Surf / pump foil — 900 mm reference front wingvsPiper J-3 Cub — a rectangular wing that works
root section a18 → usa35b · area 111865 mm² → 16577850 mm² · tip chord 76 mm → 1545 mm · mac 128 mm → 1545 mm · te thickness 0 mm → 3 mm · span 900 mm → 10730 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 5396 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
- Piper J-3 Cub — a rectangular wing that works
What changed
| Property | Surf / pump foil | Piper J-3 Cub | Change | % |
|---|---|---|---|---|
| Geometry | ||||
| Span | 900 mm | 10730 mm | +9830 mm | +1092.2% |
| Root chord | 150 mm | 1545 mm | +1395 mm | +930.0% |
| Tip chord | 76 mm | 1545 mm | +1469 mm | +1932.9% |
| Sweep parameter | 8.553 | 0.000 | -8.553 | -100.0% |
| Dihedral | -1.50° | 1.00° | +2.50° | -166.7% |
| Tip twist | -2.00° | 0.00° | +2.00° | -100.0% |
| TE thickness | 0 mm | 3 mm | +3 mm | +1100.0% |
| Sections | 30 | 40 | +10 | +33.3% |
| Tip cap peak (chord fraction) | 0.450 | 0.500 | +0.050 | +11.1% |
| Tip cap reach | 0.350 | 0.300 | -0.050 | -14.3% |
| Derived | ||||
| Aspect ratio | 7.241 | 6.945 | -0.296 | -4.1% |
| Area | 111865 mm² | 16577850 mm² | +16465985 mm² | +14719.6% |
| Taper | 0.507 | 1.000 | +0.493 | +97.4% |
| MAC | 128 mm | 1545 mm | +1417 mm | +1103.6% |
| Sections | ||||
| Root section | a18 | usa35b | changed | — |
| Shapedeviation at matched span fractions, 64 samples | ||||
| Chord deviation (max) | 1469 mm | |||
| Chord deviation (RMS) | 1421 mm | |||
| Twist deviation (max) | 2.00° | |||
| Dihedral deviation (max) | 105 mm | |||
| Tip cap deviation (max) | 5218 mm | |||
Performance
CoefficientsDimensionless — how good the shape is, independent of size and speed.
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×); “Piper J-3 Cub” integrates to CL 0.002 against the polar’s CL at the same α (this analysis predates the loading reporting its own) 0.330 (0.01×). 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
| CD | Surf / pump foil | Piper J-3 Cub |
|---|---|---|
| 0.011 | 0.254 | 0.274 |
| 0.011 | 0.274 | 0.291 |
| 0.011 | 0.284 | 0.298 |
| 0.013 | 0.320 | 0.329 |
| 0.013 | 0.322 | 0.330 |
| 0.014 | 0.363 | 0.365 |
| 0.015 | 0.377 | 0.378 |
| 0.016 | 0.416 | 0.409 |
| 0.017 | 0.446 | 0.437 |
| 0.019 | 0.481 | 0.465 |
| 0.021 | 0.529 | 0.511 |
| 0.023 | 0.563 | 0.541 |
| 0.027 | 0.621 | 0.605 |
| 0.030 | 0.667 | 0.647 |
| 0.036 | 0.737 | 0.729 |
| 0.042 | 0.803 | 0.786 |
| 0.053 | 0.891 | 0.894 |
| 0.064 | 0.985 | 0.984 |
| 0.081 | 1.09 | 1.12 |
| 0.107 | 1.24 | 1.28 |