Stall Questions

TrinidadGT20

Vice President of Awesome
I was watching a Sporty's private pilot tape and they talked extensively about stalls. One of the statements they made was the landing is a "controlled stall". If the method to recover from a stall is to push forward on the control yoke, what happens if you stall too close to the ground? Are stalls close to the ground common? A stall close to the ground has got to be dangerous. How do you recover from a stall close to the ground? As always, thanks in advance for any replies...
 

Redbirdfan

New Member
whenever you operate close to the ground you have to be extra carefull not to get yourself into a stall. This is the reason you never use more than 30 degrees of bank in the traffic patter, as bank increases stall speed. If you get yourself into a stall close to the ground, perform exactly the same recovery you do at 3000 AGL. That's why you're learning it in the first place. Instead of Power on and Power off stalls I like to refer to them as Departure stalls and Approach stalls, because that's what they're really meant to simulate.
 

RiddlePilot

New Member
I think you're thinking about this the wrong way. Of course it's bad to be in a stall close to the ground if you're on approach or departure, but it's sound technique to stall the aircraft just prior to touchdown during landing.
 

Wm226

New Member
The "controlled stall" is done during the "flare" portion of your landing. Hence the stall horn on most landings during flares.

A good landing is a stall but just close to the runway. Just don't bounce/balloon... whatever you want to call it by flaring too high up above the runway.
 

PhotoPilot

New Member
Stalls are practiced so that a pilot can recognize the approaching and imminent stall before the wings reach the fully stalled condition. By doing so, a pilot should be able to recognize the approaching stall before it is well established and recover with zero to 50 feet of altitude loss. When we practice full stalls we can often recover in 100 feet or less. The goal in practicing is the recognition and avoidance of the approach of a stall, not the stall itself.

Also, I would agree that certain short field landings should be ALMOST a full-stall landing, but most landings can be performed without coming close to a stalled condition. A nose up pitch attitude and a low- or no-power setting when applied correctly will allow you to touch down safely above the stalling point but in a speed region that still allows for a slow loss of altitude due to insufficient airspeed at the given angle-of-attack. Unless touching down at the absolute minimum speed is required for a particular landing, I would prefer to have an extra 5 or 8 or 10 knots to disipate on the ground in exchange for better go-around performance, more rudder authority, and positive airplane control to the ground. A greaser can easily be made with no floating, bouncing, or ballooning at an airspeed above/angle of attack less than a stall.
 

MidlifeFlyer

Well-Known Member
Let's separate two concepts here. One is that, for purists, the landing touchdown should be on the very edge of a stall, or even, as some have described, a "controlled stall"

I'll assume you are not talking about that, but rather, what happens/what do you do if the airplane stalls, say, 15' above the ground.

You recover from that kind of stall exactly the same way as the stall at 2000 AGL. Ask yourself these questions:

1. When the airplane is in a stall, is it flying or not flying?
2. Why do we reduce angle of attack to recover from the stall?
3. If you hit the ground, is it better to be under control or out of control?
4. What is the =best= case scenario if you =don't= recover from the stall?
5. What's the =worst= case scenario if you =do= recover from the stall?

PS: Of course it's dangerous to stall near the ground. That's why we practice stall recognition.
 

Wm226

New Member
Just to add...

All those practice power off/on stalls you do at safe altitudes are done to simulate stalls closer to the ground as well. Your goal is to minimize altitude loss upon the break to a stall.

As said above... learn to recognize a stall and MOST IMPORTANTLY: KEEP IT FROM HAPPENING.

In addition, stalls are often caused by pilot distractions.

Conclusion: don’t get distracted; fly the airplane first!
 

jdflight

Well-Known Member
Just to clarify an earlier point. It's not that you never use more than 30 degrees of bank in the pattern. It is perfectly acceptable to do so, provided you understand the bank/load factor/stall speed relationship and factor it into your decision to cross that 30 degree threshold. Face it, we make mistakes. One of those is overshooting with parallel runways. If I see that happening, I have no problem increasing my bank to decrease my radius. I also understand that I'm operating closer to my stall speed, now.
 

SteveC

Really?
Staff member
[ QUOTE ]
Just to clarify an earlier point. It's not that you never use more than 30 degrees of bank in the pattern. It is perfectly acceptable to do so, provided you understand the bank/load factor/stall speed relationship and factor it into your decision to cross that 30 degree threshold. Face it, we make mistakes. One of those is overshooting with parallel runways. If I see that happening, I have no problem increasing my bank to decrease my radius. I also understand that I'm operating closer to my stall speed, now.

