[RCSE] Netrual point calculation question

[Tom Koszuta]

Model Aircraft Aerodynamics by Martin Simons has a set of formulas in one of the Appendices that allows you to calculate the approximate neutral point and static margin of  an aircraft.  One of the parameters is the "length of the tail arm".  It does not indicate exactly what this means.  I am presuming that it is one of center of wing to center of stab, quarter chord line to quarter chord line, or wing TE to stab LE.        Can anyone shed some light on this?  Alternatively, his example uses a plane called a Bantam with a 1.25M span, which he quotes the tail arm to be 0.557M.  If anyone has one of these and can measure, that would also be appreciated.       I know that I can always start with the most conservative answer and work from there, but the engineer in me needs a more exact basis for my calculations.   Tom Koszuta Clarence Sailplane Society (Buffalo) NY