Angle of Attack: True or False

birdus said:
True or False: The stick determines elevator position and elevator position determines angle of attack. When the critical angle of attack is exceeded, the wing stalls. So, given a design with enough elevator authority, if the stick is in your lap, then the wing is stalled. If the stick is, say an inch farther forward, the wing will not be stalled. Period.

I had a conversation with a United Airlines captain (737) the other day, and he said I was wrong. As I get older, I tend to be less argumentative, so I didn't pursue it. He said some things about different size loops (don't know what that was about). When he mentioned the Amazon crash off the coast of Texas (the overall conversation was about MCAS), I said that, in a video I had seen (months earlier), it looked like the plane may have been stalled. The descent angle appeared steep and yet the angle between the longitudinal axis of the plane and the ground appeared to be significantly shallower (i.e., stalled). He said something about the descent angle being really steep and the airspeed being really high so it couldn't have been stalled.

I really wanted to say "descent angle and airspeed are irrelevant. If the pilot put the plane into a dive, gained a ton of airspeed, and then put the stick in his gut, then they were stalled." However, I dropped it.

So, are there subtleties I'm not considering? Could the stick not act as an angle-of-attack indicator (if I could position it precisely enough)? I'll try to clarify this post if necessary.

EDIT: Let's stipulate no flaps/slats, calm air, normal CG, and plenty of elevator authority.
Click to expand...

Hope you get this figured out.
 
DaleB said:
Call it whatever you want. Pretty sure I can pull up into a steep climb -- let's say 45 degrees, for the sake of argument -- let the airspeed decay to just above stall speed, relax the back pressure, pull the throttle, and the plane will stall. Again... willing to be proven wrong, but I don't think I am. Obviously, or I wouldn't say it.
Click to expand...

You actually probably would not stall, at least not in the aerodynamic sense. Without elevator back pressure, your nose will fall due to CG placement, Gravity and insufficient lift. This is not however an aerodynamic stall.

Though called a "whip stall" the aircraft does not actually stall it merely reaches the point of 0 lift and rapidly whips around to the heavy end (usually the front) first as it falls out of the sky. Its again a result of CG placement, gravity and insufficient lift as result of decaying airspeed decay's which is different from a stall which is a lift insufficiency due to airflow separation over the wing without consideration of airspeed
 
Last edited:
RoscoeT said:
Sounds like you mis-read. We were talking about stalling with neutral elevator after pulling power to idle on a steep climb. Parabolic arc, no stall. Pull steep enough and you could whip stall, but that's different from a normal stall.
Click to expand...
Pretty sure I've seen nose-high stalls where even full forward stick (to the stop) wasn't enough to immediately break the stall until after the nose fell through below the horizon. Simulating a go around where the pilot "forgets" to retract flaps in a C-172 comes to mind. The stick starts off pretty much in the middle then, IIRC. But... it's been a long long time, YMMV. Someone go try it and report back. (CAVEAT! Take a CFI with you!) (And have lots of altitude!)
 
DaleB said:
Call it whatever you want. Pretty sure I can pull up into a steep climb -- let's say 45 degrees, for the sake of argument -- let the airspeed decay to just above stall speed, relax the back pressure, pull the throttle, and the plane will stall. Again... willing to be proven wrong, but I don't think I am. Obviously, or I wouldn't say it.
Click to expand...
You have it right:

 
RoscoeT said:
Uhhh...tad steeper than 45 degrees. More like a cheated tail slide.
Click to expand...
Well, you can't really tell how steep, but you're right it's more than 45° for sure. Also for sure, it isn't 90°.
 
RoscoeT said:
Uhhh...tad steeper than 45 degrees. More like a cheated tail slide.
Click to expand...
And would you not agree that the wing exceeded its critical angle of attack, and the elevator more or less neutral or even some down elevator during that maneuver?
 
dtuuri said:
You have it right:

Click to expand...

As I commented before, while the general public thinks of this as a stall, aerodynamically, there is a difference between a stall and no lift. This plane reached a point of near 0 relative wind and therefore had near 0 lift being produced by the wings, this no lift state is quite a bit different from an aerodynamic stall.
 
apr911 said:
As I commented before, while the general public thinks of this as a stall, aerodynamically, there is a difference between a stall and no lift. This plane reached a point of near 0 relative wind and therefore had near 0 lift being produced by the wings, this no lift state is quite a bit different from an aerodynamic stall.
Click to expand...
I have to disagree. If there is truly near 0 relative wind, there is nothing to cause the plane to change pitch.

