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Faro
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Electric Field Generated In A Cfrp Airliner

Fri Jul 19, 2013 8:19 am

Do manufacturers map in 3D the electromagnetic fields generated inside an airliner by its electrical system?

Is the electromagnetic field generated (both inside and outside the airframe) in a CFRP airliner significantly different in spatial layout/intensity from that generated in a classic one?

Can a CFRP airframe concentrate electromagnetic field energy on any particular spot inside the airframe in a way not found on classic airframes?


Faro
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nomadd22
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RE: Electric Field Generated In A Cfrp Airliner

Fri Jul 19, 2013 6:55 pm

You might have to be a little more specific than "electromagnetic field". 400hz is going to be an entirely different subject than several gigahertz.
Good question though. The mesh in the fuselage is probably a better shield and ground for most frequencies than solid aluminum. But you have to add in the matter of so much framework also being composite and not being part of the grounding system.
I'd expect any device that can generate an appreciable field to be analyzed for it's effect on everything else in the plane, but I'm starting to have my doubts after some of the information coming out of some of the recent investigations. There seems to be a lot of supplier designed gear being installed with no single contractor really having a clear idea of the entire system. I'm sure there's 10,000 pages of analysis and paperwork behind every part. I'm just not sure there's a surplus of common sense behind things.

I'm taking a wild guess that you're wondering if there might be some unanticipated arcing or localized heating in places because of the lack of a metal frame.
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RE: Electric Field Generated In A Cfrp Airliner

Fri Jul 19, 2013 8:43 pm

Now you are getting into the realm of the black arts!

I do not know if they actually map the magnetic field inside of the airplane. I do know for military aircraft, they do measure the electromagnetic signals inside the airplane when subjected to sources both in side and out side of the aircraft.

As for structures smaller than an aircraft, when properly design, a composite shell can be made as effective a Faraday cage as a metal shell. It's a little more tricky with composite and the performance is not as good as metal, but it's good enough.

Quoting nomadd22 (Reply 1):
The mesh in the fuselage is probably a better shield and ground for most frequencies than solid aluminum.

What one EEE guy tell me is that the better the conductor the better the shielding. Also the more conductive material thickness wise, the better shielding. Also you must properly ground the edges of your shielded area otherwise any large gaps or holes becomes an emitter (although at a lower power).

There are other factors with wavelength, power and how pseudo conduction, as in some forms of graphite that makes this whole field a form of black magic to the rest of us.

bt
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nomadd22
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RE: Electric Field Generated In A Cfrp Airliner

Fri Jul 19, 2013 8:53 pm

Quoting bikerthai (Reply 2):
What one EEE guy tell me is that the better the conductor the better the shielding. Also the more conductive material thickness wise, the better shielding. Also you must properly ground the edges of your shielded area otherwise any large gaps or holes becomes an emitter (although at a lower power).

It' doesn't make that much difference shielding wise in airliners, since the windows are huge, gaping holes no matter how well the rest of the hull shields. Anything more than a few megahertz is going to pass right through.
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RE: Electric Field Generated In A Cfrp Airliner

Fri Jul 19, 2013 11:48 pm

Quoting Faro (Thread starter):
Is the electromagnetic field generated (both inside and outside the airframe) in a CFRP airliner significantly different in spatial layout/intensity from that generated in a classic one?

I very much doubt that, and it is almost certain to be irrelevant to you as a passenger.

Some of the stronger electric pumps and motors are below the passenger deck in a few locations, and on the 787 there are actually more of those again; Having the passenger floor no longer made of metal but CFRP as well in many newer aircraft (including some otherwise aluminium ones) removes a bit of shielding capability from that regardless of the material of the outer hull, but I seriously doubt it matters.

Emanating electromagnetic fields are generally seen as loss and inefficiency from the point of view of the respective system and they would also be unwanted sources of interference to sensitive electronics on board, so they are avoided as far as possible anyway.

Just quantitatively you're closer to even stronger electric motors and power lines when you're riding a train to work each day.

And the power lines and WiFi routers and all the WiFi and other wireless devices in and around your house and even in your pocket will likely expose you to a lot more electromagnetic fields over time than your flights on an aircraft will.

Despite many people's suspicions, there is also no actual evidence for any detrimental effects on the human body from electromagnetic fields (at least by commonly experienced ones).

Quoting Faro (Thread starter):
Can a CFRP airframe concentrate electromagnetic field energy on any particular spot inside the airframe in a way not found on classic airframes?

No.

Quoting nomadd22 (Reply 1):
The mesh in the fuselage is probably a better shield and ground for most frequencies than solid aluminum.

No, it isn't. It's a sufficient replacement for the purpose of lightning shielding, but that's about it. A structural aluminium hull would be a better shield, but that doesn't really matter as long as lightning protection is assured (and it is).

