Originally Posted by
Space Monkey
Yes they are easy to replace as a whole but expensive since when dealing with composites (unlike metals) entire wings and fuselages are one piece items... so if you were going to replace the wing tip on a harrier (for example) and not do a cast repair then you would have to remove and replace an entire wing not just the affected area.... in the 787's case this would be even more extreme since the fuselage is built in large high volume legnth and area pieces so to do what you are talking about might mean removing and replacing an entire third of the fuselage at a time... the better answer is to patch, sand and blend with more composite... much cheaper.... as for using composite in high pressure areas.... well answering this question is much more compicated since there are several factors that go into this......but to make a very long answer short... the first issue is which material truely is stronger or more flexable and more suited to the job??? then if we do decide to put composite and another material together how do we attach them??? a piece of composite may or may not blend and adhere to other materials... if they will not adhere or blend to each other should be use some sort of bracing or plating to attach them???? and how strong is the bracing or plating also by the time we do this is it really that much stronger and whats the cost??? if there is any additional cost is the extra stregnth or benefit worth it??? and the list continues... if the composites turn out to be worth it then they will be used if not then stick to conventional materials.... Hope this helps answer the question... Back to my wine now.... It''s Yellow Tail Chardonnay tonight............
Spacemonkey,
You must be incorrect, because the manner in which Airbus repairs composite material is much different than you describe.
See this picture:
http://www.ntsb.gov/events/2001/AA587/AA587_15.jpg
On AA 587, when the aircraft came off the production line, Airbus discovered a large void in the attachment lug of the vertical fin. Since there was no "approved" way to repair composite and there was no criteria under which such a repair might be certified or what resultant stiffening of the lug might do to load distribution and the Fail Safe numbers for the Part 25 certification (simulating the failure of one lug and return to base on five remaining lugs), Airbus got creative.
You can see, rather than patching the composite with sand-and blend, as you outline, the Airbus method was to take a scrap of metal plate, slap it on the outside of the identified area, drill 21 metal bolts through the composite (with resultant breaking of continuous carbon strands and introducing metal into the midst of the carbon matrix with predictable heating-and-cooling differences in the metal and carbon materials now a serious consideration) and shove it out on the line.
Jetblaster