Learning Objectives

By the end of this lesson, you will be able to:

• Understand the concept of dihedral and anhedral angles on a wing.
• Understand the the benefits and limitations of an dihedral and anhedral wing design.
• Predict how changing wing angle will affect an RC aircraft’s stability, turn behaviour, and “self‑levelling” ability.
• Perform a wing‑angle modification on your RC plane, and collect flight data to test out your prediction.

5.1 Understanding Dihedral and Anhedral – Geometry and Measurement

5.1.1 What is Dihedral? – Angle Between the Wing Plane and the Horizontal Reference

When you look at an aircraft from the front, dihedral is the upward tilt of the wings. Imagine a line from the wing root to the wing tip. If that tip is higher than the root, the angle between that line (or the whole wing chord plane) and the ground/horizontal is the dihedral angle.

Look at a Cessna 172 or a typical trainer: the wings form a shallow “V” shape. That’s positive dihedral.

5.1.2 What is Anhedral? – Negative Dihedral and its Geometric Definition

Anhedral (sometimes called negative dihedral) is the opposite: the wing tips are lower than the roots. Think of an inverted “V”.

A classic example is the Harrier jump jet or many modern fighter aircraft. Their wings droop downward from the fuselage.

Measuring Dihedral/Anhedral on Real Aircraft and UAVs (Spanwise vs. Root-to-Tip)

The angle is usually measured in degrees from the horizontal. For a straight‑tapered wing, it’s simply the angle between the wing’s quarter‑chord line (the line along the wing at 25% of the chord) and the horizontal plane. On many small foam‑board drones, the dihedral is built in by cutting an angled joint at the wing root or by bending the wing panels upward.