Abstract:
Keywords:
1.Introduction
2. problem statement
In a simple aircraft hydraulic system, the hydraulic system overheat warning
indicates excessive fluid temperature, potentially leading to system degradation,
reduced efficiency, and component failure. Overheating can be caused by fluid
contamination, excessive system load, inadequate cooling or prolonged operation.
Identifying and mitigating the root cause is important to ensure system
performance, safety and prevention of hydraulic failure during flight.
3. Brief explanation of hydraulic system
The Aircraft Hydraulic System is an advanced, high-pressure system that facilitates
the operation of important aircraft components. It is primarily used for the actuation
of flight control surfaces, landing gear deployment and retraction, and thrust
reverser mechanisms, ensuring precise, efficient, and reliable functionality
throughout various flight phases see figure 1. The system consists of pump to
pressurize hydraulic fluid, control valves to direct flow, and actuators to convert
hydraulic energy into mechanical motion. Fluid returns to the reservoir through the
return line after completing the cycle. To prevent overheating, a cooling system is
integrated, incorporating a heat exchanger, and thermal bypass valve to regulate
fluid temperature. Other major components include filters for contamination control,
pressure relief valves for overpressure protection, and check valves for directional
flow control. (Lio, 2016)
Figure 1 The interference between aircraft
hydraulic system and flight control system.
(Karki , 2021)
A simple hydraulic system operates based on Pascal’s Law, where pressure applied
to confined fluid is transmitted equally in all directions, enabling force multiplication
for efficient power transmission as shown. To illustrate more, Hydraulic systems
function as force multipliers, enabling the transfer of mechanical energy with
increased force output. When the cross-sectional area of the output cylinder is twice
that of the input cylinder, the resulting force doubles relative to the applied input
force as shown in figure 2. This fundamental property allows hydraulic lines to
amplify mechanical advantage efficiently. In aviation, this principle is important as it
enables small aircraft pistons to generate sufficient force to actuate large flight
control surfaces, such as ailerons, rudders, and elevators, ensuring precise
maneuverability and control. (NASA, 1996)
Figure 2 A hydraulic system can act as a
force multiplier. (Wood, 2022)
Figure ** on Appendix presents basic aircraft hydraulic system block diagram with
proper cooling system, The pressurized hydraulic reservoir is selected to ensure
steady fluid flow, and it shares component of the main and backup systems,
pressurized by regulated engine bleed air. After the reservoir there are two shutoff
valves on the supply line, which is an important component used to isolate
hydraulic flow in case of an emergency, maintenance or system failure see figure 1.
Figure 3 Reservoir and shutoff valve
The engine-driven pump EDP are piston pumps (fixed displacement) see figure**.
And it selected to provide the main system pressure with constant volume and fluid
flow necessary for aircraft hydraulic operations and it installed after shutoff valve to
facilitate shut-off process in emergency case and to maintain the safety of shutoff
valve. Since the pump delivers a constant flow, excess fluid is typically regulated by
pressure relief valves or hydraulic system pressure regulators to prevent over
pressurization on pressure line and reservoir.
Figure 4 Engine driven pump EDP
This system incorporates three types of filtration mechanisms to ensure hydraulic
fluid integrity. The first category comprises high-pressure filters, strategically
positioned downstream of the EDP and EMDP. These filters are important for
capturing metal particles, dirt, and debris that could compromise the functionality
of high-pressure hydraulic actuators and valves. Additionally, a bypass valve
adjacent to the high-pressure filter facilitates emergency filtration, allowing fluid to
pass a clogged filter. Furthermore, a low-pressure filter is integrated into the return
line before the reservoir, effectively eliminating impurities before the hydraulic fluid
is stored and reintroduced into reservoir.
To further component justification and discussion of latest hydraulic system
development see Appendix**.
A hydraulic accumulator (figure 4) is strategically positioned downstream of HP filter
outlet. It is specifically selected to provide a damping effect, ensuring system
stability and component longevity. Additionally, in the event of pump failure or
hydraulic system depressurization, the accumulator serves as a critical reserve
power source, enabling the continued operation of essential functions such as
landing gear deployment, braking systems and primary flight control actuation.
Modern aircraft, including the Airbus A380, incorporate advanced hydraulic system
components designed for enhanced efficiency and reliability. The A380 features
filter manifolds, which integrate multiple critical components within a single unit.
These include pressure relief valves, high-performance filters, selector valves,
bypass relief valves, and thermal relief valves, which mitigate pressure fluctuations
caused by temperature variations, ensuring optimal system performance, as
illustrated in Figure **.
Figure 6 Main filter manifold
A key advancement in hydraulic system design is the incorporation of a separation
wall within the reservoir, effectively partitioning a dedicated fluid reserve for
independent utilization in either the primary or backup systems. This design
ensures hydraulic fluid availability for critical operations, preventing complete
depletion in the event of a fluid loss or leakage within either system, thereby
enhancing system redundancy and operational reliability.
Notably, this design incorporates sampling valves positioned on the return line
Figure 7 Reservoir with
before the reservoir, specifically selected to facilitate fluid extraction for laboratory
separation wall
analysis. This ensures that the hydraulic fluid maintains compliance with CS-25
cleanliness and performance standards. Additionally, these valves support
regulatory adherence through systematic routine monitoring, enhancing fluid
quality control and system reliability.
