AFS3 DIFF combined

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Questions and Answers

What is the primary material used to construct the piston tube assembly?

Brass

Aluminum

High tensile steel (correct)

Titanium

What is the purpose of the leak hole in the metering pin shock strut cylinder assembly?

To allow for excess pressure relief (correct)

To lubricate the piston

To regulate the flow of fluid

To provide a passage for air

What is the function of the gland nut in the metering pin shock strut cylinder assembly?

To provide a seal for the piston (correct)

To secure the piston in place

To connect the piston to the axle housing

To regulate fluid flow

What component is responsible for stopping the piston in the metering pin shock strut cylinder assembly?

Piston stop Signup and view all the answers

What is the purpose of the snubber tube in the metering pin shock strut cylinder assembly?

To absorb shock Signup and view all the answers

What is the function of the axle housing in the piston tube assembly?

To connect the piston to the torque links Signup and view all the answers

What is the purpose of the flutter plate in the metering pin shock strut cylinder assembly?

To stabilize the piston Signup and view all the answers

What is the purpose of the electrically operated shutoff valve in the pneumatic steering system?

To isolate steering when gear up is selected or steering is selected off Signup and view all the answers

What happens when the left brake pedal is depressed on a tail wheel configured aircraft?

The tail wheel deflects to the left Signup and view all the answers

What is the advantage of full-swivel capability on tail wheels?

It allows tighter turns to be completed Signup and view all the answers

What is the purpose of differential braking?

To turn the aircraft Signup and view all the answers

What is the effect of applying the right brake on a tail wheel configured aircraft?

The aircraft turns to the right Signup and view all the answers

What happens to the steering control when the tail wheel pivots through more than 45° from the aircraft centreline?

It disengages Signup and view all the answers

What is the layout of the pneumatic steering system similar to?

Topic 1 Signup and view all the answers

What is the function of the metering valve in the pneumatic steering system?

To control the pressure in the system Signup and view all the answers

What type of steering is also called differential braking?

Brake steering Signup and view all the answers

What is the purpose of the pneumatic steering system?

To steer the aircraft Signup and view all the answers

What happens to the ground safety micro-switch when the aircraft is on the ground?

It is open Signup and view all the answers

What is the purpose of the micro-switch in the landing gear system?

To prevent the landing gear from retracting while on the ground Signup and view all the answers

What happens to the shock absorber struts after take-off?

They fully extend Signup and view all the answers

What is the sequence of events when the pilot moves the landing gear control lever to the 'up' position?

28 VDC is supplied to the coil of the landing gear 'up' relay, then the motor turns, driving the gearbox to retract the landing gear Signup and view all the answers

What happens to the landing gear 'up' relay when all three up-lock micro-switches open?

It is de-energized Signup and view all the answers

What is the purpose of the down-lock micro-switches?

To position the 'down' winding circuit of the motor in readiness for landing gear extension Signup and view all the answers

What happens to the 'down' winding circuit of the motor when the landing gear reaches the fully retracted position?

It is positioned in readiness for landing gear extension Signup and view all the answers

What is the purpose of the up-lock micro-switches?

To retract the landing gear Signup and view all the answers

What is the primary power source used to extend and retract most aircraft undercarriage assemblies?

Combination of hydraulic and electrical power Signup and view all the answers

What is the purpose of the ground safety micro-switch in an electrical undercarriage system?

To prevent accidental retraction of the landing gear while the aircraft is on the ground Signup and view all the answers

How are the up-lock micro-switches connected in an electrical undercarriage system?

In parallel with each other Signup and view all the answers

What is the voltage supply to the motor in an electrical undercarriage system?

28 volts of direct current Signup and view all the answers

What is the purpose of the landing gear control lever in an electrical undercarriage system?

To control the extension and retraction of the landing gear Signup and view all the answers

What is the function of the up-lock and down-lock micro-switches in an electrical undercarriage system?

To ensure power is available to drive the motor until all undercarriage legs are fully down and locked or up and locked Signup and view all the answers

What is the advantage of using an electrical undercarriage system?

