Doug Rozendaal on stalls, stall speed and bank angle

Martin Pauly

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Martin Pauly
This is a conversation I recorded with Doug Rozendaal about stalls, stall speed and its relationship (or lack thereof) with bank angle. As Doug says, "sacred cow hamburger tastes best", so in that spirit we try to explain what is fact and what is myth.

- Martin

 
He is right, dead right. He also seems to assume CFIs aren’t taking time to teach the cause of stalls isn’t the pilot doing dumb things with the elevator.
 
The link below from Pilotworkshops Tip of the Week has a pretty decent discussion of this topic.

Stall Speed While Banked and Descending

Edited to add:

This is the basis of the discussion.

"I’m familiar with charts showing how stall speed increases with bank angle. But my new CFI says that chart only applies if you’re maintaining altitude. Is that true?" — Colin R.

“Your CFI is wrong. The bottom line is as long as your vertical speed is constant, a given bank will raise your stall speed the same regardless of whether you’re level, climbing, or descending."
 
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The link below from Pilotworkshops Tip of the Week, has a pretty decent discussion of this topic.

Stall Speed While Banked and Descending
Thanks for this link. Yes, descending doesn't make a difference - it's all about acceleration, or a downwards movement of your VSI (i.e. increasing rate of descent, or decreasing rate of climb if you started in a climb).

- Martin
 
if you're trimmed and not pulling, then bank the plane, as long as you don't change the trim and don't start pulling, stall speed is unchanged by the bank.
 
if you're trimmed and not pulling, then bank the plane, as long as you don't change the trim and don't start pulling, stall speed is unchanged by the bank.

If the load factor isn't changed, stall speed is unchanged... But vertical speed will accelerate downwards.
 
Thanks for this link. Yes, descending doesn't make a difference - it's all about acceleration, or a downwards movement of your VSI (i.e. increasing rate of descent, or decreasing rate of climb if you started in a climb).

- Martin
If we let the nose fall in the base-to-final turn so that the airplane is accelerating downward, we are going to have to stop that at some point, or crash. We need to raise the nose to stop it, and that adds load factor, the very thing we were attempting to avoid when we let the nose fall.

One thing not mentioned in the video is the pilot who buzzes the runway or a friend's acreage and pulls up hard to get that spectacular zoom, maybe with a turn thrown in for even more effect. The airplane suddenly stalls and spins in instantly. That one kills way too many people. They don't understand the load factor/AoA relationship at all, and physics doesn't care about their ignorance. Even an AoA indicator or a stall horn won't save them, as things happen just too fast there. Gimmicks are no substitute for proper training.
 
He is right, dead right. He also seems to assume CFIs aren’t taking time to teach the cause of stalls isn’t the pilot doing dumb things with the elevator.
Certainly CFIs are teaching. And the pilot remembers that stuff. For a while.
 
If we let the nose fall in the base-to-final turn so that the airplane is accelerating downward, we are going to have to stop that at some point, or crash. We need to raise the nose to stop it, and that adds load factor, the very thing we were attempting to avoid when we let the nose fall.
Yes, but 1) that can be done after removing the bank, or 2) adding a little power to counter the additional descent rate.
 
...soooooo much mental masturbation just to avoid teaching angle of attack.

Nauga,
indexed
I believe discussion this is nothing more than delving into the nuances of aoa more completely than is usually done.
 
I believe discussion this is nothing more than delving into the nuances of aoa more completely than is usually done.
I'm glad you deleted the 'teaching aoa' part you originally posted but 'delving into the nuances of aoa' without introducing aoa into the discussion is the mental masturbation I was referring to. As for the 'usually done' part, you'll need to better define the scope of your 'usual,' as in my experience (scope) the relationship between AOA and stall is fundamental, and usually (again, in my experience) presented as such.

What's the stall speed of an airplane doing a level knife-edge pass?

Nauga,
unitized
 
Kinda sounds like you didn’t watch the whole video.
 
Kinda sounds like you didn’t watch the whole video.
I'm not talking about the video. I'm talking about the thread.

Nauga,
and the litany of special cases that boil down to AOA.
 
if you're trimmed and not pulling, then bank the plane, as long as you don't change the trim and don't start pulling, stall speed is unchanged by the bank.

The airplane will begin a descent and airspeed will increase. In any aircraft with positive static stability this will increase the angle of attack even without pilot input.
 
