A theory of airflow through rotors and its application to some helicopter problems

The knowledge of the flow through a rotor of a rotary-wing aircraft is essential for the study of many helicopter problems The behaviour of a helicopter with respect to stability, region of roughness, etc, depends in many cases on the airflow through the disc Most existing stability or performance theories fail when they concern low forward speed and vertical descent because of some simplifying assumptions An attempt has been made to find a rather simple expression to describe the variations in axial velocity through a rotor as a function of the azimuth angle Further, a chart is produced giving the average axial flow through the disc for all possible combinations of forward and vertical velocities, valid for all kinds of one-rotor aircraft The results are used to improve the theory of some problems as mentioned above and are applied, where possible, to the Sikorsky S51 helicopter, to compare the theory with experimental data