NASA researchers have wrapped up a series of flight experiments with Boeing's ecoDemonstrator 757 airplane, testing technologies designed to reduce fuel consumption and emissions.
The first of these tests, the Active Flow Control Enhanced Vertical Tail Flight Experiment, assessed the effect of tiny devices called sweeping jet actuators. Thirty one of these devices were installed on the aircraft's vertical tail, which provides stability and directional control during takeoff and landing, and tested to determine what – if any – effect they had on the aerodynamics of the tail and rudder surfaces.
"If we can control the flow of air over the vertical tail on demand, we believe we can provide enough side force during take-off and landing that aircraft manufacturers can safely make the tail smaller," said Mike Alexander, lead systems engineer for the flight tests at NASA's Langley Research Center in Hampton, Virginia. "The ability to reduce the size of the vertical tail would reduce weight and drag and decrease fuel consumption and emissions."
Reduced drag, greater payload
Reduced drag is the primary goal, but there are other knock on effects if the technology proves practical. Height of the vertical stabilizer has long been significant when hangaring large aircraft. The Boeing B-52 for example was originally designed with a folding vertical stabilizer to allow the airplane to be stored in than standard hangers. The new Airbus A380 uses a very large vertical stabilizer and like other large airliners, must be serviced in facilities with very large overhead height and internal volume.
To validate this theory, the ecoDemonstrator made six roundtrip flights April 9-15 between Boeing Field in Seattle and the Strait of Juan de Fuca, a body of water just north of the Puget Sound that marks the international boundary between the United States and Canada. The active flow control technology was tested in a variety of configurations and flight conditions, including simulated engine failures.
Besides the storage advantages of a smaller tail, the reduction in weight but also translate into greater lifting capacity for freight and passengers. How far could the technology go? It is conceivable that in a try jet configuration such as that used in the MD-11 or Lockheed’s L-1011, a two or three-dimensional thrust vectoring system such as that used in the F-35 could dispense with rudders and elevators entirely. Whether the price in terms of weight and complexity (compared to conventional control surface actuator technology) is worth it seems doubtful at present.
Source: NASA