SBIR Phase I Project: Compliant Leading Edge

The prototype undergoes a low speed smoke trail to aid flow visualization. The flap can alter the camber of the leading edge up to six degrees to improve aerodynamic performance.

Working with funding from the Air Force Research Labs, Air Vehicle Directorate Division, FlexSys Inc. first applied compliant system technology to an aerodynamics problem in 1998. The objective of this effort was to demonstrate that compliant mechanisms embedded in an aircraft wing can be used to change the leading edge camber by six degrees. A three-foot NACA 653-418 wing box section was designed and constructed with a leading edge compliant mechanism. The design allowed discrete actuation power to produce a continuous leading edge shape change.

A low speed wind tunnel test of the prototype experimentally validated the variable camber aerodynamic performance projections. Testing was conducted in the University of Michigan 5 ft by 7 ft low speed wind tunnel. Data recording was conducted at test speeds of 146 ft/s. Additionally, several high speed runs up to 230 ft/s were performed with no observable aeroelastic instability or structural degradation. Wind tunnel testing demonstrated a 25% increase in the lift coefficient and a 51% increase in lift-to-drag ratio. These performance improvements were primarily observed at high angles of attack (up to 15 degrees) as the leading edge camber was shifted from zero to six degrees.

Undeformed

Deformed

The NACA 653-418 compliant leading edge section is shown in the top image in its undeformed position and in the bottom image with six degrees of camber (nose droop) modifying the airfoil shape.

The plot on the left shows the coefficient of lift vs. angle of attack for the 0 degree camber and 6 degree camber prototype wing. A 25% increase in lift is observed at 15 degrees angle of attack. The plot on the right shows the ratio of coefficient of lift to coefficient of drag vs. angle of attack. A 51% increase is observed at 13 degrees angle of attack.