Hovering Model Helicopter Rotor Testing

In planning a research investigation of a hovering model rotor, a relatively large test chamber was selected because of the desire to minimize room interference effects. However, initial testing revealed large random variations of thrust, torque, and blade flapping. The source of the problem was diag­nosed as unsteady recirculation of the test chamber flow. The test chamber was modified by the addition of. a flow "straightener" which successfully reduced the variations to 1.5% of their mean values. The rotor performance was then measured outside the chamber in calm free­air conditions and was compared with the results that were obtained inside the cham­ber and its modification. The report documents the problem, the diagnosis, the solution, and it presents examples of the performance data and wake flow visua·lizations obtained inside the test chamber (before and after the fix), and outside the chamber.