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(MIT)   Do jet engines ever really stop?   (alum.mit.edu) divider line 47
    More: Misc, jet engines, gas turbines, combustion chambers, compressors, aeronautics, compressed air, idling, implements  
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4804 clicks; posted to Geek » on 07 May 2014 at 10:45 AM (28 weeks ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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ZAZ [TotalFark]
2014-05-07 09:40:06 AM  
Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.
 
2014-05-07 09:41:30 AM  
I believe there was just an experiment near Malaysia that proved that they, in fact, do.
 
2014-05-07 09:44:16 AM  
Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU
 
2014-05-07 09:46:23 AM  

ZAZ: Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.


There is a tube in the cockpit that the pilot has to blow into.
 
2014-05-07 09:55:02 AM  

Marcus Aurelius: ZAZ: Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.

There is a tube in the cockpit that the pilot has to blow into.


Yeah, but you don't really blow. It's just an expression.
 
2014-05-07 09:57:26 AM  
This starts it all:

thumbs.dreamstime.com
 
2014-05-07 10:49:50 AM  

Marcus Aurelius: ZAZ: Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.

There is a tube in the cockpit that the pilot has to blow into.


bmschwartz.files.wordpress.com

That's for the autopilot
 
2014-05-07 10:53:25 AM  

Marcus Aurelius: ZAZ: Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.

There is a tube in the cockpit that the pilot has to blow into.


And it makes a little whizzing sound like a party horn.
 
2014-05-07 10:54:38 AM  

riffraff


Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU


Thank you, start again!


shardlowcr0607.wikispaces.com
 
2014-05-07 10:57:01 AM  
Are people really that stupid?
 
2014-05-07 10:58:30 AM  

cretinbob: Are people really that stupid?


The answer is on the back of your screen.
 
2014-05-07 11:06:46 AM  

Pelvic Splanchnic Ganglion: cretinbob: Are people really that stupid?

The answer is on the back of your screen.


All it says is dy. Is this some type of code?
 
2014-05-07 11:10:25 AM  

ZAZ: Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.


It's turbines almost all the way down. Then you get to a turtle.
 
2014-05-07 11:10:45 AM  
"Most commercial aircraft have used this engine-starting method for a long time,"


Indeed, so why is this in an article today as if it were new?
 
2014-05-07 11:13:23 AM  

riffraff: Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU


Most of the turbo-fan engines on passenger jets are NOT started electrically. They are started pneumatically. I believe 787 is the exception, though I'm not sure about A380.

You have an "Air Turbine Starter" which is about the size of a 4-slice toaster or as large as toaster-oven. It has a turbine blade on one end that will spin up to about 60-70KRPM. That small turbine wheel, which is about 3-6" in diameter connects to a set of gears which have a ridiculous gear ratio and connect to an output shaft. The output shaft will spin up to about 5K rpm and is connected to the gearbox of the engine, thus getting the engine started.

The ones that are about the size of a toaster-oven, which are used on 777/A330 put out about 400hp.
 
2014-05-07 11:15:40 AM  
Jet engines should all sound like THIS when they start.
 
2014-05-07 11:16:25 AM  
MIT must have not got the $500,000 in funding this month to run a study that has already been studied.
 
M-G
2014-05-07 11:19:29 AM  
"...tens of thousands of RPMs necessary..."

*sigh*
 
2014-05-07 11:34:41 AM  

Best Princess Celestia: "Most commercial aircraft have used this engine-starting method for a long time,"


Indeed, so why is this in an article today as if it were new?


It must be a slow news day for them, so they needed something that sounded technical and sciency to justify their jobs.
 
2014-05-07 11:42:15 AM  

kidgenius: riffraff: Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU

Most of the turbo-fan engines on passenger jets are NOT started electrically. They are started pneumatically. I believe 787 is the exception, though I'm not sure about A380.

You have an "Air Turbine Starter" which is about the size of a 4-slice toaster or as large as toaster-oven. It has a turbine blade on one end that will spin up to about 60-70KRPM. That small turbine wheel, which is about 3-6" in diameter connects to a set of gears which have a ridiculous gear ratio and connect to an output shaft. The output shaft will spin up to about 5K rpm and is connected to the gearbox of the engine, thus getting the engine started.

The ones that are about the size of a toaster-oven, which are used on 777/A330 put out about 400hp.


How exactly is 12:1 to 14:1 a "ridiculous gear ratio"?

I'll start passing the word at work, since we can build up to 119:1 in a single reduction stage. We have apparently gone beyond plaid.
 
