Took the opportunity at the Friday test and tune day at Roebling Road to do some real world flow testing around the wing. The results were very interesting.
To test the flow, some homebrew "flow-vis" was mixed in a spray bottle. Flow-vis is the "paint" used by F1 and other pro teams to get a visual sense of real-world airflow around a body.
Sounds exotic if F1 teams are using it, but really it's a pretty simple formula: a solvent and a vibrantly colored solid, perhaps with an anti-caking agent mixed in. For this simple home brew, we just used some mineral spirits and orange chalk (the kind used for snapping construction chalk lines). Simply mix a healthy dose of the chalk into the mineral spirits (perhaps 4 parts liquid to 1 part solid) in a spray bottle. Give it a good shake and spray onto the desired parts.
First, starting with the clean images of the wing:
Two tests were performed: one on the upper surface of the wing, and one on the lower. The testing was concentrated on the area between the end plate and roughly 3" inboard of the mount. The wing in question is the APR GTC-300, set to a 5 degree angle of attack.
First, starting with flow at the outer edges, we see a what appears to be a significant amount of flow detachment at the endplate. This detachment is also evident farther inboard, as we some turbulent flow starting roughly 2/3rds of the way back from the leading edge, though it seems to improve significantly inside the mount, but before the shape transitions to the low-angle portion in the middle.
One thing of particular interest was the way the flow seemed to dance sideways at the transition point between the low and high angle portions. The fluid was sprayed on the outer sections, but migrated sideways roughly to the middle of the wing.
While the underside seems to have some challenges with attachment, flow stays well attached to the top......
Which leaves us with a fairly simple conclusion: this wing is not able to produce high levels of downforce due to the flow challenges on the underside of the wing, but is likely producing a significant amount of drag, as evidenced by the topside flow.