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While there was debate over why airplanes are painted white and a question about how much a new paint job costed, what hasn't been asked is why airplanes are painted at all.

I remember one airline company sent out a press release in the 1980s or 1990s that keeping its planes unpainted (i.e, a nice silver) saved several hundred gallons of paint as well as considerable cost savings because the plane was also lighter and used less fuel.

If there are considerable positives to keeping planes unpainted, why do airline companies bother painting them?

This is prompted by a recent flight I had on an US Air airplane that had just been repainted in the American Airlines livery. The captain joked that the paint was still so new that we shouldn't try touching it. Both companies are famous for always being in severe debt -- so saving every penny should have meant going for the 'naked' look.

Related: A quora question on how much money would be saved if airlines stopped painting their liveries and a Boeing white paper on painted vs unpainted

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    $\begingroup$ First two launches of the space shuttle contained also some hundred kilograms of unneeded paint. $\endgroup$ – Gray Sheep Apr 4 '15 at 5:26
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    $\begingroup$ A new twist on my question: theverge.com/2015/4/4/8344437/… $\endgroup$ – RoboKaren Apr 4 '15 at 19:38
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    $\begingroup$ You've accepted an incorrect answer. The Boeing document referenced in the answer recommends to wash all planes, whether painted or polished, in order to reduce drag. It states that both painted and polished aircraft are aerodynamically clean, and refutes the claim that paint reduces drag. $\endgroup$ – Koyovis Jun 7 '17 at 22:06
  • $\begingroup$ @koyovis - write this an answer giving references to your argument that no paint is better. You might also want to refute the maintenance argument that there's a limit to polishing metal. $\endgroup$ – RoboKaren Jun 7 '17 at 22:16
  • $\begingroup$ Give this a read, quite interesting: scienceabc.com/eyeopeners/… $\endgroup$ – Woodman Jun 8 '17 at 1:48
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I remembered hearing that paint actually reduces the drag of the plane. Searching a bit I found this Boeing document describing it.

So the painting reduces the fuel costs, instead of increasing them. Another interesting thing is, that planes are regularly repainted to keep the drag low. Of course there is the billboard effect too.

From the report:

In response to numerous questions raised by Boeing customers regarding the efficacy of surface coatings to reduce drag, Boeing has investigated some possible airflow physics explanations. Possible explanations postulated by Boeing aerodynamicists include:

  • Increased regions of laminar flow due to reduced surface roughness.
  • Reduction in surface roughness resulting in lower skin friction drag, when flow is turbulent.
  • Reduction in dirt and/or insect adhesion resulting in reduced roughness and hence reduced skin friction drag.
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    $\begingroup$ a proper polishing would also keep the plane low drag but polishing aluminum properly is harder than applying a coat of paint $\endgroup$ – ratchet freak Apr 4 '15 at 20:32
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    $\begingroup$ Polishing is a form of abrasion, which therefore removes material. How many times can an aircraft's skin be polished before the probability of failure increases unacceptably? $\endgroup$ – Bob Jarvis Apr 5 '15 at 2:04
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    $\begingroup$ polishing won't ever fill in gaps between plates, paint can provide a smooth surface by filling those gaps. $\endgroup$ – jwenting Apr 7 '15 at 20:08
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    $\begingroup$ I remember reading the story in American Airlines in-flight magazine about why they polished instead of painted, and it was all about the weight savings. Across the fleet it amounted to millions of dollars of savings in fuel. Apparently Cathay Pacific used the same justification for their freighter fleet, where polishing just 14 747s was predicted to save them aboutHK$2,800,000 in 2006 pprune.org/tech-log/… $\endgroup$ – Greg A. Woods Apr 18 '17 at 4:34
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    $\begingroup$ A more complete analysis by Boeing: boeing.com/commercial/aeromagazine/aero_05/fo/fo01/index.html $\endgroup$ – Greg A. Woods Apr 18 '17 at 4:47
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Quite apart from the paint preventing corrosion, which puts the lie to the idea that AA flies unpainted aircraft (they don't, they use a clear paint on metallic parts and metallic paint on non-metallic parts), there's the economic factor.

Those aircraft are flying billboards for their owners. They are a major part of brand recognition.

That's why they're repainted or at the very least have stickers applied when rented/leased out to other operators.

