It’s all about the BellMouth shape and Bernoulli law

The Adaptive Ducted Fan (ADF) is a variable geometry lightweight high-speed VTOL propulsion system. Depending on its type and diameters the ADF increases its efficiency up to 80% comparable with fixed geometry ducted fans. ADF variations can also be implemented in CTOL / STOL aircrafts.


The deployed ADF is a configured BellMouth convertible mechanism (the slats are deployed) at the inlet duct section. Giving a very substantial area increase, this configuration provides the maximum amount of air in the duct with minimum loss. Combined with the difference of air pressure this mode significantly increases the thrust from 40% to 80% during vertical takeoff and landing


The ADF annular slats inlet design has the individual working regime segmentation of each slat improving the flight dynamics during the transition from hover to cruise minimizing the drag and maximizing the controllability. ADF also has the uniform retracted/deployed regime. Depending on various weather conditions and different atmospheric pressure, these two regimes combined will maximize the flight control and efficiency


The retracted configuration turns the ADF inlet into a narrow and pointed gondola design. This mode significantly reduces drag and increases speed in cruising or straight flight due to the sharp aerodynamic section of the hull

* These three ADF configurations: Deployed/Transition/Retracted, are ideal for HSVTOL mission.

August – November 2021 the Continuum Dynamics Inc., validates the Adaptive Ducted Fan with the following results:

  • ADF offers good hover and cruise efficiency for eVTOL application

  • Hover performance for the Deployed ADF duct is identical to the 60% larger fixed-geometry duct (Bell X22)

  • Bell X22 Duct volume is over 4x larger than the Retracted ADF duct

  • The reduced volume of the ADF will contribute to lower weight relative to the larger fixed geometry duct

  • The Retracted ADF contributes to lower drag 20% in cruise flight, enhancing the potential for higher flight speeds and longer range

  • ADF also offers the ability to adjust the duct geometry in transition between hover and cruise – greatly assisting flight control

  • Further optimization of the ADF design may allow up to 10-15% further improvement in hover performance

ADF vs Bell X-22 DF

*ADF vs Bell X22 DF sections sized for equal hover performance