A320 tech questions
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A320 tech questions
I would really appreciate some assistance in understanding some of the following questions if anyone can help...
1. What is the purpose of the Eng N1 Mode Switches? Why is this an option on some aircraft?
2. The various schematics of the air conditioning system doesn't appear to have any mention of the Air Cycle Machine and Primary Heat Exchanger. Does each pack have an ACM and PHE each? And does the air normally go through them after passing through the pack flow control valve and before the mixing unit?
3. If you lose an engine with the Autopilot in, what compensates the rudder yaw towards the dead engine? Is rudder trim a totally manually event through the two trim motors?
4. Is it true that the A320/321 heat the aft and fwd cargo holds, and the A319 only heats and ventilates the AFT hold?
5. What does it mean to latch the sidestick?
Many thanks for your help,
John
1. What is the purpose of the Eng N1 Mode Switches? Why is this an option on some aircraft?
2. The various schematics of the air conditioning system doesn't appear to have any mention of the Air Cycle Machine and Primary Heat Exchanger. Does each pack have an ACM and PHE each? And does the air normally go through them after passing through the pack flow control valve and before the mixing unit?
3. If you lose an engine with the Autopilot in, what compensates the rudder yaw towards the dead engine? Is rudder trim a totally manually event through the two trim motors?
4. Is it true that the A320/321 heat the aft and fwd cargo holds, and the A319 only heats and ventilates the AFT hold?
5. What does it mean to latch the sidestick?
Many thanks for your help,
John
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1. At a guess its only an option on the aircraft that use EPR as a measure instead of N1. If you lose the EPR indications for some reason you can fall back to control through N1. This wouldn't be relevant on an N1 controlled engine.
2. Pass
3. Autopilot takes care of rudder trim when enaged.
4. Sounds about right.
5. Depends. I'm assuming it means holding the priority button down for a defined period in order to take control of the aircraft through your sidestick. The othe sidestick is then locked out until they press their priority button.
2. Pass
3. Autopilot takes care of rudder trim when enaged.
4. Sounds about right.
5. Depends. I'm assuming it means holding the priority button down for a defined period in order to take control of the aircraft through your sidestick. The othe sidestick is then locked out until they press their priority button.
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All correct.
To paragraph 1:
CFM engines are operated according N1, so you don't need to switch to N1 government. IAE engines are operated by EPR. If you should loose EPR (i.e. loss of a pressure sensor), you have to revert to N1.
N1 is easier anyway. I still haven't figured out this EPR. Most of the time I watch FF to have an accurate idea about my engines' power output...!
Dani
To paragraph 1:
CFM engines are operated according N1, so you don't need to switch to N1 government. IAE engines are operated by EPR. If you should loose EPR (i.e. loss of a pressure sensor), you have to revert to N1.
N1 is easier anyway. I still haven't figured out this EPR. Most of the time I watch FF to have an accurate idea about my engines' power output...!
Dani
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Q1.. If the EEC looses one of the EPR signals/sensors ie P2 or P4.9 then the EEC will revert to Backup N1 Rated mode, ie with some protection against overspeed. The crew action would be to follow up and select the N1 pushbutton for that engine as well as the other to keep them in the same mode together. If the EEC looses the T2 temp signal it will revert to N1 mode unrated, ie with no overspeed protection, so be carefull if you need TOGA
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..and flying the IAE engines in the N1 rated mode is nothing but a pain in the tailpipe......read carefully the MEL and QRH.....
and TOGA in rated N1 = new engines
for those that dont pay attention...PB
and TOGA in rated N1 = new engines
for those that dont pay attention...PB
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EPR measures the pressure ratio between the back and front of the engine. By measuring this accurately a precise measure of actual thrust can be measured.
As an engine ages the thrust will reduce for a given RPM because of tip wear, fan blade leading edge erosion, combustion chamber degradation and any number of other variables. However if the pressure ratio is X then the actual thrust is still X irrespective of how tired the engine is. Performance is therefore guaranteed.
Fuel flow is a pretty good measure of engine thrust but again, as the engine ages the EGT has to get hotter to create the same thrust as an new engine. Therefore higher EGT=higher fuel flow.
In twenty five odd years of flying EPR, have only seen two instances of a failure, neither on an Airbus.
Agreed the 'system' is not without fault....as the 737 into the Potomac vividly illustrates.
As an engine ages the thrust will reduce for a given RPM because of tip wear, fan blade leading edge erosion, combustion chamber degradation and any number of other variables. However if the pressure ratio is X then the actual thrust is still X irrespective of how tired the engine is. Performance is therefore guaranteed.
Fuel flow is a pretty good measure of engine thrust but again, as the engine ages the EGT has to get hotter to create the same thrust as an new engine. Therefore higher EGT=higher fuel flow.
In twenty five odd years of flying EPR, have only seen two instances of a failure, neither on an Airbus.
Agreed the 'system' is not without fault....as the 737 into the Potomac vividly illustrates.
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I would agree that EPR works to a point, that seems to stop (for me at least) when you see EPR's of 0.98 at low weights towards the end of a long cruise on a 340-500 with the Trent 500's! I guess I have difficulty visually getting to grips with complex integrated EPR's used on three spool arrangements.
TOD
TOD
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TOD,
EPR on a fan engine should really be called IEPR cos it's an integrated EPR value from three sources.
The back end of your Trent has only two 'holes' has it not...the jet pipe and the fan exhaust.
If we take a pressure reading in these two areas and multiply them electronically by the area of the associated outlet and then divide by the total area of the exhaust voila' we have an integrated exhaust pressure which we can now compare to the inlet pressurex inle area.
This is how I visualise it. Technically could be completely wrong but not too far off I suspect!
Our engine in descent also reads less than 1.00 EPR which I am able to rationalise but how you could still be getting positive thrust at 0.98 does seem a bit strange!!
EPR on a fan engine should really be called IEPR cos it's an integrated EPR value from three sources.
The back end of your Trent has only two 'holes' has it not...the jet pipe and the fan exhaust.
If we take a pressure reading in these two areas and multiply them electronically by the area of the associated outlet and then divide by the total area of the exhaust voila' we have an integrated exhaust pressure which we can now compare to the inlet pressurex inle area.
This is how I visualise it. Technically could be completely wrong but not too far off I suspect!
Our engine in descent also reads less than 1.00 EPR which I am able to rationalise but how you could still be getting positive thrust at 0.98 does seem a bit strange!!
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