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Fluid, weight and ride speeds

Analysis > Fluid answers the question every foiler asks first: at my weight, how fast does this wing have to go to hold me up, and is it the right size for me?

Rider and gear

Enter your weight and your board plus gear. Together they are the all-up weight, which with the wing's planform area gives the wing loading in kg/m².

Wing class

The panel places this wing in a class for your weight and lists the area range of every class. Areas are for your all-up weight, from wing loading. These bands are rules of thumb from what people actually ride, not calculated limits, and real gear straddles them.

Ride speeds

Three speeds, at lift coefficients that bracket real foiling:

• Takeoff / pump (CL 0.8): slow, working the foil up to lift-off.
• Cruise (CL 0.5): a typical steady-state riding lift coefficient.
• Fast / bear-away (CL 0.3): sheeted in and moving.

Speeds come straight from the lift equation, V = √(2W / ρ·S·CL), using this wing's planform area and your all-up weight. It's arithmetic on the geometry, not a flow simulation: real numbers move with section, twist, and how cleanly you ride. Use it to compare two wings, not to promise a takeoff speed.

Fluid

Density and viscosity used for the speed and Reynolds estimates, and for every load in the Structure checks. Water and air presets are the serious ones; the Cursed group is for science. The panel shows the Reynolds number at cruise on the mean aerodynamic chord.

System: pairing a stabilizer

Pair this wing with a saved stabilizer and estimate the combo at fixed total lift, a simplified take on an XFLR5 Type 2 polar. The stab's share shifts what the main must carry; tail volume reads out pitch authority.

• Stab arm: mast-to-stabilizer moment arm, roughly your fuselage length.
• Stab load: stab lift as a share of all-up weight. Negative is download (the usual trimmed state), so the main carries more than 100%.
• Stab angle: stab incidence relative to the main wing (negative = LE down).
• Stab height: vertical offset from the main wing plane (+ = up), typically within a few root thicknesses either way.

With a stabilizer set, the main is sized to carry the all-up weight minus the stab's share: a simplified fixed-lift pairing, not a trimmed solution. The Performance view's System trim solves the stab load and angle from the moment balance.

Full method notes: how the numbers are computed.

Next: Polar