This applies to the movements of the propellers, as well. They must move, but not generate lift. They must also be lightweight enough to speed up and slow down easily, strong enough to hold together, but fragile enough not to harm any performers if they were to come in contact with the blades.
The shape of an airplane is familiar and complicated to reproduce, so there are challenges in staying true to the shape while making it feasible for the stage. Though CAD programs can deal with a 3-D image, they can’t plot material thickness and how that interacts on a curve, so you have to have the instinct to blend it in an organic way while keeping to specific measurements, and ensuring that it is symmetrical.