To help explain, the shuttle orbiter does not rapidly (or even slowly) pitch to heavy side down while outside the atmosphere with 0 relative wind and 0 lift. You need aerodynamic forces for this to happen.

In your example, it is the rapid change in relative wind resulting in a rapid change of angle of attack that creates a rapid stall, which results in a rapid pitch change.
 
Last edited:
apr911 said:
As I commented before, while the general public thinks of this as a stall, aerodynamically, there is a difference between a stall and no lift. This plane reached a point of near 0 relative wind and therefore had near 0 lift being produced by the wings, this no lift state is quite a bit different from an aerodynamic stall.
Click to expand...
When gravity asserts itself, the nose falls through (whips) and the stalling AoA is exceeded. How can it be any other way?
 
dtuuri said:
When gravity asserts itself, the nose falls through (whips) and the stalling AoA is exceeded. How can it be any other way?
Click to expand...
When did gravity stop asserting itself?
 
dtuuri said:
FTFY. :) Discovered the hard way that timing the kick by the seat of the pants is based on TAS. The rudder responds to IAS. Not the same at a DA of 8000'.:eek:
Click to expand...

Ha...that is in no way how actual aerobatic pilots time a hammer kick. :rolleyes:
 
Jeff767 said:
Every time I do a hammerhead where I botch the pivot that is exactly what I am doing. Taking the aircraft straight up and ending at zero airspeed with the elevator Neutral. Put the slightest G on at that point and your stalled. Miss time the kick and your stalled. Neither has the stick remotely close to full aft.
Click to expand...

Sounds like you need some quality aerobatic training. :)
 
IK04 said:
Is the horizontal stabilizer/elevator or stabilator not an airfoil mounted on an aircraft?

I was never referring to the WING.
Click to expand...
I'm sorry, but you are contorting into a pretzel to validate your use of the word, incidence. Just find a different word.
 
Jeff767 said:
Gravity brings the heavy nose down.
Click to expand...
Not really.

Which falls faster a rock or a feather?
A. In a vacuum
B. With atmosphere

Why is the answer to a and b different? This is why you are wrong.
 
Salty said:
Not really.

Which falls faster a rock or a feather?
A. In a vacuum
B. With atmosphere

Why is the answer to a and b different? This is why you are wrong.
Click to expand...
A. I put a rock and a feather in my Kirby and dropped it off the roof...the Kirby took exactly the same amount of time to hit the ground either way.
B. I did the same thing off the balcony at the night club. I got arrested after dropping the rock on somebody, so it looks like he feather will take about three days longer.
 
Salty said:
I have to disagree. If there is truly near 0 relative wind, there is nothing to cause the plane to change pitch.

To help explain, the shuttle orbiter does not rapidly (or even slowly) pitch to heavy side down while outside the atmosphere with 0 relative wind and 0 lift. You need aerodynamic forces for this to happen.

In your example, it is the rapid change in relative wind resulting in a rapid change of angle of attack that creates a rapid stall, which results in a rapid pitch change.
Click to expand...

There are 3 points I'd make in counter:
A) The plane is not in a perfect vertical. If you could align the plane in a perfect vertical with all control surfaces neutral, the plane would fall straight down. Since its not, the plane's surfaces create drag that causes the plane to fall more like a piece of paper than a rock, the CG of the plane is what causes it to whip around. This is much like a ground loop in a tailwheel plane... If you can get the plane to be perfectly aligned with neutral control surfaces and no sideways movement, you would never have to worry about a ground loop since the CG and forces exterted are in a straight line but as soon as you allow the CG and forces to come out of alignment, you need to correct it with rudder or you will whip around and ground loop. The only difference is the whip stall is in the vertical with a turn through the horizontal geometric-plane and uses elevator as opposed to the ground loop which is in the horizontal with a turn through the lateral geometric-plane which uses rudder.

B) In order to hang the plane on the prop like that you need to be utilizing elevator and rudder controls to prevent the plane from falling off in whatever direction you are most out of geometric-plane. A hammerhead "stall" looks quite similar to a whip "stall" but the hammerhead stall uses rudder to initiate the fall to the left or right whereas the whip stall uses elevator. Indeed just as above the hammerhead is much like a ground loop (in fact even more so since its only the plane's orientation that changes) except it is performed in the vertical with turn through the horizontal as opposed to the horizontal with a turn through the lateral geometric-planes.

