APU ON but engines OFF!

[James Bennett 52]

Oh god please make it stop...

[AF330 0]

Yeah...

 

Tell me what you don't understand in my questions! I am just thinking logic: the bleed air goes out from the APU by 1 valve but goes to 2-4 engines! So it has to seperate somewhere!

Nuitkati said:

 

" So the APU bleed valve in your picture stays open, and the starter valve on the big engine is opened too."

 

But there are 2 -4 engines, so bleed air has to seperate.

 

But then nuitkati said that it isolates the engine you will start, and that's all. But you said that it sends bleed air to the big engine when we place the selector to START. So for BOTH engines...

 

Strange and confusing!

I am searching since this morning!!!

EDIT:

 

Wait, Nuikati said:

 

" Below the throttle quadrant there are 2-4 switches for engine start. Flick up the one you want to start. Yet another computer kicks in, isolates the APU bleed air flow so that it goes to that engine to turn it. At the right moment (maximum turn) the computer switches on the ignition, starts the fuel flow and the engine fires up"

 

But JRB said:

 

" When the pilot turns the engine start switch to "on" a valve will automatically redirect the APU bleed air away from the air conditioning packs, and will instead send the bleed air to the main engine starter."

 

Hmm....

Whrn does the air go to the engines? When we push the master switch or when put the selector to START/ON?

[vc10man 732]

Oh god please make it stop...

++++1, could not agree more.

[AF330 0]

Ok...imagine you have started a post and everyone is asking you to stop, how would you feel? Happy?...

 

Ok, found lot of things, here:

http://www.efbdesktop.com/engines/sys-5.5.4.html

 

Nuitkati was right. The bleed air is sent to engines when we push the master switch - not when we place the selector to START.

It then sends a signal to EIU.

 

Let's just leave all the questions above and take it in the right oder:

What will EIU do?

 

Will it send a signal to FADEC to open LP fuel valve and the starter valve?

Which valve will it ask ECB to close to isolate the engine we want to start?

 

Found this too: http://www.airliners.net/aviation-forums/tech_ops/read.main/21864/

 

Ok, basically when you put the selector to START, it displays the engine page on ECAM and closes 1 PFCV (Pack flow control valve).

So EIU sends a signal to 1 pack controller to close PFCV?

 

Thanks thanks thanks

[Lorby_SI 2,038]

Here we go again...

 

Hi AF,

 

these are questions for an Airbus maintenance engineer. We nerds are just talking basic principles. In the real Airbus there isn't just this valve this and that switch that. These are complicated systems comprising many many valves, pumps, regulators, governors, sensors and miles of pipes. In fact they are so complex that you need computers to operate them.

 

If you want to know in such detail how the Airbus systems work together to start an engine for which the pilot just flicks a switch you will have a few weeks of studies ahead of you. Provided you yourself have the basic requirement, like an engineering degree of some sort.

 

If you dig too deep there are no more easy answers.

[vc10man 732]

Why doesn't his Lycée club together and buy an Airbus FCOM/SOPs manual and he'd be done with?

[AF330 0]

Hahaha!

That was a good one!

 

By the way, I am not in lycée but in collège....

 

See, everything is different here:

 

Primaire (from 6 years old)

CP --> 1st grade

CE1 --> 2nd grade

CE2 --> 3rd grade

CM1 --> 4th grade

CM2 --> 5th grade

 

Collège (from 10 years old)

 

6e --> 6th grade (only class where US/UK = France)

5e --> 7th grade

4e --> 8th grade

3e --> 9th grade (my class)

 

------- Then you pass a national exam, called "brevet" to go to lycée (from 15 years old)

 

2nd --> 10th grade

1re --> 11th grade

Terminale (BAC) --> 12th grade

 

You then pass a national exam called "BAC" much bigger than "brevet".

You then go to "prepa" or universities....

 

I am in collège 3e... Is it better?

[JRBarrett 3,070]

Ok...imagine you have started a post and everyone is asking you to stop, how would you feel? Happy?...

The reason people get irritated by your questions, and ask you to stop, is because you ask highly technical questions about very complex systems, when it is very clear that you do not yet have any real understanding of the basics of aircraft systems and engineering.

 

It would be like a student coming onto a message board for advanced mathematics, and asking complex questions about the mean value theorem in calculus, when it is obvious that the student has not yet even mastered the fundamentals of elementary algebra.

 

I can appreciate your interest in wanting to know how things work, but you have to make the effort to master the basics of aircraft systems before asking the kinds of things you are always asking in these forums.

 

People who do not know your past history, have gone to a lot of effort to answer your questions, but after doing so, it becomes obvious that you do not yet have the core knowlege to understand the answers you are being given. It makes people feel like responding to you is a complete waste of time, which is why you are often asked to stop posting.

[KriVa 307]

Like nuitkati said... Once you start digging there are no more easy answers.

The period where once switch corresponded to one valve has long gone. These days, it's a LOT more complicated than that. Flicking a switch does not move a valve in itself. It just sends a request to a computer, asking it to perform quite some actions.

This level of knowledge is for those who need it (engineers and technicians mostly, but also developers like PMDG and Aerosoft). It's commendable that you want to know it, but I'm afraid there's just no easy way to explain the answers.

If you ever NEED the answers (for your job), don't worry, your employer will make sure they bore the hell out of you with various CBTs, WBTs, and exam sessions.

Without wanting to offend you, but often you're asking us to explain quantum physics to a toddler. (It's a metaphor, don't take it literally.)

[jdwgraf 52]

Good evening,

 

I was in training today at CDG....

I saw an A380 Emirates. We could see that the APU was on (the air was coming out behind, kind of air "waves").

But the engines were not turning!!!!

I asked my teacher why the engines were not turning and he said the starter was not started (or compressed air not going to the accessory gear box - AGB). But I think that there was not enough compressed air (N not at 100%)...

 

1) Is my "teacher" right? Because the APU can not work if the starter is not ON!

 

............

 

Thanks,

A.Roy

 

It started going downhill from the first question .

 

John

[AF330 0]

Yes, indeed.

 

Still thanks! Will try to search in F-COM!  ^_^

 

Have a nice W.E!

[n4gix 4,947]

...and on that note, it is time to end this thread. I thank everyone for keeping it (mostly) friendly and on track... B)