The most important aerodynamical qualities that should be aimed at in wind-tunnel design are as follows : (1) Constant and parallel direction of flow (2) Uniform velocity across all sections (3) Absence of turbulent motion (4) Constant velocity of flow. The Gottingen type of wind-tunnel with a parallel part before the working section, whose section is steadily reduced, realises in a high degree all above mentioned qualities. It is shown, that this system can easily applied for other wind tunnels for inst. N.P.L. or Eiffel type. An ultimatly constructed Eiffel tunnel of 1.25m diameter, whose design was based on this principle, gave very satisfactory results.