[MidlifeFlyer]

This is a fledgling FAQ explaining maneuvering speed. It includes a brief mention of max structural cruising speed. See if you get something out of it:

==============================

Va and the "AoA Gap"

Let's start with the definition of maneuvering speed. Euphemistically, it's the speed at which an airplane will stall before it breaks due to a gust or abrupt control movement. Putting it in slightly other terms, it's the speed at which the wings can suddenly go from their existing angle of attack to their critical angle of attack without increasing the load factor (G-force) beyond the aircraft's design. For normal category aircraft, that design maximum is 3.8 G.

Let's illustrate this with some numbers. We are flying an airplane that stalls at a 15º AoA. At it's normal 120 KT cruise, it's AoA 3º. What happens if we suddenly change the AoA from 3º to 15º? Because there is (roughly) a one-to-one relationship between increase in AoA and increase in load, we have just increased the ~1-G cruise load on the wings by a factor of 5 G (3 X 5 = 15). Too bad we suffered structural damage at 3.8!!

So the whole idea behind maneuvering speed is to lower the difference between your in flight AoA and the critical AoA (the "AoA Gap"), so that in case something closes the gap suddenly, you will stall before the G-load becomes too great.

In general the faster you go in level flight, the lower your in flight AoA and the larger the AoA Gap. In the yellow arc (above maximum structural cruising speed), the AoA Gap is large enough that even an event that doesn't close the full AoA Gap can still cause those excess G's. And an event that does close the AoA Gap is almost guaranteed to cause structural damage.

What we're really trying to do to protect ourselves is increase our AoA so that the gap between our AoA and the critical AoA is smaller. How do we do that? We slow down. When we slow down while maintaining level flight, we reduce power and increase pitch, which increases our AoA. So, let's say that flying our hypothetical airplane level at a 90 KTS takes a 5º AoA. Even that small change means that suddenly bridging the AoA Gap only involves a 3-G increase, below the 3.8 G damage point.

Why the slower speed for lower weight? Well, in general, a lighter airplane can maintain level flight at a particular airspeed with a lower angle of attack. So the AoA Gap is greater at lighter weights. We need to slow down more to get our cruise AoA where we need it to be to keep the AoA Gap manageable.
==============================