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I am attempting to design a "flying saucer." The saucer is an ellipsoidal-ish body with a RC drone inside. I plan to allow for air access to the rotors as shown in the rudimentary diagram below:

enter image description here

I am pretty sure that the drag on the air flowing through the intake and through the body of the flying saucer will reduce the thrust capacity of the drone. Can anyone confirm this? Are there any other considerations I should keep in mind (maybe there's a reason helicopters don't have a big tube surrounding the lift rotor)? I want the flying saucer to behave like a slow, mellow RC drone (I don't really want high speeds or elevations).

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    $\begingroup$ If it's all low speed/elevation, have you considered filling all that empty space with helium, and just using the propellers to steer/drive, rather than also lift? $\endgroup$
    – Jonathan R Swift
    Aug 6 '18 at 7:45
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    $\begingroup$ apart from the inlet and outlet, I would suggest caring about the acoustic reflections from the walls. The rotor blades of drones will rotate at thousands of RPM. $\endgroup$
    – mustang
    Aug 6 '18 at 9:50
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In the 50's the DARPA designed such a craft but due to aerodynamic instability it was a complete failure and abandoned. The problem you have is maintaining 4 separate intakes which have a greater volumetric capacity than each propeller can handle at maximum power in coldest conditions. You cannot combine the intakes and expect stability, it's just not possible. Each airscrew creates a pressure differential with the air cone immediately above and below it. This creates a spinning torus vortex when stationary as part of the stabilising effect of air wash. When that wash is excluded by ducting you introduce other aerodynamic effects. One of these effects is what causes a Dyson fan with a hollow centre to blow a larger volume of air. Your idea will cause the same effect external to the structure which will destabilise it.

An image is available here: USAF's 'flying saucer' on display at National Museum of the U.S. Air Force

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