Aircraft Coatings

With Earth Day being in April, it’s fitting to look at the advances in aerospace coating technology and the equipment needed to apply them and how they reduce the environmental impact for the industry.

Coatings manufacturers such as Sherwin-Williams Aerospace Coatings and AkzoNobel Aerospace Coatings are continually updating their products to match industry needs and environmental regulations.

While the industry isn’t reluctant to change, it needs to know that a product is worthy of its adoption. Product development and testing reflects this, as it may take up to three to five years to develop a product and then have OEMs test it to ensure it meets qualifications.

Coatings and equipment advances are being introduced that meet Occupational Health and Safety Administration, Environmental Protection Agency, and other safety regulations.

According to J. Marc Taylor, Sherwin-Williams director of sales, the theme for coatings manufacturers is to eliminate chrome, as well as, design coatings that allow maintenance repair operations (MROs) to reduce volatile organic compounds (VOCs) and harmful emissions.

“A manufacturer has to understand the marketplace and then try to predict what will be needed and listen to what customers are asking for,” Taylor says. “The core is to meet or exceed performance requirements and protect the assets,“ in this case aircraft.

Some of the new products reduce steps in the painting process, some reduce the time it takes, and some do both. A new primer/surfacer from Sherwin-Williams can be used as a primer and then as a surfacer, eliminating unused product that needs to be discarded. The smooth surface during application often eliminates sanding and the need for a coating between the primer and topcoat. The quicker dry time allows sanding four hours after application, enabling the same crew to accomplish both tasks during the same shift.

The traditional aerospace decorative coatings typically last five to six years, while the new technologies wil increase appearance longevity beyond that. Although maintenance requirements may include inspection for corrosion before the coating has reached its lifespan.

European influences
One of regulations concerning European coatings manufacturers is REACH. The European Community regulation focuses on chemicals and their safe use (EC 1907/2006). REACH stands for registration, evaluation, authorization, and restriction of chemical substances. The information on chemicals and the risks they create will be gathered by manufacturers and then stored by the European Chemicals Agency (ECHA) in Helsinki. Professionals and consumers will be able to access the data which will include suitable alternatives. The goal is to phase the program in over 11 years. While it is similar to EPA standards, there are different classes of chemicals. (More information is available at www.echa.europa.eu.)

Equipment technology
Besides coating developments, companies are also offering advancements in equipment design.

Research and development company Battelle has created a portable painting system for aviation maintenance applications. The system allows technicians to paint in and around the aircraft without impacting repair or installation activities. It captures harmful vapors and contaminants released during the painting process by using activated carbon filters and then reuses the contaminants in an environmentally conscious process.

The portable painting system has been tested on the aft lower lobes and wheel wells of aircraft at Oklahoma City Air Logistics Center and the Ogden Air Logistics Center. It has improved the environmental impact by reducing the amount of materials needed and reduced hazardous waste.

The key to the system is the environmental control system. It features a three-stage NESHAP-compliant filters to capture particulates including chromates and VOCs. Safety features include a VOC gas monitor and chemical fire suppression.

While production of new aircraft may slow down, there is still the need for new coatings and equipment upgrades. With the Delta-Northwest merger, nearly 250 Northwest mainline aircraft will be need to be painted by the end of the year in Delta’s red, white, and blue flagship colors. To date, 33 Northwest-branded aircraft have already been repainted, including a Boeing 747.

Temple Allen has also introduced new equipment to help in coatings applications. See more about EMMA in this section.

For more about the Battelle system, visit www.battelle.org.

Weight and Drag

How much does the coating weight affect drag and therefore reduce speed and increase fuel consumption?

The key factor with drag is airflow over the entire airframe, and the smoothness of the surface finish on the final topcoat undoubtedly makes a difference. The importance airlines already put on this issue is evident by looking at Boeing’s decision to use one color of paint on the nacelle inlet of its latest 787 Dreamliner. The company says this is because even the tiny edge created where one color is laid over another affects the airflow to such an extent that on each aircraft it could save as much as 22,000 gallons (more than 100,000 liters) of fuel per year.

The accumulated weight of the coatings is not insignificant. For example, the coatings weight on the exterior of the giant A380 Airbus is approximately 1,600 pounds (725 kgs). In comparison, the exterior coatings weight on a Boeing 747 is approximately 1,060 pounds (480 kgs). Typically the exterior coatings on these aircraft would consist of epoxy primer, high solids topcoat, separate wing coating, and a small quantity of area-specific coatings. These figures don’t include interior structural coatings, which could add another 1,600 pounds (725 kgs).

The weight and smoothness have to be balanced against environmental factors, airframe integrity, coating weight, and legislation issues in the development of new aerospace coatings to protect the aircraft structure against the extreme conditions they are exposed to daily. It is the need to reconcile all these often conflicting demands that drives research into new generations of products.
Emerging technologies

In tests, at least, laboratory work in the United States on magnesium-based primers has been found to be as effective as chromate-based products and it looks as if they will be lighter than the ones they replace, therefore helping the weight/fuel consumption issue.

Film thickness is another area that continues to see important developments. Coatings that can achieve the desired effect with fewer coats are available. While they may appear to be more expensive, in fact they work out as a better value — fewer coats are needed so less coating is used. There is a subsequent saving in labor costs and turnaround times, and the finished coating weight is less.

Increased durability is also an all-around benefit. Although this is cost driven, it has also resulted in environmental benefits in reducing the amount of coatings used and therefore any potential environmental side effects. Again, the initial price may superficially appear higher, but these products represent considerable long-term cost savings.

Lower coatings weight
All these factors have resulted in commercially available coatings that achieve the results with fewer coats, have lower VOC emissions, are more durable and are easier to apply, and are generally more environmentally acceptable.

Maintenance systems have also benefited from this research. For example, there are “selective removable” systems that enable owners to remove only the topcoat without damaging the primer or substrate. This not only saves time and coating costs in stripping and starting from scratch, it also reduces the VOC emissions resulting from re-applying the entire system.

There are effective systems on the market now that can reduce the overall coatings dry weight of an aircraft by up to 12 percent, with new generation topcoat weights offering cuts up to 20 percent.

In fuel terms, if the exterior coatings weight is 1,556 pounds (700 kg), for a typical large aircraft a reduction in the overall dry weight of 178 pounds (80 kg) (11.4 percent) could mean a savings of 33 to 55 gallons per 2.2 pounds per year (150 to 250 liters of fuel per kg), depending on the aircraft type. This would equate to a savings of 4,400 gallons (20,000 liters) of fuel per year. A savings of that order would mean a reduction in CO2 emissions of 50 tons per plane per year.

Coating weight can and does make a significant difference to the environment, but it’s not the only environmental improvement that new aerospace coatings technology offers — there are cost and operational benefits, too.

We can expect to see further breakthroughs in aerospace coatings which will benefit the industry and the environment.


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