Va ???

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The basic definition of Va has nothing to do with angle of attack and stall.

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umm...Va has nothing to do with stall? what does it have to do with?

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The main problem that I see with using the AOA explanation is the fact that people skip the whole reason that you're exceeding the critical AOA.

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?

you exceed the critical AOA becuse you pull the yoke back to the stops. if you didn't apply such a deflection, none of this would matter because you wouldn't be able to induce such an acceleration that the airplane could be overstressed.

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I think you're making this waaaaay too complicated.

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The AOA explanation is fine for a very basic understanding

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too complicated but too basic?
 
I've given two separate posts explaining my point. Whether or not you want to consider them is your call. If anyone thinks that my logic is flawed, they're more than welcome to point out where I might have gone wrong. However, I expect those people to reply in a constructive manner and to back up their reasoning.

If you'd like to add something productive, feel free. If you want to tear my head off, PM me. I just don't appreciate the sarcastic remarks on a serious thread.
 
Not in respnse to anyhting except the original question, although perhaps expanding on EatSleepFly's explanation, here's the way I teach it:

=====Maneuveing Speed and the "AoA Gap"=====
Let's go back to 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.

The whole idea of maneuvering speed is to lower the distance between your in flight AoA and the critical AoA (the "AoA Gap"), so that in case of an event that closes the gap, you will stall before the G-load becomes to 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, the AoA Gap is large enough that even an event that doesn't close the Gap can cause those excess Gs. And an event that does close the Gap is almost guaranteed to cause structural damage. So we need to close the AoA Gap, 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.

Let's fill this out with some numbers. For normal category aircraft, that design maximum is 3.8 G. Say we are flying an airplane that stalls at 15º AoA. At it's normal 120 KT cruise, it's AoA 3º. So what happens if the AoA suddenly changes from 3º to 15º?

There is (roughly) a one-to-one relationship between increase in AoA and increase in load. Going from 3º to 15º is a five-fold increase (3X5=15), so we have just increased the ~1-G cruise load on the wings to 5Gs. Too bad we suffered structural damage at 3.8!!

So what do we do to protect ourselves when we expect those kinds of gusts? 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 cruise to critical AoA gap is larger at lighter weights. So we need to slow down more to get our cruise AoA where we need it to be to keep the gap manageable.
 
I'll try my best to settle the argument without joining it and say that its possible that you're all correct. We as pilots have to understand va as a speed that we must slow to if for any reason we might have to make full and abrupt control inputs. The exact reason why va goes up with an increase in weight is not as important to us as simply knowing that it does. All of the FAA publications, the gliems, and most textbooks will state that the reason is because at a higher weight the stall speed increases and therefore there is a smaller difference between the stall speed and critical AOA and will not reqire as much control input to stall, therefore allowing for a higher va. That's a somewhat simple explanation that is probably at least on the right track, and suffices as an acceptable explanation for our purposes as pilots. The real technical explanation might be a little different, but only the engineers who design the airframes really have to understand it. If someone knows a more true reason why va increases with weight, more power to them. They have studied it more in depth than most of us have. However on an oral, the examiner will most likely know it as it is explained in the FAA publications, so its probably wise to offer that expanation when asked.
 
Please stop me! A can't help myself. I must post!!!!!
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OK, my attempt at an answer.

But before I answer the question, let me size up the person asking the question. Hmmmm, I'll bet he really not interested in my credential as a pilot, engineer, or rocket scientist, or my incredible good looks
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. I'll bet he's actually curious and wants to understand Va in simple terms.

Take two identical airplanes flying at say 100 kts.
Airplane #1 is normally loaded, thus having a 2-3 degree angle of attack.
Airplane #2 is loaded such that it is SO heavy, that the angle of attack needed to carry it's weight in level flight at 100 kts is just shy of the critical angle of attack (say 15 degrees).

If you yank back on the yoke on airplane #1, your cheeks will stretch down your face and you'll feel a couple of G's of force in your seat. You know the plane, and everything on it is being stressed.

If you yank back on the yoke on airplane #2, it will immediatly stall, since it already at the critical angle of attack. Therefore, you won't feel and G forces.

