The particular equation you posted goes back to Dr. Broek's fracture mechanics book and in fact it is also contained in his Manual TN9501. This dates back to 1980's and was in the fracture course I took under him back then. Since then, it has been cited in various FAA documents. So, that being said, it has been around for a long time. But, and this is a big BUT, most people have misused, misinterpreted and misunderstood the main point of this equation, particularly engineers that do not have an aeronautics background.
The equation Dr. Broek cited was specifically to be used to establish a 1g trimmed condition fuselage bending moment for use in developing a fatigue spectrum. It ignores any balancing tail load assuming the trimmed conditions requires little to no tail load. This must be validated for each aircraft being analyzed, it cannot be taken verbatim. So, one must know how to balance an aircraft to use this equation. Additionally, the configuration of the aircraft plays a major role in developing this. If the method is used by an "experienced" engineer, then a conservative but representative fuselage bending spectrum can be developed. Note, I know of very few experienced stress/structures engineers able to do this correctly as it requires both an aeronautics background and lots of experience in loads/stress spectrum development which few people possess.
Second, if your intent is to develop FAA limit and ultimate loads for static analysis, then this equation is not for you. The weight distribution fundamentals of the equation are acceptable but you must do much much more. You need to look at each FAA condition, balance the aircraft, calculate the resulting load factors, and then calculate the necessary tail load. For this, you should go to the book by Ted Lomax, AIAA "Structural Loads Analysis for Commercial Transport Aircraft".
Lastly, as a DER, I have watched for many years numerous people in the industry make erroneous and inaccurate statements regarding fuselage bending loads and spectra. First off, pressure is absolutely NOT the only driving factor. People have continually tried to simplify the spectrum requirements down to pressure only because they simply don't know or do not have the capability technically to do so. Also, many "simplified" approaches have been presented which are either totally devoid of basis or inaccurate, among them is the so called Chicago method. This method not only starts with Ftu as the basis but then generally assumes a 1.3g alternating load for all aircraft. One look at all of the FAA/DOT Load History documents (over 30 for all various types of aircraft) illustrates that this is not a valid assumption nor representative. There are far too many other issues with this approach for me to go into at this time.
Anyways, as most everyone else has pointed out, you need some experienced level of support for your efforts.
Good luck in your endeavors
