# Gust Envelope

> How vertical gusts affect load factor and the gust envelope diagram.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-06 — Limitations
- **Topic code:** 081-06-03
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/limitations/gust-envelope/

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## Gust Effect
A vertical gust changes the effective Angle of Attack (AoA) of the wing.
*   **Updraft**: Increases AoA -> Increases Lift -> Increases Load Factor ($n > 1$).
*   **Downdraft**: Decreases AoA -> Decreases Lift -> Decreases Load Factor ($n < 1$).

## Factors Affecting Gust Sensitivity
1.  **Airspeed (V)**: Faster speed -> Greater change in Lift for the same gust -> **Higher Gust Load**.
2.  **Wing Loading (W/S)**: Higher Wing Loading (heavier plane, smaller wing) -> Less sensitive to gusts -> **Lower Gust Load**. A heavy plane "rides" turbulence better.
3.  **Lift Curve Slope**: Straight wings (high slope) are more sensitive than swept wings (low slope).
4.  **Altitude**: Higher altitude -> Lower density -> Lower forces (for the same TAS, but gusts are usually defined in TAS or EAS). Gusts are generally stronger at low altitude.

## Gust Envelope Diagram
Superimposed on the Manoeuvring Envelope.
*   Shows the g-load imposed by a standard gust (e.g., 66 fps, 50 fps, 25 fps) at speeds $V_B$, $V_C$, and $V_D$.
*   **Vb (Design Speed for Max Gust Intensity)**: The speed to fly in severe turbulence.

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