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/wikipedia/commons/thumb/4/4c/Jet_engine.svg/1000px-Jet_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/wikipedia/commons/thumb/2/29/Turboprop_operation-en.svg/1024px-Turboprop_operation-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 (http://aviation.stackexchange.com/questions/1959/how-are-turbine-engines-started)

[PlanetEarth]

CFM LEAP | Advanced Manufacturing | GE Aviation (http://www.geaviation.com/manufacturing/CFM-LEAP.html)

[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/meccanica/mat/Rolls%20Royce%20-%20The%20Jet%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?:ugh:

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]

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..........:mad:

[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?

[john_tullamarine]

I wouldn't fuss too much about the bonus .. X% of zero doesn't add up to much.

On the face of it, probably not much ...

Consider, though, that the older, experienced, professional aviator may have a responsibility to assist those coming along behind ? Did not you have the benefit of wiser heads when you were a new chum ?

Not to mention that these threads often bring out of the closet videos and other items which may well be of interest to a wider audience ?

[glum]

Great vid Sidestick n Rudder, not seen that one before.

BOAC. You are not compelled to reply to any thread on PPRUNE, so if the OP's credentials offend you please feel free to move on and let those of us who enjoy passing our knowledge and encouragement on do so.

I'm in the engineering design side of aviation, and our industry is desperate for staff. The more we can get interested the better!

[AF330]

Ok,ok... There is a big problem. I am not at all an airline pilot, just 13 year old, and I really didn't check my profile, just clicked "yes" everywhere. My native language is french, but I am learning english. I AM NOT A PILOT!

Last question: So BLEED AIR is taken from high pressure stage or low pressure stage, depending on what we need...
But has the APU BLEED already got that air? Because at the beginning of the thread, the apu bleed air turned a box to turn the compressor, so does the APU BLEED AIR get's compressed twice, or does it come as normal air and then get's compressed?

[Tu.114]

It might help You to consider the APU a little jet engine (which it is). Just like its bigger relatives, it has a compressor (usually single-stage radial) that feeds a combustion chamber, which in turn discharges into a turbine (usually single-stage radial as well).

The bleed air is tapped from the APU compressor, diverting some air that would otherwise go to the combustion chamber into the bleed air ducting - plain old pipes basically. And these pipes will lead the APU bleed air into the engine starter: as has been explained, this is a little turbine installed on the accessory gear box that will spin the high pressure compressor of the engine. After having passed the starter turbine, the air will typically just be vented overboard.

What You need is a book on jet engine theory. I am sure that a search on common book dealer pages will return several titles in French as well, should You prefer that language.

[lomapaseo]

Last question: So BLEED AIR is taken from high pressure stage or low pressure stage, depending on what we need...
But has the APU BLEED already got that air

Both the engine (the big one) you want to start and the APU (small guy) have compressors and bleed air. Since the APU is running it has air to spare. As said before it uses this air to spin a much smaller device (the starter) which through gears turns the big engine.

The big engine has no bleed air available during start and no direct connection exist in the air between either the APU (small), plus the starter (tiny) and the big engine.

A neat little schematic might focus your mind on this rather than more words

[keith williams]

BOAC

You appear to have something of a fixation on putting down posters who are not professional aviators.

Your profile states the following:

Licence Type (eg CPL. Pilots only)
Atpl

Biography
Now retired

Location
UK

Occupation
Sit Vac

If these details are accurate then you are no longer a professional aviator.

You are an EX professional aviator. :hmm:

As such it might be more appropriate if you were to restrict your posts to those threads that are for EX professional aviators.

As JT has intimated, chasing enthusiastic youngsters (some of whom will become tomorrows professional aviators) into the far corners of pprune, will reduce the chances of them getting the information that they are looking for. In some cases this will drive them away from aviation.

[AF330]

"Both the engine (the big one) you want to start and the APU (small guy) have compressors and bleed air. Since the APU is running it has air to spare. As said before it uses this air to spin a much smaller device (the starter) which through gears turns the big engine.

The big engine has no bleed air available during start and no direct connection exist in the air between either the APU (small), plus the starter (tiny) and the big engine.

