Total Drag
Parasite Drag ($D_p$)
Drag not associated with the production of lift. Increases with speed squared ($V^2$).
- Skin Friction Drag: Due to viscosity of air moving over the surface.
- Affected by roughness (ice, rivets) and surface area.
- Laminar flow (smooth) creates less friction than Turbulent flow.
- Form Drag (Pressure Drag): Due to separation of airflow creating a turbulent wake behind the object.
- Reduced by streamlining (fairings).
- Interference Drag: Due to mixing of airflows at junctions (e.g., wing/fuselage root).
Total Drag Curve
- Induced Drag: Decreases as speed increases ($1/V^2$).
- Parasite Drag: Increases as speed increases ($V^2$).
- Total Drag: The sum of both. U-shaped curve.
Minimum Drag Speed ($V_{md}$)
The bottom of the drag curve.
- At $V_{md}$, Induced Drag = Parasite Drag.
- This is the speed for Maximum Range (for jets) and Maximum Glide Range.
- Flying below $V_{md}$ is the "Back side of the power curve" (speed instability: slower speed = more drag).