Eli5: When painting an airplane, why do you need to depaint first? Can’t they just stack the paint of top of the old paint?
In: 14
Nope. Weight is really important for planes and paint is really heavy. Plus it would be a bad idea to layer over damaged paint. Doesn’t really matter for your fence, does matter for an airplane
Weight is everything to something that flys and paint is heavy. For reference Boeing says a 747’s paint job after it dries is 555 lb and over 900 when wet.
The paint companies tell the airline what the paint procedure is and is they don’t follow it they won’t stand by their product. So the airline has the paint applied to the procedures laid out by the paint manufacturer.
If it was your own private Airbus 380, you could sand down the paint and put acrylic house paint on it if you wanted to or reapply a shiny plane paint it’ll probably last decades but the paint industry won’t make oodles of money out of it. And airlines do like their places to look nice and shiny, having a plane pull up at the terminal with peeling paint doesn’t install confidence. Have a close look at a commercial airliner if you have a chance and the paint jobs aren’t great, runs, orange peel and bits of old paint showing through. They look good from a distance they certainly don’t have the same finish as a Bugatti
As others have said, the paint is considerably heavy. A gallon of regular paint can be around 10lbs (I assume airplane paint is probably in the same neighborhood) and your standard 737 planes can take about 50gal of paint to cover.
You’re forgetting that a coat of paint on a plane weights hundreds (or thousands) of pounds. Carrying around that extra weight on every flight for nothing would be crazy. Fuel is a major cost for an airline.
Weight is #1, but removing the paint further allows a careful inspection for corrosion and other problems that paint would cover up.
Everybody keeps bringing up the weight of the paint. To put it into perspective: in the 90s, the Jaguar F1 team had issues with their choice of paint, because the pigment used in their preferred paint was [just too heavy](https://www.autosport.com/f1/news/jaguar-off-colour-over-heavy-paint-5038580/5038580/).
Ok… I love all the guesses! Here we go……
Every layer adds weight!!
First an eco-friendly chrome-free primer is applied. This is a preparatory coating that helps the adhesion of the successive layers of paint.
Next is a layer of background color, which is often white, but not always (it depends on the final color scheme).
It’s on top of this background layer that the final color pattern is applied with the help of stencils.
The last layer is a clear coat applied after all the other colored paints and adhesive films are already in place. This varnish seals everything and provides robust protection against air flow erosion, all sorts of fluids and the effects of UV rays.
The thickness of these paint layers is very important, since each additional layer of paint adds weight to the aircraft. More weight means higher fuel consumption and this adds up over the operational life of the aircraft, with significant economic and environmental consequences.
This is why painting processes have been the focus of significant technical innovation, with modern low-pressure, high-volume spraying tools and techniques aimed at reducing the amount of paint required to paint an aircraft.
Time for a makeover!!
Commercial aircraft are re-painted several times throughout their operational lives. This way, airline liveries remain bright and crisp, and well maintained paint can also help prevent potential corrosion issues.
Large airlines with hundreds of aircraft, such as United or Southwest, have a schedule to repaint their aircraft with certain regularity, usually every six years approximately.
There are firms (independent aircraft painting companys) that also take on contracts for major aircraft manufacturers when they need extra capacity that can’t be fully handled by their own painting lines.
In the case of aircraft that are already operational, it’s essential to remove the current layers of paint first. In order to do this, the aircraft must be either sanded or stripped, the latter being a more thorough procedure involving the use of chemical agents that wash away the old paint.
The method of choice depends on the state of the aircraft when it arrives at the paint shop.
Painting an aircraft usually takes around one to two weeks and the costs can vary greatly.
It all depends, of course, on the size of the aircraft and the complexity of the design.
For instance, painting a regular passenger plane costs somewhere in the region of $150,000 to $300,000, while the price for a smaller plane could be as little as $50,000.
Time and money!!
Another faster, cheaper technique sometimes employed to decorate aircraft with particularly complex designs is the use of large special adhesives, called decals.
These are, essentially, stickers (although produced to particular industry specifications) that can be printed and then stuck at the right spot on the aircraft.
But decals aren’t to everyone’s taste. Most companies rarely use them. They prefer to stick (pun intended) to paint.
Source: https://www-cnn-com.cdn.ampproject.org/v/s/www.cnn.com/travel/amp/how-to-paint-an-airplane/index.html?amp_gsa=1&_js_v=a9&usqp=mq331AQKKAFQArABIIACAw%3D%3D#amp_tf=From%20%251%24s&aoh=16486180589531&referrer=https%3A%2F%2Fwww.google.com&share=https%3A%2F%2Fwww.cnn.com%2Ftravel%2Farticle%2Fhow-to-paint-an-airplane%2Findex.html
On a fence the paint is there for aesthetic, so you can paint on old paint and that’s not a shame.
On a plane the paint is part of the plane. The paint is part of the fuselage system.
Paint provides the following: corrosion protection, mitigation of abrasion from air, water protection, making damage more visible, markings/plane recognition.
Depending on the area, paint damages can be a no-go item. An unreliable paint job can actually delay or ground planes.
So if you repaint a plane, you want to be sure the new paint will stick perfectly and last as long as possible. Having old paint below means you will have a big chance to have discontinuities that make the new paint fail and fall off, making the repainting useless.
Note also that paint has a target thickness, if you paint too much, the layer will crack with weather, and stick less. If you paint too thin, your layer will not last erosion. Removing old paint helps with making the correct paint thickness.
Trapped moisture on metal leads to corrosion. On a plane, corrosion spreads faster than COVID. Painting over paint without the prep could be bad news bears for those on the plane.
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