Boundary Layer Control

Boundary Layer Control

1. Air particles flow in two directions over a wing, one at right angles to the leading edge, other follows leading edge

   • Produces spanwise flow

2. Spanwise flow thickens boundary layer towards the wing tip, especially during low speed flight with high angle of attack

   • Wing fences reduce effects of spanwise flow

3. Flow separation risk is increased with spanwise flow

4. Vortex Generator

   • Improves boundary layer control
   • Small and low aspect ratio wing placed vertically on surface of a large wing
   • Produces lift and has associated tip vortex which is comparable to induced drag
   • Vortex is large relative to generator because of small aspect ratio
   • Takes high energy air from outside boundary layer and mixes it with low energy air in boundary layer
   • Generator must be right size and right location to go through boundary layer

5. Stall Strips (Wedges)

   • TYpically consist of small piece of aluminium triangular cross section, often 6 - 12 inches long
   • Initiates flow separation earlier than at other positions along the wing
     • Causes wing root to stall before outer portions, ensuring a progressive outward stall
       • Minimizes risk of spinning and giving maximum aileron control throughout stall