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. General Uses
Used for flight control, actuation of flaps, slats, weapons bays, landing gear, breaks
Provides the extra force required to move large control surfaces in heavy aerodynamic loads.

4. A SIMPLE HYDRAULIC SYSTEM

5. 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…

6. Hydraulic Mechanism in Airplane

7. SYSTEM A
SYSTEM B

8. STANDBY SYSTEM

9. PRINCIPLES OF OPERATION
Governed by Pascal’s law
The oil is in contact with both sides of the piston head but at different pressure. 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.

10. 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…

11. Hydraulic Accumulator
A hydraulic accumulator is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source.
An accumulator enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand, and to smooth out pulsations. It is a type of energy storage device.

12. 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

13. 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.

14. 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.

15. 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 equalizer is used.
Flow equalizer is made up of two power pumps placed side by side in which the drive gears of both pumps are connected.

16. 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.

17. 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.

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

19. Problems with Hydraulics
Heavy
High maintenance
Adds cost and creates a logistics problem
Requires space (pumps, hydraulic lines, etc.)

20. Possible Improvements
Electric Actuators:
Consists of a small electric motor, pump and actuator ram requiring about 1 pint of hydraulic fluid
Flight tested by NASA’s Dryden Flight Research Center on a modified F-18.
Provides significant weight savings by eliminating pumps and hydraulic lines
Also could decrease required maintenance