# Total Drag

> Parasite Drag, Induced Drag, and the Total Drag Curve.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-01 — Subsonic Aerodynamics
- **Topic code:** 081-01-05
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/subsonic-aerodynamics/total-drag/

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## Parasite Drag ($D_p$)
Drag not associated with the production of lift. Increases with speed squared ($V^2$).
1.  **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.
2.  **Form Drag (Pressure Drag)**: Due to separation of airflow creating a turbulent wake behind the object.
    *   Reduced by streamlining (fairings).
3.  **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).

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