Ever since i started flying pattern models, i've been curious about their aerodynamics and how the airflow is influenced by the different flying attitudes (horizontal flight, knife edge, vertical uplines, etc). Most of the time i've been too busy with designing, building, practicing and competitions but now, having a 7 weeks break between contests, i finally found time for some tests.
Tufts are an old visualization technique that is used in both flight test and wind tunnel testing to provide diagnostic information about the flow around the model. The fuselage of my Radiance prototype is completely covered in white film, so it was ideal for this kind of tests. Using many many wool tufts on the fuselage and a small keychain camera taped to the wingtip, i made a few video recordings of the airflow around the fuselage.
Taking screenshots from the videos, i put together a few images that cover the whole fuselage. The keychain camera has a narrow field of view, so i had to make separate videos for the nose and tail of the model.
As expected, the camera on the wingtip visibly affected the flying qualities of the model, but it was quite manageable. I noticed that trim was affected for all the controls, the model was flying slower than usual and needed more throttle and fuselage incidence for knife edge flight. Anyway, the camera on the wingtip was far from the fuselage, so the airflow around it was not disturbed.
As a general conclusion, the direction of the airflow doesn't seem to be affected by the spiral propeller slipstream. Please keep in mind that these pictures only show the local direction of the airflow, the speeds and pressures may still be different on the left and right sides of the fuselage.
The following images cover the horizontal flight, vertical uplines and downlines, horizontal knife edge flight and knife edge loops. I am sharing the results of these tests hoping that together we can find new ways to improve our models. As you will see, the vertical tail offers a few surprises which may explain the need for canalisers to improve the rudder authority.
Horizontal flight: