They are out of business now. I wonder why??!!

 

 

Because they were bought out.

I have to say that the stall warning on this a/c seems a little benign. It's almost like a gentle reminder and could go unnoticed if one was totally preoccupied with something else. It needs to be loud and dissonent in order to penetrate the pilot's mind and shock him/her into reacting instinctively by pushing down.

vololiberista

 

Well Colgan 3407 had a violent stick pusher and that didn't stop PF from pulling back.

 

Keep in mind in AB "FBW" it isn't a case of the FBW acting as an electro-hydraulic amplifier for the stick. Stick position is a pilot command for the aircraft to enter a certain state, and FBW adjusts flight control surfaces as needed to attain that state. Fore/aft movement is a load demand factor in cruise. Feedback gains are adjusted in Alt law as compared to Normal law irrespective of envelope protection.

 

scott s.

.

You're confusing stalling with departing. High angle of attack and high pitch attitude 'protections' like what the Airbus had will not stop an airplane from mushing into the ocean like they did. The only thing that those sort of 'protections' protect from happening is a violent, tumbling, out of control, departure of flight. That does not mean the aircraft can't sit there, all trimmed out and stable, at maximum angle of attack, maximum drag, and maximum descent into the ocean.

 

The misnomer that a lot of pilots have, is that the stick is used to control altitude. If you want to climb, you pull back, and if you want to descend, you push forward. The only thing that the stick controls is angle of attack. And in most aircraft, the only and most proximate indication of aoa is airspeed. Low airspeed indicates a high angle of attack. High airspeed indicates a low angle of attack. And the only thing that determines whether a plane is stalled or not is angle of attack. Not MCT. Not pitch attitude. By controlling angle of attack, the stick controls airspeed. By continually pulling back on the stick, the pilot was commanding the plane to fly at slowest speed and maximum angle of attack. That's what the computers were told to do by the pilot, that's what they gave him. Rate of climb or descent is a product of what you do with angle of attack. When flying at slowest speed/maximum aoa, drag is high, requiring lots and lots and lots of thrust to counteract the drag in order to maintain altitude. Even at max thrust, an airliner does not have enough 'lots' of thrust to keep a plane airborne at max aoa. That is why they descended into the ocean, as balanced and protected as they were.

 

Remember that in AF447's case the protections were offline. As you correctly say a plane will stall when it exceeds the critical angle of attack. That's why in normal law, when all the protections are working, the Airbus flight control computer will not allow the plane to reach the critical angle of attack, hence preventing a stall.

 

As a small side-note, and maybe I'm approaching this from an engineering rather than a piloting viewpoint, but the stick does not control angle of attack, it controls elevator deflection. Quite a bit of physics happens before that turns into an angle of attack change.

What you say about low airspeed indicating high angle of attack and vice versa is only true in straight and level flight by the way. It's quite possible to have a high angle of attack and a high airspeed, it just means you will be experiencing an upward acceleration.

"It's quite possible to have a high angle of attack and a high airspeed, it just means you will be experiencing an upward acceleration. "

 

Doesn't that mean you might be flying a kite rather than an aerofoil though?

"It's quite possible to have a high angle of attack and a high airspeed, it just means you will be experiencing an upward acceleration. "

 

Doesn't that mean you might be flying a kite rather than an aerofoil though?

 

Depends on your definition of high ;), but a fighter that suddenly pulls up can certainly have both a high airspeed and a high angle of attack.

The misnomer that a lot of pilots have, is that the stick is used to control altitude.

...//...

The only thing that the stick controls is angle of attack.

 

Ah basic theory....This reminds me of another thread... Yes Kevin, we know where you're coming from. And if one tries to understand what you really mean, the sentence "the only thing that the stick controls is angle of attack" is acceptable but it is technically incorrect. We all know that a stick input will ultimately result in changes in speed, altitude etc. but what the stick really does on an Airbus is control g loading, at least in most of the operating modes.

 

Whether you are in Normal, Alternate 1 or Alternate 2 law, the stick controls g loading. Only in the most degraded mode (direct law) or at specific times in the other modes (rotation at take off for example) does the stick directly control elevator position, as John Alan and many others correctly state.

 

As a small side-note, and maybe I'm approaching this from an engineering rather than a piloting viewpoint, but the stick does not control angle of attack, it controls elevator deflection. Quite a bit of physics happens before that turns into an angle of attack change.

 

Yes and no. See above please

 

Bruno

 

edited for orthograph and for concision

Depends on your definition of high ;), but a fighter that suddenly pulls up can certainly have both a high airspeed and a high angle of attack.

 

I think you're confusing what you see with what is actually happening. If I am flying a fighter jet there is a much greater thrust to drag ratio. So if I am flying straight and level at high speed and then pull up "without changing the throttle!" the original airspeed will stay much for longer and reduce much more slowly. so the "angle of attack" which is the angle of the airflow striking the wing leading edge will increase more slowly. But as the airspeed decays then so will the angle of attack increase.