It enables the landing gear to be extended and retracted by one motor Signup and view all the answers

What happens when the EMERGEY LANDING GEAR RELEASE handle is pulled in the cockpit?

The three door uplocks are unlocked and the nose gear uplock is released. Signup and view all the answers

What is the purpose of the micro switch within the mixer box?

To energize the two main gear sequence valves. Signup and view all the answers

What happens to the fluid in the up side of the jacks when the EMERGEY LANDING GEAR RELEASE handle is pulled?

It is expelled through the door sequence valves, integral NRVs, and depressurizing valve. Signup and view all the answers

What is the effect of gravity and aerodynamic forces on the nose gear?

It lowers the nose gear. Signup and view all the answers

What is the purpose of the emergency down system?

To lower the landing gear in case of hydraulic failure. Signup and view all the answers

What operates the cable system that unlocks the three door uplocks?

The EMERGEY LANDING GEAR RELEASE handle. Signup and view all the answers

What prevents cavitation in the jacks during the emergency down process?

Fluid flowing from the return line into the down side of the jacks. Signup and view all the answers

What is the function of the mixer box?

To energize the two main gear sequence valves. Signup and view all the answers

What is the purpose of the nose gear sequence valve?

To sequence the extension of the nose gear. Signup and view all the answers

What engages once the nose gear is fully down?

The downlock. Signup and view all the answers

Study Notes

Landing Gear Systems

Landing gear systems are classified into tricycle, tailwheel, bicycle, skids, or floats.
Non-shock absorbing landing gear relies on pilot skill for a soft ground contact, examples include helicopter landing gear skid and glider landing gear.
Shock absorbing landing gear absorbs impact forces of landing by converting energy into heat energy, often by forcing a fluid through a restriction.

Non-Shock Absorbing Landing Gear

Non-shock absorbing landing gear relies on the tyre to provide some cushioning effect.
An example of non-shock absorbing landing gear is the landing gear skid of a helicopter.

Shock Absorbing Landing Gear

Shock absorbing landing gear absorbs impact forces of landing by converting energy into heat energy.
The energy is generated from landing and taxiing and is dissipated into the surrounding atmosphere.
The movement of fluid generates heat, which is radiated into the surrounding atmosphere.

Components of Shock Absorbing Landing Gear

Upper cylinder
Wer cylinder
NATO inflation valve
Flutter plate
Snubber tube
Return leak hole
Piston stop
Gland packings O-ring
Brass bearing
Gland nut

Piston Tube Assembly

The piston tube assembly is constructed of high tensile steel.
It comprises of a piston head, metering pin, axle housing, and torque links.
The piston tube assembly is shown in Figure 6.

Brakes Applied

The two reservoirs supply fluid to each individual dual cylinder master cylinders.
When the toe pedals are depressed, the master cylinders supply servo pressure to the brake control valves of both systems.
Pressure from No. 1 system is metered through the Normal Brakes brake control valve, anti-skid control valve, and priority change over valve to the wheel brake cylinders.
The pressure applied to the brakes is proportional to the toe pedal depression.

Power Brake Bleeding

It is important to follow the applicable maintenance manual in detail when power brakes are bled.
The bleeding procedure is not complete until both the main and emergency systems are free of air.

Fluid Quantity and Type

The hydraulic system of a modern aircraft may use phosphate-ester-base synthetic fluid (Skydrol), mineral-base MIL-H-5606, or synthetic MIL-H-83282A fluid.

Aircraft Steering

Steering systems are used to control the direction of movement of an aircraft while taxiing.
Most aircraft are equipped with some form of steering.

Mechanical Steering

Mechanical steering systems are found on small aircraft.
The system uses bungee rods connected to the rudder pedals to control the direction of movement.

Rudder Steering

Some small aircraft have alternate steering methods that utilize cables, springs, and levers associated with the rudder system or the brakes to effect steering.
Rudder deflection causes the tail wheel to steer as the aircraft rolls forward.

