The linkages were tested on the upper wing surface as well as on the lower surface. The drag measurements were performed by traversing a wake rake in spanwise direction behind the trailing edge of the model. The resulting spanwise drag distribution was the integrated and after subtracting the basic airfoil drag, the additional drag of the setup was calculated. The lift coefficient for each Reynolds number was chosen to represent a wing loading of 40 kg/mē (Table 1).
| Reynolds number | Lift Coefficient Cl |
|---|---|
| 100'000 | 0.75 |
| 200'000 | 0.30 |
Table 1: Reynolds number and corresponding lift coefficient.
| The plots below show four typical
drag distributions, as they have been plotted from the wake
surveys. First, it can be seen, that the drag is never constant
along the span, even outside of the influence of the pushrod or
fairing. Similar results have been found later by M. Selig [31].
At the borders of the area of influence, a clearly visible reduction of the local drag occurs for all cases where the linkages are mounted on the upper surface. This is the result of vortices, which develop at the sides of the front linkage horn or in the corners of the fairing, respectively. These vortices destroy the laminar separation bubble on the upper surface, leading to a reduction in local drag. When the linkage is mounted on the lower surface, no such effect is visible. |
|
This schematic image shows how the laminar separation bubble is destroyed on both sides of the fairing. The drag in this region is reduced, whereas it increases behind the fairing due to the turbulent wake of the fairing itself. |
