Piper J-3 Cub — a rectangular wing that worksvsSurf / pump foil — 900 mm reference front wing
root section usa35b → a18 · dihedral 1.00° → -1.50° · area 16577850 mm² → 111865 mm² · tip chord 1545 mm → 76 mm · mac 1545 mm → 128 mm · te thickness 3 mm → 0 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 (5396 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.
- Piper J-3 Cub — a rectangular wing that works
- Surf / pump foil — 900 mm reference front wing
What changed
| Property | Piper J-3 Cub | Surf / pump foil | Change | % |
|---|---|---|---|---|
| Geometry | ||||
| Span | 10730 mm | 900 mm | -9830 mm | -91.6% |
| Root chord | 1545 mm | 150 mm | -1395 mm | -90.3% |
| Tip chord | 1545 mm | 76 mm | -1469 mm | -95.1% |
| Sweep parameter | 0.000 | 8.553 | +8.553 | — |
| Dihedral | 1.00° | -1.50° | -2.50° | -250.0% |
| Tip twist | 0.00° | -2.00° | -2.00° | — |
| TE thickness | 3 mm | 0 mm | -3 mm | -91.7% |
| Sections | 40 | 30 | -10 | -25.0% |
| Tip cap peak (chord fraction) | 0.500 | 0.450 | -0.050 | -10.0% |
| Tip cap reach | 0.300 | 0.350 | +0.050 | +16.7% |
| Derived | ||||
| Aspect ratio | 6.945 | 7.241 | +0.296 | +4.3% |
| Area | 16577850 mm² | 111865 mm² | -16465985 mm² | -99.3% |
| Taper | 1.000 | 0.507 | -0.493 | -49.3% |
| MAC | 1545 mm | 128 mm | -1417 mm | -91.7% |
| Sections | ||||
| Root section | usa35b | a18 | 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 — “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×); “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×). 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 | Piper J-3 Cub | Surf / pump foil |
|---|---|---|
| 0.011 | 0.274 | 0.254 |
| 0.011 | 0.291 | 0.274 |
| 0.011 | 0.298 | 0.284 |
| 0.013 | 0.329 | 0.320 |
| 0.013 | 0.330 | 0.322 |
| 0.014 | 0.365 | 0.363 |
| 0.015 | 0.378 | 0.377 |
| 0.016 | 0.409 | 0.416 |
| 0.017 | 0.437 | 0.446 |
| 0.019 | 0.465 | 0.481 |
| 0.021 | 0.511 | 0.529 |
| 0.023 | 0.541 | 0.563 |
| 0.027 | 0.605 | 0.621 |
| 0.030 | 0.647 | 0.667 |
| 0.036 | 0.729 | 0.737 |
| 0.042 | 0.786 | 0.803 |
| 0.053 | 0.894 | 0.891 |
| 0.064 | 0.984 | 0.985 |
| 0.081 | 1.12 | 1.09 |
| 0.107 | 1.28 | 1.24 |