Skygate 911

[William Seger]

27. And you still missed it by a mile

Last edited Tue Jun 3, 2014, 01:20 AM - Edit history (1)

> Notice your constant use of the word "loads" when referring to airspeed limitations.

> I am not "asserting" as such. And I have continually attempted to help you understand that you are confusing limit load "Factor Of Safety" (which is 50%), with airspeed margins of safety.

Ya know, the irony here is that you are the one who is making claims based on your own confusion about the difference between the "load" limitations shown in a Vg diagram and airspeed limitations. The "g" in Vg refers to those "g-load" numbers on the vertical axis. As important as that information is about wing performance, you're claiming that this g-load diagram also tells us how fast a 757 or 767 can fly because there's a red wall at Vd. What I'm saying is that your argument is fallacious, apparently because you don't understand what Vd really is and how it's used in aircraft engineering, and in fact you appear to be fairly ignorant of basic engineering principles.

I do wish I didn't have to repeat myself so often, but I'm using the term "load" the way structural engineers use it:

Structural loads or actions are forces, deformations, or accelerations applied to a structure or its components.[1][2]

Loads cause stresses, deformations, and displacements in structures. Assessment of their effects is carried out by the methods of structural analysis. Excess load or overloading may cause structural failure, and hence such possibility should be either considered in the design or strictly controlled.

Most of the loads that a building structural engineer deals with are gravity loads ("weight" in your definition), but buildings are also designed to resist wind loads (which is obviously not a weight). Pneumatic pressure creates very complex loads that aeronautical engineers have to account for in their designs. In your plane diagram, the thrust and drag are forces that "cause stresses, deformations, and displacements in structures" so they are loads that must be taken into account, not just weight and lift. So I'll continue to use the correct term, even if you're still confused.

> These are some of the very problems you had when attempting to debate a topic such as Mcrit. You just do not understand the language/terminology.

This, from the guy who still doesn't know the difference between "critical Mach" and "drag divergence Mach" (that thread is still around, Balsamo), the difference between "design dive speed" and "demonstrated flight diving speed," and the difference between "weight" and "load" as the term is used in engineering. But the real fun with "debating" with you about terms that people can easily look up (!) is the arrogance of your ignorance, such as:

> Would you argue with a 15 year old in high school who is trying to tell you how to be a "draftsman"? That is what it is like arguing aerodynamics with you. It's a waste of time.

Well, not only are you wasting your time foisting bogus definitions and interpretations, but you keep digging your holes deeper by continuing to do so. You really do seem to think people are too stupid to use Google or understand what they find, so they'll listen to anyone who declares himself to be an expert. And buy a video.

But back to the issue here: I claim that your entire argument about the "impossible" speeds of 9/11 planes is nothing more than an argument from Rob Balsamo's personal incredulity and backed by nothing but self-proclaimed yet undemonstrated expertise. You have no idea of how fast a 757 or 767 can fly without falling apart -- because nobody does without actually doing it -- and your "expert" opinion is actually rooted in ignorance of engineering principles.

I claim that the typical way an engineer designs a safe structure is by analyzing "limit" cases to estimate the loads the structure will need to resist. Since these calculated forces are only estimates, often derived from empirical formulas, these forces are multiplied by a Factor of Safety to get the "ultimate" loads that are fed into the design. This is to make sure that the final design will safely handle the "limit" case, at the least. Since the limit case is only an estimate of the real-world forces, how much of a "realized margin of safety" is available beyond that assumed limit can only be determined by actually loading the structure to failure, but in a well-designed structure, there certainly is one. And in that regard, your bluster aside, Boeing engineers are known for building rugged planes by making conservative assumptions. As I showed you, one of those conservative assumptions is to design planes to be flutter-free at 1.15 Vd, even though FAR 25 only requires that it be demonstrated at Vd (it appears you need to read that again).

I further claim that Vd, not Vmo, is defined as the "limit" case for speed -- the maximum speed expected in a shallow dive as defined in FAR 25. Yes, by regulation, Vmo is set to provide a "margin of safety" below Vd for normal operations, but that's not what I'm talking about. To design the plane to safely fly at Vd -- as they are required to do! -- engineers will estimate the loads that speed imposes on the structure and then multiply each of them by a Factor of Safety to feed into the structural calculations. That includes the loads that are trying to collapse the nose, buckle the fuselage, rip the wings, stabilizers, and control surfaces off -- all of the loads that can "cause stresses, deformations, and displacements" in the plane's structure.

So, I claim that there is a "realized margin of safety" beyond Vd built into the design by employing Factors of Safety to the design loads, whereas you specifically claim in post #18 that there is none.

It shouldn't be too tough to resolve this issue by asking some real experts. I'll even let you choose a neutral forum where aeronautical engineers are likely to answer: Post your diagram with it's "no factor of safety beyond Vd" claim, explain yourself any way you like, and we'll see what they have to say.

All in or fold, Balsamo.