Flashcards
Hydraulic System
Cards in this deck (31)
- 1Hydraulic SystemTransmit and controls power from engine to flight control actuators. Transmit and amplifies the pilot's inputs to move actuators with reduced efforts.
- 2What determines the aerodynamic loadings and stick force for control surfaces displacementMTOW and cruise speed
Higher speed and MTOW = extensive use of hidraulics - 3No failures allowedPrimary and secondary flight controls
- 4Expendable after a failure or they only need to be operated in one directionUtilities
- 5Components of the hydraulic system- A source of energy - A reservoir - A filter - A multiple redundant distribution system - Pressure and temperature sensors - A mechanism for hydraulic oil cooling - A means of exercising demand (actuator, motor, pumps) - A means of storing energy
- 6Advantages of working at a constant nominal pressure- Possibility of activating more than one actuator in parallel
- The sizing phase is simplified - 7Working pressure, what is best?The higher, the better:
- Smaller components/actuators
- Smaller mass flow rates: smaller velocities, lower head losses.
Limit imposed by compressiblity effect, leakages.
Standard value: 21MPa-3000psi - 8Power GenerationThe pump, normally mounted on an engine-driven gearbox.
- 9The pump speed is related toThe engine speed
- 10Universally used pumpVariable delivery, constant pressure (displacement pumps)
- 11Common piston pumps cylinders7-9
- 12The piston pumpThe cylinder block is put in rotation by the drive shaft. The pistons are attached to sliding shoes which rotate against a swash plate. The cylinder and the drive shaft carry the piston with them in rotation. The angle between the swash plate and the cylinder block can be varied changing the pump outflow.
- 13What happen if the system pressure is low?The spring sets the swash plate to its maximum angle, maximizing the pistons displacement and consequently the pump outflow.
- 14What happen with flow leakages in the piston pump?They determine a flow rate decrease at increasing pressure
- 15Pressure Control SystemThe pressure depends on the volume flow rate. Higher volume lower pressure. We want to maintain more or less the same volume flow rate two avoids sudden changes. Two types of pressure control s. :
- Pressure-relief valve
- Variable delivery pump - 16Pressure-Relief ValveSends to a tank the excess of volume flow rate with respect to the system demands. The pump has to work at the maximum power required by the systems (recirculation of oil, heating becomes important). This should be used only when the system demands are close to maximum most of the time.
- 17Variable Delivery PumpThe volume flow rate can be modified by changing the inclination of the swash plate. More efficient, more complex. Larger transient time for adjustment, larger inertia.
- 18Hydraulic Jacks (actuators)Convert the hydraulic energy in linear or rotational motion. Constituted by a cylinder and a piston. The work is done by pressure difference acting on the piston faces.
- 19Types of actuators- Single-acting (locking system)
- Balanced actuator (flight control)
- Unbalanced double-acting actuator (mechanism to raise the landing gear) - 20Types of valves- Directional Control Valves
- Check valves (non return)
- Sequence valves
- Pressure-relief valves
- Pressure Reducing valves
- Shuttle valves
-Flow- Control Valves - 21Directional Control ValveControls flow and direction. The direction of the flow in the user lines depends on the direction of the input
- 22Check valveAllows the passage of fluids only on one direction, wile blocking the opposite one
- 23Sequence ValveUsed two feed two (or more) users in a
pre-determined sequence - 24Pressure-Reducing ValveUsed to feed some subsystems whose design pressure is lower than that of the main line.
- 25Shuttle valveAllow the same user to be fed by two different hydraulic sources (normal and emergency)
- 26Flow Control ValvesControl the volume flow rate over a certain range. Can be used to reduce the speed of operation of an actuator
- 27What is an accumulator?Pressurized fluid storage devices, with the task of storing hydraulic energy and release it in case of need.
- 28Task of an accumulator- Provide emergency supply of fluid in case of emergency
- Damping of pressure fluctuations
- Absorb pressure fluctuations during transients - 29Types of accumulators- Raised weight a. = (size unacceptable)
- Spring-type a. = (heavier than c-g)
- Compressed-gas a. - 30Filters TaskRemove foreign particles from the fluid and protect the sealsand the system components from wearing
- 31Reservoir Task- Work as a heat sink
- Provide head fluid for a pump
- Isolate and separate gas trapped within the working fluid
- Absorb the volume variations
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- Sistemas Flashcards on Hydraulic System, created by Ana Castilla on 11/06/2020.
- Created by
- Ana Castilla · Jun 2020
- Updated
- Jun 12, 2020
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