[/ QUOTE ]
Actually, you *might* be operating closer to your stall speed. The book figures of increased stall speed based on bank angle are predicated on increasing back pressure to maintain altitude (resulting in an increased angle of attack). If you decrease back pressure, or even push forward on the stick, it is possible to *decrease* your angle of attack, and in fact *decrease* the indicated speed that you will stall, thus resulting in you being *farther* from a stall instead of closer. Remember, you stall based on Angle Of Attack, not indicated air speed.

Not advocating a high bank angle and strong push-over at low altitude, though. Ground comes up awfully fast when you do that. Just pointing out that increased bank angles do not necessarily mean that stall speed goes up.
 

MidlifeFlyer

Well-Known Member
[ QUOTE ]
Actually, you *might* be operating closer to your stall speed. The book figures of increased stall speed based on bank angle are predicated on increasing back pressure to maintain altitude (resulting in an increased angle of attack). If you decrease back pressure, or even push forward on the stick, it is possible to *decrease* your angle of attack, and in fact *decrease* the indicated speed that you will stall, thus resulting in you being *farther* from a stall instead of closer. Remember, you stall based on Angle Of Attack, not indicated air speed.

[/ QUOTE ]This sort of came up on a discussion of steep spirals without being resolved. Maybe you know enough about aerodynamics to answer it.

The increased AOA in a level turn is because of increased load factor resulting from the two lift vectors needed for the wings to support both maintaining altitude and the turn itself.

So "it sounds" like AOA would be less in a descending turn since altitude isn't being maintained. But is that accurate? Aren't the lift/weight/thrust/drag vectors in equilibrium in any steady state flight, whether straight, climbing or descending? Isn't the AOA pretty much the same for a stable descent as it is for level flight at that same airspeed (the relative wind is still coming straight at the airplane - the airplane's direction is downward; the relative wind is upward). Isn't an airplane in a straight ahead descent with a stabilized airspeed and descent rate pulling 1G? If that's the case, bank angle should still affect G-loading realtive to straight flight, which means increased load factor and increased stall speed.
 

SteveC

Really?
Staff member
[ QUOTE ]
This sort of came up on a discussion of steep spirals without being resolved. Maybe you know enough about aerodynamics to answer it.

[/ QUOTE ]
I'm really pretty weak at aerodynamics. I try to stick with *practical* stuff that I can use day-to-day.

[ QUOTE ]
The increased AOA in a level turn is because of increased load factor resulting from the two lift vectors needed for the wings to support both maintaining altitude and the turn itself.

[/ QUOTE ]
The way that I think of it is that the AOA has increased because I'm pulling back on the stick/yoke to maintain altitude. I like to oversimplify and think of the elevator as my AOA controller.

[ QUOTE ]
So "it sounds" like AOA would be less in a descending turn since altitude isn't being maintained. But is that accurate? Aren't the lift/weight/thrust/drag vectors in equilibrium in any steady state flight, whether straight, climbing or descending? Isn't the AOA pretty much the same for a stable descent as it is for level flight at that same airspeed (the relative wind is still coming straight at the airplane - the airplane's direction is downward; the relative wind is upward).

[/ QUOTE ]
I don't like to think in terms of all those vectors, just relative wind. Yes, I believe that the AOA *can* be the same in a descending turn as it is during level flight. It all depends on what you are doing with the elevator to control the rate of descent. Pull back to slow the rate of descent, AOA goes up. Push forward and you will reduce the AOA.

[ QUOTE ]
Isn't an airplane in a straight ahead descent with a stabilized airspeed and descent rate pulling 1G? If that's the case, bank angle should still affect G-loading realtive to straight flight, which means increased load factor and increased stall speed.

[/ QUOTE ]
Only if, when you enter the turn you increase the force on the elevator to maintain the same descent rate. If you allow the descent rate to increase as you increase the angle of bank you can maintain the same AOA, with no resultant change in indicated stall speed.

You can put a plane in a 90 degree bank without stalling. You can do it without increasing stall speed by even 0.0001 knot. You will have to accept a high descent rate (i.e. falling like a rock), but the stall speed is not affected by bank angle (at least not directly) but by Angle Of Attack. Stalls have everything to do with the direction that the air is hitting the wings (AOA), and nothing to do with the plane's attitude (other than how the attitude is related to the movement of the plane).

Don't ask me to explain the aerodynamics, though.
 

PhotoPilot

New Member
According to my understanding, you are correct. The increase in stall speed is due entirely to the load factor which increases the effective weight of the force on the wings. That means that, to maintain level flight at the critical angle of attack, the airflow over the wing must be faster to maintain enough lift to counteract the added 'weight.' If, however, you do not create a load factor in the turn, the stall speed remains the same as there is no extra weight to counter.

