THE wind tunnel described in this report forms one of the major items of equipment of the Division of Aeronautics of the Council for Scientific and Industrial Research. The primary purpose of the tunnel is for tests of firms' designs. The size of the working section was chosen so that some full size aircraft components could be tested, while the power was selected so that the Reynolds number obtained at normal speed in tests of complete models would be great enough to avoid large‐scale effects. However, as it was the only tunnel to be built, at any rate for some time, research had to be borne in mind in the design, and in addition to the requirements already stated, the air flow was to be as uniform and free from random turbulence as possible.