
The Jet Engines with 'Digital Twins' - M_Grey
http://www.bbc.com/autos/story/20170214-how-jet-engines-are-made
======
donpdonp
Everything I know about jet engines comes from the fantastic multi-year
youtube vlog of AgentJayZ of JetCity, Canada!
[https://www.youtube.com/user/AgentJayZ](https://www.youtube.com/user/AgentJayZ)

~~~
burntrelish1273
Ah... Combustors, combustor liners, vacuum-melted steel, lock-wiring... all
the good bits and crazy tolerances explained. Also, reminds me of the Rolls-
Royce docu:
[https://www.youtube.com/watch?v=UazsDDFsS7Q&list=PLFF54B91EB...](https://www.youtube.com/watch?v=UazsDDFsS7Q&list=PLFF54B91EB593DF78)

Pairs well with some
[https://youtube.com/arduinoversusevil](https://youtube.com/arduinoversusevil),
[https://youtube.com/Abom79](https://youtube.com/Abom79) and maybe some
[https://youtube.com/engineerguyvideo](https://youtube.com/engineerguyvideo)

And, if you like aviation:
[http://www.flywithcaptainjoe.com](http://www.flywithcaptainjoe.com)

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coredog64
> They’re so difficult to make, in fact, the companies that build aircraft
> don’t make their own engines.

Airframe manufacturers are prohibited from doing so. The "United" in "United
Airlines" harks back to when Boeing, Pratt& Whitney and an airmail company
were integrated into a single company.

Today, when an airline buys a commercial airliner, the airframe and engine
purchases are separate even though the airframe is specific to a single engine
type.

~~~
M_Grey
Could they unite those elements of the industry again if given the chance, or
has it moved on to just be too specialized?

~~~
klodolph
I found this discussion on Quora:

[https://www.quora.com/Why-are-airframes-engines-developed-
ma...](https://www.quora.com/Why-are-airframes-engines-developed-manufactured-
by-separate-companies-especially-on-airliners-How-did-this-symbiotic-
relationship-evolve)

And this Wikipedia article:

[https://en.wikipedia.org/wiki/Air_Mail_scandal](https://en.wikipedia.org/wiki/Air_Mail_scandal)

It sounds like a combination of antitrust concerns and just the fact that
airframes and engines don't have much in common.

~~~
M_Grey
That was a good read, and I agree with your conclusion.

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Merad
If you find jet engines interesting, check out AgentJayZ [0] on youtube. He
runs a shop in Canada that repairs and overhauls smaller jet engines (think,
Learjet size rather than 777 size). He has a mix of good videos, including a
long running Q&A series.

[0]:
[https://www.youtube.com/user/AgentJayZ](https://www.youtube.com/user/AgentJayZ)

------
zellyn
The article made it unclear what the difference between a "digital twin" and
an engine-specific record is. I assume the difference is that they're building
a model of some kind, but you wouldn't know that from searching for [twin] in
the article.

~~~
nullpage
It is some tech out of GE Digital that, from what I understand, uses sensor
data + machine learning against a digital representation of the system to
predict failures and tune performance. A friend of mine just recently took a
job at a start-up using this technology
([https://veerum.com/about/](https://veerum.com/about/)), however I haven't
had a chance to catch up with him and really understand how this stuff works.

There is some more information here: [https://www.ge.com/digital/power-
digital-twin](https://www.ge.com/digital/power-digital-twin)

[https://www.ge.com/digital/blog/rise-digital-
twins](https://www.ge.com/digital/blog/rise-digital-twins)

~~~
roymurdock
It's a part of the Predix platform offering:

 _In large-scale systems, sensor information can be in different locations
separated by great distances. For example, a pipeline system may have some
assets in a central terminal as well as assets in the field miles away from
the terminal - and all of these must be connected to a single asset model to
monitor the health of the system as a whole.

Asset data can be ingested through a REST API using files in JSON format or
created using a user interface. The data is stored in a graph database that is
optimal for searching hierarchies of assets. Tags that indicate pressure or
temperature can be associated with each asset. These tags can then be used to
bring in and associate time series data and analytics to build digital twins
of a complex asset.

