Aircraft Composites Repair Decides the Future

The Commercial Aircraft Composites Repair Committee CACRC

It is task groups include:

Composite repair materials, composites repair techniques, inspection, composite materials, composites design, service training, airline inspection and repair of composite conditions
This work has progressed.

It should be remembered that the CACRC about the current problems in the operation and it is primarily concerned with thin components, which often focuses SandwichStructures (eg, ref SAE AE-27, the "Guidelines for the design of durable, repairable and maintainable aircraft composites", whose design case studies are mostly sandwiches) parts. As in the service of confidence grows in composite materials are introduced, especially in lightweight sandwich panels or bonded structures in aircraft cabin interiors, more composite primary structures. Today, for example, we find the Airbus vertical and horizontal slats tailplanes composite and the outerwingboxes the ATR72s by Aerospatiale. But this design is the monolithic and usually a greater thickness than the secondary structures. Experience has shown that these structures are very tolerant of operational risks associated with the result that an increase in unscheduled maintenance costs due to repair of complex processes (compared to metals) are insignificant given the limited number of occurrences. Nevertheless, efforts must be continued in order to be better, tothe current repair techniques. It is a different emphasis on different aspects of the composites placed between the airlines. For example, the increased use of composite primary structure is very encouraged by some, others are more cautious. There will be some customers out all their composite service in-house, there are other outsourcing to a third party. Stripping the color relates to some, not glued and screwed or other similar repair techniques have theirSupporters.

Operational risks for the use of aircraft composites:

As with most industries, the companies are, the more and more competitive economic environment, a consequence of this is the intensive use of the aircraft themselves maximize revenue. Aircraft turnaround times of only 30 minutes to ensure that risks gse the impact of aircraft … Catering trucks, passenger stairs, service trucks, tractors, buses, etc. are alwayspresent. Reliability of the product, it is of utmost importance, as no unexpected downtime is reflected directly in the profits of airlines. This has a greater impact than in previous years and today we can take a passenger easily be able to get a flight on board the aircraft to a competitor. However, maintenance of the aircraft, whether planned or unplanned, is a cost effective, operators must develop in order to keep them in an airworthy condition. It is understood the OEM's responsibility tothe working environment of the aircraft, so that both the admission requirements are met and the maintenance costs of its products are reduced to a minimum. The operator needs a design that is reliable and tolerant in service threats.

There are many and varied threats to the in-service aircraft, as used in a hostile environment.

Threats are
a) Impact of tire debris
b) the effects of engine debris (large and small)
c)Fire Engine
d) Lightning
e) High Intensity Radio Frequencies
f) local heating of the structure of Fuel Pump Running Dry
g) the effects of bird strike
h) hot-air impingement channel burst
i) General impact (hail, dropped tools, "Hangar rash", fueling nozzles, runway dirt, etc.)
j) General Environmental Effects

Despite the evidence that thick monolithic laminates are extremely damage tolerant, it will always embody the potential requirement fora major repair.

There are only carried out very little experience with the airlines, major repairs to thick composite monolithic structure where, for example, thicknesses greater than 1 cm in some areas from one Airbus aircraft wing box. Be repaired Considering thin plates typically by gluing, this technique with additional difficulties, as is growing to meet the structural strength. Scarfing on currently accepted angle means that the original damaged area to grow significantlySize and lead to the neighboring structural features, the repair process even more difficult. Consistent application of heat and consolidation will be difficult unless performed in several lay-ups, but the down time for the completion of each treatment may unacceptably long. Finally, to assure adhesive gap thickness is still a question that is often raised, and must be answered if the wing box structure, the additional complication has to be applied,Connect with long-term fuel suspended. It may be that screwed patches (either composite or otherwise) with metallic type processes are the better approach if major repairs are whereas the required minor damage can be restored with bonding techniques.

Corrosion at interfaces with metallic components.

Cause corrosion of metallic structures that the aviation industry enormous effort during maintenance inspection, repair or testing, it is prevention. Without a doubt, one of themain advantages of composites is the enormous scope for reduction of this burden, however, there will always be metallic components on the aircraft and the potential for corrosion at the interfaces with carbon must be taken very seriously. There are already many airframes existing which have completed high flight cycles and many years in service without suffering such damage. Adequate protection schemes exist to prevent these problems and careful design and maintenance should be sufficient to realize a significant cost savings. Special care must be at major ports like a box outside to the inside wing joint and the design should be considered reasonable access for inspection.

Stripping for aircraft painting.

Stripping and repainting is a regular maintenance operation for the airline, either refresh the cosmetic appearance, have the company logo or change due to the owner. An airplane is generally repainted every 3 – 5 yearsthough it be quite common, the wings with any other revision. Concern has been expressed that this will be more expensive on a composite wing box as grinding procedures are required as a chemical removal. The sophisticated equipment which allows such abrasive methods is required (dry ice, wheat starch, water jet, laser, etc.) requires a large investment, the operators are not willing to spend on.

Pickling risks damage to the composite and not apractical option at present but the research continues to paints, so that the outer coat is easily removed by a mild stripper, but the primer remains in effect to develop. Alternative solutions may pigments with resin or adhesive films, which can be renewed without paint removal.

Opinions about carbon composites in the aerospace industry are both positive and negative, and are mainly components of thin laminates and / or sandwich construction is based. To win, runningExperience and hence confidence in their performance have often used it to replace metallic secondary structures in places that are vulnerable to the impact. Consequently, damage on a regular basis (as if it with foil) and repairs are needed. The ingress of moisture has caused problems with very thin laminates (usually from 2 locations), but good design should be by a minimum of 3 or 4 layers, the solution is found. It is recognized that this type of compoundParts are time consuming to repair than their metal equivalents, and so incurred unplanned maintenance costs. This situation is exacerbated by the permissible levels of damage of composite materials as a conservative small. These disadvantages are recognized and the aviation industry is working together to improve the situation.

For thicker monolithic composite laminates are employed, in-service experience shows that their tolerance to the operatingEnvironment is excellent, and used when it is too wingboxes production, are protected by the majority of the impact sources. Nevertheless, it is increasingly rare opportunity to require the action to overcome the greater damage and the resulting cost of unplanned maintenance can be higher in fact than metallic equivalent. However, when considering the overall expected reduction of the LCC, which are obtained by the operators of the advantages of fatigue, corrosion, reduces plannedInspections and fuel consumption (and these benefits are already estimated by the airlines), we should continue to make positive efforts to realize the potential benefits of composite applications on a large scale in the civil aviation can too. The importance of the LCC is increasingly valued by the industry in general, but we're still in the early stages of using the tools available for evaluating and monitoring their implementation. Therefore, it is difficult to accurately forecast the size of the financialThe benefit is great in through the replacement of a metallic component with a well-developed composite.

Manufacturers must recognize that their customers will only accept large-scale application of composite technology, where economic benefits can be demonstrated both in the initial purchase price and life cycle costs. This is one of the challenges for the OEMs in the present and it is their duty, the demand by intelligent design and the correct application of the performanceMaterial.

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