stall practice question
- Thread starter muleywannabe
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Interesting. Thank you for the input, I'll have to think about that a bit more.
Edit to add a few thoughts: I use the phrase release back pressure because it is the position of the yoke that directly correlates to the main wing AOA; and as such the stall. If the yoke is at the critical AOA point you stall. If you release it the AOA is lower and the stall goes away.
An aircraft will stall at the same yoke position all day long. Granted at higher speeds it will take longer to reach that stall point due to excess energy. Hmm.
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Jaybird180
Final Approach
Question: is the act of relaxing the elevator position sufficient in itself to break the stall or does it require the act of unloading the wing (even an infinitessimally small amount)?
dtuuri
Final Approach
You don't consider them the same thing?Although I've seldom ever used the terminology "unload the wing" I think I know what it means when others use it. In normal flight, concerned you may be too close to the stall, you release back pressure, i.e., "unload the wing". In the stall, if you release back pressure you'll be in less of a stall, or back to normal flight if you've released a sufficient amount. But, if not sufficient in the area of reverse command, did you "unload the wing"? If you go back to normal flight, then are you "reloading the wing"? I don't like the phrase.
dtuuri
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Jaybird180
Final Approach
No, this is not a semantics question and I'd imagine that an acro pilot would know the difference. I read about some stalls that require the elevator to be held forward to break the stall. Unloading the wing means n value minus 1.0G.
dtuuri
Final Approach
I edited my comment before I saw your reply. So, shouldn't it be called "reloading the wing" when you recover from a stall?
dtuuri
1600vw
Pattern Altitude
Even in a stall would the wing not be loaded? Its just loaded on the underside during a negative G and on the topside during a positive G. Is this not correct? During a stall the wing loading on the bottom of the wing might be slight but would there still not be forces acting upon the bottom of the wing?
Tony
Tony
dtuuri
Final Approach
Clark1961
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Isn't it always amazing when folks take a simple concept and make it as confusing as possible?
Dan Thomas
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Dan Thomas
Relaxing back pressure is to reduce the angle of attack below the stall angle. "Unloading the wing" is a bit misleading. The AoA will increase as the airplane stalls and starts heading downward with its nose still high, and a small reduction in pitch angle might not be enough to unstall the wing.
There's more to getting flying again than just letting off back pressure. One should be in the habit of going to a high power setting, too. If you were to stall on final, say, just reducing the pitch angle will kill you. You need a bunch of speed as well.
Dan
There's more to getting flying again than just letting off back pressure. One should be in the habit of going to a high power setting, too. If you were to stall on final, say, just reducing the pitch angle will kill you. You need a bunch of speed as well.
Dan
gismo
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No kidding. All I was trying to do is explain why "releasing back pressure" isn't always sufficient to "break" a stall. If anyone want's proof of this, take a 172 loaded with the CG near the aft limit, slow to about 60 KIAS with flaps up, run the trim all the way up, select full flaps while applying full power, and take your hands off the wheel. Yes this is an extreme case but there are plenty of more "normal" situations where simply "releasing the back pressure" won't "unload the wing" sufficiently to "break" a stall.
The key point here is that I think pilots should understand that reducing the AoA on the wing is what's required to terminate a stall. IMO this goes far beyond the commonly uttered "you can stall at any airspeed and in any attitude" which while fairly true offers little or nothing WRT stall behavior, prevention, and recovery.
In simplest terms unloading means reducing the AoA and hence the g force felt by the pilot. Clearly when upright and pulling positive g this involves moving the yoke/stick forward but it's quite possible to push into a stall while upright and "releasing back pressure" isn't going to help then. Unloading also means centering the ailerons or at least reducing aileron deflection and in many critical situations aileron and elevator movement is very interrelated. For example, many of us understand that significant aileron deflection when flying slow can/will precipitate a stall/spin, but IME it's less understood that at the same speed an airplane can remain unstalled with the same aileron deflection at a significantly lower airspeed if the average lift produced by the wings is reduced.
