AFS Topic 1 Module 1

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Questions and Answers

What is the primary purpose of practical hydraulic systems in modern aircraft?

To provide oxygen to the cabin

To generate power

To transmit power from one place to another (correct)

To cool the engine

What type of pumps are used in modern aircraft to move an incompressible fluid under pressure?

Vacuum pumps

Pneumatic pumps

Engine driven or electrically driven pumps (correct)

Manual pumps

What is the advantage of hydraulic systems over electric or pneumatic systems in modern aircraft?

They are relatively lightweight and efficient (correct)

They are slower and more labor-intensive

They are only used in emergency situations

They are heavier and more complex

What is the fundamental principle underlying hydraulic systems, as described by Blaise Pascal?

Any increase in pressure on a confined liquid is transmitted equally and undiminished to all parts of the container Signup and view all the answers

What is the unit of measurement for force in practical fluid power?

Pounds or grams (g) or kilograms (kg) Signup and view all the answers

What is the definition of pressure in the context of hydraulic systems?

The force applied over a given area Signup and view all the answers

What is the unit of measurement for pressure in hydraulic systems?

Pounds per square inch (PSI) or grams per square centimetre (g/cm²) Signup and view all the answers

What is the term for the cause of motion or change in the context of hydraulic systems?

Force Signup and view all the answers

What is a key characteristic of the fluid used in hydraulic systems?

Incompressible Signup and view all the answers

What is the purpose of an electrical system interface in a hydraulic system?

To interface with other aircraft systems Signup and view all the answers

What is the main advantage of using hydraulic systems in aircraft?

High power-to-weight ratio Signup and view all the answers

What is the role of hydraulic systems in aircraft landing gear?

To control the movement of the landing gear Signup and view all the answers

What is the relationship between hydraulic systems and fluid power systems?

Hydraulic systems are a type of fluid power system Signup and view all the answers

What is the mechanical advantage of a hydraulic system achieved by?

varying the size of the pistons Signup and view all the answers

What is the unit of measurement for the flow rate in a hydraulic system?

gallons per minute Signup and view all the answers

What is the relationship between horsepower and gallons per minute, pounds per square inch, and a constant value in a hydraulic system?

Horsepower = Gallons per minute x pounds per square inch x 0.000583 Signup and view all the answers

What is the advantage of a hydraulic system over other mechanical systems?

both A and B Signup and view all the answers

What is the pressure produced by a piston of one square inch pressing down with a force of one pound?

one pound per square inch Signup and view all the answers

How much force will be produced by a piston with an area of 20 square inches if it is connected to a cylinder with a piston of one square inch pressing down with a force of one pound?

twenty pounds Signup and view all the answers

What is the volume of fluid displaced by a piston of one square inch pressing down with a force of one pound for every inch it moves?

one cubic inch Signup and view all the answers

What is the relationship between the output force and the input force in a hydraulic system?

output force is greater than the input force Signup and view all the answers

What is the primary function of the selector valve in a hydraulic system?

To control the flow of fluid to the actuating cylinder Signup and view all the answers

What is the purpose of the reservoir in a hydraulic system?

To store an adequate supply of fluid for the system Signup and view all the answers

What is the function of the accumulator in a hydraulic system?

To store energy in the system Signup and view all the answers

What is the function of the heat exchanger in a hydraulic system?

To cool or heat the hydraulic fluid Signup and view all the answers

What is the primary purpose of the pumps in a hydraulic system?

To pressurize the hydraulic fluid Signup and view all the answers

What happens to the hydraulic fluid after it leaves the actuating cylinder?

It is filtered before returning to the reservoir Signup and view all the answers

What is the role of hydraulic system components in aircraft?

To control and transmit power Signup and view all the answers

What is the relationship between hydraulic systems and fluid power systems?

Hydraulic systems are a type of fluid power system Signup and view all the answers

What is the purpose of the electrical system interface in a hydraulic system?

To interface with other systems Signup and view all the answers

What is the characteristic of hydraulic systems that makes them suitable for use in aircraft?

They provide a high mechanical advantage Signup and view all the answers

What is the primary function of an accumulator in a hydraulic system?

To provide a temporary storage of hydraulic fluid under pressure Signup and view all the answers

What is the purpose of a heat exchanger in a hydraulic system?

To cool the hydraulic fluid Signup and view all the answers

What is the primary function of a valve in a hydraulic system?

To regulate the flow rate of the hydraulic fluid Signup and view all the answers

What is the primary function of a filter in a hydraulic system?

To filter contaminants from the hydraulic fluid Signup and view all the answers

What is the primary function of an actuator in a hydraulic system?

To convert hydraulic pressure into mechanical energy Signup and view all the answers

What is the product of force and distance?

