Just to assume that wing spar strength is the only limiting factor in gross
weight and in the determination of maneuvering speed or maximum normal
operating speed seems to be a gross simplification (pun intended).

Gary,

 

Correct, every component should be considered within the boundaries of the Gross Weight design.  Note that I said "design," not what later testing and experimentation provide.  In an airplane built conforming to a Standard Type Certificate, the design and rigorous testing has been done resulting in meaningful published limitations.  We, however, ride the waves in a different boat, a You-Boat.

 

Here is a personal example.  I fly with a Harmonic Dampener mounted on the forward face of the Lycoming starter flywheel and the prop dynamic balance weights are mounted on the forward face of that and extend 1/4" beyond the outside circumference of the Dampener, even though much was filed off the weights.  This "experiment" reduces the margin betwixt the flywheel and the cowling.  I also had 4-year old "soft" sagging Lord mounts supporting the engine.  In the Kitty Hawk to OSH race, as I started to descend at a very high speed (well into the yellow arc) to make the low pass at Aurora, a canard configured boat appeared suddenly in the lower portion of my windshield - "Drat!" I think I said, as I pulled hard up and to the left.  Later examination revealed where the weight had almost chewed through the lower cowling during that high-G maneuver.  I have replaced the mounts to once again restore the safety margin.

 

Remember the first 3 rules of You-Boat component analysis:

 

1.  Can it withstand constant vibration?

 

2.  Can it withstand G-loads, Negative, Positive and Deceleration?

 

3.  Can it withstand extremes of temperature and humidity?

 

4. ........

 

The blue sky is calling me now.....