Aviation question for boffins...
Discussion
Just to wade through the funniness for one second....
Aircraft have static wicks to remove....yes, you guessed it....static electricity.
Commercial aircraft have lightning strike capabilities designed in from day one. Metallic structures are fine for lightning strike, and there are zones for lightning strike protection (major strike areas are wing tips, nose, tail and other extremities) and design rules for conductivity are used to satisfy the required minimum conditions. The only dodgy bit is any arcing in fuel tanks - generally leading to explosion! this is got round using non-conductive sealant on bolts and by spacing bolts and structure so that there is a minimum gap between points. Composite aircraft such as A350XWB will include some sort of wire mesh as a near final ply in the wing skins and fuselage. This will form the required electrical network along with earthing straps.
Small aircraft and mil I am not soo sure about as I have not worked on them.
Essentially, as with a car you form a faraday cage to protect the occupants.
There are other solutions to the problem, these are just some I know of...
Coanda
Aircraft have static wicks to remove....yes, you guessed it....static electricity.
Commercial aircraft have lightning strike capabilities designed in from day one. Metallic structures are fine for lightning strike, and there are zones for lightning strike protection (major strike areas are wing tips, nose, tail and other extremities) and design rules for conductivity are used to satisfy the required minimum conditions. The only dodgy bit is any arcing in fuel tanks - generally leading to explosion! this is got round using non-conductive sealant on bolts and by spacing bolts and structure so that there is a minimum gap between points. Composite aircraft such as A350XWB will include some sort of wire mesh as a near final ply in the wing skins and fuselage. This will form the required electrical network along with earthing straps.
Small aircraft and mil I am not soo sure about as I have not worked on them.
Essentially, as with a car you form a faraday cage to protect the occupants.
There are other solutions to the problem, these are just some I know of...
Coanda
coanda said:
Do you have a source bushmaster? I don't doubt that there has been crashes because non-covered composite parts will explode under a lightning strike...so would be interested to see how long ago the crash was, and just what part was struck and how it failed.
It was either 'aircrash investigations' on Discovery Channel or a similar disasters-type show.I know there have been helicopter crashes where composite structures have failed on the tail rotor blades after lightning strikes.
I haven't heard of fixed wing aircraft made with composites having sections failing. The military have been using composites for years but their use in commercial aircraft is still not that widespread.
http://en.wikipedia.org/wiki/Bristow_Flight_56C
I haven't heard of fixed wing aircraft made with composites having sections failing. The military have been using composites for years but their use in commercial aircraft is still not that widespread.
http://en.wikipedia.org/wiki/Bristow_Flight_56C
Edited by anonymous-user on Thursday 25th September 17:59
Military aircraft are earthed using the airframe, in much the same way as a car. Everything is bonded to everything else by either physical contact of 2 metal surfaces, or by bonding leads or strips. Any composite panels usually hve metal strips running through them which are bonded to the frame or adjoining panels. And then they have the static dissipating strips on the trailing edges as mentioned before.
When 'parked' on the ground, they then have an earth lead attached from a mounting point on the airframe - or sometimes from the undercarriage leg - to anchor points on the ground. For refuelling, they are then also bonded to the fuel bowser too, so nothing is at a different potential, to reduce the risk of static sparks.
When 'parked' on the ground, they then have an earth lead attached from a mounting point on the airframe - or sometimes from the undercarriage leg - to anchor points on the ground. For refuelling, they are then also bonded to the fuel bowser too, so nothing is at a different potential, to reduce the risk of static sparks.
every panel on a commercial AC is "bonded" to the next, they have carbon inserts that carry current embedded and all should be more conductive than a mag alloy panel.
The issues happen if this is not done properly then a lightning strike could be disastrous and would blow that panel and anything attached to it off the AC
The issues happen if this is not done properly then a lightning strike could be disastrous and would blow that panel and anything attached to it off the AC
littleandy0410 said:
Military aircraft are earthed using the airframe, in much the same way as a car. Everything is bonded to everything else by either physical contact of 2 metal surfaces, or by bonding leads or strips. Any composite panels usually hve metal strips running through them which are bonded to the frame or adjoining panels. And then they have the static dissipating strips on the trailing edges as mentioned before.
When 'parked' on the ground, they then have an earth lead attached from a mounting point on the airframe - or sometimes from the undercarriage leg - to anchor points on the ground. For refuelling, they are then also bonded to the fuel bowser too, so nothing is at a different potential, to reduce the risk of static sparks.
For power systems. The thing is though, that signals (so if you're thinking about central locking or CAN bus equivalents, in an aeroplane) are not single ended like in a car. They're all balanced or at least differential, so as not to compromise or be compromised by the faraday cage of the airframe. Intermodule signals don't use a ground for reference at all (for high isolation and CMRR). Each module should (although perhaps may not) connect to the inside of it's equipment chassis at one point only.When 'parked' on the ground, they then have an earth lead attached from a mounting point on the airframe - or sometimes from the undercarriage leg - to anchor points on the ground. For refuelling, they are then also bonded to the fuel bowser too, so nothing is at a different potential, to reduce the risk of static sparks.
Edited by dilbert on Thursday 25th September 20:43
to be picky nothing needs a earth. a earth in only for a closed circult fault to stop exposed live parts from going live.
so a plane or space shuttle would be its own earth and the earth would return to the supply e.g. a battery.
if that doesnt help ill dig the pages of the BS7671 out tht cover this.
so a plane or space shuttle would be its own earth and the earth would return to the supply e.g. a battery.
if that doesnt help ill dig the pages of the BS7671 out tht cover this.
Ok, so, not being heavily into lightning strike protection.....if an aeroplane is hit by lightning at the wingtip whilst flying (quite a likely position), the current will run through the airframe and dissipate into the nearest sink (avoiding the use of the word earth/ground....) and that sink would be a battery? so there would be the possibility of frying some systems?
Confuzzled of Wiltshire....
Confuzzled of Wiltshire....
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