[skykooler]

Diamond is a very poor structural material. It is very hard, but also quite brittle; it breaks easily, is heavy, and is flammable. Additionally, airplane wings specifically need to be flexible to absorb turbulence (like the suspension system on a car), while diamond is very stiff.

[marcosdumay]

It's brittle, but very strong. So strong that the brittleness is irrelevant for a huge number of applications, because you simply won't push them far enough. It will usually sustain more load than the same weight of aluminum.

About flammability... Technically it is flammable. If you heat it enough, it will react with oxygen. Steel will melt way before that point, I would be it would burn before that point too.

[sandworm101]

Diamond is stuff just like any other type of carbon. Solid diamond wings would be silly. But engineered microstructures of diamond could be very flexible where needed, and stiff where not. Diamond ropes, like bundles of carbon nanotubes, could do all sorts of things.