A commercial jet is quite a different kettle of fish in terms of performance to a fighter jet so you shouldn't use the comparison especially as modern fighter jets are "unflyable". (They need a computer to fly).

 

The AF PF pulled up and initially the a/c climbed until the airspeed decayed and the a/c stalled because the critical AoA had been reached. Thereafter the a/c was mostly maintained in a full nose up attitude. The airspeed was nominal probably simply caused by the act of falling out of the sky so fast.

The wings were experiencing an airflow for which they were not designed to fly. It's not difficult to imagine: The airspeed (the effective forward movement of the wing through the air) was very low less than 70kts. This is in itself well below the stall !!! Add to that upward airflow over the wing created by its downward movement which was about 108kts. This creates an enormous amount of drag and the resulting buffet from the turbulent air would be very high and uncomfortable. You can test this by putting your hand out of a car window whilst moving and turning your hand flat to the wind. There was effectively no lift coefficient at all. The angle of attack was well outside the design flight envelope so the instrumentation and computers had a real headache. That's why the a/c went into alternate law. Which is just a fancy way of saying "I (the computer) can't fly the aeroplane. So it's over to you boys to do some of your pilot stuff!" The problem is that they didn't!

Whenever a stall warning sounds you drop whatever you are doing however important it is, however life threatening it is and perform a stall recovery.

Pilots who do not react in this way here are taken immediately of line and sent for retraining.

vololiberista

 

PS Whole books have been written about lift equation and how much lift can be obtained from how much AoA. So the above is a very simple explanation so please don't say I've forgotten this or that. The BEA have done their sums in this respect. If I have time this weekend I will try to calculate the lift coefficient of a brick as a comparison.

Depends on your definition of high ;), but a fighter that suddenly pulls up can certainly have both a high airspeed and a high angle of attack.

 

The airspeed may be high, but it is still less than what it was before the stick was pulled aft.

Ah basic theory....This reminds me of another thread... Yes Kevin, we know where you're coming from. And if one tries to understand what you really mean, the sentence "the only thing that the stick controls is angle of attack" is acceptable but it is technically incorrect. We all know that a stick input will ultimately result in changes in speed, altitude etc. but what the stick really does on an Airbus is control g loading, at least in most of the operating modes.

 

Whether you are in Normal, Alternate 1 or Alternate 2 law, the stick controls g loading. Only in the most degraded mode (direct law) or at specific times in the other modes (rotation at take off for example) does the stick directly control elevator position, as John Alan and many others correctly state.

 

 

 

Yes and no. See above please

 

Bruno

 

edited for orthograph and for concision

 

There's been more than one thread before. LAdamson and I have enjoyed many threads about this even before these two crashes. This topic goes back to the flight instructor that is still in me. When I used to teach people to fly, I taught them that the stick controlled speed, not altitude. Yes, I admit that I'm skipping a lot of steps with that sentence, such as that the actually stick manipulates pulleys and cranks, moves elevators, changes forces on the tail surfaces, changes moments around the plane's CG, etc., but I am speaking about aircraft control and not aircraft design and repair, as a flight instructor. Whether the stick moves the elevator, stabilator, elevator tabs, or G-load, the ultimate purpose of its movement is to make a pitch change of the longitudinal axis of the aircraft which ultimately and consistently results in an adjustment of the plane's angle of attack in flight. And whether you are flying an A340, an F-18, or a C152, a movement of that control will make a change to your aoa and your airspeed will reflect this.

 

Japascoe, a fighter jet is just like any airplane. A plane is a plane. These rules apply to the F-18 just as well as the A340. When you pull back the stick on an F-18, you tell the plane that you want to increase the G loading just the same as on an A340. In response to this desire, the computers move the stabilators such that it causes an 'upward' (I put in quote since upward is only relative to top of the pilot's head sitting in the cockpit.) pitch of the aircraft's nose. The result is an increase in angle of attack and a decrease in airspeed. Whether all this occured at 250kts, or 500kts, makes no difference, the results were the same, higher aoa and lower airspeed after the movement of the stick. Once the stick is returned to neutral, the command to increase G is cancelled and the aircraft will fly at the new higher aoa and lower airspeed. If you pull the stick back very hard, and command a 7 G pitch up, then obviously, it will jerk the nose way up very fast, resulting in a high airspeed, high aoa situation. Obviously, one can do anything in transition, one can swap ends of an aircraft in transitory flight and fly backwards, however, the plane will have to catch up to a steady state at some point or else it will crash. Once the G-command is returned to neutral, the plane will still find itself at a much higher aoa and much lower airspeed.

 

The reason I chose to use the stick for speed line as a fundamental understanding for my students, was so that they need not ever have to make a mental change of gears while controlling the plane. When a student understood that the stick and the elevator trim were correlated to its speed, then there need not have to be change in how they used the controls depending on whether they were flying fast or slow. It applied the same in all parts of the flight envelope. The reason it applied to all parts of the envelope was because that was how those controls actually were meant to work.