There are times when simplifying a subject does more harm than good and I'm pretty sure this is one of them.
gismo
Touchdown! Greaser!
I disagree with pretty much all of that. If reducing back pressure would always decrease the AoA sufficiently below the critical AoA that would be an adequate description of terminating a stall but that's not always the case. Unloading the wing (i.e. decreasing AoA and lift) OTOH will always be the right move regardless of the control movement's necessary to accomplish it.
And yes the AoA does increase in a stall (that's what makes it "break"), but once the stall occurs, the goal should be reducing AoA and lift, not necessarily a specific change in pitch attitude.
Finally, in many if not most airplanes it's important to get the wing below it's critical AoA before adding significant power. Going to full power while stalled generally will not reduce the amount of altitude loss and can easily lead to a spin.
Jaybird180
Final Approach
No such thing as less stalled, despite what is taught about spins (one wing more stalled than the other). It's like being a little pregnant.
A true stall is the disturbance of airflow over the wing where the wing is no longer producing lift.
Speed and power have nothing to do with a stall. Hint for you, what is the stall speed at 0G?
There IS such a thing as more stalled. An airplane can be forced beyond the critical angle of attack. You're still stalled, you're just at a slightly higher AOA.
Untrue. Stalled wings still produce quite a bit of lift - it's just less than unstalled wings, and typically not enough to maintain level flight. If stalled wings produced NO lift, the airplane would literally fall out of the sky like a rock once stalled. The airplane is still "flying" in a stall, it is just descending, and not producing lift as efficiently with turbulent airflow over the wings vs. streamline airflow.
Not sure your point, but you are not speaking to his point, which was that if you stall at very low altitude and dump the nose down too much to unstall the airplane and try to regain flying speed, you will become a lawn dart. You want to unstall the airplane, avoid excessive descent rate, and regain flying speed while losing as little altitude as possible. This requires minimizing the forward movement of the yoke/stick to unstall the airplane. It also requires full power.
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Jaybird180
Final Approach
Roscoe and Dan seem to belive that power and stalls are tied together. They are not. In fact, there are cases where power can aggravate a stall.
Discussion: P-A-R-E
Power (idle)
Aileron (neutralize)
Rudder (not applicable to this discussion - but the mnemonic is opposite spin)
Elevator (briskly forward and held until stall breaks)
This is the universal spin recovery technique which is required academics for stall recovery (cannot spin if you're not stalled - spiral is different)
Discussion: P-A-R-E
Power (idle)
Aileron (neutralize)
Rudder (not applicable to this discussion - but the mnemonic is opposite spin)
Elevator (briskly forward and held until stall breaks)
This is the universal spin recovery technique which is required academics for stall recovery (cannot spin if you're not stalled - spiral is different)
Jaybird180
Final Approach
They do fall out of the sky. Just because training airplanes typically begin recovery with minimal pilot input is not germane to the academics of stall recovery.
dtuuri
Final Approach
Never heard of a "deep stall"? I think there are degrees, so yes, a plane can be "less stalled".
dtuuri
Not following the reason for your tangent. If you stall at 50' on final. I surely suggest you apply full power during stall recovery if you would like to avoid a very unfortunate arrival. I don't know what your simple non-statement of "power and stalls are not tied together" is supposed to mean.
You are severely lacking in aerodynamic knowledge. Stalled wings do in fact create quite a bit of lift. So if you go up in your 172, pull power off, and hold the yoke fully aft, you think this is the same thing as a rock falling to the ground? The same thing as the airplane suddenly not having wings at all? The airplane is still flying - just not very efficiently.
Critical AOA in most airplanes is typically between 15-20 degrees. The bottom surface of the wing will still push quite a bit of air downward when flying at this AOA. The top surface may be turbulent, which reduces the total downwash of air, or "lift", but quite a bit of lift is still generated when the wing is stalled. Just like sticking your hand out of the car window at a 20 degree angle. You are in need of some aerodynamic education. Nothing wrong with being ignorant, but it's the arrogant ignorance that makes internet forums such unpleasant places at times.