A neat little schematic might focus your mind on this rather than more words"

Thanks,
But so this is the route of APU BLEED:
APU has it's compressor, combuster. So basically, at the end it will turn a gear which will turn the turbine (so the big fan and the big compressor and the axe, am I right?

"BOAC

You appear to have something of a fixation on putting down posters who are not professional aviators.

Your profile states the following:

Licence Type (eg CPL. Pilots only)
Atpl

Biography
Now retired

Location
UK

Occupation
Sit Vac

If these details are accurate then you are no longer a professional aviator.

You are an EX professional aviator.

As such it might be more appropriate if you were to restrict your posts to those threads that are for EX professional aviators.

As JT has intimated, chasing enthusiastic youngsters (some of whom will become tomorrows professional aviators) into the far corners of pprune, will reduce the chances of them getting the information that they are looking for. In some cases this will drive them away from aviation."

Thanks keith williams, I appreciate, I really didn't want to write that I was a pilot!

[Turbine D]

AF330,

I've been watching this thread and I am glad to see some posters are attempting to help you with the technical question you have asked. Just ignore some of the old posting dinosaurs, who have nothing to contribute in response to your question. Here is another source of information that could be helpful to you and it is in French.

Keep asking questions, it is the way to learn:ok:

Groupe auxiliaire de puissance ? Wikipédia (http://fr.wikipedia.org/wiki/Groupe_auxiliaire_de_puissance)

[AF330]

Thanks a lot Turbine D!

[BOAC]

Regarding my 'qualifications', at least I don't lie.

[megan]

The OP might like to work his/her way through these.

Engines (http://www.grc.nasa.gov/WWW/K-12/UEET/StudentSite/engines.html)

http://www.scribd.com/doc/51618999/Rolls-Royce-The-Jet-Engine#page=217

[lomapaseo]

I'm sorry to see this thread getting personal.

Sure, all opinions are valid, but lets' keep it simple.

Many OPs are confusing for a variety of reasons. Maybe the answers should be simplified down to communicating with the large numbers who read this forum rather than trying to personalize the posters.

[AF330]

Well, see BOAC, I really didn't "lie", It was just an error. I really wanted to post my first question (about SELCAL I think...) and I pressed "YES- CONFIRM". If I really wanted to lie, I would not show "13" as my age.

I hope you understand. I am sorry if you didn't appreciate it. Again, sorry...
Thanks to everyone to have helped me!

[Turbine D]

Hi AF330,

I thought maybe a couple of engine cutaways might help you to visualize the location of the starter in a large fan engine.
http://i1166.photobucket.com/albums/q609/DaveK72/CF6-6_engine_cutaway_zpsb1b26446.jpg (http://s1166.photobucket.com/user/DaveK72/media/CF6-6_engine_cutaway_zpsb1b26446.jpg.html)
Just at the rear of the accessory drive section is the starter. In the next cutaway, you will see how that connects to the main engine rotor shaft to turn it beginning the process of engine starting.
http://i1166.photobucket.com/albums/q609/DaveK72/general-electric-ge-cf6-50-cutaway_zps19307b43.jpg (http://s1166.photobucket.com/user/DaveK72/media/general-electric-ge-cf6-50-cutaway_zps19307b43.jpg.html)
Now you can see the starter and the shaft that goes from the starter upward to the engine rotor shaft. Note the gear at the end of the starter shaft meshes with a gear that is attached to the main engine shaft. So, as the power coming from the APU in the tail of the aircraft energizes the starter to start turning the main engine shaft, rotational speed of the engine rotors will increase. At a certain rotational speed, fuel will be sprayed into the combustor and ignited. As rotor speeds continue to increase the starter is disengaged and the engine becomes self sufficient with no need for external support. In case you are wondering, the depicted engine is the GE CF6-50 that was used to power the A-300, Boeing 747 and also, the DC-10.
Hope this really helps you.

[phiggsbroadband]

So we have learnt that the main engine is started by a starter motor, that is spun up by the air from the APU...


That leaves just one question... How does the APU start?

[cosmo kramer]

It uses bleed air from an even smaller jet engine called the AAPU :E (sorry couldn't resist).

[Mecaniquito84]

AFR 330.
Another way to explain, hope it helps.

