# Stability

The aim of stability analysis is to determine if a design is statically and dynamically stable.

### The pitching moment coefficient and the concept of the neutral point

The moment about the y-axis of the body-fixed coordinate system affects the stability of the design. To have a design that is "statically stable" the moment about the y-axis should be restoring. What is meant by a restoring moment?

If the the center of gravity is behind the neutral point, the design will be statically unstable. If the center of gravity is in front of the neutral point, the design will be statically stable.

### Example

The neutral point is calculated from the previously derived expression:

The free-wake simulations give more accurate prediction for the neutral point location as they account for the wake deformation. This is confirmed by forced-pitch oscillation simulations. The neutral point locations obtained from forced-pitch oscillation simulations and from free-wake simulations agree well.

Once the neutral point location is determined, the location of the center of gravity can be calculated using the following equation:

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