Hydraulic Systems Summary

Hydraulic Systems Overview

Advantages of Hydraulic Systems

  • Lightweight: More efficient power-to-weight ratio.

  • High Reliability: Reliable operation with minimal failure rates.

  • Low Maintenance: Easier upkeep compared to electric systems.

  • Flexibility: Small pipe diameters allow flexible installation.

  • Load Tolerance: Can withstand overloads without damage.

Hydraulic Circuit Design

  • Critical vs Non-Critical Systems:

    • Critical: Primary flight controls; must function reliably.

    • Non-Critical: Utility functions (e.g., cargo doors) can tolerate some failure.

Components of Hydraulic Systems

  • Main Components:

    • Reservoir

    • Pump

    • Accumulator

    • Valves (Directional, Pressure Control, Flow Control)

    • Actuator

Hydraulic Fluids

  • Types:

    • Vegetable-based: Used in older aircraft.

    • Mineral-based: Common in general aviation (e.g., MIL-H-5606).

    • Synthetic fluids: For high-performance aircraft (e.g., Skydrol).

  • Properties:

    • High flash point

    • Optimal viscosity over temperature range

Hydraulic Actuators

  • Types:

    • Single-acting: Moves in one direction; requires external force to return.

    • Double-acting: Moves in both directions; can be balanced or unbalanced based on piston area.

Applications in Aircraft

  • Simple aircraft: wheel brakes, landing gear.

  • Larger aircraft: flight controls, flaps, thrust reversers.

Emergency Power Sources

  • Accumulators: Provide short-term pressure.

  • Electric Motor Pumps: Serve essential functions briefly during failures.

  • Ram Air Turbines (RAT): Used for continuous emergency power; deployed during failures.

Monitoring and Status Indications

  • Pressure transducers, filter blockage indicators, and temperature warnings ensure system health.

Hydraulic System Design Questions

  • Key parameters: pressure, flow rate, duty cycle, emergency power needs.

  • System must accommodate heat load and dissipation requirements.

Common Aircraft Systems Examples

  • A320 and B767 utilize multiple independent hydraulic systems for redundancy and safety.