1. A/C on ground, no power. You switch batteries (28vdc) and start APU.
2. APU ON. APU generator is powering whole a/c electricall system (115 vac) and part of the air compressed by APU compressor, necessary for APU own operation, is BLEEDED to supply a/c Pneumatic system (+/- 30 psig)
3. A/C pneumatic system feed air conditioning packs,,ENGINE STARTERS and several minors users. Depend of cockpit selections
4. MAIN ENGINE START: APU keep supplying electrical power to whole aircraft. All APU pneumatic supply is dedicated to one at a time engine start, (air conditioning is switched of during Engine Start). APU Bleed air is directed though air valves to a PNEUMATIC ENGINE STARTER where pneumatic pressure energy is transformed into mechanical torque that, through drive box, makes main engine rotor turn. When MAIN ENGINE ROTOR reaches certain speed, MAIN ENGINE Compressor is able to compress inlet air to a certain pressure at which combustion make take place, so fuel is inyected, ignition plugs are switched on and voilá -combustion. After a short time, MAIN ENGINE is capable of turning and acelerating on his own power, so Pneumatic Starter is mechanically disconected and no more pneumatic power is directed to this starter

Engine Ignition System - DutchOps.com powered (http://www.dutchops.com/Portfolio_Marcel/Articles/Engines/Starter_System.htm)

Of course there are differences, this is just a basic explanation. And sorry, I'm not an instructor

Keep asking!!!

[Turbine D]

The APU is started by means of an onboard battery, or an electrical external power source or, depending on the kind of APU, a hydraulic accumulator that provides compressed gas to the APU. Some APUs aren't capable of being started in the air, but for ETOPs aircraft the APU must have the capability of being started up to an altitude of 40K feet.

[DevX]

TurbineD, you said, "As rotor speeds continue to increase the starter is disengaged......"

If I may elaborate a little to make it a bit clearer for AF330: The start air valve, which is adjacent to the starter, is closed off during the start cycle (circa 50% N3 on most R-R engines) thus shutting off bleed air to the starter motor. The starter motor shaft continues to rotate as it's driven by the gearbox once the engine is self sufficient and cannot actually be mechanically disengaged (unlike the IDG drive), but pawls within the starter mechanism mean that the starter turbine itself ceases to rotate.

[Turbine D]

If I may elaborate a little to make it a bit clearer for AF330:

Thanks DevX:ok:

[AF330]

Thanks TurbineD, Mecaniquito84, DevX!
Well, I have to collect all the information given by everyone!

1)But in your photo, TurbineD, does the apu air bleed go bellow the compressor? Does the APU bleed air turn the fan??

2) But does the fan already start taking air inside? Or does it block something till we start the engine, if not, I imagine that apu bleed air is then only for packs for A/C.

3) If for example, we put thrust TOGA, will they put all the fuel required for TOGA thrust in the combuster or will it keep giving fuel till we reach TOGA thrust? (Well I think it will keep giving fuel, not the entire amount required!)

4) Ok, so the APU bleed air is normal air which goes inside a compressor and then travels inside pipes to finally arrive at the pneumatic engine starter, then the drive box, and turns the main engine rotor. What is the main engine rotor? The fan? So is it the inverse process? The fan turning the compressor and the turbine? So no mixing with fuel for apu bleed air in the combuster?

5) Could anyone show me on a photo, where is the pneumatic engine starter, drive box?

[DevX]

Here's a Trent 700 starter motor, IDG, anti icing valve and external gearbox:
http://www.pprune.org/rumours-news/248980-emirates-a330-fan-blade-dxb-18-oct-4.html#post2944866

The starter motor is on the left of the picture, the IDG is the black lump with wires on the right of the picture, the anti icing valve is at the top of the picture and the external gearbox is in the middle.

Also, the biscuit coloured area above the starter is the multi layer Kevlar wrap which goes around the fan case to (hopefully) contain a fan blade, or parts of, from piercing the fuselage after a failure. The small piece of titanium plate above the starter is to prevent pieces of the starter turbine from damaging the Kevlar wrap in the event of a failure. When a motor does fail, usually due to lack of maintenance/oil, it goes off like a huge Catherine wheel!
The unit, extreme top right of the picture is the IDG cooler which uses fan air to cool the oil.