[Edited 2013-07-19 16:50:15]
 
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bikerthai
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RE: Electric Field Generated In A Cfrp Airliner

Mon Jul 22, 2013 2:06 pm

Quoting nomadd22 (Reply 3):
It' doesn't make that much difference shielding wise in airliners, since the windows are huge, gaping holes no matter how well the rest of the hull shields. Anything more than a few megahertz is going to pass right through.

Quite true. Which leads me to a question.

How does the 787 electrical work? Is the shading layer conductive or semi-conductive? If it is, then could the window now be an effective EMI barrier?

bt
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nomadd22
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RE: Electric Field Generated In A Cfrp Airliner

Mon Jul 22, 2013 7:03 pm

Quoting Klaus (Reply 4):
No, it isn't. It's a sufficient replacement for the purpose of lightning shielding, but that's about it. A structural aluminium hull would be a better shield, but that doesn't really matter as long as lightning protection is assured (and it is).

Rf shields are rarely solid metal. The size of the grid determines how it will pass rf. Solid metal can often re-radiate rf and make for a much poorer shield than a grid. I do this stuff for a living, and am not just quoting the back of whatever serial box some people get their information from.



Quoting bikerthai (Reply 5):
How does the 787 electrical work? Is the shading layer conductive or semi-conductive? If it is, then could the window now be an effective EMI barrier?

Good question. I can't say I've ever considered electro-chromatic glass effects on rf. It could bring up some very interesting possibilities if it did block it depending on it's state.
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Klaus
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RE: Electric Field Generated In A Cfrp Airliner

Mon Jul 22, 2013 9:46 pm

Quoting nomadd22 (Reply 6):
Rf shields are rarely solid metal. The size of the grid determines how it will pass rf. Solid metal can often re-radiate rf and make for a much poorer shield than a grid.

I just wasn't talking about RF.

Quoting nomadd22 (Reply 6):
I do this stuff for a living, and am not just quoting the back of whatever serial box some people get their information from.

I'm just wondering what your favourite brand of breakfast serial chips is and what you're pouring on them...!   

[Edited 2013-07-22 14:48:59]
 
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RE: Electric Field Generated In A Cfrp Airliner

Tue Jul 23, 2013 4:52 pm

Quoting nomadd22 (Reply 6):
Rf shields are rarely solid metal.

Peace my friend. You are getting into the radar absorption/reflection realm of Rf, in which case your case for the mesh may be true.

From a pure EM interference/pass through prevention stand point, solid conductors are still the best.

bt
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nomadd22
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RE: Electric Field Generated In A Cfrp Airliner

Tue Jul 23, 2013 7:05 pm

Quoting Klaus (Reply 7):
Quoting nomadd22 (Reply 6):
I do this stuff for a living, and am not just quoting the back of whatever serial box some people get their information from.

I'm just wondering what your favourite brand of breakfast serial chips is and what you're pouring on them...!

It's an old joke from my Motorola days that wasn't that funny back then.

Quoting bikerthai (Reply 8):
Peace my friend. You are getting into the radar absorption/reflection realm of Rf, in which case your case for the mesh may be true.

From a pure EM interference/pass through prevention stand point, solid conductors are still the best.

Rf is rf. Absorbtion and reflection are actually the easy parts to figure. I've personally analyzed solid metal containers for rf blockage. If you sweep a solid metal surface with a wide range of rf, the results are going to be all over the place. Some frequencies won't be measurable on the other side. Others will travel along the surface and re-radiate out somewhere else with little loss. Slight changes in direction of the object will act like a coil to high enough frequencies, further complicating things. You really can't make blanket statements because of the vastly different behaviors for that wide of a range. A grid can absolutely make a better shield or reflector for wide ranges and particularly for specific frequencies because depending on how and where you ground it, it's behavior can be much more predictable.

[Edited 2013-07-23 12:07:24]
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Klaus
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RE: Electric Field Generated In A Cfrp Airliner

Tue Jul 23, 2013 8:23 pm

Quoting nomadd22 (Reply 9):
It's an old joke from my Motorola days that wasn't that funny back then.

Come on... with the number of people dwindling every day who actually still know what a "serial box" might even be, it's going back to becoming an in-joke more and more...!   

Quoting nomadd22 (Reply 9):
Rf is rf.

Yeah, and RF is not what the mesh in CFRP fuselages is all about.
 
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bikerthai
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RE: Electric Field Generated In A Cfrp Airliner

Tue Jul 23, 2013 9:39 pm

Quoting nomadd22 (Reply 9):
Others will travel along the surface and re-radiate out somewhere else with little loss.

Ah there's there crux. The re-radiate you talk about is a function of hardware design and interfaces, another part of the black arts . . .   

bt
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