Active Flow Control
Sweeping jet actuator in action.
The vertical tail on modern, multi-engine commercial aircraft is typically sized for the emergency situation of an engine failure at low airspeed. As a result, it is oversized for normal operating conditions. Active flow control (AFC) devices can be employed to delay flow separation over the tail and increase the side force it generates. Aircraft can thus be built with smaller tails.
Various actuation methods haven been researched and have shown different degrees of effectiveness. Sweeping jet actuators, which emit a continuous jet that flips from one side of the outlet nozzle to the other, demonstrate significant side force enhancement. In 2015 and 2016 the technology was successfully demonstrated on a full-scale aircraft.
These actuators are also attractive because they have no moving parts. However, they require a steady supply of compressed air to run. The current focus is therefore to improve the jets' internal design and optimize their distribution along the tail so that the amount of supply air required is as low as possible for the aerodynamic effectiveness desired.
For more information, please see: http://www.caltech.edu/news/sweeping-air-devices-greener-planes-43987