“Our goal was to figure out the AFC configuration for the flight demonstration, the most efficient arrangement of actuators that meets our performance criteria,” he says. “Once we found that, we compared it with the air supply on the aircraft to balance performance with supply. We identified a couple of viable configurations and conducted broader testing of those, including safety-of-flight mitigation, so we understand the overall effect when we fly.”
Boeing previously evaluated synthetic-jet actuators, but selected sweeping jets because they scale up uniformly, Whalen says. Originally developed as logic devices for fluidic computers, and now used in windshield washers for cars, they are solid-state actuators in which an internal feedback loop causes the air jet to sweep across an arc. This increases their effectiveness in re-energizing and re-attaching separated flow over the deflected rudder.
In a practical application, there would be actuators on both sides of the tail. They would be on-demand, on/off devices that would activate on the appropriate side of the tail when the rudder deflects beyond a certain angle, to increase sideforce.
For the 2015 Eco Demonstrator flight trials, the AFC actuators on the 757 tail will be powered by air generated by the aircraft’s auxiliary power unit. Flights will be funded under Phase 2 of NASA’s ERA program.
“We are proceeding with the flight demonstration, working the contract with NASA and designing the flight AFC system,” Whalen says.