Piper J-3 Cub — a rectangular wing that worksvsDownwind glide foil — high aspect reference front wing
root section usa35b → e818 · dihedral 1.00° → -2.50° · area 16577850 mm² → 121109 mm² · tip chord 1545 mm → 48 mm · te thickness 3 mm → 0 mm · mac 1545 mm → 104 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
- Downwind glide foil — high aspect reference front wing
What changed
| Property | Piper J-3 Cub | Downwind glide foil | Change | % |
|---|---|---|---|---|
| Geometry | ||||
| Span | 10730 mm | 1240 mm | -9490 mm | -88.4% |
| Root chord | 1545 mm | 130 mm | -1415 mm | -91.6% |
| Tip chord | 1545 mm | 48 mm | -1497 mm | -96.9% |
| Sweep parameter | 0.000 | 9.717 | +9.717 | — |
| Dihedral | 1.00° | -2.50° | -3.50° | -350.0% |
| Tip twist | 0.00° | -2.50° | -2.50° | — |
| TE thickness | 3 mm | 0 mm | -3 mm | -93.3% |
| Sections | 40 | 30 | -10 | -25.0% |
| Tip cap reach | 0.300 | 0.400 | +0.100 | +33.3% |
| Derived | ||||
| Aspect ratio | 6.945 | 12.696 | +5.751 | +82.8% |
| Area | 16577850 mm² | 121109 mm² | -16456741 mm² | -99.3% |
| Taper | 1.000 | 0.369 | -0.631 | -63.1% |
| MAC | 1545 mm | 104 mm | -1441 mm | -93.3% |
| Sections | ||||
| Root section | usa35b | e818 | changed | — |
| Shapedeviation at matched span fractions, 64 samples | ||||
| Chord deviation (max) | 1497 mm | |||
| Chord deviation (RMS) | 1448 mm | |||
| Twist deviation (max) | 2.50° | |||
| Dihedral deviation (max) | 121 mm | |||
| Tip cap deviation (max) | 5051 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×); “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 | Piper J-3 Cub | Downwind glide foil |
|---|---|---|
| 0.009 | 0.231 | 0.293 |
| 0.010 | 0.258 | 0.328 |
| 0.011 | 0.277 | 0.355 |
| 0.011 | 0.291 | 0.371 |
| 0.013 | 0.330 | 0.423 |
| 0.013 | 0.345 | 0.446 |
| 0.015 | 0.378 | 0.480 |
| 0.017 | 0.437 | 0.550 |
| 0.019 | 0.457 | 0.577 |
| 0.021 | 0.511 | 0.612 |
| 0.027 | 0.605 | 0.680 |
| 0.035 | 0.714 | 0.775 |