AFS Topic 3 MOD

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Questions and Answers

What is the primary function of air-oil struts in an aircraft undercarriage system?

To reduce aircraft weight

To increase aircraft speed

To improve aircraft maneuverability

To cushion landing impacts and carry aircraft weight (correct)

What is the name of the valve used to inflate the oleo strut with nitrogen?

Flutter plate valve

Return leak valve

NATO inflation valve (correct)

Snubber tube valve

What is the purpose of the snubber tube in the cylinder assembly?

To regulate nitrogen flow (correct)

To reduce oil displacement

To increase air compression

To absorb landing impacts

What is the name of the type of air-oil strut discussed in the content?

Metering pin strut Signup and view all the answers

What is the purpose of the piston tube assembly in the metering pin air-oil strut?

To regulate hydraulic fluid flow Signup and view all the answers

What is the material used to construct the cylinder assembly?

High tensile steel Signup and view all the answers

What is the function of the flutter plate in the upper cylinder?

To contain a small hole Signup and view all the answers

What is the purpose of the return leak hole in the flutter plate?

To allow excess fluid to leak out Signup and view all the answers

What is the principle behind the operation of shimmy dampers?

Slowing fluid flow from one chamber to another through a restrictor Signup and view all the answers

What is the purpose of the shimmy damper in Figure 11?

To slow down the fluid flow from one chamber to another Signup and view all the answers

What type of damper is shown in Figure 13?

Vane type Signup and view all the answers

What should be checked periodically in shimmy damper maintenance?

The fluid quantity in the replenishment reservoir Signup and view all the answers

What is the result of worn mountings on the shimmy damper?

The damper becomes loose on the nose wheel Signup and view all the answers

What can be renewed in the fittings of the shimmy damper?

The bolts and bushings Signup and view all the answers

Why should the mount bolts and fittings of the shimmy damper be checked closely?

To check for evidence of wear and replace bushings if necessary Signup and view all the answers

What type of shimmy damper is shown in Figure 12?

Piston type Signup and view all the answers

What is the purpose of the gap between the rotor segments in a segmented brake assembly?

To increase brake cooling Signup and view all the answers

What is a characteristic of carbon brake discs?

Low weight and excellent wear characteristics Signup and view all the answers

What materials are brake discs often manufactured from?

High strength steel and carbon materials Signup and view all the answers

What is the purpose of the retraction pin in a single disc brake?

To indicate brake lining wear Signup and view all the answers

What is a characteristic of modern brake assemblies?

They use organic composition linings Signup and view all the answers

What is a benefit of carbon brake discs?

They are light and absorb tremendous amounts of kinetic energy Signup and view all the answers

What is the purpose of the brake lining sections in a segmented rotor?

To increase brake friction Signup and view all the answers

What is a characteristic of organic composition brake linings?

They have good friction, wear and thermal characteristics Signup and view all the answers

What is the purpose of the safety switch in an aircraft?

To prevent collapse of the gear when the aircraft is on the ground Signup and view all the answers

What type of ground lock is designed to fit around extension/retraction actuator pistons?

Distance tube Signup and view all the answers

What is the purpose of the red streamers attached to ground locks?

To readily indicate whether or not they are installed Signup and view all the answers

When should ground locks be fitted?

Whenever the aircraft is released for maintenance Signup and view all the answers

What should be done after replacing or adjusting components in the retraction system?

A retraction test should be performed Signup and view all the answers

Why should components never be removed from the system?

Because it is under pressure from the hydraulic accumulator or pneumatic supply bottle Signup and view all the answers

What is a common type of ground lock?

A pin installed in aligned holes Signup and view all the answers

What should be tripped or removed when work is carried out on the landing gear system?

The appropriate circuit breakers or fuses Signup and view all the answers

What happens to the shuttle valves when emergency braking pressure is ported to them?

They move across, allowing the emergency pressure to pass to the brake assemblies. Signup and view all the answers

What is the purpose of the park brake valve?

To compensate for thermal expansion and contraction of the trapped brake fluid. Signup and view all the answers

Why should you consider brake assembly temperature before setting the park brake?

To prevent serious damage such as welding or warping. Signup and view all the answers

What happens to the spool valve in the priority change over valve during emergency operation?

It moves across to connect the No 2 Emergency Brakes brake control valve to the brake units. Signup and view all the answers

In what manner is braking provided in emergency operation?

