Schempp-Hirth Standard Cirrus — 15 m, two Wortmann sections

A 1969 Standard-class glider: 15 m span, 10 m² of wing, aspect ratio 22.5. It is here because it is the rare wing whose root and tip sections are both published by designation — most aircraft specifications name one section, or none.

Two sections, not one

foil.tools interpolates the Kulfan weights root to tip, so a two-section wing is the case this tool models most directly. What the specification tables do not say is where along the span the wing gets from one to the other, so this model does the simplest thing and blends linearly across the whole half-span. A real wing more usually finishes the transition well inboard and runs the outer section unchanged from there out; if that is what this one does, the model is carrying too much of the thick root section outboard.

Both sections are startlingly thick

Nineteen and eighteen per cent, on a glider that does 38:1. That is the Wortmann approach at sailplane Reynolds numbers: hold laminar flow a long way back on both surfaces, accept a low-drag bucket that is narrow and must be flown inside, and take the thickness as free spar depth. A modern 15 m wing is thinner and has a wider bucket, which is a different bargain, not obviously a better one at this span.

Published performance for comparison, and the two sources do not quite agree: Jane's gives 38.5:1 at 90 km/h, the factory Flight and Service Manual max L/D 38 at 85 km/h and min sink 0.57 m/s at 70 km/h. Both are the whole sailplane. The polars below are the wing by itself, and will be better than either.

Not published here

Span, area and both sections are published. The chord distribution is not — so root and tip chord here are chosen to land the published 10 m² at a taper ratio typical of the class, exactly as the Cessna 172 post does. Dihedral and washout are likewise not in the cited sources; the model carries small conventional values.

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: Schempp-Hirth Standard Cirrus (Wikipedia), specifications from Jane's All the World's Aircraft 1976–77 · Standard Cirrus Flight and Service Manual — glide ratio, min sink, weights · Bergman, A Study of the Standard Cirrus Wing Lift Distribution Versus Bell Shaped Lift Distribution, Cal Poly MS thesis, 2020, a full XFLR5 model of this wing if you want to go further than this one does

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.