Ultra-Low Noise Vertical Takeoff and Landing (VTOL)

A unique type of vertical lift propulsor is being designed/analyzed/ developed to push blade passage frequency harmonics above the human audible range, while also having low tip speeds to limit the other low broadband noise components of community noise. Use of distributed electric motors enables small propulsors to be designed in this way, with tight integration across the airframe. This strategy is shown in the figure, comparing the new 20,000 Hz and 285 ft./sec propulsor to 1.5' and 9.7' diameter propellers which have blade passage harmonics at the peak human hearing frequencies along with almost twice the tip speeds (with higher broadband ). Use of these small propulsors, each capable of 25 lbf thrust, enables their use in far more distributed ways than merely using propellers or fans. This enables advanced concepts to be developed that leverage airframe shielding to a much greater extent for further noise reduction, along with propulsor positioning to achieve directional reflectivity that causes the remaining noise to be focused upwards, and away from the community.