A320 Landing Gear / Shock Absorber

Dear All,

We are going to brief some information regarding the A320 Landing Gear (Shock Absorber). Below you will find a cross section photo for the shock absorber which will be good to follow while reading the description.

Note: The photo is taken from A320 AMM - Aircraft Maint. Manual- /It's here for studying purposes only. It's not allowed to use it for trading purpose without prior notice from AIRBUS.

1) Compression:

During the compression, the sliding tube goes into the barrel of the main fitting. The capacity of the shock absorber reduces, which compresses the gas. The fluid goes through the damping head and lifts the compression-orifice plate off its seat, to let the fluid flow fully.
Initially, the fluid also flows from the compression chamber to the 1st stage gas chamber, through the first-stage orifices of the damping tube. While the shock absorber compresses, the damping tube and the first-stage orifices go through the damping head. The flow through the first-stage orifices stops, and the flow limits to that through the compression-orifice plate. This produces a two-stage damping effect. The gas compression in the 2nd stage chamber, pushes on the floating piston to help the damping. It also helps to make the damping effect and the compression effect of the oleo smooth.
At the same time, the fluid goes from the 1st stage gas chamber into the recoil chamber, through the openings in the upper bearing. This flow of fluid moves the recoil-orifice plate against the flange of a retaining ring, to let the fluid flow fully. The gas compression and the fluid transfer absorb the shock-loads from the MLG.

(2) Recoil :

The energy in the gas, which is in the 1st stage and the 2nd stage gas chambers, starts the recoil travel. The fluid goes through the recoil-orifice and the compression-orifice plates. The flow of fluid moves these plates to their almost closed position, so that the fluid movement is slow. This decreases the speed of the recoil travel.
A flow of fluid through the first-stage orifices in the damping tube only occurs if the recoil-orifice and the compression-orifice plates go into the compression chamber again. The gas in the 2nd stage chamber helps to make the extension effect of the shock absorber smooth.

(3) Compression and Recoil - 2nd Stage Gas Chamber:

The compression and the expansion of the gas in the 2nd stage gas chamber helps to make the effect of the shock absorber smooth. This is transmitted through the floating piston to the oil and then to the remaining parts of the shock absorber assembly. This procedure helps to make a smooth landing.

I hope the information above is helpful to understand hints of the A320 Shock ABsorber.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Aircraft Engines Tones / Noises

Dear All,

Can someone distinguish between the aircrfat engine types from its noise?

Let me give you some noise related factors in a way of giving some differences between two types of engines installed on A320/A321.

These engines are V2500 and CFM56-5A/5B.

The V2500 has different noise tone than the CFM56-5A/B. Some of differences related factors are:

1- The V2500 has different number of stages (Compressor Stages / Turbine Stages) from CFM56-5A/B.

2- There are something called noise acoustic panels installed at the inlet of engines. These panels are used to absorb the noise coming out from the engine. Also, these panels are different in shapes, sizes, and material between the V2500 and the CFM-5A/B.

3- Every Turbo Fan Engine inlet air is divided into two parts:
A) Primary Air which goes into the engine compressor stages and turbine stages through the combustion chamber. This air that cause the engine to run. This air will be exhausted outboard. B) Secondary Air that is withdrawn by the fan at the engine inlet and discharged overboard through bypassing around the main engine components and not inside the engine. At the end also the secondary air will be discharged outboard the engine to the air.

Now on the CFM56-5A/5B the exhausted primary air will be discharged seperately to the outboard from the secondary discharged air. The primary air will be discharged through component called "Center Body". On the V2500, it is different as both the primary engine air and the secondary engine air will meet together when discharged in a component called CNA - Common Nozzle Assembly.

This design gives alot of advantages for the V2500 engines. One of the important advantages is REDUCING THE NOISE. Again mixing the discharged PRIMARY AIR with SECONDAR AIR will reduce the noise or at least smoothen it.

