[augstein]

Was wondering that too. Also can‘t the rotors be shrouded or does that affect the power/agility negatively?

[pininja]

It’s a lot of weight for little reward. A duct/shroud may not even improve the safety in a significant way (if it were thick enough it could, but it’d need to very light)

[sandos]

This is really very light so I suspect the weight penalty is too much.