at which the fluid flows throughout the system by decreasing or increasing the diameter of the opening the hydraulic fluid flows through
• Direction control valves


  • Can stop, start and change the direction of the flow of hydraulic fluid
  • The simplest of these valves is called a check valve and it allows the hydraulic fluid to flow in one direction, while blocking fluid flow in the other direction
• Filters


  Prevent the hydraulic system from being contaminated, essential to ensure the system works effectively and safely
• Suction line filter


  Stops any contaminants in the reservoir fluid getting into the rest of the hydraulic system, located at the input side of the hydraulic pump
• Properties required for hydraulic fluid


  • High Flash Point
  • Adequate Viscosity
  • Lubricant Properties
  • Thermal Capacity/Conductivity
• Lack of maintenance of hydraulic systems is the leading cause of component and system failure yet most maintenance personnel don't understand proper maintenance techniques of a hydraulic system
• Areas of concern for proper hydraulic system maintenance


  • Preventive Maintenance
  • Corrective Maintenance
• Preventive Maintenance tasks for a hydraulic system


  • Change the hydraulic filter
  • Obtain a hydraulic fluid sample
  • Filter hydraulic fluid
  • Check hydraulic actuators
  • Clean the inside of a hydraulic reservoir
  • Clean the outside of a hydraulic reservoir
• Knowledge required for a hydraulic troubleshooter


  • Mechanical Principles / force, work, rate, simple machines
  • Math / basic math, complex math equations
  • Hydraulic Components / application and function of all hydraulic system components
  • Hydraulic Schematic Symbols / understanding all symbols and their relationship to a hydraulic system
  • Calculate flow, pressure, and speed
  • Calculate the system filtration necessary to achieve the system's proper ISO particulate code
• Skills required for a hydraulic troubleshooter


  • Trace a hydraulic circuit to 100% proficiency
  • Set the pressure on a pressure compensated pump
  • Tune the voltage on an amplifier card
  • Null a servo valve
  • Troubleshoot a hydraulic system and utilize "Root Cause Failure Analysis"
  • Replace any system component to manufacturer's specification
  • Develop a PM Program for a hydraulic system
  • Flush a hydraulic system after a major component failure
• General hydraulic knowledge


  • Filters / function, application, installation techniques
  • Reservoirs / function, application
• Preventive Maintenance Task for Hydraulic System

  • Check and record hydraulic pressures
  • Check and record pump flow
  • Check hydraulic hoses, tubing and fittings
  • Check and record voltage reading to proportional or servo valves
  • Check and record vacuum on the suction side of the pump
  • Check and record amperage on the main pump motor
  • Check machine cycle time and record
• During earlier times, weights are lifted using


  Pulleys, levers, blocks and tackles