Efficient, quiet, safe.
Volerian have developed a new propulsion system designed for moving fluids, especially air. It uses a flapping wing encased in a specially shaped duct with static downstream wings (stators). Sets of these 'wing in duct' units are typically placed together to form an array. In many of the aircraft concepts this array itself forms a wing, leading to a highly integrated propulsion, control and lifting structure.
Equal pressure changes down the length of the flapping wing create a consistent flow of air with energy evenly spread throughout the jet.
Normal fans have significant pressure variations down the length of the blade, owing to the speed increasing towards the tip. This results in flow with an uneven velocity.
Energy losses at the tips of the flapping wings are small because the wing length is very long for a given thrust area and the wing speed is the same across the entire span. When combined with carefully designed wing tips or end plates, energy losses can be kept to a minimum.
Normal fans develop an energy sapping tip vortex due to the pressure differences around the blade ends.
Specially shaped duct walls and downstream stator wings help recover vortical energy from the flow and absorb sound.
The close proximity of the duct walls to the flapping wing causes increased pressure changes, leading to a higher airflow velocity for a given flapping frequency.
The large wing (and duct) length to thrust area ratio helps spread energy more evenly across a larger area which is good for noise, safety and has considerable cost and structural advantages.
Moving parts are well contained within the ducts, so the system can be used safely in close proximity to people and animals.
Ducts can be shaped to generate lift for more efficient cruising flight and low speed flight performance. Changing the flapping frequency within an array of such ducted flapping wings moves the centre of lift in what is effectively one large, controllable 'propulsive wing'.
When the propulsion is carefully integrated into a wing-like array every surface can perform useful work; either creating low pressure that draws air into the duct, creating lift, or acting as a pressure recovering diffuser. The supporting structures can be entirely contained within the lift and thrust producing parts.