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Obviously I'm not and expert in this field as you can see from the question itself :) but...

My assumption is that there are plastics lighter and stronger than the materials used to build planes. So that would make plane lighter and thus would consume less fuel which pollutes less and so on. Maybe it would be more maneuverable, go faster, be safer as you may be able to safely land it with a number of parachutes in case of engine fail... I don't know.

Can someone shed some light on this for me? :) Ty

Let's take ABS, which is an extremely common plastic used for 3D Printing. At a typical flight altitude, the exterior air temperature will be in the order of -51°C/-60°F. The lowest rated temperature for ABS is -20°C. I hope you can see why this alone might be a problem.

Wikipedia also says that ABS and PLA, which is the other major 3D printing plastic, are damaged by sunlight. Planes generally see a lot of sunlight.

Also, in regards to "you may be able to safely land it with a number of parachutes in case of engine fail", two quick points:

1. although plastic is less dense than aluminium, it's not as if the plane is suddenly going to be that much lighter


2. planes are decent at gliding in the unlikely situation of all engines failing

More information about why parachutes don't make sense can be found at Why don't big commercial planes have full aircraft parachutes?.

In case you weren't aware, the Boeing 787 fuselage is principally made up not of aluminium, but of a carbon fibre reinforced polymer, which is a material based off of plastic. So there is work going on to make sure planes out of different materials, but it's not particularly simple or straightforward.

My assumption is that there are plastics lighter and stronger than the materials used to build planes.

That is not a correct assumption.

Typical 3D printer plastics have a best-case tensile strength of 45-50 MPa.

7075, a common aerospace alloy, has a tensile strength of 500-570 MPa.

Even when you divide by weight, that's at a 1:4-1:5 ratio of specific strength. There is no significant application in which 3D printer plastics, the properties of which are driven by the need to be easy to print with, would offer better strength-to-weight than aerospace metals and fiber reinforced composites.

Some amount of 3D printed plastics will likely appear in cabin interiors, but load-bearing parts require high strength and high strength-to-weight ratio. If it's too heavy, it won't take off, and if the material's too weak, it won't stay in one piece.

So the brief answer is, they don't build airplanes from 3D printer plastic (or clay, or plaster, or thatch) because they want them to fly.

The plastics used for airplanes are a lot like reinforced concrete, where both high compression and tensile strength is needed. The plastic compound itself, polysester, vinylester, or most commonly, epoxy resin, provides the compression strength and stabilizes the fibre component, like the concrete, and the fibre component, either glass or carbon, provides most of the tensile strength, more or less like the rebar in concrete.

Like a reinforced concrete structure, the problem becomes one of how to or orient the fibre component so that the fibres can continuously carry the tensile loads. You can see right away that a resin compound by itself won't work for a high stress part; you have to have a tensile load bearing element embedded in the resin, and this load bearing element should be more or less continuous along the load path.

Random fibre segments in a resin matrix, like the chopped fibre fibreglass used in boats, won't do for something like a highly stressed beam. The fibres have to be continuous from end to end, again, a lot like a reinforced concrete beam. So this tends to rule out a process where a 3D printer could deposit resin and fibres at the same time.

It is possible to make certain aircraft parts from 3D printed plastic where the plastic by itself is replacing, say, an aluminum casting and the plastic resin is as strong, has the required hardness, and can handle the temperatures. Currently such parts would most likely be made by injection molding, 3D printing being so new. But you will certainly see lower stress casting-equivalent parts start to emerge in aviation by 3D printing, especially for low volume parts where the process is just crying for a viable application and a certifiable process. It's a conservative industry, so you have to give it time.

The challenge for now is how to make a resin matrix part, that needs high tensile strength, that can somehow be 3D printed with both the compression and tensile strength elements incorporated, and correctly oriented in the 3D print process. Not so easy.

What will probably happen in the next 10 years is someone will come up with a radical new plastic compound incorporating something like graphene in it that has all the desired properties in all directions and can be machined from a block or deposited and cured in a printing process. Then we'll have 3D printed wing spars, frames and skins.

As other answers mention, the strength of molded or printed plastics is an order of magnitude lower than that of typical aerospace metals. But also the stiffness is much lower. We once tried to build a wind tunnel model in a 3D-printer. Looked nice when it was finished. But when it was subjected to the loads in the tunnel, it warped out of shape horribly. The results were unusable. A 3D-printed wing would not only break, but before doing so would warp and twist completely out of shape.