[MrSnuggles]

AF330

Just wanted to welcome you and wish you the best of luck in the future. You have already gotten lots of help here and I hope to see you in an engineer's costume/pilot's uniform somewhere in the world some day!

[Mecaniquito84]

Hi

Engine rotor is the part that moves (rotates) in an Turbine engine. It consist in the Compressor (to the right in the img below) and the turbine in a one axle.
And again:
1. something external (air starter) makes the whole axle (compressor + turbine) rotate.
2. When axle is rotated, compressor start to compress intake air.

3. When the air has enough pressure it is mixed with fuel, ignited by spark plugs. Air + fuel ignited, (called gas from now on) had adquiered extra energy from combustion.

4 High energy gas impact the turbine and gas energy is transformed in a mechanical movement: gas turns the turbine. With turbine, whole axle is turned including compressor, who compress more aire and (go to 2.:))

http://nihrecord.nih.gov/newsletters/2005/08_26_2005/images/cogen-GG-rotor-after-balanc.jpg

[Turbine D]

Hi AF330,

1. The APU bleed air goes only to the starter motor. The starter motor uses this air to turn a shaft that is connected to the compressor of the main engine. The fan is turned by the rotation speed of the Low Pressure Turbine at the rear of the engine.
2. The fan takes air in but keep in mind, most of that fan air goes around the engine, not through it.
3. Your question isn't clear enough to answer.
4. To answer this question I would suggest you go to this Rolls Royce learning site and go through each of the 4 presentation stages. It will help you to understand the different sections of a turbo-fan jet engine and how they relate to one another:

Journey through a jet engine (http://www.rolls-royce.com/interactive_games/journey03/)

I hope you will enjoy this!

[FE Hoppy]

This thread reminds me of some of my less successful tech reviews.

Hint: 13 year old french kid. Obviously bright but unfamiliar with any technical terms. May need description reduced to simplest form!



Suck, squeeze, bang, blow.

[Tu.114]

Let us look at a car engine; maybe this will clear things up a bit.

Such a piston engine cannot start to run on its own; it needs to have its crankshaft turned by some external power source in order to get the air/fuel mixture, ignition, oil system etc. in motion. As soon as there are the first one or two charges igniting in the cylinders and driving the pistons, the engine can run on its own and no assistance from outside is needed.

The external power source used for this is typically an electric motor that will turn the engine; its power normally comes from an accumulator.

In analogy to this: Neither can a jet engine get running on its own. Its shafts will need to be spun up to a certain speed by an external power source so the compressors feed the combustion chambers enough air. As soon as there is a steady flame in the combustion chambers (requiring a constant supply of air and fuel), the compressors are kept running by the power delivered by the turbines and no outside assistance is needed any more.

And also here: You need some means to get the compressors up to speed. An electric motor is definitely eligible but comes at some costs that makes it less than optimal in most cases. So a pneumatic motor is used instead. The place of the batteries is taken by the APU here.

As soon as the starter has done its job of accelerating the engine (be it piston or jet engine) to a self-sustaining speed, it is disengaged. The power needed to sustain the engine then comes from the power stroke (in case of a piston engine) or from the turbine section of the jet engine.

I would advise You to get a good understanding of gas turbine basics first. Many postings in this thread contain links that will help You a lot. And once You have a good grip of what happens in a steadily running gas turbine, it will be the time to look at how a gas turbine is started, governed and operated. For Your question 3, You will likely find this thread (http://www.pprune.org/tech-log/545584-what-determines-spool-up-time.html) of interest.

EDIT: I found a cutaway picture of a pneumatic starter on this page (http://www.dutchops.com/Portfolio_Marcel/Articles/Engines/Starter_System.htm).

http://www.dutchops.com/Portfolio_Marcel/Articles/Engines/Images/Air_Start_Motor.jpg

The APU bleed air enters from the left, passes a row of stator vanes before working on the turbine and is then vented via the annular grille overboard. As such a turbine runs at rather high RPM, its speed is translated to a lower RPM and higher torque (remember, p=T*n*const.) in order to drive the engine shaft: this is why there is a planetary gearbox installed. Typically, such a starter also has a clutch that allows the starter to drive the engine but keeps the engine from driving the starter.