C) Because of airfoil design, this maneuver is much easier to perform when executed into the inverted. As the plane falls off the top and relative wind is again created across the wings, the wings will generate lift that will force the airplane towards the ground. To maintain inverted flight, you would combat this with elevator but in a whip stall/reverse you'd go with it allowing this force toward the ground to combine with gravity and elevator control pressures to bring the plane around into the vertical in the opposite direction.

Part of what makes Maroney's Whip Stall impressive is that he does not perform it in the inverted but he is able to whip the plane around before the wings start generating upward lift in opposition to gravity. He whips it around so quickly that the wings never have time to catch a relative wind capable of producing lift. A more amateur pilot taking longer to whip the plane around or allowing the plane to fall out of the vertical earlier at a higher airspeed before the wings reach no/negligible lift would allow the wings to generate upward lift in opposition to gravity and the whipping action would be much less impressive as the pilot has to then fight the lift generated by the wings with elevator. Note that the wings are going from no lift or very little lift to producing lift as a result of relative wind, not an aerodynamic stall.

A much more amateur pilot trying to prevent the plane from whipping around might experience a rapid stall as the wings begin producing lift and the plane remains in a high angle of attack due to the low airspeed but an aerodynamic stall is not required or desired in the performance of the whip "stall" illustrated in the video and experiencing an aerodynamic stall in this maneuver would likely be indicative of a poorly performed maneuver
 
Last edited:
Salty said:
Not really.

Which falls faster a rock or a feather?
A. In a vacuum
B. With atmosphere

Why is the answer to a and b different? This is why you are wrong.
Click to expand...

I have never flown in a vacuum however close a few times. In the environment I fly if I drop a rock and a feather the rock is going to hit the ground far sooner.
 
Jeff767 said:
I have never flown in a vacuum however close a few times. In the environment I fly if I drop a rock and a feather the rock is going to hit the ground far sooner.
Click to expand...
True, but not because gravity acts differently on the rock than it does the feather; it doesn't. That is the point that you are still missing.

An arrow does not fall head first because the head is heavier than the tail (gravity). It falls head first because the tail has more drag than the head.
 
Jeff767 said:
I have never flown in a vacuum however close a few times. In the environment I fly if I drop a rock and a feather the rock is going to hit the ground far sooner.
Click to expand...

What if you drop a box of rocks and an equal size box of feathers from a Cirrus?
 
birdus said:
When he mentioned the Amazon crash off the coast of Texas (the overall conversation was about MCAS), I said that, in a video I had seen (months earlier), it looked like the plane may have been stalled. The descent angle appeared steep and yet the angle between the longitudinal axis of the plane and the ground appeared to be significantly shallower (i.e., stalled).
Click to expand...
It didn't look stalled to me at all. And in fact you can tell because the airplane was maneuvering with a positive load even in the short video. It would not be able to do it when stalled.
 
DaleB said:
Call it whatever you want. Pretty sure I can pull up into a steep climb -- let's say 45 degrees, for the sake of argument -- let the airspeed decay to just above stall speed, relax the back pressure, pull the throttle, and the plane will stall. Again... willing to be proven wrong, but I don't think I am. Obviously, or I wouldn't say it.
Click to expand...
Except for the pull the throttle part, that's pretty much exactly how I got into the only non-intentional stall I ever experienced. First season towing banners. I had been getting progressively more aggressive with my pitch angle during the pickup over the course of the season without really realizing it. Tankered up with fuel, first pickup of the day I came through the poles and put the stick in my belly. pushed hard forward and brought the nose to level as I was looking down and seeing the banner lead pole come off the ground. I moment later I realized something wasn't right. Felt just a touch mushy and then the wing dropped. Realized what was happening, kept the stick centered, buried opposite foot into the firewall and stick forward just a bit to get it flying again.

It was still flying when I pushed the nose over. Stopped flying a second or two later. Recovered losing only 50-75' (only had 150' to start with) and flew off. According to the OP, it could not have stalled:
birdus said:
...if the stick is in your lap, then the wing is stalled. If the stick is, say an inch farther forward, the wing will not be stalled. Period.
Click to expand...
The stick was well more than an inch forward of my lap when it stalled on me. So while I won't argue the physics or aerodynamics of what goes into a stall, I will simply say it has not been my experience that so long as the stick is an inch farther forward than full aft, the wing will not be stalled.
 
I'm still shaking my head that so many (that passed the Faa written exam presumably) think it's gravity that's causing the nose to pitch down after a stall.
 
Salty said:
I'm still shaking my head that so many (that passed the Faa written exam presumably) think it's gravity that's causing the nose to pitch down after a stall.
Click to expand...

