Learn how dihedral and anhedral affect aircraft stability, how sideslip creates a restoring roll, and why designers use each wing angle.
In real-world aviation, dihedral is an upward angle of the wings from root to tip when viewed from the front; anhedral is a downward angle. Dihedral generally increases lateral, or roll, stability by creating a restoring rolling moment during a sideslip. Anhedral reduces that tendency, which can permit more responsive handling.
What do dihedral and anhedral mean?
Dihedral and anhedral describe the angle of a wing relative to the aircraft’s lateral reference plane. A wingtip above the root has dihedral; a wingtip below the root has anhedral.
| Feature | Dihedral | Anhedral |
|---|---|---|
| Wingtip position | Higher than the root | Lower than the root |
| Usual contribution | Increases positive dihedral effect | Reduces or reverses dihedral effect |
| Typical purpose | Greater passive lateral stability | Less excessive stability and quicker roll response |
The visible angle is only geometric dihedral. Aerodynamicists also use dihedral effect to describe how strongly an aircraft rolls in response to sideslip. An aircraft can therefore have some geometric anhedral while retaining a positive overall dihedral effect.
How does dihedral improve lateral stability?
Dihedral improves lateral static stability by converting sideslip into a rolling moment that tends to oppose the disturbance.
- A disturbance occurs: A gust or control input banks the aircraft.
- Sideslip develops: Unless the motion is corrected or maintained as a coordinated turn, the aircraft begins moving sideways through the air.
- Wing lift becomes unequal: The sideways airflow meets the angled wing panels differently, changing their effective angles of attack and lift.
- A restoring roll appears: The resulting lift difference tends to roll the aircraft against the sideslip and towards its previous attitude.
This is why dihedral is often described as self-levelling, but that shorthand has limits. In a properly coordinated turn, sideslip is close to zero, so the dihedral restoring moment may be small. An aircraft with positive dihedral effect can also enter a slowly tightening spiral if its overall roll–yaw dynamics allow it.
Dihedral does not replace the ailerons. Those remain the pilot’s direct roll controls, as covered in our explanation of how ailerons and the other control surfaces command aircraft motion.
Why would an aircraft use anhedral?
Designers use anhedral when the rest of the airframe would otherwise produce more positive dihedral effect than the required handling qualities call for.
Swept wings usually add substantial positive dihedral effect. A high-mounted wing and the aerodynamic interaction between the wing and fuselage can add more, so high-wing swept transports often need visible anhedral to avoid excessive lateral stability. Some combat aircraft use it to reduce resistance to rolling and improve manoeuvrability.
Anhedral does not automatically make an aircraft dangerously unstable. Designers balance it against wing sweep, vertical-tail characteristics, centre-of-gravity position, mass distribution and any stability-augmentation or fly-by-wire system. The target is a suitable net response, not the largest possible restoring moment.
Is wing angle the only factor in lateral stability?
The visible wing angle alone cannot predict an aircraft’s complete lateral behaviour.
- Wing sweep: In a sideslip, the two wings experience different effective sweep angles and lift, usually adding positive dihedral effect.
- Wing height and fuselage interference: A high- or low-mounted wing changes airflow and the position of aerodynamic side forces relative to the centre of gravity.
- Vertical surfaces: The fin, fuselage and other side area affect yaw, which is closely coupled to roll during sideslip.
- Flight condition: Airspeed, angle of attack, flap position and loading can all alter the strength of the response.
- Control systems: Yaw dampers and fly-by-wire laws may mask or reshape the natural airframe behaviour.
The common explanation that a high-wing aircraft is stable because its weight hangs beneath the wing like a pendulum is incomplete. An aircraft rotates about its centre of gravity rather than hanging from a fixed suspension point; aerodynamic side forces and wing–fuselage interaction are the more useful explanation.
Can an aircraft have both dihedral and anhedral?
An aircraft can combine both angles across different wing sections, an arrangement usually described as polyhedral or a gull-wing configuration.
The Fairey Gannet is a clear example: its cranked wing uses inboard anhedral and outboard dihedral. Our FSX Fairey Gannet model shows this unusual wing geometry. Each panel contributes to the final aerodynamic effect, so neither section should be assessed in isolation.
Near-vertical winglets should not be treated as extreme dihedral. They are wingtip devices primarily intended to manage tip flow and induced drag; our guide to how winglets influence aerodynamic efficiency explains that separate function.
What should dihedral feel like in a flight simulator?
In a flight simulator, correct-looking wing geometry does not prove that the lateral stability is modelled correctly.
Depending on the simulator and aircraft, the response may come from geometric calculations, aerodynamic coefficients, lookup tables or control laws. The rendered aircraft model can be largely independent of those values. Our overview of how flight models turn geometry and aerodynamic data into aircraft motion provides the underlying context.
A mistake we see often is rolling into a coordinated bank, releasing the controls and treating the result as a pure dihedral test. With little sideslip, there may be little dihedral response. A controlled sideslip at a matched airspeed and configuration is more relevant, although the result remains qualitative without validated sideslip, control-force and stability data.
- Assists still active: Autopilot, yaw damping or stability assistance can hide the natural response.
- Configuration changed: Comparing different fuel loads, flap settings or centres of gravity introduces other aerodynamic and inertial effects.
- Only the first twitch observed: Rudder input creates several coupled roll and yaw effects; the initial movement does not isolate dihedral.
- Visual angle treated as proof: A convincing 3D model can still use inaccurate lateral-stability coefficients.
Dihedral and anhedral are therefore best understood as tools for tuning the aircraft’s complete roll–yaw behaviour. Dihedral usually adds a stabilising response to sideslip, while anhedral subtracts some of that response where the airframe would otherwise be too laterally stable.