Downwind glide foil — high aspect reference front wingvsPiper J-3 Cub — a rectangular wing that works
root section e818 → usa35b · area 121109 mm² → 16577850 mm² · tip chord 48 mm → 1545 mm · te thickness 0 mm → 3 mm · mac 104 mm → 1545 mm · root chord 130 mm → 1545 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.
- Downwind glide foil — high aspect reference front wing
- Piper J-3 Cub — a rectangular wing that works
What changed
| Property | Downwind glide foil | Piper J-3 Cub | Change | % |
|---|---|---|---|---|
| Geometry | ||||
| Span | 1240 mm | 10730 mm | +9490 mm | +765.3% |
| Root chord | 130 mm | 1545 mm | +1415 mm | +1088.5% |
| Tip chord | 48 mm | 1545 mm | +1497 mm | +3118.8% |
| Sweep parameter | 9.717 | 0.000 | -9.717 | -100.0% |
| Dihedral | -2.50° | 1.00° | +3.50° | -140.0% |
| Tip twist | -2.50° | 0.00° | +2.50° | -100.0% |
| TE thickness | 0 mm | 3 mm | +3 mm | +1400.0% |
| Sections | 30 | 40 | +10 | +33.3% |
| Tip cap reach | 0.400 | 0.300 | -0.100 | -25.0% |
| Derived | ||||
| Aspect ratio | 12.696 | 6.945 | -5.751 | -45.3% |
| Area | 121109 mm² | 16577850 mm² | +16456741 mm² | +13588.3% |
| Taper | 0.369 | 1.000 | +0.631 | +170.8% |
| MAC | 104 mm | 1545 mm | +1441 mm | +1383.2% |
| Sections | ||||
| Root section | e818 | usa35b | 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 — “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×); “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 | Downwind glide foil | Piper J-3 Cub |
|---|---|---|
| 0.009 | 0.293 | 0.231 |
| 0.010 | 0.328 | 0.258 |
| 0.011 | 0.355 | 0.277 |
| 0.011 | 0.371 | 0.291 |
| 0.013 | 0.423 | 0.330 |
| 0.013 | 0.446 | 0.345 |
| 0.015 | 0.480 | 0.378 |
| 0.017 | 0.550 | 0.437 |
| 0.019 | 0.577 | 0.457 |
| 0.021 | 0.612 | 0.511 |
| 0.027 | 0.680 | 0.605 |
| 0.035 | 0.775 | 0.714 |