Downwind glide foil — high aspect reference front wingvsGossamer Albatross II — same span, two-thirds the area

← open Downwind glide foil open Gossamer Albatross II →

root section e818 → l7769 · area 121109 mm² → 45296522 mm² · tip chord 48 mm → 1404 mm · span 1240 mm → 29260 mm · mac 104 mm → 1552 mm · root chord 130 mm → 1651 mm

← all designs pick the second from the gallery

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.

Downwind glide foil — high aspect reference front wing
Gossamer Albatross II — same span, two-thirds the area

What changed

Property	Downwind glide foil	Gossamer Albatross II	Change	%
Geometry
Span	1240 mm	29260 mm	+28020 mm	+2259.7%
Root chord	130 mm	1651 mm	+1521 mm	+1170.0%
Tip chord	48 mm	1404 mm	+1356 mm	+2825.0%
Sweep parameter	9.717	7.476	-2.241	-23.1%
Dihedral	-2.50°	3.60°	+6.10°	-244.0%
Tip twist	-2.50°	0.00°	+2.50°	-100.0%
TE thickness	0 mm	2 mm	+1 mm	+650.0%
Sections	30	40	+10	+33.3%
Tip cap reach	0.400	0.200	-0.200	-50.0%
Derived
Aspect ratio	12.696	18.901	+6.205	+48.9%
Area	121109 mm²	45296522 mm²	+45175413 mm²	+37301.3%
Taper	0.369	0.850	+0.481	+130.3%
MAC	104 mm	1552 mm	+1448 mm	+1390.0%
Sections
Root section	e818	l7769	changed	—
Shapedeviation at matched span fractions, 64 samples
Chord deviation (max)	1521 mm
Chord deviation (RMS)	1451 mm
Twist deviation (max)	2.50°
Dihedral deviation (max)	948 mm
Tip cap deviation (max)	14408 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 — “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×); “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.

Efficiency

mixed fluids (water (sea), air)

data

V (kt)	Downwind glide foil	Gossamer Albatross II
9.63	29.27	22.41
9.91	31.15	23.80
10.67	32.59	27.60
11.27	33.73	29.30
11.71	33.63	30.52
12.64	33.40	32.92
12.75	33.27	33.21
13.78	32.11	35.55
14.00	31.87	35.83
14.82	30.52	36.94
15.36	29.65	36.92
15.86	28.68	36.90
16.72	27.04	35.76
16.90	26.69	35.53
17.93	24.69	33.46
18.08	24.41	33.17
18.97	22.73	31.37