2014-05-07 11:45:07 AM  

markie_farkie: Jet engines should all sound like THIS when they start.


They should make the same sputtering sound on shutdown, too.
 
2014-05-07 11:47:13 AM  
There are 4 kinds of jet engine starters.

Electric. Like your cars starter, on steroids.

Pneumatic. An APU or huffer cart generates air pressure which spins a turbine and turns the engine.

Hydraulic. An APU pumps oil to spin the engine.

Pyrotechnic. no longer commonly used because explosives.
 
2014-05-07 11:49:59 AM  
While TFA is interesting, they fail to point out the whole thing that makes it interesting. Turbines are wonderfully efficient engines, but they suffer from requiring very high compression to operate. For example, one turbine I'm familiar with can only operate (unassisted) once it reaches 50% of it's maximum speed. An APU has to spin it up to about 20% of it's max speed, and then it uses igniters to get it up to 50%. Only once it spins fast enough does it have the necessary compression to be self-sustaining.

For analogy, it'd be like if your car would only operate between 2000-4000 RPM, and you needed a second special motor to get the primary motor up to 2000RPM.
 
2014-05-07 11:53:16 AM  

fluffy2097: Pyrotechnic. no longer commonly used because explosives.


Reminds me of this:

http://en.wikipedia.org/wiki/Coffman_engine_starter

I assume you're talking about something similar.
 
2014-05-07 11:53:54 AM  
Of course they do... just ask the people on flight 370.
 
2014-05-07 11:57:59 AM  
Too bad they don't have a video or something like that. The sound of a turbine engine starting is incredible. I can't access youtube right now but there is a video of a Bell helicopter starting and it is sweet. You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.
 
2014-05-07 12:02:16 PM  

Tobin_Lam: You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.


I came.
 
2014-05-07 12:04:44 PM  

fluffy2097: There are 4 kinds of jet engine starters.

Pyrotechnic. no longer commonly used because explosives.


But fun to watch.
 
2014-05-07 12:09:15 PM  

riffraff: fluffy2097: There are 4 kinds of jet engine starters.

Pyrotechnic. no longer commonly used because explosives.

But fun to watch.


A wet start can be pyrotechnic.
 
2014-05-07 12:11:48 PM  

Fubini: fluffy2097: Pyrotechnic. no longer commonly used because explosives.

Reminds me of this:

http://en.wikipedia.org/wiki/Coffman_engine_starter

I assume you're talking about something similar.


More or less. The combustion gasses basically drove the starter turbine like any other air start technique. Except for the obvious added bonus of explosives.
 
2014-05-07 12:30:25 PM  

kidgenius: riffraff: Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU

Most of the turbo-fan engines on passenger jets are NOT started electrically. They are started pneumatically. I believe 787 is the exception, though I'm not sure about A380.

You have an "Air Turbine Starter" which is about the size of a 4-slice toaster or as large as toaster-oven. It has a turbine blade on one end that will spin up to about 60-70KRPM. That small turbine wheel, which is about 3-6" in diameter connects to a set of gears which have a ridiculous gear ratio and connect to an output shaft. The output shaft will spin up to about 5K rpm and is connected to the gearbox of the engine, thus getting the engine started.

The ones that are about the size of a toaster-oven, which are used on 777/A330 put out about 400hp.


I guess it really depends on the airplane. I've seen the APU from C-130Js and they aren't small at all. They are more along the lines of large truck engine.
 
2014-05-07 12:36:55 PM  

Tobin_Lam: I guess it really depends on the airplane. I've seen the APU from C-130Js and they aren't small at all. They are more along the lines of large truck engine.


He's talking about the starter turbine, not the APU. The air start turbine is usually a vaguely electric-motor-looking thing (connected to bleed air lines) on the outside of the engine. Pretty tiny.
 
2014-05-07 12:41:36 PM  

costermonger: Tobin_Lam: I guess it really depends on the airplane. I've seen the APU from C-130Js and they aren't small at all. They are more along the lines of large truck engine.

He's talking about the starter turbine, not the APU. The air start turbine is usually a vaguely electric-motor-looking thing (connected to bleed air lines) on the outside of the engine. Pretty tiny.


Got it. No reason for that to be big.
 
2014-05-07 12:42:22 PM  
"The exhaust is from the auxiliary power unit," Brand says. "The APU is like a mini jet engine, usually located in the back of the plane, containing a compressor, combustor, and turbine, that provides the plane with electricity and compressed air for the air conditioning system while the plane is on the ground." The APU also provides the first step in starting the jet's main engines and causing its blades to rotate at the tens of thousands of RPMs necessary for the engine to become sufficiently self-sustaining and propel the plane through liftoff and flight.