Without anti-skid protection. Signup and view all the answers

What must be done to the brake pedals to release the park brake?

They must be depressed. Signup and view all the answers

Where is the park brake handle or lever located?

In the cockpit. Signup and view all the answers

What is the result of setting the park brake when the main brakes are hot?

The brake fluid will expand and cause damage. Signup and view all the answers

What is the function of trunnions in a landing gear assembly?

To provide a pivot point for movement Signup and view all the answers

What is the purpose of shock struts/Oleos in a landing gear assembly?

To absorb shock loads Signup and view all the answers

What is the purpose of fairings in a landing gear assembly?

To reduce drag Signup and view all the answers

What is the purpose of drag, torque, and side links in a landing gear assembly?

To support and stabilize the assembly Signup and view all the answers

Why is it important to be aware of different manufacturers' terminology in landing gear systems?

Because different manufacturers use different terms for the same basic components Signup and view all the answers

What is the primary purpose of non-shock absorbing landing gear?

To transfer the shock energy throughout the airframe at a different rate Signup and view all the answers

What type of landing gear is commonly found on helicopters and sailplanes?

Rigid landing gear Signup and view all the answers

What is the primary function of the tyre in a glider's landing gear?

To cushion the ground contact Signup and view all the answers

What is the advantage of rigid landing gear in helicopters and sailplanes?

It relies on pilot skill for a soft ground contact Signup and view all the answers

What is the classification of landing gear based on its arrangement?

Tricycle, tailwheel, bicycle, skids, or floats Signup and view all the answers

What is the purpose of the airframe structure in rigid landing gear?

To flex and absorb the shock energy Signup and view all the answers

What should be done to fluids that are bled or drained from the system?

Discard them Signup and view all the answers

What is the primary function of aircraft tyres?

To provide a cushion of air to absorb shocks Signup and view all the answers

What should be done to components containing fluid before installation?

Prime them Signup and view all the answers

What are wheel assemblies made up of?

Tyre and hub Signup and view all the answers

What happens to the pressure in the chamber over the diaphragm when the wheel receives an impact on landing?

It increases Signup and view all the answers

What is the purpose of the shaped rod contour in the air/oil shock absorber?

To vary the orifice size during the piston rod stroke Signup and view all the answers

What is the primary function of the piston during the bounce phase?

To close the gate Signup and view all the answers

What is the purpose of the oleo pneumatic undercarriage inspections?

To check for wear at pivot points and cracks or damage to the mounting structure Signup and view all the answers

What happens to the fluid flow during the shock phase?

It varies depending on the orifice size Signup and view all the answers

What is the result of the shock absorber operation during the first shock phase?

The impact energy is absorbed Signup and view all the answers

During the bounce phase, what happens to the piston in the diaphragm?

It closes the gate Signup and view all the answers

What is the function of the gate in the air/oil shock absorber?

To control the fluid flow Signup and view all the answers

What is the main difference between duo-servo and non-duo-servo brakes?

Duo-servo brakes aid in brake application in both forward and rearward directions Signup and view all the answers

What happens when the brakes are applied in a duo-servo brake system?

The pistons in the brake cylinder move out, pushing the linings against the drum Signup and view all the answers

Why is rapid cooling important for aircraft wheel brakes?

To reduce the risk of overheating and losing braking efficiency Signup and view all the answers

What are the four types of aircraft brake systems mentioned in the content?

Drum, single disc, multiple disc, and segmented rotor disc Signup and view all the answers

What is the significance of servo-action in aircraft brakes?

It aids in brake application through the use of a floating back plate Signup and view all the answers

Why should aircraft brakes not be used for parking over lengthy periods?

Because they may overheat and lose braking efficiency Signup and view all the answers

What is the result of friction in the braking process?

It converts the aircraft's kinetic energy into heat energy Signup and view all the answers

Study Notes

Air-Oil Struts (Oleo Struts)

Widely used in non-retractable and retractable undercarriage systems
Operate on the principle of restricting oil displacement and air compression to cushion landing impacts and carry aircraft weight
Two main types: metering pin and air-oil separated

Metering Pin Shock Strut

Consists of a cylinder and piston tube assembly
Contains hydraulic fluid and nitrogen
Cylinder assembly is constructed of high tensile steel and is divided into upper and lower cylinders

Cylinder Assembly

Upper cylinder contains a NATO inflation valve for inflating the oleo strut with nitrogen
Snubber tube sits in the cylinder and has a flutter plate containing a small hole and a return leak hole in the lower end

