AGK systems Lesson 2 Flashcards
Input force x input distance =
output force x output distance
A Smaller piston displaces a volume equal to area multiplied by?
the distance moved (its stroke)
Force =
area x pressure
area x pressure =
force
Passive hydraulic systems use _____ _____ to raise pressure
Passive hydraulic systems use human power to raise pressure
Active hydraulic systems use one or more _____
pumps
Closed centered systems provides
Constant pressure all the time
Active systems can supply:
Constant pressure all the time - closed centered systems
Pressure only when demanded - open centered systems.
Open centered systems provides
Pressure only when demanded -
What fulid do we put into an aircraft system?
Correct specification from an unopened container.
Hydraulic fluid must have these properties:
Low viscosity to allow it to flow freely through the system
Resistance to foaming or creating sludge
Good lubrication qualities
Corrosion resistance
Resistance to heat and thermal stability across the temperature range
High boiling point and low freezing point (e.g., +80°C to -70°C)
Chemically inert
Non-flammable with a flash point above 100°C
Good storage properties.
Hydraulic fluid is available in two common forms:
Synthetic
Hydro-carbon based - Used in systems with butyl rubber/Teflon seals – may be Orange in colour
Phosphate Ester (Synthetic) – Skydrol – usually purple in colour
Mineral
For example DTD 585 which is coloured red
Hydraulic fluids can be very _________ so avoid contact and wear protective clothing
corrosive
Which hydraulic fluid is red?
Mineral Based
Kerosene
Red
Suitable for high pressure systems
Good resistance to foaming
High Boil and Flash Point although flammable
Synthetic rubber seals
Which hydraulic fluid is purple?
Synthetic Based
Phosphate Ester
500A purple in colour
Skydrol
3 Grades in use
500 500A 700
Can be used at very high pressures
Must only be used with the following:
Butyl Rubber Ethylene Propylene
Teflon seals
Advantages of Hydraulic Systems
Excellent for providing large amounts of power
Very little energy is lost in the transmission process
Other advantages include:
> Leaks are relatively easy to spot
Reduced weight when compared to mechanical system
Provide large amounts of force to operate heavy services.
Disadvantages Hydraulic System
The fluid is highly corrosive
The forces generated can require strong structures
Large systems can be quite heavy
Susceptible to fluid contamination
Damage to hydraulic lines
Hydraulic fluid is health risk and environmentally hazardous.
What are the basic components of a hydraulic system
Reservoir
Accumulator
Pump
Double acting cylinder
Non return valves
4 port rotary selector valve
What is the operating range of a hydraulic system?
3000 - 4000psi
Does a hydraulic cylinder provide the same force in both directions?
No, the area is different in each direction due to the rod coming out of the system
Reasons for hydraulic pump failure
Electrics
Engine
No fluid
What does an actuator do?
Convert hydraulic pressure into movement
What’s the difference between single and double acting hydraulic actuators?
Single is pushing against a spring and has one feed.
Double has a double feed, the fluid pushes the piston in each direction?
What are the types of selector valves?
Closed centre selector
Open centre selector
Linear (spool) valve selector
There are two fundamental types of system:
Passive - No hydraulic pump
Active - Mechanically driven pump.
Most ‘transport category’ aircraft have what type of hydraulic system?
Closed centre system
Describe the type of system that’s likely to be seen in a king air?
Uses a self-contained hydraulic power pack, operated by a reversible DC electric motor
Which two liquid storage systems would need pressurising?
Hydraulic fluid
Fuel
Describe the hydraulic system
Stores the hydraulic fluid sufficient for all actuators at full extension
Normally pressurised but may be vented to atmosphere
It allows for fluid thermal expansion and replenishment of system loss
Accepts fluid returning from the low pressure side, usually after cooling
Holds excess fluid to compensate for leaks
Has a sight glass to check the level when:
All system components are at the correct setting
Accumulators are fully charged.
Half atmospheric pressure is at what altitude?
18,000ft
Why use a pressurised reservoir?
Prevents the fluid from boiling at altitude
Provides positive pressure at the pump inlet
Which gas is used in a Hydraulic accumulators?
Nitrogen
EDP is a shortening of
Engine driven pump
Hydraulic pumps may be pressurised by:
Engine driven
Electrical motor driven
Hand operated
Driven by a Ram Air Turbine (RAT)
Driven by a hydraulic motor or Power Transfer Unit (PTU)
Hydraulic pump may break mechanically. How is the accessory gearbox protected from this?
Quill Drive (illustrated) provides a weak ‘shear’ link. In the event of pump seizure the quill drive shears and disconnects – protects the driveline and engine.
Constant Delivery Pump
Constant delivery or fixed volume pump provides fluid
Typically spur gear system
Flow rate dependent on speed of rotation of the gears
Normally requires an automatic cut out valve (ACOV).
Constant delivery pump is always paired with an
automatic cut-out value
An automatic cut-out valve is always paired with a
constant delivery pump
What type of pump is based on a swash plate and provides a constant pressure. It only demands power when pressure is being demanded.
Swash-plate pump
Multiple piston pump
The swash-plate pump is at nil stroke at what point?
When the swash plate is perpendicular to the shaft
A Swash-plate pump may get hot in low demand situations. How is this rectified?
A case drain will allow a calibrated amount of hydraulic fluid can escape and return to the reservoir.
What type of pump does the following describe?
Pump output is not dependent on speed
Output volume is regulated by the control piston
No ACOV or accumulator required
Driven by a gearbox linked to the engine
On start up:
The pump swash plate is at minimum deflection = 0° (upright)
A blocking valve off-loads the pump – recirculates oil inside the pump – pressure to suction
The pump is lubricated by the hydraulic fluid.
Constant pressure pumps
Hydraulic motors are like another component in reverse?
Swash-plate pump
Tell me about hydraulic filters
Micron type filters used using a pleated element with a shape retaining spring
The element is designed to capture contaminants greater than 10 microns diameter
What happens if the filter gets blocked?
If the filter begins to clog:
Differential pressure sensor operates warning light
Or a red filter pop-out button protrudes from main casing
A bypass valve automatically allows unfiltered fluid to flow.
What does a restrictor valve (choke valve) do?
Slows flow in one direction.
What does a shuttle valve do?
Selects between two independent supplies
Aircraft tyres have a carbon content to do what?
Earth the aircraft
Oleo contains:
Nitrogen and oil
What does the oil in an oleo control
compression and extension
In an oleo, what is the spring medium
nitrogen
In an oleo, what is the medium used for dampening.
Hydraulic oil
DTD 585
What type of switches are used for weight-on-wheels and landing gear?
Microswitches
or
proximity switches
When is an undercarriage leg is subject to the greatest tortional load?
the strut on the inside of a tight turn
VLO stands for
Velocity Landing Gear Operating (Travelling (doors open)
VLE stands for
Velocity Landing Gear Extended (Down (doors closed)
VLE is higher for ferry flights
Beware of fuel consumption