If we let the nose fall in the base-to-final turn so that the airplane is accelerating downward, we are going to have to stop that at some point, or crash. We need to raise the nose to stop it, and that adds load factor, the very thing we were attempting to avoid when we let the nose fall.

One thing not mentioned in the video is the pilot who buzzes the runway or a friend's acreage and pulls up hard to get that spectacular zoom, maybe with a turn thrown in for even more effect. The airplane suddenly stalls and spins in instantly. That one kills way too many people. They don't understand the load factor/AoA relationship at all, and physics doesn't care about their ignorance. Even an AoA indicator or a stall horn won't save them, as things happen just too fast there. Gimmicks are no substitute for proper training.

I have posted several times the math that shows how increasing the bank without adding load factor will result in an uncontrollable descent with a pegged VSI in a matter of seconds. Yet there is a movement where every time the topic of load factor increasing in a turn comes up a bunch of pseudo-intellectualists have to jump in and announce the false claim of "bUt tHAT's OnlY in LevEL fligHt!!!1"
 
Great video.

Amazing how many instructors do exactly what Doug picks on.
 
I have posted several times the math that shows how increasing the bank without adding load factor will result in an uncontrollable descent with a pegged VSI in a matter of seconds. Yet there is a movement where every time the topic of load factor increasing in a turn comes up a bunch of pseudo-intellectualists have to jump in and announce the false claim of "bUt tHAT's OnlY in LevEL fligHt!!!1"
I have yet to go out of control into the ground when banking harder and not pulling back on base to final. Just lucky I guess.
 
Your load factor isn't 1 then. Math doesn't lie.
It might be only 1, but at the cost of an accelerating descent rate. The problem with that has to do with the eventual recovery: it takes AoA and therefore considerably more load factor to stop that descent, and close to the ground, at approach speed, that's not desirable. A controlled load factor increase in the turn is much safer.

There are no freebies in physics. The folks that think that not pulling back in the turn is safer are not accounting for the loads in slowing the descent, loads that can kill in a place like that.
 
It might be only 1, but at the cost of an accelerating descent rate. The problem with that has to do with the eventual recovery: it takes AoA and therefore considerably more load factor to stop that descent, and close to the ground, at approach speed, that's not desirable. A controlled load factor increase in the turn is much safer.

There are no freebies in physics. The folks that think that not pulling back in the turn is safer are not accounting for the loads in slowing the descent, loads that can kill in a place like that.

Salty was saying his descent rate has never gone out of control at steep bank angles at load factor of 1...I'm just saying both can't be true. Otherwise we agree completely.
 
it’s pretty easy to add a little power to counter the loss of lift. And I like to be a bit high anyway, so can afford to lose a bit.

You don’t need extra aoa to recover, go back to wings level and you get your lift back without increasing aoa.

Im not sure how lose of control enters into it. :confused:
 
Salty was saying his descent rate has never gone out of control at steep bank angles at load factor of 1...I'm just saying both can't be true. Otherwise we agree completely.
Not at all. I’m saying I never went out of control and crashed into the ground because of it. You’re making it sound much worse than reality. A bit more power, or start with extra altitude and nothing to worry about.
 
Not at all. I’m saying I never went out of control and crashed into the ground because of it. You’re making it sound much worse than reality.

You're saying you can make a stabilized, safe descent in the traffic pattern at steep bank angles without increasing the load factor and that is a provably false conclusion.
 
Ok, I'm curious. Show your math.

If my math is right, you still have 75% of your lift at a 40deg bank. For maybe 10 seconds at most I would think. Hardly going to create a crater from 750 feet.
 
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Ok, I'm curious. Show your math.

If my math is right, you still have 75% of your lift at a 40deg bank. For maybe 10 seconds at most I would think. Hardly going to create a crater from 750 feet.

I don't consider a 40 degree bank to be steep so I'll use 45, which would reduce the vertical component of lift by 29.3%. Acceleration due to gravity is 32fps/s or 1920fpm/s. Acceleration at 29.3% that rate is 563fpm/s. That's slightly under four seconds to peg a 2000fpm VSI.
 
I don't consider a 40 degree bank to be steep so I'll use 45, which would reduce the vertical component of lift by 29.3%. Acceleration due to gravity is 32fps/s or 1920fpm/s. Acceleration at 29.3% that rate is 563fpm/s. That's slightly under four seconds to peg a 2000fpm VSI.
Well, first off, I don't think I've ever pulled a 45 degree bank on a base to final turn, but....