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Jaybird180
Final Approach
1 - I didn't bring speed and power into the discussion. Someone else did, I just responded. [edit] Adding power is part of the recovery phase (pullout) but not breaking the stall.
2- C-172 is a poor example of stalls during an academic discussion of the subject matter. And from a purely academic perspective, stalled wings produce no lift.
There is no arrogance or rancor in my statements.
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Jaybird180
Final Approach
Unfortunately, that article misses proving a definition, as there may be many depending upon context. Many people think of them as successive recovery and secondary stall conditions. I do not think that is a matter of degree of stalls rather stall > recovery > stall ....
[edited answer]
the article does provide a definition, but it's unrelated to the discussion:
A deep stall (or super-stall) is a dangerous type of stall that affects certain aircraft designs,[27] notably those with a T-tail configuration. In these designs, the turbulent wake of a stalled main wing "blankets" the horizontal stabilizer, rendering the elevators ineffective and preventing the aircraft from recovering from the stall.
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dtuuri
Final Approach
Then why not just say "reduce the angle of attack"? I don't know how many times I've heard pilots say they "unload the wing" to prevent a stall during a steep bank from base to final. Of course, it might not stall, but it won't turn either. Somehow the concept of "unloading" seems to lead to a thinking that it's sort of a free lunch on the part of many pilots, IMHO.
dtuuri
Dan Thomas
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Dan Thomas
You're talking about a spin recovery there, not a simple stall recovery. Power in stall recovery alters the airplane's glidepath, flattening it and reducing the AoA by adding thrust. An airplane will climb at full power in the same pitch attitude that a power-off stall can occur, so the power is making a difference in the AoA.
Dan
You responded with an inarticulate statement that is unclear on the point you're making and how it applies the Dan's statement about using power during stall recovery. I still don't know what the heck you're trying to get at with respect to the statements Dan made. Do you disagree that adding power during a stall recovery minimizes descent rate and altitude loss? Maybe you should go back and re-read the post, because your comments basically went off the tracks. Or you maybe you get it, and the rest of us just don't.
So there is something unusual about a 172? What would be a better example? A Cherokee? Not sure what this supposed "academic perspective" is. Academia is the accumulation of knowledge. If you want to talk academia, you can't ignore physics and aerodynamics. To say wings produce no lift, and that the airplane actually falls out of the sky like a rock when stalled is not a very "academic perspective".
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dtuuri
Final Approach
HOWEVER.. a deep stall doesn't happen at the break (necessarily, although perhaps it might). It happens as the angle of attack increases enough that the down wash envelopes the T-tail making recovery impossible. Recognize it soon enough, and you won't go there. Delay at your peril.
dtuuri
MooneyDriver78
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Tom
I was taught that buffeting was onset or partial stall, the break was a full stall.
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James331
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James331
Practice falling leaf stalls, ride the thing down 3-4k feel and that'll fix ya.
Spin training is a really good idea, I did it before solo.
Best thing isn't to do it in some acro plane you're not going to fly again, do it in a airframe that most closely resembles what you're going to be flying on the norm.
Also you don't need a parachute for spin training, unless your CFI doesn't know what he's doing (and has rather poor airmanship). If you don't know how to jump from a plane and/or get stable and deploy a parachute, it is kinda a odd thing to bother with anyway.
Spin training is a really good idea, I did it before solo.
Best thing isn't to do it in some acro plane you're not going to fly again, do it in a airframe that most closely resembles what you're going to be flying on the norm.
Also you don't need a parachute for spin training, unless your CFI doesn't know what he's doing (and has rather poor airmanship). If you don't know how to jump from a plane and/or get stable and deploy a parachute, it is kinda a odd thing to bother with anyway.
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Jaybird,
All that is necessary to break a stall is to bring the relative wind closer to the chord line of the wing (closer for the sake of this discussion being less than the critical angle of attack). You can do this by moving the elevator, which in turn moves the wing in relation to the wind, or by moving the whole plane with power, or a combination of the above. There are certainly airplanes that can fly out of a stall without pushing on the yoke/stick (in an upright stall).
