Schempp-Hirth Standard Cirrus — 15 m, two Wortmann sectionsvsDownwind glide foil — high aspect reference front wing
root section fxs02196 → e818 · tip section fx6617a2 → — · sweep parameter 2.946 → 9.717 · dihedral 2.00° → -2.50° · area 10001997 mm² → 121109 mm² · span 15000 mm → 1240 mm
units
These analyses are not directly comparable
- different fluids (air vs water-salt) — density and viscosity both differ, so the drag numbers are not on the same footing
- different trim loads (3237 N vs 932 N) — each wing is carrying a different weight
The geometry comparison below is unaffected — it is a comparison of shapes, not of runs.
- Schempp-Hirth Standard Cirrus — 15 m, two Wortmann sections
- Downwind glide foil — high aspect reference front wing
What changed
| Property | Schempp-Hirth Standar… | Downwind glide foil | Change | % |
|---|---|---|---|---|
| Geometry | ||||
| Span | 15000 mm | 1240 mm | -13760 mm | -91.7% |
| Root chord | 855 mm | 130 mm | -725 mm | -84.8% |
| Tip chord | 345 mm | 48 mm | -297 mm | -86.1% |
| Sweep parameter | 2.946 | 9.717 | +6.771 | +229.8% |
| Dihedral | 2.00° | -2.50° | -4.50° | -225.0% |
| Tip twist | -2.00° | -2.50° | -0.50° | +25.0% |
| TE thickness | 2 mm | 0 mm | -2 mm | -90.0% |
| Sections | 40 | 30 | -10 | -25.0% |
| Tip cap reach | 0.450 | 0.400 | -0.050 | -11.1% |
| Derived | ||||
| Aspect ratio | 22.496 | 12.696 | -9.800 | -43.6% |
| Area | 10001997 mm² | 121109 mm² | -9880887 mm² | -98.8% |
| Taper | 0.404 | 0.369 | -0.034 | -8.5% |
| MAC | 705 mm | 104 mm | -601 mm | -85.2% |
| Sections | ||||
| Root section | fxs02196 | e818 | changed | — |
| Tip section | fx6617a2 | — | changed | — |
| Shapedeviation at matched span fractions, 64 samples | ||||
| Chord deviation (max) | 725 mm | |||
| Chord deviation (RMS) | 584 mm | |||
| Twist deviation (max) | 0.50° | |||
| Dihedral deviation (max) | 289 mm | |||
| Tip cap deviation (max) | 6956 mm | |||
Performance
CoefficientsDimensionless — how good the shape is, independent of size and speed.
Spanwise
withheld — “Schempp-Hirth Standar…” integrates to CL 0.052 against the polar’s CL at the same α (this analysis predates the loading reporting its own) 0.541 (0.10×); “Downwind glide foil” integrates to CL 0.061 against the polar’s CL at the same α (this analysis predates the loading reporting its own) 0.446 (0.14×). A loading that does not integrate back to its own wing’s CL is not a coarse curve, it is a wrong one.
mixed fluids (air, water (sea))
data
| CD | Schempp-Hirth Standar… | Downwind glide foil |
|---|---|---|
| 0.008 | 0.330 | 0.256 |
| 0.009 | 0.368 | 0.289 |
| 0.009 | 0.369 | 0.290 |
| 0.010 | 0.416 | 0.326 |
| 0.011 | 0.451 | 0.355 |
| 0.011 | 0.472 | 0.370 |
| 0.012 | 0.541 | 0.421 |
| 0.013 | 0.571 | 0.446 |
| 0.014 | 0.625 | 0.477 |
| 0.017 | 0.731 | 0.548 |
| 0.019 | 0.768 | 0.577 |
| 0.022 | 0.867 | 0.613 |
| 0.028 | 1.04 | 0.691 |
| 0.035 | 1.20 | 0.775 |