INSIDE AN ENGINE;

[AF330]

Hi,
I had a doubt on this, inside an engine, there is a compressor and a com-bustor, but on ground we still give compressed air to the turbine with the APU BLEED, so does the compressor and the com-bustor don't work when the engines are not on? We give compressed air to the turbine but why? During the flight, it takes the air from outside, so why not before start?

Thanks to explain...

[ACMS]

The only time APU bleed air goes to the Engine is during start to turn the starter motor via the start valve. It doesn't go into the Compressor or Turbine section it only turns the starter motor.

Apart from that I don't know what you are on about?

I suggest reading a few good books or Google Jet Engines.

[lomapaseo]

I'm having a little problem understanding what you wrote, but I'll take a stab at an explanation that might address your question.

APU air does not get inside the engine you are starting, it only drives are tiny turbine in a starter connected to the engine gearbox.

This external starter motor is connected to the compressors and turbine through the gear box and spins the engine compressors just fast enough to allow fuel to be burned in the combustor

[AF330]

Thanks,
See this photo: http://upload.wikimedia.org/wikipedi...engine.svg.png
Where is the motor? I didn't really get what you meant by motor...
What is the engine gear box?

EDIT: http://upload.wikimedia.org/wikipedi...ion-en.svg.png

Do you mean that the apu bleed is normal air which enters in the gearbox, and then goes to compressor and then the combustion chamber to finally turn the turbine, which will turn the prop? But why can't it take air from "outside"?
Thanks to help (very important for me)

[VinRouge]

The accessory gearbox is wrapped around the front section of a modern turbofan. It includes things like the electrical generators (to supply the aircraft electrical systems) hydraulics pumps to power flight controls, the engine oil sump and pumps and start motor. On the ground, the engine is started using typically an electrical motor for smaller engines or an air start nmotor, which is like a car turbo, which takes high pressure apu air and converts it into rotation. Tis rotation is fed, via a clutch, into the engine gear box via a shaft.

THis then starts the engine turning. Once the engine is rotating fast enough, usually at around 20% core speed, fuel is introduced. The air that is being sucked through the engine is used, the engine does not use the apu air for combustion. The starter typically disengages once the engine is 'self sustaining', his usually occurs at around 50-60% core speed.

Wikipedia helps:

http://en.m.wikipedia.org/wiki/Accessory_drive

That image you have on is a much simplified version of a turbojet,it is good for explaining how a jet works but jot much else!

[ACMS]

I think reading this may help.

How are turbine engines started? - Aviation Stack Exchange

[PlanetEarth]

CFM LEAP | Advanced Manufacturing | GE Aviation

[ACMS]

AF330-----no no no

The Bleed Air is only used to run the starter motor.
The Starter motor is physically connected to the Engine and turns it over. During start the Engine turns over faster and faster sucking fresh Air in the front mixed with fuel and ignited. The Engine then runs at Idle all on it own with the starter motor now disconnected.

Start bleed air is NOT blown in the Engine to turn it over for start.

[DevX]

AF330, this could also be a good source of information for you: http://www.valentiniweb.com/piermo/m...t%20Engine.pdf

[Sidestick_n_Rudder]

I'd suggest to start by watching this little video:

How Does An Engine Works - Icomene / CFM on Vimeo

[BOAC]

Just like to point out that AF330 is type-rated on Airbus aircraft. makes you think, eh?

Now read the poster's 'previous posts'................................

[Piltdown Man]

...but I fully believe his quoted age of 13. And reading his previous posts suggests that if AF330 spent more time learning english he might actually be able to answer his own questions.

[barit1]

Starting alternative system

All the above is not applicable to Boeing's newest, the 787.

Its engines are started via an electric motor. Once started, the starter functions as a generator.

And this is hardly the first time this starting system has been used. The CT7 turboprop uses it, and long before that, the ancient J47.

[barit1]

Here's a video that should help:

Gearbox installation - Turbine Engines: A Closer Look - YouTube

[ACMS]

BOAC-------thanks I just looked through his previous posts. I hope to hell he's not a "real" Pilot flying an Airbus..........

[barit1]

I don't think any of us begrudge lending some technical (or quasi-tech) knowledge to an interested novice. That was my profession for a decade or so, and I've learned to quickly assess a student's initial knowledge.

But trying to pass oneself off as a typerated pilot is a quick way to wear a whole heap of scorn in the real world...

[john_tullamarine]

Young lads have to learn a bunch of lessons on their pathway through the Industry .. some perhaps are a bit more like Walter at the start than others ?

Best result is to provide the information - there will be others reading who, for whatever reason, chose not to ask the question themselves.

[BOAC]

Missed this one, John?

Spectators Balcony (Spotters Corner) If you're not a professional pilot but want to discuss issues about the job, this is the best place to loiter. You won't be moved on by 'security' and there'll be plenty of experts to answer any questions.

[john_tullamarine]

.. and elsewhere they go if they move too far from what is useful here ..

[BOAC]

So, apart from the loss of the advertising 'pay per view' revenue from your Christmas bonus, John what loss would that be to we professional aviators?