With regard to the stall-recovery-stall nose bob deal, this is because the cg is ahead of the center of lift and when stalled, the plane begins to rotate about the center of lift due to the moment from the center of gravity. If your CG and center of lift were in the same place there would be no uncommanded nose drop. you would be stalled, nose high. Some planes with a CG far enough aft and lots of elevator authority and some power can probably get into a similar condition, but I haven't flown any that do.
This whole "all or nothing" view of a stalled wing is bogus. Go fly something with aft CG and a lots of elevator authority, go up real high and ride a stall down and play with it. Fighter jets can fly WAY beyond the critical angle of attack. Google "NASA high alpha research".
All that is necessary to break a stall is to bring the relative wind closer to the chord line of the wing (closer for the sake of this discussion being less than the critical angle of attack). You can do this by moving the elevator, which in turn moves the wing in relation to the wind, or by moving the whole plane with power, or a combination of the above. There are certainly airplanes that can fly out of a stall without pushing on the yoke/stick (in an upright stall).
With regard to the stall-recovery-stall nose bob deal, this is because the cg is ahead of the center of lift and when stalled, the plane begins to rotate about the center of lift due to the moment from the center of gravity. If your CG and center of lift were in the same place there would be no uncommanded nose drop. you would be stalled, nose high. Some planes with a CG far enough aft and lots of elevator authority and some power can probably get into a similar condition, but I haven't flown any that do.
This whole "all or nothing" view of a stalled wing is bogus. Go fly something with aft CG and a lots of elevator authority, go up real high and ride a stall down and play with it. Fighter jets can fly WAY beyond the critical angle of attack. Google "NASA high alpha research".
Jaybird180
Final Approach
I will admit to a misinterpretation, if you all are willing to join me.
Take a look at this
https://www.grc.nasa.gov/www/k-12/airplane/incline.html
and you can see that we were close, but not quite right.
Wings do lose lift abruptly post stall, but as the article states, it is difficult to mathematically describe and or plot in wind tunnel tests. This explains why the graph terminates. The suggestion of quite a bit of lift after the break, is a radical departure from the truth.
When I mentioned that power is not as related as was advanced, I was referring to simply the actions required to break a stall. Yes, the addition of power aids in recovery and helps to arrest altitude loss quicker, but we must be careful that we do not create mental connections that power can save a stall (unless you're flying something with sufficient excess thrust sufficient to do a Viking Departure or Cobra Maneuver).
The prop creates prop wash which reduces AoA, and forward Cg assists by initiating corrective actions for the pilot. (Most of our airplanes also contain washout at the wing tips which help keep the outboard potions flying a bit longer that the inboard portion of the wing.) Thrust also assists by encouraging the relative wind, and it is this (relative wind) that is responsible, not the increasing whirring of the fan. May seem a trifle distinction but it's more than semantics.
Personally, I am comforted by knowing that I can unload the wing to break any stall, provided I can reduce load factor to the necessary value approaching 0G, because I KNOW a wing can never stall there (even beyond critical AoA), and hence my reason for mentioning it.
Take a look at this
https://www.grc.nasa.gov/www/k-12/airplane/incline.html
and you can see that we were close, but not quite right.
Wings do lose lift abruptly post stall, but as the article states, it is difficult to mathematically describe and or plot in wind tunnel tests. This explains why the graph terminates. The suggestion of quite a bit of lift after the break, is a radical departure from the truth.
When I mentioned that power is not as related as was advanced, I was referring to simply the actions required to break a stall. Yes, the addition of power aids in recovery and helps to arrest altitude loss quicker, but we must be careful that we do not create mental connections that power can save a stall (unless you're flying something with sufficient excess thrust sufficient to do a Viking Departure or Cobra Maneuver).
The prop creates prop wash which reduces AoA, and forward Cg assists by initiating corrective actions for the pilot. (Most of our airplanes also contain washout at the wing tips which help keep the outboard potions flying a bit longer that the inboard portion of the wing.) Thrust also assists by encouraging the relative wind, and it is this (relative wind) that is responsible, not the increasing whirring of the fan. May seem a trifle distinction but it's more than semantics.