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  • $\begingroup$ Well, American definitely doesn't fly unpainted aircraft now! $\endgroup$ – Sean Mar 13 at 3:22
  • $\begingroup$ @Sean AA never flew them unpainted. They were painted in a transparent coating only, then later metallic silver paint over non-metallic parts and a clear coat over the rest. And now indeed they're dull boring grey. $\endgroup$ – jwenting Mar 13 at 4:47
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Painted aircraft can be kept looking clean with a relatively quick wash, while unpainted metal requires comparatively more effort and time (thus, money) to be kept shiny. The fuel savings may simply be more than offset by the maintenance fees.

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I think more importantly it also helps the ground crews and the air traffic control tower responsible for ground traffic. When looking at a line up of planes from a distance, you can eliminate a majority of planes right away because they are either the wrong airline or wrong type. Now you only have to compare the tail numbers of a couple aircraft.

Several years back I was getting a tour from a friend of orlando's control tower, and as you can imagine it is a pretty busy place especially up top where they are relying on their eyes to organize the traffic on the ground. When tracking an aircraft that's taxing, they have two pieces of information, tail number and airline. So if you have a lineup that goes AA, United, UPS, United, Frontier for instance, you don't even have to break out the binoculars to know what their tail numbers are except to maybe to differentiate between the two united flights. Speeds up the process and also cuts down on careless error.

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    $\begingroup$ ground crews would respond to a specific parking spot, no reason to look at each aircraft in a long line "nope, wrong owner. nope, wrong type. wrong owner. wrong owner. hmm, could be the one. nope, wrong serial. wrong owner. ah, here we are!" isn't how they operate :) $\endgroup$ – jwenting Apr 5 '15 at 4:42
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    $\begingroup$ @jwenting ground crews are just a second benefit, air control is the primary because airplanes easily get out of order during peak times. On a side note, if you think that the correct aircraft is in the correct spot and the information is correct relayed to the ground crews all the time then i definitely need to start flying out of your airport! :P Not to mention all the airports that have an overflow lot where airlines line up like a car parking lot with very little indication or reasoning, they just need to get the airlines off the taxiways. $\endgroup$ – BenW301 Apr 5 '15 at 4:49
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    $\begingroup$ This is an interesting benefit, but I'd guess it's a secondary benefit at most. At the many of the busiest fields (including the busiest one in the world by far) the vast majority of the traffic is from a single airline with a single livery on almost every aircraft at the field. This helps if you have AA, United, UPS lineup, but not so much when you have a Delta, Delta, Delta, Delta, Delta, Delta lineup (or FedEx, FedEx, FedEx, FedEx in Memphis.) It would be useful at Orlando, but not as much at the hubs. $\endgroup$ – reirab Apr 5 '15 at 5:48
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Why are aircraft painted at all?

  • Because of the flying billboard function. Marketing determines the colour scheme, not techical reasons such as weight savings (which is true) or drag reduction from paint (which is false).

  • Because of protection. The paint protects against small scratches from sand etc which may start fatigue cracks. If the polished skin is re-buffed 3 times a year it is closely scrutinised - but preventing is better than curing. Polishing removes a very thin layer of aluminium oxide and I could find no references that the amount of removed material would be a problem during the lifetime of an aircraft.

On a 737-800, the coat of paint weighs about 70 kg, on a B-777 about 200 kg. The cost increase due to higher maintenance requirement is about 60 kUSD in 1998 dollars or 85,000 dollars/year now, for an airline with 100 B737s this equates to higher maintenance cost of 8.5 mUSD/year. This is offset by the reduced fuel costs from the weight savings, depending on air miles.

Corrosion prevention is an often quoted reason for the coat of paint. However there is a specific type of corrosion occurring only on painted aircraft. From a 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.

Another Boeing document addresses claims that paint may reduce drag. It effectively refutes these claims, stating that both painted and polished aeroplanes are aerodynamically clean. It does recommend to keep them that way, by washing all planes at least three times a year, due to accumulated dirt and insects which do cause increase of drag. Something that was found by the regular buffing of polished aircraft, I believe that in the past polished aircraft were found to have lower operating cost which was first attributed to weight savings but later turned out to be due to less insect residue.

All in all, aircraft are painted for good reason. And sometimes they are not painted, also for good reason.

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    $\begingroup$ Actually, Airbus requires their planes to be painted, for protection. $\endgroup$ – Peter Kämpf Jun 7 '17 at 22:46
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    $\begingroup$ Yes that makes sense. An insurance policy for if the required increase of maintenance is not followed. $\endgroup$ – Koyovis Jun 7 '17 at 22:51
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    $\begingroup$ And I think there is still no proof that advertising actually works. $\endgroup$ – user7241 Dec 10 '17 at 15:50

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