Work Signup and view all the answers

What is the unit of force in the MKS system of units?

Newton Signup and view all the answers

What is power in terms of force, distance, and time?

Force multiplied by distance divided by time Signup and view all the answers

If 1 newton-metre equals 1 joule, what is 1 joule equal to in foot-pounds?

0.7376 ft-lb Signup and view all the answers

What is the unit of distance in most power computations?

Feet Signup and view all the answers

What is the formula for calculating work?

Force multiplied by distance Signup and view all the answers

What is the formula to calculate power in a hydraulic system?

Power = Gallons per minute x pounds per square inch x 0.000583 Signup and view all the answers

What is the mechanical advantage achieved in a hydraulic system?

Ratio of output force to the input force applied to a mechanism Signup and view all the answers

What is the resulting force produced by a piston with an area of 20 square inches connected to a cylinder with a piston of one square inch pressing down with a force of one pound?

20 pounds Signup and view all the answers

How much horsepower is produced by one gallon per minute of flow under a pressure of one pound per square inch?

0.000583 horsepower Signup and view all the answers

What is the volume of fluid displaced by a piston of one square inch pressing down with a force of one pound for every inch it moves?

1 cubic inch Signup and view all the answers

What is the advantage of hydraulic systems over other mechanical systems?

Ease of transmission of force over large distances and into and out of sealed compartments Signup and view all the answers

What is the unit of measurement for flow rate in a hydraulic system?

Gallons per minute Signup and view all the answers

What is the primary function of a ball check valve?

To hold the ball or cone on its seat when there is no flow Signup and view all the answers

What type of valve is used to relieve excessive pressures that may exist due to thermal expansion of the fluid?

Thermal relief valve Signup and view all the answers

What is the purpose of a system relief valve?

To prevent pressure from building to a point where it might blow seals, burst or damage components Signup and view all the answers

What happens when pressurized fluid in the line builds to an excessive amount in a thermal relief valve?

The valve poppet is forced off its seat Signup and view all the answers

What type of valve is illustrated in this Figure?

Simple ball type relief valve Signup and view all the answers

What is the purpose of a relief valve in a hydraulic system?

To prevent pressure from building to a point where it might blow seals, burst or damage components Signup and view all the answers

Why are pressure relief valves used in hydraulic systems?

To prevent pressure from building to a point where it might blow seals, burst or damage components Signup and view all the answers

What is the main characteristic of a double-acting balanced actuator?

It has the same surface area on both sides of the piston. Signup and view all the answers

What is the function of the teeth on the piston shaft in a rotary actuator?

To mesh with the teeth in a pinion gear. Signup and view all the answers

What is the primary purpose of a heat exchanger in a hydraulic system?

To cool the hydraulic fluid. Signup and view all the answers

Where are heat exchangers typically located in a hydraulic system?

In the return side of the system. Signup and view all the answers

What is an example of an application where a rotary actuator is used?

In the landing gear system of a small aircraft. Signup and view all the answers

What is a characteristic of the fluid used in a double-acting balanced actuator?

It is incompressible. Signup and view all the answers

What is the purpose of the pinion gear in a rotary actuator?

To mesh with the teeth on the piston shaft. Signup and view all the answers

What is a type of heat exchanger used in hydraulic systems?

All of the above. Signup and view all the answers

What is the primary function of the No. 1 system in the GENFLY Hydraulic System?

To supply the primary flying controls, secondary flying controls, and general services Signup and view all the answers

What is the function of the electro-hydraulic pump (EHP) in the No. 1 system?

To pressurise the No. 1 user services if the engine is not running or the EDP has failed Signup and view all the answers

What is the function of the hand pump circuit in the GENFLY Hydraulic System?

To be used during ground maintenance / testing Signup and view all the answers

What is the function of the pressure relief valves in the GENFLY Hydraulic System?

To prevent over-pressurisation Signup and view all the answers

What is the function of the filters in the GENFLY Hydraulic System?

To filter the hydraulic fluid Signup and view all the answers

What is the function of the No. 2 system in the GENFLY Hydraulic System?

To supply a tandem supply to the primary and secondary flying controls supplied by No. 1 system Signup and view all the answers

What is the function of the engine driven pumps (EDPs) in the GENFLY Hydraulic System?

To pressurise the hydraulic fluid Signup and view all the answers

What is the purpose of the individual reservoirs in the GENFLY Hydraulic System?

To store the hydraulic fluid Signup and view all the answers

Study Notes

Hydraulic Systems

Open hydraulic systems, like rivers, can produce great amounts of power, but practical systems are used to transmit power from one place to another.
Engine-driven or electrically driven hydraulic pumps are used in aircraft to move an incompressible fluid under pressure to actuators to perform tasks like raising or lowering landing gear or flaps.