Newer airports have GPU (Ground Power Units) that basically plug-in the plane to the building like an electric car, to further reduce emissions from parked aircraft, and consumes none/less of the aircrafts fuel.

They either connect from the ground, or are built in to the jetway.


Same with refueling. at an older gate, you have the truck come and connect to the aircraft like a car.  At more advanced gates, the fuel system is underground, and you just need a hose to connect the two. Makes for less vehicle traffic on the apron.
 
2014-05-07 12:53:24 PM  
It's all ballbearings now a days.
 
2014-05-07 12:57:06 PM  
That last part of the article about redundancy just doesn't feel right.
 
2014-05-07 12:57:30 PM  

LemSkroob: the fuel system is underground, and you just need a hose to connect the two. Makes for less vehicle traffic on the apron.


Its a tad more than just a hose. To utilize a center point fueling system on an aircraft from underground storage, you'll notice they use a relatively small cart which has a pump, and flow metering hardware, and a filtering system.

Something that can look like this:


i65.photobucket.com
 
2014-05-07 03:16:54 PM  
Suck, squeeze, bang, blow.

Jets and porn.
 
2014-05-07 03:36:48 PM  

uberaverage: It's all ballbearings now a days.


Sounds like you guys could use a refresher course?! And where's my steak sandwich?
 
2014-05-07 04:28:09 PM  
/CSB

When our unit got rid of F-105's, they had a 24 jet fly-over.  Only 10 Dash-60's to provide bleed air for starts, so they decided to "Cart-Start" all 24 of them, at once.  BOOM!  Big clouds of smoke billowing, and the satisfying whine and spool up of 24 Pratt-Whitney J-75's.  Pilots were told, if you've got an engine, hydraulics, and radio, you're going.  They all went.

upload.wikimedia.org
Pretty awesome for a young Airman.

/CSB end
 
2014-05-07 05:30:05 PM  

markie_farkie: Tobin_Lam: You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.

I came.


Then you probably should use Private Browsing settings for this.
 
2014-05-07 06:00:34 PM  

Sliding Carp: markie_farkie: Tobin_Lam: You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.

I came.

Then you probably should use Private Browsing settings for this.


The SR-71 is the only model I ever built as a kid. Still have it, 30+ years later.
 
2014-05-07 09:55:27 PM  

Marcus Aurelius: ZAZ: Is there a little turbine to start the APU turbine, and a littler turbine to start that one?  No wonder MIT has a nanotechnology lab.

There is a tube in the cockpit that the pilot has to blow into.


The ignition interlock is part of his sentence for flying drunk.
 
2014-05-07 10:43:02 PM  

Fubini: While TFA is interesting, they fail to point out the whole thing that makes it interesting. Turbines are wonderfully efficient engines, but they suffer from requiring very high compression to operate. For example, one turbine I'm familiar with can only operate (unassisted) once it reaches 50% of it's maximum speed. An APU has to spin it up to about 20% of it's max speed, and then it uses igniters to get it up to 50%. Only once it spins fast enough does it have the necessary compression to be self-sustaining.

For analogy, it'd be like if your car would only operate between 2000-4000 RPM, and you needed a second special motor to get the primary motor up to 2000RPM.


True, but the flipside of that is that you have access to something like 50% of your engine power in the top 3% of RPM. Unbelievably smooth operation compared to recips.

It's a shame the materials required for a reliable hot section are so expensive, turbine-electric hybrid cars would be awesome.
 
2014-05-08 03:18:11 AM  
AgentJayZ on youtube is a dude who rebuilds LM-1500 turbines for industrial use.

His videos are amazing, and they take you all the way through the mechanical ins and outs of turbine engines.

Any gearhead will want to watch all his videos, and everyone will want to watch the engine tests.

http://youtu.be/4wKPTWXD2Z0
 
2014-05-08 03:50:50 AM  

fluffy2097: AgentJayZ on youtube is a dude who rebuilds LM-1500 turbines for industrial use.

His videos are amazing, and they take you all the way through the mechanical ins and outs of turbine engines.

Any gearhead will want to watch all his videos, and everyone will want to watch the engine tests.

http://youtu.be/4wKPTWXD2Z0


I've been a fan of his for years. Heh. But seriously, came here to give his channel a plug.
 
2014-05-08 07:07:08 AM  

Angry Drunk Bureaucrat: I believe there was just an experiment near Malaysia that proved that they, in fact, do.


Aren't we still waiting for the results on that one?
 
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