Aeronautical research and development require the same as ever a lot of wind tunnel testing work although the computational possibilities have grown up extremely during the last two decades. Both, experiment and computation, complete each other in an ideal manner, since mathematical methods can describe aero-mechanical functions and tendencies, verified by significant experiments under selected conditions. This paper deals with aerodynamic experiments, in general, as far as they have to be applied for aircraft development, shown with the vertical take-off and landing (VTOL) fighter VAK 191 B as an example, which has been developed in Germany, successfully. With this complex system as a guide, the experimental steps from the lay-out up to the completion of the flight test period are shown. Tests in Low and High Speed Wind Tunnels and in special test facilities, such as Reingestion Test Rig, have been conducted. Overall forces and moments, pressure distributions, sectional loads, jet decay characteristics and rein-gestion temperature distributions have been measured and analysed in order to get reliable predictions on longitudinal and lateral flight performances, manoeuvrability and hovering as well as on structual load estimation. Some kinds of flow visualization techniques are described, supporting the comprehension of flow me-chanisms, in detail.