STAR, Inc. has been under contract with the Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio, since May of 2000 to analyze and develop multi-winglets for the reduction of induced drag without increasing the span of aircraft wings.  Under a Phase I Small Business Innovation Research (SBIR) contract, STAR, Inc. designed and fabricated several wind tunnel models, using a NACA 0012 airfoil for the wing and flat plates for the winglets, for testing in two different subsonic wind tunnels at Reynolds numbers of 161,000 to 800,000.  STAR, Inc. obtained lift and drag measurements from wind tunnel balances, and wingtip vortex information from laser flow visualization.  The Cobalt60 unstructured solver generated flow simulations of the experimental configuration via time-averaged Navier-Stokes equations, as well as the Euler subset of these equations.  The experimental wind tunnel results, confirmed by the Navier-Stokes analysis, showed that certain multi-winglet configurations reduced the wing induced drag and improved L/D by 15-30% compared with the baseline 0012 wing.

In a follow-on Phase II SBIR contract, STAR, Inc. is producing prototypes of passive and active multiple winglets to reduce induced drag and to reduce wing dynamic responses for improved ride.  Applying multiple winglets similar to those used by soaring birds, STAR, Inc. demonstrated that the multiple winglets split and reduce the strength of the tip vortices; by controlling the individual winglet angles of attack and dihedral, mission adaptation of these winglets can enhance performance characteristics of air vehicles.  Phase II is developing and demonstrating prototype smart-structure-controlled multiple winglets that can be used for a variety of applications in unmanned air vehicles, general aviation craft, and commercial airliners.  The total combination of multiple winglets, smart structures, and active control will produce maximum reduction in induced drag, leading to improved range and endurance, and reduction on wing dynamic response, leading to improved ride quality and fatigue life.  Multiple winglets will have wide commercial and military potential, which will be demonstrated by this Phase II program.  They will enable shorter wingspans for cruise missiles and uninhabited air vehicles, allowing for tighter storage and more weapons to be carried in space-limited cargo and bomber aircraft holds.  They will also improve range and endurance of micro air vehicles.   In general aviation aircraft, they can be retrofitted for improved fuel economy.  For airliners, they can improve ride quality and increase wing fatigue life.  Prototype multi-winglets will be produced and delivered to the Air Force in the spring of 2003.