Originally Posted by
matthewlai
Ah! It makes sense if the stress limit is in G's.
But then the next question would be, why are airplanes rated in G's, and not absolute forces?
A heavy airplane and a light airplane pulling the same G definitely stress the airframe differently?
As others have speculated, the overall load limit could be set by items whose breaking point does not change with airspeed (as does the max load provided by the wings) so it occurs at a certain acceleration (aka G). And for the G to be kept the same, a difference in weight must be matched by a difference in lift, which can only be provided (if we’re already at max AOA) by a difference in speed. Unlike the the breaking point of a wing root, which occurs at a certain force (aka lift) of which the maximum of a certain value, occurs at one speed only.
As an aside, I find it kind of amusing how many replies you got (even almost a decade later) which didn’t understand your question, didn’t catch on to the difference in constant-G vs. constant-force limits, and simply blurted out the basic PPL 101 explanation of why the constant G speed changes with weight (one of which, amazingly, pointed you to “think about the load factor” as if your original post wasn’t already based on it, at a level far beyond the basic quip that was the rest of that post).
Goes to show how so much of what passes for reasoning is really just word association. Hear a thing mentioned in a question, and just blurt out the soundbyte that you associate with that thing… no engagement with what the question is actually asking about that thing, how it relates to the other items in the related conditions, etc.