B787 Theretical question

[rampman]

I was having a discussion today with a few people and we were trying to work something out. Is the 787 easier to hole than a metal aircraft hull if it was in a identical accident say with a baggage belt and would it be more costly to fix the hole on the 787

[FlightPathOBN]

thats easy...right now, there are none in operation, so as the old adage goes, if you make a hole and no one is around to hear it, did you really make a hole..

on a serious note..

If you look into the operators manual for the 787, Boeing has stated you are not allowed to do that...

so far, only burnt holes in batteries have been addressed...

and you see where that has got them.

(should not be a problem to re-glas the area, wait for it to cure, fix the interruption in the titanium wires though the area for lightning protection, and of course, deal with the flaming batteries because this was done in the maint mode, miswired through the APU battery)

[ZFT]

(should not be a problem to re-glas the area, wait for it to cure,

I seem to recall reading somewhere that this required some quite stringent temperature and humidity controls to accomplish?

[Romulus]

depending on the size it can be as little as a 1 hour operation to patch the carbon fibre.

Lest I be accused of spruiking the brochure Boeing claim 30 minutes.

[deptrai]

rampman, this will inevitably become a practical question

to answer the 1st part: "[Boeing and Airbus] assert that composite fuselages are in any case tougher than those of metal and will be more resistant to damage. "

(however..."despite positive spin from the airframers, the industry is to an extent feeling its way on this issue and experts agree that not all the answers are yet in place")

The 1-hour-fix which was mentioned is a band aid that can be used until the next heavy maintenance. A pre-cured composite patch is epoxy bonded to the outside of the damaged area and a chemical heat pack is applied to cure the resin – which will cure at relatively low temperature. It can be applied at the gate if necessary. It is primarily intended for light damage and not for more serious cases where load path integrity is at stake.

Gliders have been fixed with bonded composite repair for 40 years now. One issue with composite repairs may be that some materials need to be stored in a temperature controlled environment, and have a limited shelf life, after which they need to be discarded. Some airlines with smaller fleets may elect not to stock them.

As an alternative to bonded composite repair, bolted/hi-lok titanium patches can be used, just like for conventional tin can airframes

On this topic, the airframe engineering manager at LH Technik, Christian Sauer, was quoted saying: "While accepting that bolt-on repairs may be familiar and quick, we would prefer bonded repairs if the regulatory hurdles could be overcome. It’s certainly a shame to have to make holes [for bolts] in nice continuous fibre lay-ups. But bonded repairs are not yet accepted [for commercial airliners] by the airworthiness authorities except, essentially, as a cosmetic fix."

All quoted from this article here

Meeting the challenge of composite fuselage repair - Reinforced Plastics

[fizz57]

Interesting podcast of an interview with Christopher Tang, distinguished professor in UCLA’s department of business administration, on IEEE Spectrum here: Are Boeing's Battery Difficulties Part of a Much Bigger Problem? - IEEE Spectrum (don't know if it requires a login).

Besides dealing mostly with Boeing's outsourcing business model, he also mentions some concerns with the composite construction, along the lines of:

In the long run, I think Boeing needs to pay close attention to the issue of inspection and maintenance at different airports for the 787 program. This is because they’re utilizing a lot of carbon fiber. They need to find easy ways to inspect for cracks on the aircraft. Unlike an aluminum plane, you can check for cracks. For carbon fiber, based on my understanding, they need either X-ray or ultrasound to check for cracks on the composite material. Then the question is, how can they utilize X-ray and ultrasound in different airports around the world? Can they actually do the maintenance and the inspection effectively?

[westhawk]

Unlike an aluminum plane, you can check for cracks. For carbon fiber, based on my understanding, they need either X-ray or ultrasound to check for cracks on the composite material.

To answer the distinguished professor's concern regarding inspection of composite aircraft structures, yes these procedures can be conducted at airports.

In fact, x-ray, ultra sound and all other NDT inspection methods have been being conducted at airports for many decades. The bizjet shop I worked in at LAX had the equipment and trained personnel to conduct ultra sound, eddy current, dye penetrant and magnetic particle inspections. X-ray inspection was contracted to a mobile specialist company due to cost efficiency considerations, but could have easily been added to the repair station rating had there been more call for it. As it was, we provided some outstation services to airline customers, but they all saw to their own heavy mx at their own mx bases. After all, our specialty was business aircraft and doing contract airline line mx just a sideline rather than part of the core business plan.

The above mentioned NDT technologies used in structural inspections are completely mobile and could be transported to outstations along with the inspectors as needed. However it is extremely rare that such an inspection needs to be accomplished at an outstation. Structural inspections are normally accomplished during scheduled maintenance checks at a mx base. Field evaluations are normally only necessary in cases of in-service damage incidents. In these cases, visual inspection is normally sufficient to decide whether a temporary repair can be applied, or it is safe to ferry the airplane back to base, or whether further evaluation or repairs must be conducted in place. While all of the above is applicable to aluminum airplanes with limited composite components, I don't see composite structures being treated any differently with respect to where and when NDT inspections are performed.

[fizz57]

Ah, just another pumped-up academic MBA spouting off outside his depth then. Pity they've got them in the real world too.

[TURIN]

You can hit the CFRP with a sledge hammer and it will just bounce off.
Hit it with something heavy doing more than 2 mph and you're in trouble. The damage is not visible. A small NDT ultra sound go-nogo device has to be used and if necessary access to the area immediatly behind the impact point to check delamination.
At least one 787 customer has had the honour of a major repair after a catering truck put an L shaped hole in the fuselage.
All very hush hush.

[cockney steve]

You can hit the CFRP with a sledge hammer and it will just bounce off.

But, just as with a lot of modern car-bumpers, there is SERIOUS structural damage hidden in the depths with absolutely NO visual indication that an impact ever took place.

[TURIN]

You misunderstand Steve.

A sledge hammer will bounce off causing no damage. The CFRP is THAT strong! In fact the traditional 'cut here' red markings are useless if you want to get in with an axe. Fire services will have to use cutting blades such as rotary saws to get through the skin.
I also understand that the traditional cockpit axe is not fitted either as it's next to useless on a 787.

It takes something heavy with momentum to actually cause serious damage.

IE. Catering truck or hi-loader.

[FlightPathOBN]

from the Lazy B...

"In addition to using a robust structural design in damage-prone areas, the 787 has been designed with the capability to be repaired in exactly the same manner that airlines would repair an airplane today — with bolted repairs. "

AERO - Boeing 787 from the Ground Up