[Chu Chu]

Another way to think about is that if you burned fuel in the middle of an engine without the compressor turning, you'd just get flames coming out both ends of the engine.

[barit1]

The physical link between starter and core rotor is two sets of bevel gears, one in the accessory gearbox (I'll call it AGB) and the other on the core shaft; these two are linked by a shaft called the radial driveshaft or quill shaft.

Go back to post #14 to see the AGB and quill shaft.

During starting the starter is turning the engine, along with fuel pump, oil pump, electrical generator etc. Once the starter drops out, the engine is turning those accessories.

[AF330]

Hi everyone,
Before confirming/asking what I have learnt, I would like to thank you all to help and support me in my passion!

"AF330

Just wanted to welcome you and wish you the best of luck in the future. You have already gotten lots of help here and I hope to see you in an engineer's costume/pilot's uniform somewhere in the world some day!"

Thanks a lot for your welcome! I really appreciate, and yes, I hope to wear a pilot's uniform! It is my biggest dream, fly the A330! Well, again, thanks a lot for your great welcome MrSnuggles!

"This thread reminds me of some of my less successful tech reviews.

Hint: 13 year old french kid. Obviously bright but unfamiliar with any technical terms. May need description reduced to simplest form!

Suck, squeeze, bang, blow."

Thanks for your compliment! I loved your hint! But, I really don't mind technical words, even If I don't understand them! I really love to learn about aviation. I have noticed that there is alway something new to learn, when you finish with SELCAL, you don't understand A/THR, when you understand that, you get confused with Alpha Floor! You are absolutely right, when you say that I am unfamiliar with technical terms, but when It talks about aviation, I am ALWAYS ready to learn it! Thanks a lot for your post Fe Hoppy!

"Of course there are differences, this is just a basic explanation. And sorry, I'm not an instructor

Keep asking!!!"

No, don't say that Mecaniquito84! You really have helped me a lot! Thanks for your help!

I also would really like to thank TurbineD, DevX, barit1, Tu.114, lomapaseo and many more for their great explanations and answers on my boring and, I am sure, not professional questions that you expect on this forum.

Thanks a lot to everyone!

Well, let's say that I have more or less got the concept, and here is a nice photo that I found: http://www.aviation-news.co.uk/archive/media/CFMd2.gif

The APU BLEED AIR goes inside a compressor, it travels in different pipes to the accessory drive section, which is outside the aircraft, and then enters inside the gear box, where it stops it's route and turns an impeller, which turns the horizontal drive shaft, then turns the radial drive shaft by the help of the transfer gearbox, am I right till here?

Thanks a lot to confirm and help!

[FE Hoppy]

Pretty good.

With my instructor head on just for a second (I try not to bring it home with me), I would just say this:

Air is air. It only becomes "Bleed air" when it is taken from a compressor for some other use.

So our little Auxiliary Power Unit at the back of the aircraft normally has a valve on its compressor which when open allows air to "bleed" away from the APU along a network of pipes known as the pneumatic system where it can be used for many different tasks.

Examples might be:
Air conditioning,
Pressurisation of the cabin,
Pressurisation of the water systems,
Toilet flush!
Anti-ice systems (though not usually as the demand is too high)
and engine starting.

For engine starting, the air goes through a valve called the start valve to an air driven starter motor known often as an Air Turbine Starter motor. Because of course it is a motor which uses a turbine to convert pressure (of the bleed air) into mechanical rotation. This ATS is connected to the gearbox and therefore turns not only the gearbox and all the other pumps and things connected to the gearbox but also as you said the engine itself.

On your picture the yellow shaft is connected to the red "spool" or "rotor" and this will then rotate. When this spins the compressor on the front of that rotor starts to draw air through the engine from the inlet to the exhaust.
The picture you posted is a "twin spool" or "dual rotor" engine so the air entering the engine flows past the "Fan" and low pressure compressor shown in blue before passing through the high pressure compressor then through the combustion section, out through the high pressure turbine (which is doing no work at this stage) the low pressure turbine (which is extracting energy to help turn the fan) and out the back.