Personally, I am comforted by knowing that I can unload the wing to break any stall, provided I can reduce load factor to the necessary value approaching 0G, because I KNOW a wing can never stall there (even beyond critical AoA), and hence my reason for mentioning it.
Jaybird180
Final Approach
Ianovic said:
NASA cheated. They used thrust vectoring and other trickery. So I consider the High Alpha stuff irrelevant.
Jaybird180
Final Approach
Deep stall is irrelevant to the discussion
Jaybird180
Final Approach
Buffeting is the boundary layer breaking and restabilizing. A warning per se.
The airfoil (better term than saying wing as wings typically contain different aerodynamic zones) either is stalled or it is not. It's that simple.
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dtuuri
Final Approach
How do you envision a scenario in which you could possibly have an AoA "beyond critical" (or not, for that matter) and at the same time have 0G?
dtuuri
dtuuri
Final Approach
It's relevant to the notion you've now retreated from that there is no such thing as a "less stalled" wing. If there wasn't, you would recover from a stall, in your language, by "unloading the wing" even by the slightest amount. You know in your heart the deeper the stall, the more "unloading" you need to do. (Gee, I really hate using that language.
)dtuuri
gismo
Touchdown! Greaser!
Because most GA airplanes have no AoA display and without that how do you know when you've reduced the AoA? As already pointed out with a wing stall, the AoA increases even if the pitch attitude remains unchanged. That said, I have no problem if we substitute Reduce the AoA" for "unload the wing" as they are virtually synonymous.
To me, unloading is a "seat of the pants" thing. IOW you can easily feel when you've reduced the AoA by virtue of a lessening of the g force your body is subjected to.
You can lower the AoA in a steep bank but (assuming you maintain coordination) as you say the resulting loss of lift means the plane will be accelerating towards the ground and at some point you'll have to pay back the g loading. The turn won't stop however unless you reduce the g force to zero. Reducing the g load to that required for a level turn at a smaller bank angle does result in a shorter turn radius than you'd get using that smaller bank angle in level flight. For example a 45° bank in a level turn requires ≈1.4g and a 35° bank in level flight takes ≈1.22 g. The turn rate in a 45° bank while pulling 1.22 g generates a turn rate more than 23% greater than a level turn with a 35° bank.
dtuuri
Final Approach
I suppose that could be true if the accelerating, corkscrewing dive doesn't kill you first. I'd like to see the mathematics with realistic numbers for salvaging a turn gone bad from base to final. How much altitude would you lose, speed would you gain vs radius you would shorten with the bank angles you gave?
dtuuri
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Jaybird180
Final Approach
It's relevant to the notion you've now retreated from that there is no such thing as a "less stalled" wing. If there wasn't, you would recover from a stall, in your language, by "unloading the wing" even by the slightest amount. You know in your heart the deeper the stall, the more "unloading" you need to do. (Gee, I really hate using that language.
dtuuri
You're either stalled or not. I haven't been convinced otherwise.
Jaybird180
Final Approach
Simple: if I pull my AoA beyond critical, the wing stalls. If I want to live and recover right now, I PUSH (not just relax) the yoke and the wing immediately begins flying again.
1600vw
Pattern Altitude
My comment was not about lift but about loading of a wing. My point was even in a negative G, the wing is loaded just loaded to the underside. Its not a comment about lift.
Tony
Jaybird180
Final Approach
I reviewed post 47 and 53 to try to understand what you mean 
dtuuri
Final Approach
That isn't what I was looking for. You wrote, re: 0G, "...I KNOW a wing can never stall there (even beyond critical AoA)..." So, I asked:
because "even beyond critical AoA" there is still some lift and you won't be at 0G. If you think you can have one without the other, I suspect you're mistaken--at least as far as normal flight regimes go. Then the next thing is, you'll be "unloading your wing" from base to final, so as to tighten your turn without any penalty. That's a big no-no, IMO.
dtuuri
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