For example, you could create an asset model that describes the logical
component structure of all pumps in an organization, and then create instances
of that model to represent each individual pump. Or you could create custom
modeling elements that meet your unique domain needs if a particular pump has
a few differences with the generic version._

[https://www.predix.io/services/service.html?id=1171](https://www.predix.io/services/service.html?id=1171)

------
DrScump
I was hoping that this was about a discovery that jet engines can become
quantum-entangled.

~~~
M_Grey
It's all fun and games until a careless measurement causes one set of engines
to be "on" and the other to be "off".

~~~
DrScump
You gotta make sure that both entangled engines don't end up on the _same
plane_.

~~~
M_Grey
At worst... you'd go in circles. At best you'd just sort of lazily zig-zag to
your destination.

"Goddamn it Roger, port #2 is in a superposition of existing and not existing
again!" "Calm down Wilco, just take a good hard look at her and she'll settle
down."

------
davidgould
Rolls Royce publish an excellent book "The Jet Engine" with a great deal of
information about the design and manufacture of jet engines. I purchased the
latest print edition and it's well worth it. However there is an online PDF of
an earlier edition at
[http://airspot.ru/book/file/485/166837_EB161_rolls_royce_the...](http://airspot.ru/book/file/485/166837_EB161_rolls_royce_the_jet_engine_fifth_edition_gazoturbinnyy_dviga.pdf)

~~~
mnw21cam
Oh, wow. Grew up with that book in the house (probably the first edition), and
yes it is fantastic.

------
joshuahaglund
> In the second module an air compressor takes air in and puts it under high
> pressure, which shrinks the volume of the air and allows the engine to be
> smaller (because compressed air takes up less space).

Does this reporter know what they're talking about? I always thought
compressors were an essential part of a jet engine (compression heats the air,
then fuel is sprayed in which auto-ignites, expanding, and turning the turbine
blades). Not just because compressed air takes up less space.

~~~
WalterBright
The compressor does not heat the air to the ignition point. The flame that is
already in the engine provides the ignition, and the flame is prevented from
blowing out the back by "flame holders".

[https://en.wikipedia.org/wiki/Flame_holder](https://en.wikipedia.org/wiki/Flame_holder)

The ignition at engine start is done with spark plugs.

The purpose of the compressor is to provide dense enough air to support
combustion, and the pressure is needed to prevent the exhaust gases from
blowing out the front of the engine.

~~~
mschuster91
> and the pressure is needed to prevent the exhaust gases from blowing out the
> front of the engine

Out of curiosity: has that ever happened and how does such an event look like?

~~~
jabl
See "compressor stall",
[https://en.wikipedia.org/wiki/Compressor_stall](https://en.wikipedia.org/wiki/Compressor_stall)

A compressor stall can be severe enough to damage or even destroy the engine,
though I don't think there's (usually, at least?) actually exhaust blowing out
the front.

~~~
Scramblejams
I read a book in which the author related the story of an F-8 Crusader which
suffered an in-flight failure during refueling, causing flame to shoot forward
from the intake. Apparently there was photographic evidence, which came in
handy when the manufacturer insisted that was impossible. Believe it was one
of D.K. Tooker's books, probably "The Second Luckiest Pilot." Very
entertaining read, highly recommended if you like vignettes of danger in the
skies.

------
Shivetya
the detonation engine, would is sound like a hyperactive V1?

------
agumonkey
digital twin seems like the first start of a humonculus.

------
dorfsmay
This article does a terrible job at explaining how jet engines work. Spending
10 minutes on wikipedia will give you a better idea. Do look for high vs low
bypass. Jet engine s are fascinating, the theory behind them is fairly simple,
but a huge challenge to make it happen in the physical world, high
temperatures as mentioned but also extremely high rotational speed, which
requires parts as close to perfection as possible, and very robust, hairline
fractures in engines have resulted in plane crashes.

~~~
azernik
I think it does a fairly good job - I read through it in about _one_ minute,
and (having already spent some time studying jet engine principles) think it
got the essential concepts across. e.g. it doesn't use the word "bypass" but
does explain the principle. In such a small amount of space and with the
constraints on vocabulary/prior-knowledge assumptions of a mass audience,
going into the design tradeoffs of different specific designs is overkill.

~~~
PhantomGremlin
_I think it does a fairly good job_

Yes, I agree. I also loved that they mentioned something I think is really
cool --- the gas stream is hotter than the melting point of the turbine
blades, and yet the designers have found an ingenious solution.