Shimmy Damper

Directly attached to both the lower (piston) and upper (cylinder) of the nose landing gear
Slows oscillating forces produced from the wheel assembly through the restriction of fluid flow within the shimmy damper
Types: vane type and piston type

Damper Inspections

Check for leakage and effectiveness of operation
Check fluid quantity in replenishment reservoir and add fluid of specified type if necessary
Inspect mount bolts and fittings for wear

Ground Locks

Devices that prevent collapse of the gear when the aircraft is on the ground
Types: pin installed in aligned holes in two or more units of the landing gear support structure and distance tube designed to fit around extension/retraction actuator pistons

General Precautions

Fit ground locks whenever the aircraft is released for maintenance
Trip circuit breakers or remove fuses when working on the system
Perform a retraction test after replacing or adjusting components in the retraction system
Never remove components while the system is under pressure

Segmented Brake Assembly

Rotor has multiple blocks riveted to both sides
Provides more brake cooling due to the gap between rotor segments and space between brake lining sections

Brake Construction Materials

Brake housings: aluminium or magnesium alloys
Brake discs: high strength steel or carbon materials
Organic composition linings: good friction, wear, and thermal characteristics
Brass or copper particles may be embedded in the material to provide friction characteristics

Automatic Adjusters

On single disc brakes, a retraction pin is often attached directly to the operating piston
Amount of pin left visible indicates how much the linings are worn on the brake assembly

GenFly Brake System Emergency Operation

In the event of No 1 system failure, the spool valve in the priority change over valve moves to connect the No 2 Emergency Brakes brake control valve to the brake units

Park Brakes

Sub-assembly of the normal hydraulic brake system
Always consider brake assembly temperature before setting the park brake
Hot brakes should be allowed to cool before the park brake is applied

Classification of Landing Gear

There are two basic classifications of landing gear: fixed or retractable.
The arrangement of landing gear varies greatly under these classifications and can be tricycle, tailwheel, bicycle, skids, or floats.

Non-Shock Absorbing Landing Gear

Non-shock absorbing landing gear dissipates the energy of the aircraft contacting the ground during landing by altering and transferring the shock energy throughout the airframe at a different rate.
Types of non-shock absorbing landing gear include rigid, shock cord, and spring type gear.
Rigid landing gear is commonly found on helicopters and sailplanes and is rigidly mounted to the aircraft with no specific component to cushion the ground contact.

Shock Absorbing Landing Gear

Shock absorber operation involves the transmission of impact received by the wheel on landing to the shock absorber piston rod, generating a positive pressure in the chamber over the diaphragm and a lower pressure in the lower chamber.
The difference in pressure produces the displacement of the piston, which opens the gate, and a part of the impact energy is absorbed during this first shock phase.
During the bounce phase, the pressure direction is reversed, and the piston in the diaphragm tends to close the gate, restricting the flow of fluid from one chamber to the other, thus dissipating the largest part of the energy accumulated by the landing.

Maintenance

Oleo pneumatic undercarriages should be subjected to regular inspections, including examinations for cracks or damage to mounting structure, corrosion, and wear at pivot points.

Components

Landing gear assemblies are made up of various components designed to support and stabilize the assembly, including actuators, trunnions, drag, torque, and side links, shock struts/oleos, and fairings.
Different manufacturers may use different terms for the same basic components.
New components should be examined and cross-checked with the appropriate maintenance publication to ensure correct installation.

Wheel Assemblies

Wheel assemblies are made up of two major assemblies: tyre and hub.
Aircraft tyres provide a cushion of air that helps absorb shocks and roughness of landings and take-offs, support the weight of the aircraft while on the ground, and provide necessary traction for braking and stopping.

Aircraft Wheel Brakes

The primary purpose of an aircraft wheel brake is to stop the aircraft within a specified distance.
Braking involves converting the aircraft’s kinetic energy into heat energy by friction.
Rapid cooling is of prime importance, as brakes will lose efficiency if the heat is not dissipated quickly.
Types of aircraft brake systems include drum, single disc, multiple disc, and segmented rotor disc.
Drum brakes are of the duo-servo type, using the weight of the aircraft to aid in the application of the brake.

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Description

This quiz covers the basics of oleo struts, also known as air-oil struts, used in aircraft landing gear systems. Learn about their operating principles and different types.