# Shock Waves

> Formation and characteristics of Normal and Oblique shock waves.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-02 — High Speed Aerodynamics
- **Topic code:** 081-02-02
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/high-speed-aerodynamics/shock-waves/

---

## Formation
When airflow accelerates to supersonic speeds and then decelerates back to subsonic speeds, the pressure change is not gradual but instantaneous. This thin boundary is a **Shock Wave**.

## Normal Shock Wave
Perpendicular to the airflow.
*   **Before Shock**: Supersonic ($M > 1$).
*   **After Shock**: Subsonic ($M < 1$).
*   **Changes**:
    *   Velocity: Drops.
    *   Static Pressure: Increases (Density increases).
    *   Temperature: Increases.
    *   Total Pressure: Decreases (Energy is lost as heat).

## Oblique Shock Wave
Inclined to the airflow. Occurs at corners/wedges (e.g., nose of a supersonic jet).
*   **Before Shock**: Supersonic.
*   **After Shock**: Still Supersonic (but lower Mach).
*   **Bow Wave**: A detached shock wave formed in front of a blunt nose.

## Expansion Wave
Occurs when supersonic airflow follows a convex corner (turns away).
*   Velocity: **Increases**.
*   Pressure/Temp/Density: **Decrease**.
*   No energy loss (isentropic).

## Wave Drag
The energy dissipated in the shock wave creates a new form of drag called **Wave Drag**. It increases drastically in the transonic region.

---

Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.