Pneumatic Steering

The system layout was previously covered in Topic 1, except there are no return lines and are vented overboard at the steering metering valve.
An electrically operated shutoff valve is normally incorporated in the system to isolate steering when gear up is selected or steering is selected off.

Brake Steering

Brakes can be used for steering on tail wheel and tricycle (front wheel) configured aircraft.
This type of steering is also called differential braking.
Depressing the left brake pedal causes the left brake to be applied, which causes the tail wheel to deflect to the left as the aircraft's tail deflects to the right, resulting in a turn to the left.

Extension and Retraction Methods

Most aircraft undercarriage assemblies use a combination of hydraulic and electrical power for extension and retraction.
Emergency extension can be achieved by back-up hydraulic systems, pneumatics, mechanical crank systems, or gravity systems.

Electrical Undercarriage Systems

The system enables the landing gear to be extended and retracted by one motor.
The 28VDC supply to the motor is controlled by the landing gear control lever, landing gear up and down relays, and up-lock and down-lock position micro-switches.
Each undercarriage leg has its own set of up-lock and down-lock micro-switches.
All three up-lock micro-switches are connected in parallel to each other, as are the down-lock micro-switches.
A ground safety micro-switch is used to prevent accidental retraction of the landing gear while the aircraft is on the ground.

Retraction

The ground safety micro-switch closes when the aircraft is airborne and the shock absorber struts fully extend.
When the pilot moves the landing gear control lever to the ‘up’ position, 28VDC is supplied to the coil of the landing gear ‘up’ relay.
The motor turns, driving the gearbox to retract the landing gear.
As each landing gear leg begins to move, the contacts of its down-lock micro-switch automatically close.
Once each landing gear leg reaches the fully retracted position, the respective up-lock micro-switch is actuated and its contacts open.
When all three up-lock micro-switches open, the landing gear ‘up’ relay is deactivated and the DC voltage supply to the ‘up’ winding of the motor is interrupted.

Emergency Landing Gear Release Handle

Located in the cockpit, this handle is used to provide a restricted flow during down selection and a free flow during retraction when the down line is connected to return.
Purpose is to control the rates of retraction and extension, and compensate for the effects of gravity.

Emergency Up Override Lock Toggle Switch

Mounted on a black and yellow striped area to the right of the landing gear selector lever.
Allows the landing gear to be retracted when on jacks for ground maintenance purposes, as the airspeed will be below 150 knots.

Depressurising Relay

Energized to make contacts in the up or down power line if all of the landing gear actuators and doors are not in the selected position when the Landing Gear Selector is initially placed into a new selection.
De-energized once all of the landing gear actuators and doors have reached the new selected position.
Allows power to the landing gear selector valve solenoids, which port flow to the up or down lines as directed by the landing gear selector, and places the landing gear selector valve in the neutral position when de-energized.

Landing Gear Down Selection

The depressurising relay is energized to allow power to the landing gear selector valve solenoids, which port flow to the down lines.
The landing gear doors open, assisted by spring struts, and fluid is expelled from the up side of the jacks.

Emergency Down System

Used in the event of failure of No.1 hydraulic system to lower the landing gear.
The system mechanically unlocks the three doors and releases the nose gear uplock, and opens a valve to allow compressed nitrogen to pressurize the main gear jacks and lower the main gear.
Initiated by turning and pulling the EMERGY LANDING GEAR RELEASE handle in the cockpit.

Gear Retracting

When the nose door is fully open, it mechanically operates the nose gear sequence valve.
The nose gear sequence valve directs pressure through the gear up inhibiting valve, which unlocks the NLG downlock and ports fluid to the nose gear actuator to retract the nose gear.
The MLG door jacks reach the fully open position, its individual ‘door fully open’ switch is closed, and an electrical signal changes the ports on the gear sequence valve to allow fluid to flow to the retraction side of the MLG retraction jack.

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Description

Landing gear systems classification, types and functions. Non-shock absorbing and shock absorbing landing gear systems explained.