const auto loading_factor = sqrt(GetTotalMass() / reference_mass);
  const auto inv_bugs = 1. / bugs;

  polar.a = inv_bugs * ideal_polar.a / loading_factor;
  polar.b = inv_bugs * ideal_polar.b;
  polar.c = inv_bugs * ideal_polar.c * loading_factor;

Stolen from XCSoar source code. Assumes the usual quadratic 3-number polar
as a, b and c.

So you square root of difference between the masses to get the loading
factor, divide a by the loading factor, leave b the same, multiple c by the
loading factor.

Doesn't account for the change in reynolds numbers though (the polar is
probably slightly better than this accounts for)

On Tue, Oct 25, 2016 at 5:01 PM, Adam Woolley <[email protected]> wrote:

> G’day All,
>
>
>
> Just wondering whether anyone knows the formula for converting a baseline
> empty polar curve (speeds/sink rates) to a ballasted polar curve? I’ve read
> it somewhere in the past, but cant find it easily now.
>
>
>
>
>
> Cheers,
>
> WPP
>
> _______________________________________________
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> http://lists.base64.com.au/listinfo/aus-soaring
>
>
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