Flexible materials do not have a reasonable structural rigidity of their own. Internal pressure is therefore used to keep a structure made from flexible materials in its desired shape creating a flexible structure. Because the fabric acts as a membrane, these structures are also called inflatable membrane structures.

Advantages of flexible structures are:

• Can crash without having damage to the system

• More safe to operate for the people on the ground

• Lightweight

• Small in volume for transportation

• Cheap materials

• Cheap in production

The kites that are used for the kitepower system are made of flexible materials which give the kite the ability to morph during flight. The following picture shows an extreme example of this morphing behavior of a kite during flight:

Extreme deformation of a kite by applying a large steering input

Such a wing does not need bearings or other rotational joints which keeps the structure very simple in concept. The flexible nature of the wing can also be used to increase performance. Under high loads the camber of the airfoil increases which increases the lift coefficient of the wing. This results in a larger generated aerodynamic force per m² of surface area.

Disadvantages of flexible structures are:

• Shorter lifespan

• Modeling the aerodynamic behavior is challenging

• A lower Lift-to-Drag ratio compared to a rigid wing in general