Try this now. Wings level
If the wings are level weight does not play a roll.
Weight becomes a factor as soon as you're banked.
houston said:
Why does Vmca go down as weight goes up?
I've already answered this, but perhaps rewording it, devoid of formula, will help.
When the aircraft is partially banked weight no longer acts parallel to it's vertical axis. Instead, it acts to some degree, equal to the bank angle, off vertical. The result is a portion of weight acting along the lateral axis and a portion acting along the vertical axis. Since yaw is both a transitional action along the lateral axis (inertia part here) and a rotational action along the vertical axis (moment of inertia part here), we can conclude that inertia, in both traditional and rotational senses, is present.
Why don't we find explanations like this in our traditional aviation books? Simple, inertia isn't a force and it isn't something previous subject material has covered. And they definitely haven't introduced the 6 degrees of freedom. In other words, there would be more to explain than simply reexplaining an already touched on topic like HCL. Keep in mind, inertia exists in any object that has weight and moves along the x, y or z axis (transitional). Similarly, moment of inertia exists in any object that has weight and is moving about the x, y or z axis (rotational).
Interestingly, I've read and reread the sections pertinent to this discussion in almost a dozen aerodynamic books over the course of our discussion here. Not one mentions inertia. Not one mentions HCL. Why? I'm not certain, but I'd guess it's because they are not there to provide the reader with memory aids. What we are arguing here is just that, a memory aid aimed to assist in correlating these ideas to help the reader better remember them.
For what it's worth, I would still stick with teaching HCL as well. For the reasons mentioned above, but also because mentioning inertia carries with it some baggage that an intuitive student may cling to later on. For example, explaining Va's shifting with weight and, remembering our chat about inertia, concluding that the heavier airplane is more sluggish. For thrust causing an acceleration, sure. For Va going down, nope. What's the difference? Transition. Rotation. Still, a problem I'd rather avoid so I'll stick with HCL to explain this, but I won't claim the inertia explanation wrong either.