Chris Collins

Tools · rc

Model plane designer

Design a model plane's wing: straight, tapered, swept, multi-panel, delta or flying-wing planforms → area, aspect ratio, MAC drawn on the planform, neutral point with the tail, CG range by static margin, wing and cube loading, stall speed; NACA 4/5-digit or pasted .dat airfoils; laser-cut ribs with spar notches, sheeting and lightening holes as SVG, DXF or a 1:1 PDF.

Added

Works with

How to use it

I kept redoing the same sums on paper for every model: where the MAC is on a wing with three panels, where the CG goes once the tail is in, and what the ribs of a tapered wing measure. This does all three from one description of the wing, and draws the ribs ready for the laser cutter.

How to use it

  1. Wing & CG — start from one of the examples (straight, tapered, swept, multi-panel glider, delta, flying wing) and change it: the root chord, then each panel from root to tip with its own span, tip chord and leading-edge sweep. The planform shows the mean aerodynamic chord on both halves (blue, with its quarter-chord point), the neutral point (red) and the CG range (green).

  2. Add the horizontal tail — span, root and tip chords, sweep, and where its root leading edge sits behind the wing’s — and the tool works out the tail arm, the tail volume Vh and the neutral point with the tail in. Untick it for a flying wing or delta: the neutral point is then the wing’s own quarter-MAC point. Fill in the fin area and arm for the vertical tail volume.

  3. Enter the flying weight for the wing loading (g/dm² and oz/ft²), the cube loading (WCL, with what that loading is usually flown as) and the stall speed at the CLmax you give. Type your CG (distance behind the root leading edge) to see its static margin.

  4. Airfoil — a NACA 4-digit (2412, 0012) or 5-digit (23012; 23112 is the reflexed mean line) section, or paste coordinates from the UIUC database or airfoiltools.com: Selig or Lednicer format, in any units, either way round. Open a .dat file reads one from disk.

  5. Ribs — one rib at the root, each panel break and the tip, and evenly between at no more than the spacing you set, each at its own chord. Set the sheeting thickness (and how far back it goes), the leading- and trailing-edge stock to cut off, spar notches (position as % of chord, width, depth, top, bottom or both) and lightening holes. They are packed onto sheets the size of your laser bed. SVG and DXF are 1:1 in millimetres, one file per sheet; PDF and Print put them on A4, Letter or A3 at actual size with a 100 mm and a 4 in scale bar to measure.

  6. Template — one full section at any chord with the chord line ticked every 10%, for a hot-wire template or checking a built wing.

Choose mm · g or in · oz at the top; files are always in millimetres. Share link carries the whole design.

How it works

The MAC is (2/S)∫c²dy over the half wing and sits at the area centroid; for straight-tapered panels that is exact, panel by panel. The wing’s aerodynamic centre is at a quarter of the MAC. With a tail, the neutral point moves back by η·Vh·(at/aw)·(1 − dε/dα) MACs, where Vh = St·lt/(S·MAC) (tail area and arm, wing area and MAC), the lift-curve slopes at and aw come from the DATCOM formula with aspect ratio and half-chord sweep, and the downwash gradient is 2aw/πA. The CG range is the neutral point less the static margins you set (5–15% is a usual range for a conventional model, 5–10% for a flying wing). Wing cube loading is ounces over square feet to the power 1.5, so models of different sizes compare.

NACA sections come from the published equations with cosine spacing (they match the ordinates in Abbott and von Doenhoff to the fourth decimal). Ribs are the section scaled to each chord, offset inwards for the sheeting, cut square at the stock depths, notched with flat-bottomed slots, and given round holes as big as a fraction of the local depth allows.

This is a design aid, not a substitute for a test glide: balance the model at the forward end of the range for the first flight. For aircraft weight and balance sheets, see the weight and balance tool; for a pack, battery packs; for throws and servos, servo & control surfaces.

Browser support

Any current browser. Printing at exact size depends on the print dialog: choose 100% or “Actual size”, not “Fit to page”, and measure the scale bars.

Privacy

Everything is worked out in your browser; pasted or opened airfoil files aren’t uploaded. Your design is kept in this browser’s local storage, and in the link if you share one.

Runs entirely in your browser; nothing you type leaves this page.