A duct (shroud) around a propeller changes how air enters and exits the disk — and significantly changes efficiency, thrust-to-size ratio, and handling. Tiny whoops (Mobula, BetaFPV Meteor — 1S, 65–75 mm) and larger ducted cinewhoops (BetaFPV's 2.2" Pavo20, 3S) use ducts primarily for prop protection, but the …