EVA examines the multilayered, multicoloured challenges and technologies of aircraft paint and coatings
“An airplane might be sitting on the tarmac in 50°C heat, then minutes later it’s flying at altitude and the air temperature’s -50°C. It’s expanding and contracting, but the paint doesn’t break. Then it sees UV exposure, closer to the sun than pretty much anything else ever gets, and resists damage. And on top of all that, it looks great!” So enthuses Julie Voisin, Global Marketing Manager at Sherwin-Williams Aerospace Coatings.
She makes an interesting point, since unless it draws attention through special design, bright colours or unusual effects, an aircraft’s external finish is typically something taken for granted. Executive and VIP aviation liveries have traditionally been conservative, historically perhaps to the point of blandness – a white aeroplane with a modest brown cheatline is unlikely to set pulses racing.
Yet for many travellers anonymity is among the key attractions of executive aviation and there are real benefits to parking a white jet on a ramp loaded with white jets. There is also the case for keeping your colour scheme conservative so as not to create a repainting headache for a future buyer, especially if resale value in the relative near term is important.
Nonetheless, there is a trend towards more ambitious corporate and personal aircraft finishes, promoting a brand, identifying a company or simply expressing individual creativity. Customers are looking for bespoke colours and dramatic design, and the paint manufacturers are responding with a startling palette of hue and effect.
Voisin reports: “There is a group in the business jets sector looking for a way to express their brand. We’ve had celebrities wanting to say ‘Hey, this is me, this is my brand!’, and a couple of NASCAR drivers also expressing their brand. For others it’s just personal choice.”
Founded in Hamburg, Germany but operating globally, Mankiewicz has an aviation division producing specialist exterior, structural parts and interior paint products. The airlines are among its largest customers, and their desire to differentiate between brands has driven colour and effects development. Etihad Airways uses a ‘full-body mica’, for example, which is equally applicable in the VIP business, but how does a company capable of producing paint in sufficient quantity for an Airbus A380 fleet also produce a cost-effective bespoke solution for a business jet?
Stefan Jacob, Sales Director Aviation in Germany, explains: “We manufacture at our affiliated companies worldwide and we’re able to match colour shades at many locations, making samples available promptly. We have a department dedicated especially to this task, its experts creating colours to satisfy the individual wishes of every customer.”
Matching an aircraft finish to that of a favourite car is a common theme. An automotive paint is unsuitable for the harsh environments of flight and aircraft ground operations, but colours can be precisely matched, as Roger Soler Palau, Segment Manager – Speciality Coatings at AkzoNobel explains: “We can either match a colour upon request, or help the customer choose by providing a standard set of colours. We recently completed a project in Germany where the customer was a passionate sports car enthusiast and his aircraft livery included several shades to recreate the exact silver colour of one of his cars and the carbon fibre used within it. Using only the colour name and car model we accessed the exact colour master and recreated it in an aerospace paint within a few days, thanks to our strong presence in the automotive segment.
“The other colours in the design came from a standard set called Color Universe, which we’ve designed for aerospace and yacht applications. It contains a standard selection of almost 10,000 shades covering the most popular in the automotive industry. They are real colour samples chromatically ordered and complemented by a view tool app and a pocket-size colorimeter for designers and painters. Through this, we provided the seven colours needed for the German project, matched exactly to the samples provided.
“Our wide presence in aerospace, automotive, yachts, decorative coatings and other areas eases the task, since colour information and some technologies are shared and enable the production of small quantities for individual aircraft applications. We produce coatings on a ‘building blocks’ concept, using pigment dispersions that provide the colour and the resin matrix that delivers the performance and durability for each requirement. The system is very flexible and allows the production of hundreds of thousands of colour variations with only a few dozen building blocks. It means we can realistically manufacture quantities from a quarter gallon up to 2,000 gallons.”
Sherwin-Williams also prides itself on its ability to match customer requirements. “It’s something we’re really good at,” Voisin says. “We get customer samples everyday, asking us to match a favourite car, shoe, tie or carpet colour, a variety of materials are submitted for us to colour match. Either locally or through our worldwide distributor network, we then produce that colour and support the customer throughout the scheme’s life. We keep a digital library of colour standards so that we can reproduce the colour exactly, anywhere in the world, at any time.”
Warja Borges at Unique Aircraft agrees there’s greater interest in more colourful schemes for business jets, except where owners are concerned over resale values, but says the same is generally not true of VVIP machines, where those that aren’t anonymous are finished in a fleet livery. Having said that, it was she who designed the dramatic scheme unveiled on the 737BBJ demonstrator at EBACE earlier this year…
A customer will often have an idea for a scheme, but… “In the case of the BBJ, I was given free reign to sketch my ideas. The process then is to put them into Photoshop and add some colours. I send my ideas to ACA, a local company specialising in 3D aircraft visualisation, so we can them from all angles. That’s the view that I send to the customer.
