Boundary layer: laminar, turbulent, transition point
Boundary layer: thin layer of air over wing surface, no more than about a hundredth of an inch (0.25 mm) thick (TP 1102). Friction slows it. Two parts:
| Layer | Shape | Drag | Verdict |
|---|---|---|---|
| Laminar | Smooth, conforms to wing shape from leading edge | Least skin-friction drag | Desirable |
| Turbulent | Thicker, rougher, starts where laminar breaks down | More drag | Undesirable |
Transition point (laminar to turbulent), per TP 1102:
- Not fixed: moves between leading and trailing edges with flight conditions.
- Moves forward (toward leading edge) as stalling speed approached, faster on laminar-flow wing than conventional aerofoil.
- Forward = more of wing turbulent = more drag.
- Laminar-flow wing: point of maximum camber much farther aft than conventional wing.
Trap: transition point moves forward near stall, not aft. Aft = more laminar, less drag.
References
- TP 1102 ch.1 Basic Principles of Flight (Boundary Layer)