Accessing array of datatables

TypeError: oTables[i].fnSettings is not a function

oTables=$(".reportResult").dataTable(
			{
				"aLengthMenu":[[10, 25, -1],[10, 25, "All"]],
				"iDisplayLength" : 10 
			});
function showAll()
{
	for(var i=0;i<oTables.length;i++)
	{
	  var oSettings = oTables[i].fnSettings();
          oSettings._iDisplayLength = 50;
          oTables[i].fnDraw();

	}
}