Drela SuperGee II — a 1.5 m discus-launch glider, drawn to the plan

Most model aircraft are undocumented in the way commercial hydrofoil wings are — a span, a "wing area", and nothing about the section. Mark Drela's designs are the exception: the plans are published free, and they carry the geometry.

SuperGee II, plan dated 30 April 2003: 59 in span, 336 in² (0.217 m²), 8.0 oz all up, 3.4 oz/ft². Aspect ratio 10.4. A discus-launch glider — a peg at the wingtip, a spin, and the model leaves the hand at the top of a discus throw, which is why the plan spends as much ink on the layup as on the aerodynamics.

The section changes three times

Same idea as Daedalus at a twentieth of the scale, and for the same reason: chord falls toward the tip, Reynolds number falls with it, and a section that is right at the root is too thick and too cambered to work out there. This model carries AG455ct at the root and AG47ct at the tip — foil.tools blends between two, so it gets the direction of the change but not the three-panel step.

Re·√CL, and why the plan quotes it

The plan labels each panel with a Reynolds number times the square root of lift coefficient: 52 k at the root, 40 k at the break, 25 k at the tip. That looks like an odd thing to tabulate until you notice it does not depend on how fast the model is flying. Speed falls as 1/√CL at a fixed wing loading, so Re·√CL collapses to chord times the square root of wing loading — one number per panel, fixed by the design, that says what the section has to cope with. At 25 k the tip panel is in the regime where an ordinary section simply stops working.

Where this model simplifies

The real planform is a double taper — 7.2 in, 5.5 in, 3.4 in. This tool draws one taper. This model keeps the plan's root chord (7.2 in) and the plan's area, which puts the modelled tip chord at about 3.7 in rather than 3.4 in. The outboard wing is therefore slightly wider here than on the plan and the tip Reynolds number correspondingly optimistic. Dihedral is not a figure the plan states in text; the model carries a conventional one.

This is a fit to published dimensions, not a replica. foil.tools draws a single-taper planform shaped by four splines; the real wing has structure this model does not carry. Span, area and section match the published figures — the metrics above are what this geometry actually produces, so where they differ from a published number, the difference is the fit.

Sources: SuperGee II plan, Mark Drela, 30 April 2003 — span, area, mass, per-panel chords, sections and Re·√CL all read off the plan · Charles River Radio Controllers, Mark Drela designs

The polars above are foil.tools' own analysis of this model, not published performance data for the aircraft. They are AeroBuildup — strip theory with NeuralFoil sections — for the wing alone, so they exclude the fuselage, the undercarriage and everything else that makes a real aeroplane slower than its wing. Read them for how this shape behaves, and for comparison against the other wings here — not as a figure for the aircraft. Open it in the designer and run your own.