# Forces in Flight

> Equilibrium equations for level flight, climbs, descents, and turns.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-08 — Flight Mechanics
- **Topic code:** 081-08-01
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/flight-mechanics/forces-acting-on-an-aeroplane/

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## Straight and Level
*   **Lift = Weight** ($L = W$)
*   **Thrust = Drag** ($T = D$)
*   (Technically, the tail load must also be considered for moment equilibrium).

## Climb
*   **Thrust > Drag**: Thrust must overcome Drag PLUS the rearward component of Weight ($W \sin \gamma$).
*   **Lift < Weight**: Only a component of Weight ($W \cos \gamma$) is supported by Lift. The rest is supported by Thrust.

## Descent (Glide)
*   **Thrust = 0** (or Idle).
*   **Weight Component** ($W \sin \gamma$) acts as Thrust to overcome Drag.
*   **Gliding for Range**: Fly at $V_{MD}$ (Max L/D ratio).

## Turning
*   To turn, we bank the lift vector.
*   **Vertical Component**: Must equal Weight ($L \cos \phi = W$).
*   **Horizontal Component**: Provides Centripetal Force ($L \sin \phi = CPF$).
*   **Load Factor ($n$)**: The ratio of Lift required to Weight.
    *   $n = \frac{1}{\cos \phi}$
    *   Example: 60° bank = 2.0g ($1 / 0.5$).

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