get checked values with dynamic classes

I have 8 tables, each table having several radio button groups.  I am trying to get the sum of the checked values for each table, which I am calling 'sections'.  I have 8 input boxes that will be holding the sums for their section.  For the radio buttons in section one I have a class of "S1". The radio buttons in section two have a class of S2, and so on.  I want to loop 8 times to get the totals of each section but I don't know how to reference the checked by class dynamically.

Here is one of the things I have tried:

$('#survey').submit(function()
{
    var result = 0;
    for (var i=1; i<3; i++)
    {
    result = 0;
    $(".S"+i).attr("checked").each(function () {
        result += parseFloat($(this).val());
    });
    $("#sectionTotal"+i').val(result);
    }
    return false; 
});

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