2000 fpm for 10 seconds is 333 feet. A bit of power will overcome most of that. No smoking crater.
 
Actually, I think you can do a 90 degree turn in a 45 degree bank at 70 knots in less than 6 seconds. so that's 200 feet if you stayed in the bank for the enter turn, which sounds pretty crazy to me.

So maybe we agree? Don't pull a 45 degree bank for an entire base to final turn. Sure, I can agree with that.
 
2000 fpm for 10 seconds is 333 feet. A bit of power will overcome most of that. No smoking crater.

It's ~2,000 fpm after four seconds. Not 10 seconds. At 10 seconds it's 5,630 fpm.
 
Actually, I think you can do a 90 degree turn in a 45 degree bank at 70 knots in less than 6 seconds. so that's 200 feet if you stayed in the bank for the enter turn, which sounds pretty crazy to me.
That 6 second turn is not at 1g though. If you don't increase the total lift, the horizontal component of lift will be less than a normal turn. Since it's a 45 degree bank and the vertical component is 29% less, the horizontal component is also 29% less. Making your 45° 1g turn more like a 35° turn. The turn will take approximately 11 seconds and will lose 570 feet, not to mention you will have a 6,193 fpm descent rate to arrest at the end of the turn, which you are ignoring. You can't arrest such a descent rate without increasing the load factor far above what it would have been if you just performed a normal, stable turn where the weight is balanced by VCL in the first place.

In other words, it's f**cking stupid to pretend that you can turn without increasing the load factor. And it's stupid to tell people stall speed doesn't increase in descending turns. It's going to kill people.
 
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In other words, it's f**cking stupid to pretend that you can turn without increasing the load factor.

"Use the bank angle that you need to execute a good, smooth clean pattern and if you are banking don't pull back on the yoke 'cause if you don't pull back on the yoke the airplane's not going to stall."


While it won't stall, it won't turn either, so this statement in the OP's video can be misinterpreted because it is contradictory.
 
"Use the bank angle that you need to execute a good, smooth clean pattern and if you are banking don't pull back on the yoke 'cause if you don't pull back on the yoke the airplane's not going to stall."


While it won't stall, it won't turn either, so this statement in the OP's video can be misinterpreted because it is contradictory.
Uh. Ok, so if it doesn't turn, where is the energy going that was lost due to the bank?
 
ok. where did the lift go, since now we are plummeting to our death and not turning?
Let me say it my way, "In order to turn, i.e., deflect the flight path, you need to use the wing (more surface area than, say, the side of the fuselage) by pulling the stick. That incurs load factor as the result. If you don't have load factor, you aren't deflecting the flight path. Some might say it's centrifugal force, which is fine by me. Don't have much of it? You don't have much of turn either."
 
To sum up the comments on this thread, we have gone from "If you bank you will stall and die" to "If you bank you will fall and die". Interesting...
 
To sum up the comments on this thread, we have gone from "If you bank you will stall and die" to "If you bank you will fall and die". Interesting...
I find it amazing how intelligent, experienced pilots can disagree so much on a fundamental. And I'm not including myself in that group.
 
Time to go back to the textbooks. You cannot turn the airplane without banking (unless you skid it around in a flat turn, which is not only dangerous but takes a long time and uses up a lot of airspace), and you cannot get the coordinated turn without using some elevator. The wing, in the bank, is not only lifting the airplane, but is deflecting its flight path toward the banked side. Asking it to do both jobs increases its workload, which requires increased AoA.

If one just uses rudder in the turn, no elevator, the nose heads for the ground faster. This should be self-evident; in a left bank, left rudder will lift the tail and lower the nose. And in any bank, raising the elevator will not only raise the nose but point it farther toward the direction desired.

Anything less will result in the development of a spiral dive, with ever-increasing airspeed and descent rate, if left long enough.
 
"If you are banking don't pull back on the yoke..."
That's how I teach emergency descents. We peg the VSI in a 45° bank in a few seconds, just like the math shows. Yet people want to argue with both the theory and the empirical data because they "feel" that they know better.

To sum up the comments on this thread, we have gone from "If you bank you will stall and die" to "If you bank you will fall and die". Interesting...
Stalling in the pattern is bad, but so are ballistic descents. You get to pick one or the other.
 
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