So how will the dielectric composite skin of the 787 deal with lightning? Other Updates

This little interesting tidbit came up while reading an update on the 787. It seems that the compostie fuselage is dielectric. So arching between section can occur if they are not tight. It also has a different lightning protection system. A mesh that is incorporated into the skin is used to dissapate the strike. The high pressure hydraulic system also effected designs. The controll systems are smaller resulting in smaller fairings which also help reduce drag.

Lightning protection is one area where we’ve had a lot of discussion to make sure that [composite structures] are comfortable” with FAA regulations, says Cogan.

Unlike aluminum alloy airframes, the composite skin is dielectric. Boeing and Mitsubishi’s concern was that gaps between fasteners and composites might cause arcing, Cogan said. The redesign produced fasteners with tighter seals.

Boeing regards the 787’s lightning protection system as proprietary. What is known is that strikes are dissipated with a phosphor bronze wire mesh interwoven into the composite fabric.
Shocking

Yes it is interesting FredT, but slightly puzzling. I don't quite no why Boeing is trumpeting its solution as new however.

Funnily enough I was recently looking at a single piece rear fuselage section for an MD Notar Explorer helicopter. The piece itself had been a factory reject at the HDH(now Boeing) facility in Bankstown, Sydney. Hawker De Havilland did a lot of airframe development work on the design for what was then MDC helicopters in the late 80's early 90's. Upon inspection I could clearly see the phosphor bronze mesh mentioned in the 787 article. Not realizing exactly what it was I asked a composites expert I was with and he told me its function. It appears to be laid down in the mould as an initial layer so it is near the finished surface. I would hazard a guess that imbedding it too deeply or on the inner surface could result in the carbon fibre bursting if hit by lightning, obviously an undesirable outcome. In appearance it strongly resembles the more traditional types of metal mesh found on windows and fly screen doors.

What would have been the difficult part was finding a way to produce fastener gaps with tighter tolerances and seals, whilst guaranteeing the fasteners and composite panels remain electrically isolated to preclude the usual problems of electrolysis in carbon fibre. As I say no mean feat when talking about large numbers of fasteners in a mass production scenario.

LEE.

I'm much more concerned with production tolerances with the composite fueselages...

[And I am still concerned about maintainability, inspite of being shown various NDT approaches to inspecting the 787 elsewhere]


If you make them from bigger parts, there is more to go wrong and that can cause greater wastage.


It'll be very interesting to see if Boeing can ramp production, while maintaining efficiency levels.

Originally posted by kilcoo316

[And I am still concerned about maintainability, inspite of being shown various NDT approaches to inspecting the 787 elsewhere]


If you make them from bigger parts, there is more to go wrong and that can cause greater wastage.

Yeah It will be interesting to see how they repair a 787 the first time some moron drives a ground service vehicle along and takes the side out of one. I remember when some clown did this to a brand new Qantas 747-400 some years back. Took out about 20ft of skin and it cost a fortune to repair. I would like to know if you can easily remove fuselage panel sections in situ, or whether something far more drastic is needed requiring jigs and weeks or months in dock. The system Airbus is talking about for the A-350XWB sounds more repairer friendly. Then again I doubt Boeing hasn't thought of these problems allready, and devised accepatable solutions.

LEE.