“With this project I learned how much is involved in applying the scheme from the computer onto the real aircraft; it’s really complicated! RUAG did the work at Oberpfaffenhofen. They’re known for their quality application of really complex schemes. They used massive plastic masks, with perforated lines in them following the lines of my drawings. The masks are taped onto the base coat as accurately as possible, and then used to mark dots onto the surface. Tape is then applied along the dots to mask the area for painting. It’s real craftsmanship!”
“And if you’re using pearlescent or metallic colours, the application method is really important for consistent appearance. Everything is sprayed by hand, and a different person applying the finish will result in a different appearance.”
Diamond Crystals
Manufacturers typically offer very high gloss finishes, along with special effect coatings, nonetheless designed to withstand the exacting demands of aerospace application. Palau says: “AkzoNobel developed a technology for the automotive industry that changes a coating’s colour depending on viewing angle and this is now available to aerospace customers as a non-standard offering in the Alumigrip range.”
The technology is exciting and the effect dramatic, but as Borges says, success relies on careful application. “These very special effects require the correct equipment and heightened painting skills for a good result, especially on larger surfaces. The degree of colour change can also be modulated and the more dramatic the change required, the more challenging the application. We’ve been working with an OEM customer to offer these coatings for large fuselage areas and the process will be available very soon.”
Working with Jean Boulle Luxury, AkzoNobel has also developed the extremely unusual Sun King Diamond Coating. Jean Boulle Luxury has a long heritage in the diamond industry and perfected a proprietary technique to create a natural gem diamond coating suitable for anything from a luxury car to a super yacht.
Transferring the coating to the aerospace industry was a challenge that forced AkzoNobel not only to meet the demands of the finish itself, but also to define the means of its application. Palau explains: “Diamond is the hardest material and it’s not easy to handle either, especially in the range of microns we use. It’s also relatively dense and we had to find the right balance of ingredients, particle size, concentrations and production method so that a proven aerospace paint could ‘hold’ the diamonds in suspension, not pose too much of a challenge to the painters and meet standard aerospace requirements once applied.
“Now we’ve delivered Sun King for aerospace, yacht and automotive. As a proof of concept we painted a Global Express and completed smaller areas, including stripes and logos. The effect as light catches the diamonds is impressive. It’s a very special finish.”
Interior Finishes
Mankiewicz’s catalogue includes a wide variety of interior coatings, but Jacob notes that its entire colour palette is available in interior and exterior products, as is a large selection of mica and metallic effects. “Paint systems used for interiors increase the perceived quality of surfaces,” he says. “By meeting the demands of wear and chemical resistance for the aircraft’s lifespan, they also ensure durable quality.
“Textile-effect paints, including the ALEXIT Suede Coating, are used whenever a bridge is needed to interface with textiles – like carpets or leather – in the cabin. It produces an extremely matt, warm and unreflective surface. It’s particularly relevant in the cockpit of commercial aircraft, creating the most matt finish available and preventing dazzling reflections, but in the context of a VIP or business jet it could be used anywhere in the interior.”
Conversely, ALEXIT FST Metallic BaseCoat is capable of producing a high-gloss metallic finish and is typically applied to seats, cabinets and monuments. A two-layer system, its base coat contains metallic pigments. A clear varnish is applied over the metallic base and may be selected for different grades of finish, from matt to high gloss. In addition to specific colour and metallic effects, the finish can also be further customised, since the shinier the varnish the more intense and deep the colour shades. In addition to its aesthetic properties, the clear coat seals and protects the base coat pigments, prolonging their life.
The Mankiewicz range also includes ALEXIT FST Antimicrobial Topcoat. “This special paint prevents bacteria from growing and continues doing so for years. Bacteria are otherwise quite comfortable in an aircraft with a full climate control system, and the product offers important advantages for commercial and VIP aircraft.”
Application
Painting aircraft was once a toxic, environmentally unfriendly affair, but developing technologies in application and paint formulas has helped the industry clean up its act. Jacob notes: “Mankiewicz has had water-based interior products in its portfolio for decades, for standard interior top coats and most design effects. Not only are these safer than solvent-based paints to apply, but they’re also more environmentally friendly. It means a drastic reduction in the solvent footprint of operators and since we were the first to offer water-based interior coatings we have experience under every imaginable condition.”
