4.1 Hydraulic Systems Flashcards
Why use Hydraulics?
effective and efficient method of power amplification, precise control of load rate, position and magnitude, ability to handly multiple loads simultaneously, smooth vibration free power output, hydraulic fluid transmission medium for heat transfer/lubricant
What are some hydraulic system loads?
Landing gear, primary flight controls, secondary flight controls, utility systems (thrust reverser, cargo handling, doors, ramps, emergency electrical power generation)
What are some design challenges for hydraulics?
system complexity scales with size/weight, high level of redundancy, leakages, contamination, bad heat dissipation (low vel), flow losses, temperature sensitive fluid properties, heavy load
What are important fluid properties to consider for hydraulics?
Viscosity (high for good seal, low for low flow resistance, power loss and lower temperature), Chemical stability (no oxidation and deterioration), Flash Point (temperature where a fluid ignites momentarily), Fire Point
What types of Hydraulic fuels exist?
Mineral oil based(HL, HLP, HLPD for military, not fire resistant), Environmentally acceptable fluids, Fire-resistant water containing fluid, fire resistant water free fluids (HFDU, HFDR, synthetic anhydrous fluids composed of phosphate esters, e.g. Skydrol used in civil)
What are the Key Hydraulic System Parameters and what do they mean?
- Pressure: common are 3000psi and 5000psi
- Integrity: flight critical system or loss or degradation can be tolerated
- Flow rate
- Emergency or reversionary use
- Heat load and power dissipation
- Duty cycle - ratio of energy demand -> load profile
Name top level hydraulic system design conventions for conventional aircraft:
- Multiple independent centralized systems (each engine drives dedicated pumps, no fluid transfer between systems to maintain integrity)
- System segregation
- Multiple control channels - flight control: needs multiple indep. actuators or control sufaces, - fail-safe failure modes
Name top level hydraulic system design conventions for more electric aircraft:
same as conventional but: More local and dedicated electrical systems:
tail zonal system for pitch, yaw
aileron actuators for roll
electric driven hydraulic power pack for emergency landing gear and brake
What power sources for pumps exist?
displacement pumps:
engine driven pump EDP
Electric motor pump EMP - more backup or during ground operations
Air driven pump ADP
Name all Types of Pumps:
Gear pump:
fixed displacement, used on engine fuel conrols, gearbox lube systems, contamination tolerant, not good above 1500psi
Vane pump:
contamination tolerant, catastrophic failure modes, high pessure capability
Gerotor Pump
fixed displacement, used on gearbox lube systems, contamination tolerant, not good above 1000psi
Piston pumps:
fixed or variable displacement pump
not contamination tolerant
standard solution for aircraft hydraulics, high pressure tolerant >5000psi
What are some pump losses to consider?
leakage, bypass, internal fluid and mech friction
What is the purpose of hydraulic filters?
to clean the hydraulic fluid, preventing foreign particles and contaminating substances
What are some filter element types
micron(specifically treated paper solids > 10 micrometer are filtered)
porous metal
magnetic
What type of valves exist
flow control valves -> control flow direction
pressure control valves -> control speed and pressure
What do accumulators do?
store an amount of pressurized hydraulic fluid, dampen pressure surges
