[Figure 1-75]  When the aileron is moved from the neutral  position, differential pressure builds up on one side of the  balance panel. This differential pressure acts on the balance  panel in a direction that assists the aileron movement. For  slight movements, deflecting the control tab at the trailing  edge of the aileron is easy enough to not require significant  assistance from the balance tab. (Moving the control tab moves  the ailerons as desired.) But, as greater deflection is requested,  the force resisting control tab and aileron movement becomes  greater and augmentation from the balance tab is needed. The  seals and mounting geometry allow the differential pressure  of airflow on the balance panel to increase as deflection of  the ailerons is increased. This makes the resistance felt when  moving the aileron controls relatively constant. Antiservo tab Stabilator pivot point Figure 1-76.  An antiservo tab moves in the same direction as the  control tab. Shown here on a stabilator, it desensitizes the pitch  control.  Vortex generators are small airfoil sections usually attached  to the upper surface of a wing.  [Figure 1-78]  They are  designed to promote positive laminar airflow over the  wing and control surfaces. Usually made of aluminum and  installed in a spanwise line or lines, the vortices created by  these devices swirl downward assisting maintenance of the  boundary layer of air flowing over the wing. They can also  be found on the fuselage and empennage.  Figure 1-79  shows  the unique vortex generators on a Symphony SA-160 wing. A chordwise barrier on the upper surface of the wing, called  a stall fence, is used to halt the spanwise flow of air. During  low speed flight, this can maintain proper chordwise airflow  reducing the tendency for the wing to stall. Usually made  of aluminum, the fence is a fixed structure most common  on swept wings, which have a natural spanwise tending  boundary air flow.  [Figure 1-80] There may be other structures visible on the wings of an  aircraft that contribute to performance. Winglets, vortex  generators, stall fences, and gap seals are all common wing  features. Introductory descriptions of each are given in the  following paragraphs.  A winglet is an obvious vertical upturn of the wing’s tip  resembling a vertical stabilizer. It is an aerodynamic device  designed to reduce the drag created by wing tip vortices in  flight. Usually made from aluminum or composite materials,  winglets can be designed to optimize performance at a desired  speed.  [Figure 1-77] Other Wing Features Antiservo tabs, as the name suggests, are like servo tabs but  move in the same direction as the primary control surface.  On some aircraft, especially those with a movable horizontal  stabilizer, the input to the control surface can be too sensitive.  An antiservo tab tied through the control linkage creates an  aerodynamic force that increases the effort needed to move  the control surface. This makes flying the aircraft more  stable for the pilot.  Figure 1-76  shows an antiservo tab in  the near neutral position. Deflected in the same direction as  the desired stabilator movement, it increases the required  control surface input. Figure 1-77.  A winglet reduces aerodynamic drag caused by air  spilling off of the wing tip.  Figure 1-75.  The trailing edge of the wing just forward of the leading  edge of the aileron is sealed to allow controlled airflow in and out  of the hinge area where the balance panel is located.  1-34 Balance panel