Sherwin-Williams’s Julie Voisin echoes Jacob’s thoughts on environmental performance. “We still sell a product that we created in 1977. But it’s evolved to reflect industry efforts to reduce solvents and emissions. The industry has also modified primers to reduce their chrome content.”
She explains further fundamental changes. “About five years ago the industry moved into a base coat/clear coat ‘wrap’ technology. Basically, all the colours are applied and then a clear coat goes on top. It’s opened the door to more exotic schemes, achieved in shorter timescales.” The base coat/clear coat process also applies to white aircraft of course, so has the application of white actually improved compared to a decade ago?
Voisin responds: “I wouldn’t say the white’s got better, but we can implement the process faster. An airplane typically has detail striping and since you’re then applying multiple colours, the base coat/clear coat technology results in an improved finish. The process also brings some UV advantages with the improved ‘wrap’ overall.”
Mustard Stains
Paint’s aesthetic qualities are obvious, but its most critical function is as a safety device, protecting airframe structures on the outside, on the inside and everywhere in between. Voisin reckons around 30% of an aircraft’s paint goes onto structures a passenger will never see and another 30% onto cabin and cockpit areas, for which Sherwin-Williams offers its JetFlex Elite and Soft Swade coatings. Challenges in the cabin, include scratch and stain resistance and, she says: “Two of the really difficult things we look at with staining are coffee and mustard. There are also the flammability regulations, which are very strict.”
Areas hidden from the passenger – wing ribs, the interiors of avionics bays, undercarriage components – are painted purely for protection and may never be painted again in the aircraft’s lifetime. “Corrosion protection is important and special paints are employed,” says Jacob. “The conditions paints are exposed to are very different depending on their area of use and so are the coatings themselves. Paints for structures have to cope with hydraulic fluids and corrosion, exterior paints must withstand extreme changes of temperature, jet fuel and immense UV exposure, while interior paints resist difficult substances, including mustard and cola, and withstand collisions with luggage. Last but not least, they must also comply with the strict technical requirements of the aviation authorities as they relate to FST [fire, smoke and toxicity] and heat release.”
Cleaning, de-icing and other fluids also affect aircraft finishes, but hydraulic fluids are particularly aggressive. Voisin says: “The clear coat protects the paint finish from hydraulic fluid. It’s not common for an aircraft to be cleaned after every use, but even so, it’s surprising that few of the cleaning products are as aggressive as hydraulic fluid.
“We do a range of tests, including one where we leave a particularly aggressive hydraulic fluid on the paint for 30 days to make sure it doesn’t eat through. We also test against jet fuel, de-icing and cleaning fluids. Business jet customers want their aircraft to remain as pristine as possible and the clear coat also helps with minor repairs.” Even the most resilient finish is likely to change in shade a little over a period of years, but the clear coat can often be repaired after a minor knock or scrape, removing the need for colour matching.
In another aspect of paint that customers seldom realise, while the clear coat is protecting the finish, the coating system is protecting the exterior metals and composites of the airframe, a far more important job than simply looking good. “The reality is that the paint’s there to prevent corrosion. That’s its critical function, since even today, most of an aircraft still comprises aluminium. That’s why we have a complete system of paint that protects the metal, then a base coat that looks good and a clear coat on top.”
That said, composite materials are finding ever-wider application in business aviation – the 787 BBJ airframe is almost 50% composite for example – and these materials pose their own finishing challenges. “When you paint it, it shows a weave, like a very tight chequerboard, as the paint is absorbed. So with composites, instead of worrying about corrosion we have to ensure the weave is properly filled before we attempt to get that typical glass-like finish on top.”
Colouring the Future
There will always be a requirement for anonymity in executive and VIP aviation, but the technology, will and enthusiasm are there for operators to adopt spectacular finishes and the first truly dazzling schemes are now emerging. AkzoNobel’s Roger Soler Palau reckons: “Individual/corporate aesthetic requirements are increasing and liveries are becoming more complex in shape and colour. Technology is advancing to facilitate that, but also to adapt to new lighter substrates and revised regulations, and greater process time efficiency for painters, as well as including new functionalities like self-cleaning, and increased durability and colour retention.
“The industry is changing very quickly. Robotic painting is already a reality at some OEMs and we’ve adjusted our paint to suit, while our state-of-the-art chrome-free primers give longer-term protection from corrosion, and new coating techniques to improve speed and transfer efficiency are already in advanced testing with the OEMs. 3D-printed parts will also become more common and require a new coating technique. It’s very exciting to see the bright future that’s coming to aviation!”