Lesson 11: Aircraft Hydraulic Systems
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Transcript of Lesson 11: Aircraft Hydraulic Systems
Lesson 11: Aircraft Hydraulic Systems
Aircraft Hydraulic Systems
• The Average modern aircraft utilizes hydraulic systems to operate several systems.
• Landing gear• Wing flaps• Speed and wheel brakes• Flight controls
Aircraft Hydraulic Systems
• Pascal’s Law• Pressure exerted on a fluid in an enclosed
container is transmitted equally and undiminished to all parts of the container and acts as right angles to the enclosing walls.
Aircraft Hydraulic Systems
• Hydrostatic Paradox• The pressure exerted by a column of liquid is
determined by the height of the column and is independent of its volume.
Aircraft Hydraulic Systems
• Neither the shape nor the volume of a container affects the pressure. Only the height of the column does this.
Changes In Velocity and Pressure (Bernoulli)
• When a fluid or gas is supplied at a constant flow rate through a duct, the sum of the pressure energy and velocity energy is constant.
• If pressure increases, velocity decreases proportionally or, if pressure decreases, velocity increases proportionally.
• Kinetic Energy = Velocity (Ram Pressure)• Potential Energy = Pressure (Static Pressure)
Changes In Velocity and Pressure (Bernoulli)
Aircraft Hydraulic Systems
• Relationship Between Pressure, Force, And Area
• Pressure is a measure of the amount of force that acts on a unit of area.
• Pressure is measured in pounds per square inch (psi).
• Force = Pressure x Area
Aircraft Hydraulic Systems
• Relationship Between Pressure, Force, And Area
Aircraft Hydraulic Systems
• Relationship Between Area, Distance, And Volume
• The area of the piston, the distance it moves, and the volume of the fluid displaced.
• Volume = Area x Distance
Aircraft Hydraulic Systems
• Relationship Between Area, Distance, And Volume
Aircraft Hydraulic Systems
• Mechanical Advantage In A Hydraulic System
• Two major advantages
–Ease with which force can be transmitted over large distances and into sealed compartments.
– Large gain in mechanical advantage made possible by varying the size of pistons.
Aircraft Hydraulic Systems
• Mechanical Advantage In A Hydraulic System
Aircraft Hydraulic Systems
• Mechanical Advantage In A Hydraulic System
• If a large amount of movement is need but only a small amount of force we can use a large piston to drive a smaller one.
• The fluid moved by the large piston will enter the cylinder with the small piston and move it a distance equal to the volume of fluid divided by the area of the small piston.
Aircraft Hydraulic Systems
• All hydraulic systems are essentially the same, whatever their function.
• Regardless of application, each hydraulic system has a minimum number of components, and some type of hydraulic fluid.
Hydraulic Fluid
• The fluid used in aircraft hydraulic systems is one of the system’s most important parts.
• The fluid must flow with a minimum of opposition.
• Must be incompressible• Good lubricating properties• Inhibit corrosion and not attack seals• Must not foam in operation
Hydraulic Fluid
• Some characteristics that must be considered.
• Viscosity• Chemical Stability• Flash Point• Fire Point
Hydraulic Fluid
• Viscosity is the internal resistance to flow.
• Gasoline flows easily (has a low viscosity)• Tar flows slowly (has a high viscosity)
• A satisfactory liquid for a hydraulic system must have enough body t give a good seal at pumps, valves and pistons; but it must not be so thick that it offers excessive resistance to flow.
• The average hydraulic liquid has a low viscosity.
Hydraulic Fluid
• Chemical Stability is the ability of the liquid to resist oxidation and deterioration for long periods.
• Excessive temperatures have a great effect on the life of a liquid.
• Liquids may break down if exposed to air, water, salt, or other impurities.
Hydraulic Fluid
• Flash Point is the temperature at which a liquid gives off vapor in sufficient quantity to ignite momentarily when a flame is applied.
• High flash point is desirable for hydraulic fluids.
Hydraulic Fluid
• Fire Point is the temperature at which a substance gives off vapor in sufficient quantity to ignite and continue to burn when exposed to a spark or flame.
• High fire point is required of desirable hydraulic fluids.
Types Of Hydraulic Fluid
• Vegetable-base
• Mineral-base
• Synthetic Fluid
Types Of Hydraulic Fluid
• Mineral-base Fluid• MIL-H-5606 is the most widely used hydraulic
fluid in general aviation aircraft.
• Kerosene-type petroleum product.
• Dyed red for identification
Types Of Hydraulic Fluid
• Synthetic Fluid
• Non-petroleum base hydraulic fluid for use in high performance piston engine and turbine powered aircraft.
• Most commonly used fluid of this type is Skydrol
• Colored light purple.
Basic Hydraulic Systems
• Open Hydraulic System
Basic Hydraulic Systems
• Closed Hydraulic Systems
Basic Hydraulic Systems
• More modern brake system
Basic Hydraulic Systems
Power-pack Hydraulic System
Basic Hydraulic Systems
• System Components
• Reservoirs• Pumps• Selector Valves• Check Valves• Hydraulic Fuses• Accumulators• Actuators
System Components
• Reservoirs
• In an in-line reservoir, space is provided in the reservoir for fluid expansion and the escape of entrapped air.
• Jet aircraft that operate at altitudes where there is not enough air pressure to assure a positive feed of fluid to the pump have hydraulic reservoirs pressurized.
System Components
• Hydraulic reservoir pressurized by hydraulic system pressure.
System Components
• Pumps
• Powered Pumps
–Constant displacement moves a specific volume of fluid each time its shaft turns.
–Variable displacement does not move a constant amount of fluid each revolution, but only the amount the system will accept.
System Components
• Constant Displacement Pumps
• Gear Pump
• Gerotor Pump
• Vane Pump
System Components
• Gear Pump
• Medium volume of fluid
under pressure.
System Components
• Gerotor Pump
System Components
• Vane Pump
• Moves a large
volume of fluid
under low pressure
System Components
• Valves
• Selector valve• Sequence valve• Priority valve• Pressure Control valves
Plug-Type Selector Valve
• Low pressure
systems
Popper-Type Selector
Sequence Valves
Priority Valves
Hydraulic Fuses
System Components
• Accumulators
• All accumulators consist of a high strength container divided by some form of movable partition into toe sections, or compartments.
• One compartments connected to the hydraulic pressure manifold, and the other is filled with compressed air or with nitrogen.
System Components
• Accumulators
System Components
• Actuators
• Single-Acting Linear
• Double-Acting Unbalanced Linear
• Double-Acting Balanced Linear
System Components
• Single-Acting Linear (Brakes)
System Components
• Double-Acting Unbalanced Linear (Landing Gear)
System Components
• Double-Acting Balanced Linear (Flight Controls)