Stalls in turbulence

[pacerpilot]

Thank you very much, I really appreciate.

If you have time and patience to help me with some questions that, as you also said, were not clarified during my training, actually because I haven't know about them then.

Regarding "my first question, headwind shifts to tailwind, you said 15 kts and sincerely I don't get it why it's so". I figure out that if the headwind will decrease suddenly, there should be a change in airspeed, e.g. 15kts headind changes to 5 kts headwind, if it's suddenly, the airspeed decreases 10 kts. "So, why when it suddenly shifts from 15kts to 15 kts tailwind there is no a 30 kts drop?"

Also, what is not clear to me is the difference between a wingdrop and an incipient spin. I figure out that you may have a wingdrop even if you are coordinated, because the wingdrop may be induced by engine power effects and other factors, not necessary yaw, so, with ball centered you may have a wingdrop, but not a spin, right?

If that wingdrop is abrupt, what be will be the outcome? The wing will tuck under and the result will be a spiral with nose pointing down?

During a coordinated turn descent, I know that the AOA of the inside wing is higher than of the outside, in this case, you may have a spin even if you had ball centered?

And during decrabbing, when you introduce pro-spin controls, i.e. rudder to decrab and opposite aileron just to prevent banking in the direction of the rudder, why there is no wingdrop? Considering a stall landing, the airplane is very close to stall when we introduce these controls.

Steve,

I know you're not going to want to here this but you need to get with a flight instructor. Not the same one who did your initial training either. Whoever that was left you with a serious and dangerous lack of knowledge and understanding of aerodynamics and flight conditions. Your misunderstanding of simple airspeed verses groundspeed and wind is disturbing. How do you plan cross countries? Using your current understanding, you could run short of fuel far from a destination-or needlessly stop to refuel. The whole stall thing has been rehashed ad nauseum here in the last few days. I am sure you're not "refusing" to accept information, your just not "seeing" what everybody is telling you. A short ground session will clear all your questions up.

[martymayes]

One at a time:

Regarding my first question, headwind shifts to tailwind, you said 15 kts and sincerely I don't get it why it's so. I figure out that if the headwind will decrease suddenly, there should be a change in airspeed, e.g. 15kts headind changes to 5 kts headwind, if it's suddenly, the airspeed decreases 10 kts. So, why when it suddenly shifts from 15kts to 15 kts tailwind there is no a 30 kts drop?

When a plane leaves the ground, it flies in a mass of air. All the plane senses is it's motion relative to that mass of air. The whole air mass may also be moving, however, all that does is affect the airplane's speed and track over the ground. Example: You are flying South in an airplane at 120 kts, relative to the air. The airspeed indicator reports 120 kts. Now the whole air mass begins moving North at 15 kts. The airspeed indicator still reports 120 kts, however, the airplane's speed over the ground is now 105 kts, 120 - 15 = 105. That is the ONLY way you know there is 15 kts of headwind, the groundspeed changes. Speed relative to the air mass, or airspeed, does not change. Now the air mass begins moving South at 15 kts. The airspeed still reports 120 kts, however, the airplane's speed over the ground is 135 kts, 120 + 15 = 135. Had that change occurred instantaneously, it would represent a 15 kt change relative to the mass of air. So for the sake of discussion, that's what you "could" see on the airspeed indicator if the plane did not react, a 15 kts loss, not a 30 kt loss.

In the real world, even if the change in speed relative to the airmass is instantaneous, i.e. windshear, the airplane reacts. It can't react immediately because it has inertia (although for a light plane, not much inertia). So you may see the airspeed fluctuate slightly, like 3-4 kts. You won't see more because the airplane has already begun to adjust to the new airmass. A 50 ton airplane has more issues in an abrupt wind shear because it can't react as fast and it may be several seconds before it regains lost AIRspeed, that is it's speed relative to the air mass.

[Steve Jeff]

Steve,
How do you plan cross countries? Using your current understanding, you could run short of fuel far from a destination-or needlessly stop to refuel.

Maybe I should tell you that I know the fact that headwind decreases groundspeed and tailwind increases i.e. more time to reach destination with a headwind. In my doubts above I was talking about sudden wind changes which CAUSE airspeed to change, so what is your point?

One at a time:

Had that change occurred instantaneously, it would represent a 15 kt change relative to the mass of air.

Let's take an other example which bothers me to not understand it. We have 20 kts headwind, airspeed 150. Headwinds change to 10 kts. Had this change occurred instantaneously, would it be a momentary change in airspeed? Of course groundspeed will increase 10kts. But what about airspeed?

[CarlOrton]

Let's take an other example which bothers me to not understand it. We have 20 kts headwind, airspeed 150. Headwinds change to 10 kts. Had this change occurred instantaneously, would it be a momentary change in airspeed? Of course groundspeed will increase 10kts. But what about airspeed?

Think of it this way: You're in your airplane, flying along. Imagine if you were in a giant bottle. The bottle is hurtling thru the atmosphere at 100 kts. Now the bottle starts flying thru space at 120 kts. You're still flying at the same airspeed as when you when you started, since the air around you hasn't changed. The change in headwind is not affecting your airspeed. The entire mass of air is travelling at that speed. Yes, it affects groundspeed, but YOU are still flying within that mass, then entire mass of which has changed, *not* just the air hitting your wings/prop/fuse/etc.

I haven't chimed in here before, but I'll agree with the others. The $50 or so you'll spend for an hour of groundschool with a seasoned instructor will pay huge benefits. I've been flying since 1978, and I *still* learn new ways to comprehend stuff from *every* instructor I use. Ask around to see who is good. Age is irrelevant. Some instructors are just better communicators than others. I've even learned stuff from this thread.

[martymayes]

Let's take an other example which bothers me to not understand it. We have 20 kts headwind, airspeed 150. Headwinds change to 10 kts. Had this change occurred instantaneously, would it be a momentary change in airspeed?

No. The airspeed indicator does not display aircraft speed + headwind.

[Steve Jeff]

So, in headwind to tailwind shift, reversing its direction makes the airspeed momentary changed and not the mass speed change itself?

[martymayes]

So, in headwind to tailwind shift, reversing its direction makes the airspeed momentary changed and not the mass speed change itself?

In your example, the airplane's AIRspeed didn't change, only the ground speed changed.

http://www.physicsclassroom.com/mmed...tors/plane.cfm

[Steve Jeff]

In your example, the airplane's AIRspeed didn't change, only the ground speed changed.

One at a time:
Had that change occurred instantaneously, it would represent a 15 kt change relative to the mass of air. So for the sake of discussion, that's what you "could" see on the airspeed indicator if the plane did not react, a 15 kts loss, not a 30 kt loss.

[martymayes]

"Windshear" is a change of wind direction and/or velocity that abruptly occurs within the airmass. The only way for the airspeed indicator to report a change in airspeed would be to fly through a windshear, imagine the transition occuring over a distance the thickness of a sheet of paper.

[Steve Jeff]

Yes and all my examples were related to a windshear event, although I said abrupt/sudden change instead of using the term "wind shear". So, all what I ask is windshear, not gradually change. Well, why is there a change in airspeed when it shifts in direction and there is no airspeed change when it shifts in speed? This is what you seem to say and it makes no sense for me. Maybe I'm too dumb, please explain me why is so to clarify it.