Simple answer. A heavily loaded airplane at a given speed, will be closer to it's stall (critical angle of attack).

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Extra credit...
One of the posters suggests that manufacturers set Va based on parts hanging on the airframe. Makes sense to me. Just like in the example with airplane #1, if you're being pressed into the seat, the engine is trying to rip itself off of the wing.
 
I'm surprised you guys can even argue over something as solid as an equation. It's not like they're made up...anyone thats taken aerodynamics since 1965 has seen them still being taught and straight from the Aerodynamics for Naval Aviators book everyone uses
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I don't understand how this question wasnt resolved by the end of the first page.
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I'm surprised you guys can even argue over something as solid as an equation. It's not like they're made up...anyone thats taken aerodynamics since 1965 has seen them still being taught and straight from the Aerodynamics for Naval Aviators book everyone uses
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I don't understand how this question wasnt resolved by the end of the first page.
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Simple. Because for some of us seeing (and even understanding) a concept from a mathematical viewpoint is not the same is knowing it in an intuitive way. Sometimes people like to have a greater understanding of a concept, above and beyond what is required for, say, a knowledge or practical test.

A good example is the question in another thread on why or how airplanes turn. For some, the simple answer of "horizontal component of lift" is plenty. It is correct and accurate. Others are really interested in the finer points of the concept and happily discuss the nuances in great detail.
 
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Simple. Because for some of us seeing (and even understanding) a concept from a mathematical viewpoint is not the same is knowing it in an intuitive way. Sometimes people like to have a greater understanding of a concept, above and beyond what is required for, say, a knowledge or practical test.

[/ QUOTE ]What a great answer! For those of us who are instructors, our job is to do the best we can to explain it in terms that our students can understand and apply. Sometimes those are simple and sometimes complex. The technical among us might argue that only the mathematical complex answer is the "true" one and that accuracy is lost when it's made simple. That probably somewhat true, but a substantially accurate statement that is understood is far more valuable than a technically accurate statement that is not.
 
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What a great answer!....

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<all this and modest, too. what's not to love?>
 
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Others are really interested in the finer points of the concept and happily discuss the nuances in great detail.

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I can understand that, I guess I just missed the happily discussing feeling in this thread. lol
 
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Fair 'nuff. Next time I feel like explaining a technically correct point, I'll consider my audience.

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OOOOOOooohhh! Was that a burn?!?!
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Fair 'nuff. Next time I feel like explaining a technically correct point, I'll consider my audience.

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OOOOOOooohhh! Was that a burn?!?!
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Seems that way to me!
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If ya can't take the heat, get out the kitchen
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damn thats hick lol
 
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OOOOOOooohhh! Was that a burn?!?!
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Huh?

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damn thats hick lol

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What are you saying here?
 
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damn thats hick lol

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What are you saying here?

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Talking about how i phrased the "if you can't take the heat..." line in a "redneckish" fashion.
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Well, equations and all aside, Thanks to a combination of MidLifeFlyer's post and Sixpack's example I understand it now. Thanks guys.

Ethan
 
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Fair 'nuff. Next time I feel like explaining a technically correct point, I'll consider my audience.

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I think we should be saying that to you if you still think thats how Va is defined...
 
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Fair 'nuff. Next time I feel like explaining a technically correct point, I'll consider my audience.

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I think we should be saying that to you if you still think thats how Va is defined...

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Let's hear it then. I'm all ears. Just be prepared to back yourself up, hoss.
 
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Fair 'nuff. Next time I feel like explaining a technically correct point, I'll consider my audience.

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I think we should be saying that to you if you still think thats how Va is defined...

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I'm pretty sure he covered this in our aerodynamics courses...doubt the laws of physics and aerodynamics changed in the last year...not to mention it's not hard to read ANA
 
this thread deteriorated pretty fast after a few posts which contained the right answer. sad, cuz it's actually a good topic.

the problem with the mathematical equation that you guys are using is that it doesn't explain HOW such a load gets put on the airplane - or WHY the wings have to generate so much lift. explaining it by that way only tells you why the plane overstresses - it doesn't explain why a certain speed corresponds to a certain weight.
 
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