It is a system where liquid under pressure is used to transmit this energy. Hydraulics systems take engine power and converts it to hydraulic power by means of a hydraulic pump. This power can be distributed throughout the airplane by means of tubing that runs through the aircraft. Hydraulic power may be reconverted to mechanical power by means of an actuating cylinder, or turbine.

1. AIRCRAFTS HYDRAULIC
SYSTEM

2. INTRODUCTION
 Hydraulics is based on the fact that liquids
are incompressible
 Hydraulic system is a system where liquid
under pressure is used to transmit energy
 In it a hydraulic pump converts mechanical
power to hydraulic power
 An actuating cylinder converts hydraulic
power to mechanical power.

3. A SIMPLE HYDRAULIC SYSTEM

4. DEVICES USING HYDRAULIC
SYSTEMS IN AIRCRAFTS
 Gun turrets
 Auto pilot
 Shock absorption systems
 Dive, landing, speed and flap brakes
 Bomb bay doors
 Doors and hatchways
 Landing gears, wing flaps, etc…

5. PRINCIPLES OF OPERATION
 Governed by Pascal’s law
 The oil is in contact with both
sides of the piston head but
at different pressures. High
pressure oil may be pumped
into either side of the piston
head.
 The selector valve
determines to which side of
the actuating cylinder the
high pressure oil (red
colored side) is sent.

6. PARTS OF THE POWER
SYSTEM
 RESERVOIR
 ACCUMULATOR
 FILTER
 POWER PUMP
 SYSTEM RELIEF VALVE
 PRESSURE REGULATOR

7. POWER SYSTEM

8. RESERVOIR
FUNCTIONS
 Holds reserve supply oil to account for normal
leakage, emergency supply of oil, volume
changes, thermal contraction of oil,
 Provides pressure head on the pump, a place
to remove air or foam from liquid, air space for
expansion of the oil due to temperature changes
etc

9. RESERVOIR
CONSTRUCTION
 Material: 5052 aluminium
 Size: takes into account all oil
volumes in operational
requirements, thermal expansion,
leakage, etc.
 Shape: domed cylindrical shape,
due to ease of construction &
mounting

10. ACCUMULATORS
PRINCIPLE
 Gas valve lets in
compressed gas at ½
system pressure
 Diaphragm pops up &
oil is sent through
system
 When system
pressure>accumulator
pressure, diaphragm
deploys

11. ACCUMULATORS
USES
 Absorbs the shocks due to rapid pressure
variations in a hydraulic system
 Helps maintain a constant pressure within
the hydraulic system
 Helps the hydraulic pump under peak
pressure loads
 It is an emergency source of power
 Spherical shape is preferred for
accumulators

12. POWER PUMPS
FUNCTION
 Is to change mechanical horsepower to
hydraulic horsepower
TYPES
 Gear pumps: move fluid based upon the
number of gear teeth and the volume
spacing between gear teeth.
 Piston pumps: move fluid by pushing it
through the motion of the pistons within
the pump

13. POWER PUMPS
PRINCIPLES OF GEAR
PUMPS
 The liquid from the
reservoir is pushed
between the gear teeth.
 The oil is moved around
to the other side by the
action of the drive gear
itself and sent through
the pressure line.

14. POWER PUMPS
PRINCIPLES OF
RECIPROCATING
PISTON PUMP
 As the cylinder block
rotates, space
between the block and
the pistons increase,
letting in more oil.
 As the block rotates
from bottom dead
center, the reverse
occurs and the pistons
push oil out through
the outlet

15. SYSTEM RELIEF VALVE
PRINCIPLE
 The adjustment
screw is set for a
certain pressure
value P2.
 When the pressure
increases, the
poppet will move
up, forcing the
excess liquid in

16. Douglass Pressure Regulator
 high pressure oil from
the power pump opens
valve C and also act
on piston A
 piston A pushes Ball B
off seat D, the oil goes
through passage D
into the center
chamber back to the
reservoir.

17. HAND PUMPS

18. Selector Valves
 Position (1) is the position of the selector valve, for
example, upon the extension of the landing gear or the
lowering of flaps.
 Position (2) is the position of the selector valve upon
retraction of the landing gear or the raising of the flaps

19. FLOW EQUALISER
 If wing air loads on one wing are
greater than on other, during
wing sweep back or sweep
forward, motion occurs
unevenly.
 To synchronize wing sweep
back or sweep forward flow
equaliser used
 flow equalizer is made up of two
power pumps placed side by
side in which the drive gears of
both pumps are connected

20. ACTUATION CYLINDER
 The function is to take the
pressure & hydraulic fluid flow &
change them into linear or rotary
motion.
 Single piston double rod is an
equal displacement cylinder used
in aileron system or automatic
guidance system
 Double piston-double rod
actuating cylinder used in bomb
bay doors

21. ADVANTAGES
 It is lighter in weight than alternate existing
systems.
 It is dead beat, that is, there is an absence of
sloppiness in its response to demands placed on
the system.
 It is reliable; either it works or doesn't.
 It can be easily maintained.
 It is not a shock hazard; it is not much of a fire
hazard.
 It can develop practically unlimited force or
torque.

22. CONCLUSION
Hydraulic systems determine flight worthiness,
usability and reliabity.