Let’s have a look at the current progress of Bartini, the eVTOL development company, at the National University of Science and Technology prototyping and engineering center.
Here is Bartini half-sized functional prototype.Though it is not a vehicle ready to get passengers on board yet, it is a significant milestone on a roadmap to a certified passenger aircraft — scaled ground and flight tests.
There are essential differences between this model and the full-scale aircraft in the future. Firstly, the size, secondly, the ring cowlings were not intended to take part in the flight tests but provided critical info during the ground tests.
It takes a lot of time and investments to design the shape of coaxial props to work with a fenestron. It is better to do it for the exact weight and thrust required. So it is only feasible to do for the full-scale vehicle.
Before embarking on that task, Bartini had to establish that they mastered materials and manufacturing that will yield a cowling with certain levels of stress and vibration resistance at a specific weight. Done! If you stand on a fenestron, it will only bend 2 mm.