Pascal's Law

Pascal's Law states that any increase in pressure on a confined liquid is transmitted equally and undiminished to all parts of the container, acting at right angles to the enclosing walls.
This means that if a force is applied to a piston in an enclosed vessel, the increase in pressure will be the same anywhere in the system.

Force and Pressure

Force is energy exerted or brought to bear, causing motion or change, expressed in pounds or grams.
Pressure is force applied over a given area, expressed in pounds per square inch (PSI) or grams per square centimeter (g/cm²).

Hydraulic Systems Components

Hydraulic systems consist of pumps, actuators, and other components that work together to transmit power.
Hydraulic systems are used in aircraft for tasks like landing gear and flight control systems.

Mechanical Advantage

Mechanical advantage is the ratio of output force to input force applied to a mechanism.
Hydraulic systems have a large gain in mechanical advantage due to varying piston sizes, allowing for the transmission of force over large distances and into and out of sealed compartments.

Power Transmission

Power in hydraulic systems can be computed by considering the flow rate in gallons per minute and pressure in pounds per square inch.
One gallon per minute of flow under a pressure of one pound per square inch produces 0.000583 horsepower.

Hydraulic Systems Introduction

Hydraulic systems use pressurized liquid to generate, control, and transmit power.
Hydraulic systems are used in aircraft, including landing gear and flight control systems.
Hydraulic systems are a branch of fluid power systems, which move fluid to do work.

Components of Hydraulic Systems

Reservoir: stores hydraulic fluid, supplies the operating needs of the system, and replenishes fluid lost through leakage.
Pumps: engine-driven or hand-driven, boost hydraulic fluid pressure to system requirements.
Valves: control the flow of fluid, directing it to the actuating cylinder.
Filter: removes contaminants from the hydraulic fluid.
Accumulator: stores energy by compressing gas or fluid, releasing it as needed.
Heat exchanger: cools or heats the hydraulic fluid as needed.
Actuators: convert hydraulic pressure into mechanical motion.

Hydraulic System Operation

Hydraulic fluid flows from the reservoir to the pump, then to the selector valve, which directs fluid to the actuating cylinder.
The actuating cylinder moves in response to the direction of fluid flow.

Pascal's Law

States that pressure applied to a confined fluid is transmitted equally in all directions.

Mechanical Advantage in Hydraulic Systems

Hydraulic systems can provide mechanical advantage, increasing force or speed with minimal input force.

Maintenance and Safety

Regular maintenance is essential to ensure hydraulic system reliability and safety.
General hydraulic safety precautions include following proper procedures and wearing protective gear.

Units of Pressure and Distance

Other units of pressure may be encountered, but they can be converted back into basic units of force and area.
Distance is a key concept in practical mechanics, often expressed in feet (Ft) or metres (M).

Work and Power

Work is done when a force causes an object to move, calculated by multiplying the force used on the object by the distance it travelled.
Work is expressed in foot-pounds (lb-ft) or kilogram-metres (kg-m).
Power is the rate of doing work, calculated by multiplying force by distance and dividing by time (P = F × D ÷ T).
In hydraulic systems, power can be computed by considering the flow rate in gallons per minute and the pressure in pounds per square inch.

Mechanical Advantage in Hydraulic Systems

Mechanical advantage is the ratio of output force to input force applied to a mechanism.
Hydraulic systems have two major advantages: ease of transmitting force over large distances and into sealed compartments, and large gain in mechanical advantage by varying piston sizes.

Relief Valves

Relief valves are pressure-operated valves that bypass pump delivery pressure to the reservoir.
System relief valves are used as safety devices against pump failure, while thermal relief valves are used to relieve excessive pressures due to thermal expansion of the fluid.

Actuators

Double-acting balanced actuators have the same surface area on both sides of the piston and are used where the amount of force required is the same in both directions.
Rotary actuators use a piston with a rack of teeth that meshes with a pinion gear, and are used in systems such as landing gear and steering systems.

Heat Exchangers

Heat exchangers are components that transfer heat from one body to another.
They are used to cool hydraulic fluid in hydraulic systems, often located in the return side of the system.
Heat exchangers are available in various forms, including air-cooled and fuel-cooled types.

Hydraulic System Layout and Operation

On the GENFLY Trainer, hydraulic power is used to operate various systems, including ailerons, spoilers, rudder, elevators, flaps, and slats, landing gear, nose wheel steering, and wheel brakes.
The hydraulic system is divided into two independently pressurized systems, No. 1 and No. 2, with individual reservoirs and engine-driven pumps.
Pressure relief valves and filters are used to prevent over-pressurization and contamination, respectively.

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Description

Learn about the application of hydraulic systems in modern aircraft, including engine driven or electrically driven hydraulic pumps and their uses.