The donut-shape is a very special shape, it's a circle made out of circles. More about this. For VTOL an aircraft often has to use Thrust for Lift. Lift is more fuel efficient than Thrust. An aircraft uses immense amounts of energy to stay airborne.
Most airplanes burn fossil fuel with air to get energy, but that has no future.
More about this. More about this. The most efficient way to get lift in forward flight, is to use a wide slim wing, like a sail plain. The most efficient way to get lift in VTOL flight, is to use a wide slim rotary wing, like a large helicopter. It's an aeroplane that has to carry the capability to hover for Vertical Take Off and landing.