When the two rotors are turning fast enough (often this is dictated only by the speed of the red high pressure rotor) we can add fuel and a spark. The combustion of that fuel with a small % of the air going through the engine adds pressure at the two turbine sections, this makes the engine accelerate, as the engine accelerates the amount of air (mass) passing into the combustion section increases and we can add more fuel which in turn creates more pressure.

This continues until the energy from combustion alone is enough to keep the engine turning. This is known as "self sustaining" speed. At this point we no longer need the help of the ATS and the start valve can close.

But the yellow drive shaft is still connected so now the engine is providing the power to drive the gear box and all connected pumps and things. We don't need the ATM to turn anymore so some kind of clutch or freewheel device is incorporated to allow it to stop. This is important as the ATS is one of the fastest rotating devices on the aircraft. 50,000rpm on some models and we don't want them turning when not needed.

Hope that helps a bit. I would also suggest looking at many different engine types and aircraft too as you will find many variations in design and names for things but the general principal is roughly the same.

Bonne Chance young man!

[DevX]

Nicely explained Hoppy, and then there are the engines fitted with an electric starter/generator, known as a VFSG, or Variable Frequency Starter Generator. The GenEx and Trent 1000 engines use these on the Dreamliner and have 2 units fitted per engine. They are quite complex pieces of kit (not to mention expensive!:ooh:) as once the units have started the engine, they convert into generators to supply the aircraft with electrical power.

See here: 787 Propulsion System (http://www.boeing.com/commercial/aeromagazine/articles/2012_q3/2/)

[Amadis of Gaul]

Thanks for your compliment! I loved your hint! But, I really don't mind technical words, even If I don't understand them! I really love to learn about aviation. I have noticed that there is alway something new to learn, when you finish with SELCAL, you don't understand A/THR, when you understand that, you get confused with Alpha Floor! You are absolutely right, when you say that I am unfamiliar with technical terms, but when It talks about aviation, I am ALWAYS ready to learn it!



I don't know if in French-speaking cultures they use the "building block" theory of learning. Essentially, such a theory would have it that one ought to start with more simple concepts before advancing to more advanced ones, from the unknown to the known, so to speak. You seem to be starting with the pretty advanced before getting the basics covered. On one hand, I admire the dedication, but on the other, lament the time you'll waste trying to crack things you're not ready for.

How is your mechanical aptitude in general? Do you know, for example, how to replace a spark plug on a motorcycle (or even a lawnmower)? How about where the air filter is on your Dad's Citroen? I'm not asking you this to put you down, I'm only suggesting that many mechanical concepts translate from the small to the large, just the means of execution differ.

I'm sure there are plenty of books in French on engines in general, never mind turbofans. Starts small, then go big, the big isn't going anywhere.

[Turbine D]

AF330,

Quote by Amadis of Gaul: I'm sure there are plenty of books in French on engines in general, never mind turbofans. Starts small, then go big, the big isn't going anywhere.
To add to the suggestion Amadis made, just outside Paris on the A6, Exit E50, are two jet engine companies. CFM International has their main engine assembly plant there. SNECMA, who are half owners of CFM International (the other half is owned by GE), have offices and engine assembly facilities there as well. SNECMA's Evry-Corbeil address is:
10 Allée du Brévent 91019 Courcouronnes
+33 1 69 87 09 00
snecma.com

I think if you contact them, they can provide you with information to help you. If you explain to them your age and your dedication to understand and learn about jet engines there could even be more opportunities besides written information.

[Amadis of Gaul]

They'd probably give him a tour, if he asked nicely.

[AF330]

Thanks a lot!
Just would like to confirm these for the apu bleed air route at the beginning:
So apu air bleed get's compressed and then travel's into pipes and then goes inside a start valve and the air turbine starter. It ends it's route there. The ATS spins the accesory drive box, so the gearbox, the impeller, which turns the horizontal drive shaft, then turns the
radial drive shaft with the help of the transfer gear box. Am I right here?

Thanks a lot to confirm!

PS: I am now in 3e- since 1 day! (9th grade, I think, but not sure at all) and I will have to do a small "formation" in any company I would like to for just 3 days. As I am 13 (going to be 14 in November), I thought that I would do one in Air France as I want to become a pilot (and my friend's father is a 777 captain) ! But I could really try your address! Thanks a lot!