4- Every engine type build from different materials, specifications, inlet area, outlet area, valves such as VSV - Variable Stator Valve - , VBV - Variable Bleed Valve, VBSV - Variable Boost Start Valve, number of fan blades, area size of the fan blades,....etc other than the other type of engines.

Believe me, every engine and if I can use the word TONE has different tone from another engine type BUT all engines from the same type has the SAME TONE.

I believe that what I have briefed above are so far helpful information as I also believe we can talk alot about many other factors. But I can say the above are the main factors.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Turbine Inlet Temperature - TIT SENSOR

Turbine Inlet Temperature Sensor (Engine):

The turbine engine is basically composed of different stages of compressors, combustion chamber, turbine stages. Now, when the engine is running, the air will ingested into the engine and will be compressed through the compressor stages. After that the air will enter the combustion chamber as an element for combustion to take place with the fuel. then, the discharged hot exhausted air will leave the combustion chamber under very high in both (Pressure and Temperature). This exhausted air is used to hit the turbine (High Pressure Turbine) causing them to rotate at which in turn will rotate the compressor and so on.

It is used to measure the temperature of the discharged air coming from the combustion chamber and hitting the turbine. the sensing of this temperature is very useful to control the engine operation by the computer that is used this information and according analysis the engine combustion effeciency and at the same time control the power output of the engine automatically through a computer called ECU - Engine Control Unit -. the ECU is a computer that receives different signals from different sensors and systems of the aircraft. One of these inputs is the Turbine Inlet Temperature.

Turbine Inlet Temperature Sensor (Aircondition System):

There is also a sensor called TIT sensor installed on the airconditioning pack. The aircondition system pack. This pack composed of
1- ACM - Air Cycle Machine - (FAN, Compressor, and Turbine)
2- Heat exchangers
3- Condenser
4- Reheater.

Now, the aircondition system is controlled by computer called Pack Controller and another computer called Zone Controller. Now the engine bleed air is delivered to the airconditioning packs to be conditioned both (Temperature and pressure) in the following sequence:

1- the bled air enters the pack via a pack flow valve.
2- the hot bled air enters the primary heat exchanger to be cooled little bit before entering the ACM compressor at which the air is going to be compressed so its pressure will increase.
3- the air will leave the compressor with high pressure and very high temperature due to the compression.
4- then the air will enter the main heat exchanger to be cooled. Then the air will enter the reheater to increase its temperature so we can eliminate any water particle suspended in the air before entering the turbine - The elimination of any water particle is useful to protect the turbine blades from being daamaged or corroded-. Then the turbine will cause the compressed air to extract due to giving force for the turbine to rotate. At this point the air entering the turbine will be so hot and the air leaving is so cold.

Now the computer controlling the system operation needs input to control the flow rate of air entering the packs and also to control the air entering the heat exchangers. Also the computer needs these inputs for maintenance personal analysis and to monitor the efficiency of packs.

Turbine inlet temperature sensed will be signaled to the pack controller which in turn with another sensors signals will control the aircondition system operation.

Ayman Shak'ah
Licensed Aircraft Engineer

A320 Passenger Oxygen System

Dear All,

The A320 has a very nice safe system controlling the passenger oxygen masks. But always please note that we are dealing with machines that you will never get a 100 % efficiency of any machine.

I will brief you little bit about the passenger oxygen masks operation and when they are going to be deployed.

The passenger oxygen masks are installed in PSU - Passenger Service Unit - above each group of seats. This PSU has a door (Panel Which cover the masks container). This door is stay locked electrically by solenoid.

When the solenoid is energized, the door will open and the masks will drop by gravitydown infront of the passenger. The door solenoid is energized by two means.

Either 1) automatically and this is controlled by relays connected to cabin pressure sensor that when heavy drop of pressure is measured at above certain altitude (on A320 above 14000 cabin altitude then this electrical "AND GATE" will make the door solenoid to be energized automatically causing the masks to drop.

2) Manually by the pilot, using a switch that when switched will cause the doors solenoids to be energized so the door will open and the masks will drop.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer