Laminar flow of air in a boundary layer adjacent a face of an aircraft component exposed to air flow over it has been controlled by injecting air into the boundary layer or by withdrawing air from it through a multitude of small holes drilled through the component. To avoid the disadvantages of drilling holes a low drag component (12) is provided which includes a cellular face region (13) which includes a front face (15) exposed to air flow and which has an open celled structure which permits gaseous fluid flow through the face (15) of the component (12). Manifolds (41) are provided at the rear of the face region (13) to permit or cause gaseous fluid flow from or to the boundary layer through the open celled structure of the face region. In one form, the face region is made from a porous permeable thermoplastics material by powder sintering the thermoplastics material.
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