I came upon this article, referring to American Airlines' roll-out of a 737-800 in their Astrojet livery. In the article it describes this as 'polished aluminium'.

enter image description here (Photo supplied by American Airlines)

This got me to wondering:

Is this actually polished aluminium, or has some sort of clear lacquer been applied?

If it is polished aluminium,

  • What is the impact of exposing the airframe to the elements, rather than protecting it with a layer of paint?
  • What benefits might accrue from this in weight-saving, fuel burn, etc.?

Yes it is polished aluminium.

On the 737 in your photo, the weight difference with a fully painted plane is about 70 kg, and this yields operating cost savings of about USD 60,000 per year in 1998 dollars, about equal to USD 88,500 in 2016 dollars.

The paint coat is repainted every couple of years, the aluminium polish must be re-buffed 3 times per year.

From the same Boeing document:

Polished surfaces are protected from corrosion by regular buffing after washing. Painting protects against oxidation, salts, and jet fuel spills. However, unrepaired chips and cracks in paint collect dirt and moisture and so may become corrosion sites. Painted surfaces are also susceptible to filiform corrosion, or worm corrosion, which begins between metallic surfaces and paint and erodes both. It creates hydrogen and lifts up the paint layer as it travels across the surface.

Also, the paint protects against small scratches from sand etc which may start fatigue cracks, however since the polished skin is very closely scrutinised during the re-polishing that is not really an issue.

  • $\begingroup$ Paint actually decreases fuel burn, because the surface is not so rough. It's cheaper to fly with paint than without. $\endgroup$ – Noah Krasser Jun 7 '17 at 7:16
  • $\begingroup$ From the Boeing document referenced above: Less paint reduces takeoff weight and fuel consumption considerably. The weight of paint for a typical decorative paint scheme varies among Boeing airplanes. Note that the paint weights given are representative of a typical paint scheme with a 4-mil* (0.1016-mm) paint thickness. Paint thickness varies between 3.5 to 5.5 mil (0.0889 to 0.1397 mm). *mil=0.001 in $\endgroup$ – Koyovis Jun 7 '17 at 9:09
  • $\begingroup$ This Article only speaks about the weight, the paint adds. But due to the surface that isn't rough, the plane, it saves even more fuel. See this documment by Boeing as well: flightshield.com/docs/Boeing%20Report.pdf $\endgroup$ – Noah Krasser Jun 7 '17 at 14:53
  • $\begingroup$ It doesn't say that. It recommends that all aircraft, whether painted or polished, should be washed regularly. You've misunderstood what the referenced document says. $\endgroup$ – Koyovis Jun 7 '17 at 21:42