Surf / pump foil — 900 mm reference front wingvsGossamer Albatross II — same span, two-thirds the area
root section a18 → l7769 · area 111865 mm² → 45296522 mm² · span 900 mm → 29260 mm · tip chord 76 mm → 1404 mm · mac 128 mm → 1552 mm · root chord 150 mm → 1651 mm
units
These analyses are not directly comparable
- different fluids (water-salt vs air) — density and viscosity both differ, so the drag numbers are not on the same footing
- different trim loads (932 N vs 991 N) — each wing is carrying a different weight
The geometry comparison below is unaffected — it is a comparison of shapes, not of runs.
- Surf / pump foil — 900 mm reference front wing
- Gossamer Albatross II — same span, two-thirds the area
What changed
| Property | Surf / pump foil | Gossamer Albatross II | Change | % |
|---|---|---|---|---|
| Geometry | ||||
| Span | 900 mm | 29260 mm | +28360 mm | +3151.1% |
| Root chord | 150 mm | 1651 mm | +1501 mm | +1000.7% |
| Tip chord | 76 mm | 1404 mm | +1328 mm | +1747.4% |
| Sweep parameter | 8.553 | 7.476 | -1.077 | -12.6% |
| Dihedral | -1.50° | 3.60° | +5.10° | -340.0% |
| Tip twist | -2.00° | 0.00° | +2.00° | -100.0% |
| TE thickness | 0 mm | 2 mm | +1 mm | +500.0% |
| Sections | 30 | 40 | +10 | +33.3% |
| Tip cap peak (chord fraction) | 0.450 | 0.500 | +0.050 | +11.1% |
| Tip cap reach | 0.350 | 0.200 | -0.150 | -42.9% |
| Derived | ||||
| Aspect ratio | 7.241 | 18.901 | +11.660 | +161.0% |
| Area | 111865 mm² | 45296522 mm² | +45184658 mm² | +40392.3% |
| Taper | 0.507 | 0.850 | +0.344 | +67.8% |
| MAC | 128 mm | 1552 mm | +1424 mm | +1109.1% |
| Sections | ||||
| Root section | a18 | l7769 | changed | — |
| Shapedeviation at matched span fractions, 64 samples | ||||
| Chord deviation (max) | 1501 mm | |||
| Chord deviation (RMS) | 1425 mm | |||
| Twist deviation (max) | 2.00° | |||
| Dihedral deviation (max) | 932 mm | |||
| Tip cap deviation (max) | 14575 mm | |||
Performance
CoefficientsDimensionless — how good the shape is, independent of size and speed.
ForcesNewtons and watts — what each wing actually carries and costs at this condition.
Spanwise
withheld — “Surf / pump foil” integrates to CL 0.022 against the polar’s CL at the same α (this analysis predates the loading reporting its own) 0.363 (0.06×); “Gossamer Albatross II” integrates to CL 0.118 against the polar’s CL at the same α (this analysis predates the loading reporting its own) 0.613 (0.19×). 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 (water (sea), air)
data
| V (kt) | Surf / pump foil | Gossamer Albatross II |
|---|---|---|
| 9.63 | 22.12 | 22.41 |
| 10.45 | 24.17 | 26.48 |
| 10.67 | 24.48 | 27.60 |
| 11.30 | 25.35 | 29.36 |
| 11.71 | 25.57 | 30.52 |
| 12.15 | 25.81 | 31.66 |
| 12.75 | 25.85 | 33.21 |
| 13.00 | 25.87 | 33.78 |
| 13.78 | 25.59 | 35.55 |
| 13.85 | 25.57 | 35.63 |
| 14.70 | 24.96 | 36.77 |
| 14.82 | 24.84 | 36.94 |
| 15.55 | 24.15 | 36.91 |