Our initial imitation of birds was perhaps inevitable, but nonetheless unfortunate. Evolutionary constraints guarantee that we will not see a suitable bird to imitate any time soon.
I suggest a different starting point - a craft that is circular as seen from above or below, and approximately elliptical as seen from the direction of the horizon - another words, a saucer. This basic configuration offers many options for propulsion, optimum sonic stealth and maximum vertical to horizontal air resistance. It is the shape that produces the least sonic boom.
Some propulsion options require the outer shell to spin about the center. In this event, the crew must be standing or sitting on a non-spinning platform and viewing outside scenes through either a transparent band of the outer shell or a video representation. A non-spinning platform can be arranged if some of the mass of the craft is spinning in the direction opposite to that of the outer shell and has an inertial stabilizer such as a gyroscope. This mandates at least three frames of reference - two suspended by a vertical shaft at the center.
If aerodynamic propulsion and a spinning outer shell is chosen, either articulating peripheral blades (small compared to the diameter) or a multiplicity of peripheral jet-exhaust ports are indicated. Electromagnetic propulsion can be used with or without a spinning outer shell.
For a craft intended exclusively for the atmosphere and using aerodynamic propulsion, a split outer shell is possible. The top half and the bottom half would spin in opposite directions and use either articulating peripheral blades or a multiplicity of peripheral jet-exhaust ports to avoid the necessity of inertial stabilization.
Contact
https://www.futurebeacon.com/jamesadrian.htm