Do those steep spirals without adding load factor and your stall speed is the same as in level flight. You'll have to accept an increase in the rate of altitude loss as you steepen your bank, however.
 

E_Dawg

Moderator
Just because you're descending doesn't mean the stall speed won't rise (I know no one said that).

Sure your AOA won't increase if you don't add back pressure, but your turn rate won't be much either unless you allow the airplane to accelerate downwards (VSI decreasing) while turning. Chances are you are already pretty close to the ground if you're on base - final so that's not an option unless you're high.

Probably the best way to figure how close to stall you are is by sound and feel regardless of bank and airspeed. Stall increases as sq root of load factor, so anytime you feel heavy, you're stall speed is higher regardless of climb/descent/airspeed/back pressure.
 

MidlifeFlyer

Well-Known Member
[ QUOTE ]
The way that I think of it is that the AOA has increased because I'm pulling back on the stick/yoke to maintain altitude. I like to oversimplify and think of the elevator as my AOA controller.


[/ QUOTE ]Go ahead. I'll avoid the obvious, "so it you trim off the pressure in a steep turn your AOA decreases?"


Instead, try this.

At altitude start a 500 fpm straight ahead descent at 80 knots and trim it off. Now put the airplane into a 45º bank and maintain that 500 FPM descent. I bet you pull back. When level you pulled back to maintain a 0 descent rate. Now you'll pull back about as much to maintain the 500 FPM.
 

MidlifeFlyer

Well-Known Member
[ QUOTE ]
Do those steep spirals without adding load factor and your stall speed is the same as in level flight. You'll have to accept an increase in the rate of altitude loss as you steepen your bank, however.

[/ QUOTE ]I think that's right. And they key to what you say is "an increase in the rate of altitude loss." You'd have to accept a continually increasing rate of descent. The load factor is not increasing so long as your rate of descent continues to increase (accelerate). Once it stabilizes, probably because you're applying back pressure to keep that spiral descent from becomming a spiral dive,
, load factor begins to increase again.
 

PhotoPilot

New Member
Agreed, Midlife. I'm not suggesting that a zero-load factor steep spiral is the correct way to perform the maneuver or that it would have a more satisfactory outcome than the standard method. In reality, the increase in load factor during a steep spiral ups the stall speed only very slightly and it shouldn't be an issue if you maintain the appropriate airspeed.

During a base-to-final turn, the increase in load factor would have a much more serious effect because your airspeed would probably be much lower. However, proper planning and traffic pattern profiles should avoid the need for steeper banks in the pattern. We all know that the majority of fatal accidents occur during approach or landing, so extra caution and careful planning should be used.

Fly carefully out there!
 

SteveC

Really?
Staff member
[ QUOTE ]
[ QUOTE ]
The way that I think of it is that the AOA has increased because I'm pulling back on the stick/yoke to maintain altitude. I like to oversimplify and think of the elevator as my AOA controller.


[/ QUOTE ]Go ahead. I'll avoid the obvious, "so it you trim off the pressure in a steep turn your AOA decreases?"


[/ QUOTE ]
Nope. Force on the elevator doesn't change when you trim. You're just balancing the *apparent* force that the pilot feels at the yoke.
[ QUOTE ]
Instead, try this.

At altitude start a 500 fpm straight ahead descent at 80 knots and trim it off. Now put the airplane into a 45º bank and maintain that 500 FPM descent. I bet you pull back. When level you pulled back to maintain a 0 descent rate. Now you'll pull back about as much to maintain the 500 FPM.

[/ QUOTE ]
I think we're saying the same thing. Go back and read mine again.
 

say_speed

New Member
I don't know if this is going to help or not...
I try to think in term of weight. To maintain altitude, the wings have to produce a certain weight. As bank angle increases, (if you want to maintain altitude), the wings have to create more wieight, therefore you have to increase AOA. Since the wing stalls at a determined AOA, by increasing the AOA, you are reducing the margin between the critical AOA and actual AOA, so you will reach the critical AOA earlier, therefore stall at a higher indicated speed. Crystal clear?
 

say_speed

New Member
I think we went away fro the original discussion about the landings...
Here is my view on that: it is always dangerous to stall the airplane close to the ground, but if I heard the stall warning at 20 ft, I would not recover by pushing the stick forward... I would add power, and just ease the back pressure on the yoke. Ground effect will also help.
I don't think it is a good practice to stall the airplane just before touchdown; you can make a smooth landing without having the stall horn coming off.
The reason why we practice stalls in different configurations is because a lot of accidents involved stalls in the traffic pattern (not on landing though), when turning from base to final, on take-off, ...
 
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