Researchers Test Morphing Leading Edge To Reduce Drag

 - September 24, 2012, 12:10 PM
A morphing leading edge replacing conventional slats would cut noise and drag by eliminating the gap downstream of the slat.

German aerospace research center DLR has just completed a series of wind-tunnel tests on a wing segment that incorporates both a morphing leading edge and a laminar profile for reduced drag. The trials took place between August 27 and September 7 at the TsAGI institute in Zhukovsky, near Moscow. Airbus, EADS Innovation Works and Cassidian Air Systems partnered with DLR on the project.

The morphing leading edge would replace slats as a high-lift system. It cuts drag and noise during the landing phase by eliminating the gap between the slat and the rest of the wing. The leading edge can droop by up to 20 degrees via integrated actuators.

DLR says it tested the system’s operation and performance under “realistic conditions.” Leading-edge high-lift devices account for about one third of the lift produced during landing.

In the quest for laminar airflow, DLR researchers have made surfaces “as flat as possible” to reduce drag by up to 12 percent.

The dual goals present conflicting requirements, however. The structure needs to remain elastic to morph to the required shapes. Conversely, it needs rigidity to maintain the laminar profile, explained DLR department head Hans-Peter Monner.

A glass-fiber-reinforced material proved most suitable. The skin on the front edge of the wing is just curved, not stretched, thereby limiting stress on the material, the DLR chief said. Designers positioned layers one on top of the other, creating “a structure that has a customized rigidity distribution.”

DLR and its partners have begun considering further developing the concept to meet industrial requirements such as lightning protection, de-icing and the ability to withstand bird strikes.

Wing morphing or warping, one of the fundamentals of early aviation, has attracted renewed interest in recent years. For example, NASA tested an F/A-18 fighter with a wing warping system, enabling outer wing panels to twist up to five degrees. Finally, European manufacturers have tested it on helicopter rotor blades and Boeing plans to employ a form of the technology in a so-called adaptive trailing edge on its 737 ecoDemonstrator. That device works with an actuator that can deflect the last four percent of the airfoil up or down, thereby cutting fuel burn by making the wing more aerodynamically efficient and reducing takeoff noise by improving the airplane’s climb performance.