Would you not agree that the combination of center of gravity location relative to center of lift location, and gravity is what causes the nose to pitch down after a stall? If not, please explain.
 
birdus said:
Would you not agree that the combination of center of gravity location relative to center of lift location, and gravity is what causes the nose to pitch down after a stall? If not, please explain.
Click to expand...
No, I would not agree, and I've already explained why. Objects do not fall faster based on weight. Objects fall faster based on density - because of aerodynamic forces - NOT because of gravity. Gravity exerts the same force on all objects regardless of mass. If the plane were in a vacuum it would not pitch down if dropped level - because there would be no aerodynamic forces to cause it to pitch down. It would fall flat, straight down. This isn't even aerodynamics, it's physics 101 stuff.

 
I will concede that the aerodynamic forces combined with gravitational forces is what determines the direction of the pitch change, but gravity alone doesn't do squat. The plane isn't spinning around on it's CG to heavy side down if there is no relative wind. That is the incorrect thought I'm fighting against.
 
Salty said:
No, I would not agree, and I've already explained why. Objects do not fall faster based on weight. Objects fall faster based on density - because of aerodynamic forces - NOT because of gravity. Gravity exerts the same force on all objects regardless of mass. If the plane were in a vacuum it would not pitch down if dropped level - because there would be no aerodynamic forces to cause it to pitch down. It would fall flat, straight down. This isn't even aerodynamics, it's physics 101 stuff.
Click to expand...

The semantics are getting thick here. If you hold a hammer by the handle palm up and let go, the hammer will rotate heavy end toward the ground because of gravity. This does not prove or disprove the fact that all objects in a vacuum are subject to the same gravitational acceleration rate.
 
RoscoeT said:
The semantics are getting thick here. If you hold a hammer by the handle and let go, the hammer will rotate heavy end toward the ground because of gravity. This does not prove or disprove the fact that all objects in a vaccum are subject to the same gravitational acceleration rate.
Click to expand...
No, it won't. It would only rotate because you held on to the handle slowing the handle while the head fell. Drop it while holding it perfectly level and it will not rotate (unless you drop it a couple stories so that wind resistance will rotate it NOT GRAVITY) You are still missing the fundamental physical principle
 
Salty said:
No, it won't. It would only rotate because you held on to the handle slowing the handle while the head fell. Drop it while holding it perfectly level and it will not rotate (unless you drop it a couple stories so that wind resistance will rotate it NOT GRAVITY) You are still missing the fundamental physical principle
Click to expand...

Held palm up. This conversation is getting really stupid all around.
 
RoscoeT said:
f you hold a hammer by the handle palm up and let go, the hammer will rotate heavy end toward the ground because of gravity.
Click to expand...
Nope.
The light end falls at 32.2 ft/sec^2 (9.81 m/sec^2 if you prefer), and the heavy end falls at 32.2 feet/sec^2. If it does rotate then that is cause by aerodynamic effects.
Try throwing the hammer straight up - the same effects should make it tend to travel with the heavy end first.
 
RoscoeT said:
Held palm up. This conversation is getting really stupid all around.
Click to expand...
Indeed it is. You should watch the video I posted. You should also try it with a hammer yourself since you seem impervious to gaining knowledge any other way.
 
Ok, just did the experiment with a hammer.
I wrapped a thin wire around the handle so it would balance horizontally then dropped it from about 30 feet above the ground. The head hit just slightly before the handle - no surprise because the handle is going to have more drag then the head.
 
Salty said:
Indeed it is. You should watch the video I posted. You should also try it with a hammer yourself since you seem impervious to gaining knowledge any other way.
Click to expand...

Hey smart guy - I said hold a hammer in your hand palm up and open your hand. The hammer rotates around your palm same way the airplane's CG rotates around the center of lift in a stall. YOU try the hammer like I said and tell me what you find. I knew it was only a matter of time before this thread went full flown POA stupid level. I'm not arguing with your vacuum video in case you're having trouble deducing that, which you seem to be.
 
RoscoeT said:
Hey smart guy - I said hold a hammer in your hand palm up and open your hand. The hammer rotates around your palm same way the airplane's CG rotates around the center of lift in a stall. YOU try the hammer like I said and tell me what you find. I knew it was only a matter of time before this thread went full flown POA stupid level. I'm not arguing with your vacuum video in case you're having trouble deducing that, which you seem to be.
Click to expand...

Your palm is the equivalent of the aerodynamic force. Remove it and you get the hammer drop I just showed you. It is NOT GRAVITY.
 
You must log in or register to reply here.
Back
Top