Seminar Air craft hydraulic system Report PPT Download
Hydraulics is based on a very simple fact of nature – you cannot compress a liquid. You can compress a gas (think about putting more and more air into a tire, the more you put in, the higher the pressure). If you’re really strong you can compress a solid mass as well. But no matter how much pressure you apply onto a liquid, it isn’t possible to compress it. Now if you put that liquid into a sealed system and push on it at one end, that pressure is transmitted through the liquid to the other end of the system. The pressure is not diminished.
Aircraft Hydraulics Definition
It is a system where liquid under pressure is used to transmit this energy. Hydraulic systems take engine power and convert 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) – A hydraulic pump converts mechanical power to hydraulic power
(2) – An actuating cylinder converts hydraulic power to mechanical power
(3) – Landing Gear
(4) – Engine power (mechanical HP)
If an electrical system were used instead of a hydraulic system, a generator would take the place of the pump and a motor would take the place of the actuating cylinder
Some Hydraulic Systems in Aircrafts
1. Primary control boosters
2. Retraction and extension of landing gear
3. Sweep back and forth of wings
4. Opening and closing doors and hatchways
5. Automatic pilot and gun turrets
6. Shock absorption systems and valve lifter systems
7. Dive, landing, speed and flap brakes
8. Pitch changing mechanism, spoilers on flaps
9. Bomb bay doors and bomb displacement gears
Principles of Operation
Part of the hydraulic system is the actuating cylinder whose main function is to change hydraulic (fluid) power to mechanical (shaft) power. Inside the actuating cylinder is a piston whose motion is regulated by oil under pressure. 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 is sent. The piston rod of the actuating cylinder is connected to the control surface.
As the piston moves out, the elevator moves down. As the piston moves in, the elevator moves up. The selector valve directs the high pressure oil to the appropriate side of the piston head causing movement of the piston in the actuating cylinder. As the piston moves, the oil on the low pressure side returns to the reservoir since return lines have no pressure!
The differential in oil pressure causes movement of the piston. The force generated by this pressure difference can be sufficient to move the necessary loads. Each cylinder in
the plane, boat, etc., is designed for what it must do. It can deliver the potential it was made for; no more, no less. Air loads generally determine the force needed in aircraft applications.
A hydraulic system transmits power by means of fluid flow under pressure. The rate of flow of the oil through the system into the actuating cylinder will determine the speed with which the piston rod in the actuating cylinder extends or retracts. When the cylinder is installed on the aircraft, it is already filled with oil. This insures that no air bubbles are introduced into the hydraulic system, which can adversely affect the operation of the system.
Aircraft Hydraulic System Reservoir
Functions of the Reservoir
1. Provides air space for expansion of the oil due to temperature changes
2. Holds a reserve supply of oil to account for
a. thermal contraction of oil.
b. normal leakage – oil is used to lubricate piston rods and cylinder seals. When the piston rod moves, it is scraped to remove impurities that might collect on the rod when returning into actuating cylinders. If many actuating cylinders are operating at the same time, then the amount of oil lost is greater.
c. emergency supply of oil – this case occurs only when the hand pump is used.
d. volume changes due to operational requirements – oil needed on side 2 of piston head is less than that needed on side 1 of cylinder piston (which occurs during actuation).
3. Provides a place to remove air or foam from liquid.
4. Provide a pressure head on the pump, that is, a pressure head due to gravity and depends upon the distance of the reservoir above the power pump.
The best shape is a domed cylindrical shape. Not only can it be mounted easily, but it can be made to order.
Hydraulic System Hand Pumps
1. Hydraulic system hand pumps are used to test the hydraulic system when the plane is on the ground; and,
2. acts as an Emergency system of power
Principles of Operation
The hand pump converts the power of a human being to hydraulic horsepower. For this reason, such pumps are used in older model aircraft.
Real planes have segments called ailerons inserted in the wings and segments called rudders and elevators inserted respectively in the vertical fin and horizontal stabilizer. The pilot controls their position from the airplane cockpit. When the pilot moves them into the air-stream, they cause the plane to react to air pressure. The pilot uses them to go right or left and also up and down.
Advantages of Hydraulic Systems Over Other Systems
1. It is lighter in weight than alternate existing systems.
2. It is dead beat, that is, there is an absence of sloppiness in its response to demands placed on the system.
3. It is reliable; either it works or doesn’t.
4. It can be easily maintained.
5. It is not a shock hazard; it is not much of a fire hazard.
6. It can develop practically unlimited force or torque.
The actuating cylinder can change hydraulic power to linear or rotating motion. It has a reduction gear in it to reduce rotating motion to that amount which is needed.
Previously, systems used to control motion by using steel cables connected by pulleys between the controlling mechanism (such as the pedals) and the controlled surface (such as the rudder). The cables were affected by expansion rates of the cables due to temperature changes. Hydraulic systems can control motion without worrying about the effect of temperature since it is a closed system (not open to the atmosphere) compared to a cable system. This means better control of the plane and less lag time between the pilot’s movement to control the plane and the response by the control surface.
Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.