How Slits Turn a Sheet into a Wing express
A flat sheet with slits in a flow of water or air behaves like self-adjusting blinds. The pressure opens the gaps, and each strip of material tilts, turning into a miniature wing. Thus, even a sheet placed perpendicular to the flow generates not only drag but also significant lateral lift.
By altering the cut pattern or material stiffness (e.g., carbon fiber), you can switch the surface between 'flight' and 'braking' modes without any moving parts. The aerodynamic function is encoded in the pattern itself, and the reversibility of the opening means that entropy barely increases, and the material doesn't wear out.
Original abstract
as written by the authors arXiv:2603.27227
Flexible surfaces can modulate fluid forces through deformation, enabling passive adaptation to flow conditions. Here we show that kirigami sheets, planar surfaces patterned with arrays of parallel slits, provide a simple route to tunable aerodynamics by transforming into three-dimensional porous meso-architectures that can be reversibly reconfigured in flow. When exposed to crossflow, parallel-cut kirigami buckle out of plane to form a lattice of inclined plate-like elements. Experiments reveal that this architecture generates not only drag but also a substantial transverse lift force, even when the sheet is held perpendicular to the incoming flow. Because the mesostructure can switch between distinct states, a single sheet produces large and selective variations in drag and lift under identical flow conditions, in some cases partially decoupling these forces. The evolving mesostructure also alters the scaling of forces with flow speed, influencing both instantaneous loads and their velocity dependence. Force measurements collapse when expressed in terms of the Cauchy number, identifying stiffness, set by the cutting pattern, as the dominant control parameter, a relationship captured by a continuum elastic model. These results show how kirigami architectures encode aerodynamic functionality and behavior directly through their structure, providing a scalable platform for surfaces with reprogrammable fluid forces.
The term 'kirigami' comes from the Japanese words 'kiru' (to cut) and 'kami' (paper). Unlike origami, cuts are not only allowed here but are a key design element.