A method and apparatus for forming a winglet formed as a one-piece composite for an aircraft is presented. The winglet comprises a first blade, a second blade, and a root region. The first blade includes a first leading edge and a first trailing edge. The second blade includes a second leading edge and a second trailing edge. The second blade is positioned at an angle to the first blade. The root region is co-cured with the first blade and the second blade to form the winglet. The root region is configured to receive an attachment system for attaching the winglet to a wing of the aircraft.