Ah basic theory....This reminds me of another thread... Yes Kevin, we know where you're coming from. And if one tries to understand what you really mean, the sentence "the only thing that the stick controls is angle of attack" is acceptable but it is technically incorrect. We all know that a stick input will ultimately result in changes in speed, altitude etc. but what the stick really does on an Airbus is control g loading, at least in most of the operating modes.

 

Whether you are in Normal, Alternate 1 or Alternate 2 law, the stick controls g loading. Only in the most degraded mode (direct law) or at specific times in the other modes (rotation at take off for example) does the stick directly control elevator position, as John Alan and many others correctly state.

 

 

 

Yes and no. See above please

 

Bruno

 

edited for orthograph and for concision

 

I'd contend that the stick on an Airbus still merely controls elevator deflection, with the caveat that there is a computer in between so that a given stick deflection will not always result in the same elevator deflection. Rather the computer will process the stick position to generate an elevator deflection that will produce a certain G loading. Though from a pilot's perspective yes, the stick effectively controls G-loading.

 

There's been more than one thread before. LAdamson and I have enjoyed many threads about this even before these two crashes. This topic goes back to the flight instructor that is still in me. When I used to teach people to fly, I taught them that the stick controlled speed, not altitude. Yes, I admit that I'm skipping a lot of steps with that sentence, such as that the actually stick manipulates pulleys and cranks, moves elevators, changes forces on the tail surfaces, changes moments around the plane's CG, etc., but I am speaking about aircraft control and not aircraft design and repair, as a flight instructor. Whether the stick moves the elevator, stabilator, elevator tabs, or G-load, the ultimate purpose of its movement is to make a pitch change of the longitudinal axis of the aircraft which ultimately and consistently results in an adjustment of the plane's angle of attack in flight. And whether you are flying an A340, an F-18, or a C152, a movement of that control will make a change to your aoa and your airspeed will reflect this.

 

Japascoe, a fighter jet is just like any airplane. A plane is a plane. These rules apply to the F-18 just as well as the A340. When you pull back the stick on an F-18, you tell the plane that you want to increase the G loading just the same as on an A340. In response to this desire, the computers move the stabilators such that it causes an 'upward' (I put in quote since upward is only relative to top of the pilot's head sitting in the cockpit.) pitch of the aircraft's nose. The result is an increase in angle of attack and a decrease in airspeed. Whether all this occured at 250kts, or 500kts, makes no difference, the results were the same, higher aoa and lower airspeed after the movement of the stick. Once the stick is returned to neutral, the command to increase G is cancelled and the aircraft will fly at the new higher aoa and lower airspeed. If you pull the stick back very hard, and command a 7 G pitch up, then obviously, it will jerk the nose way up very fast, resulting in a high airspeed, high aoa situation. Obviously, one can do anything in transition, one can swap ends of an aircraft in transitory flight and fly backwards, however, the plane will have to catch up to a steady state at some point or else it will crash. Once the G-command is returned to neutral, the plane will still find itself at a much higher aoa and much lower airspeed.

 

The reason I chose to use the stick for speed line as a fundamental understanding for my students, was so that they need not ever have to make a mental change of gears while controlling the plane. When a student understood that the stick and the elevator trim were correlated to its speed, then there need not have to be change in how they used the controls depending on whether they were flying fast or slow. It applied the same in all parts of the flight envelope. The reason it applied to all parts of the envelope was because that was how those controls actually were meant to work.

 

I've bolded the crux of why we're disagreeing, you're approaching this as a flight instructor, whereas I'm approaching it as an engineer, which results in two slightly different viewpoints, both of which are correct and basically differ in how many intermediate steps one is hand waving. Of course the purpose of the explanations is also different; solving a full set of flight dynamics equations to work out which control input to give is not an efficient method of piloting, unless you are a computer.

 

In straight and level flight indeed low airspeed means high AoA and vice versa, otherwise lift would not equal weight and you would get a vertical acceleration. I agree that pulling back on the stick in an equilibrium state will result (eventually, though in a relatively short span of time) in a new equilibrium state with a higher AoA and a lower airspeed. What happens in between is that the higher AoA (caused by pulling back) causes the drag to be greater and as a result (given no change in thrust) the airspeed starts to decay, the drop in airspeed will lower the drag again until thrust and drag are once again equal. (Ignoring complicating factors like changes in the direction of the velocity vector effecting the AoA). The drop in airspeed is a consequence of the increased AoA, rather than something that happens at the same time (though for a pilot it might very well be sufficient to assume that they do happen at the same time).

I've bolded the crux of why we're disagreeing, you're approaching this as a flight instructor, whereas I'm approaching it as an engineer, which results in two slightly different viewpoints, both of which are correct and basically differ in how many intermediate steps one is hand waving. Of course the purpose of the explanations is also different; solving a full set of flight dynamics equations to work out which control input to give is not an efficient method of piloting, unless you are a computer.

 

In straight and level flight indeed low airspeed means high AoA and vice versa, otherwise lift would not equal weight and you would get a vertical acceleration. I agree that pulling back on the stick in an equilibrium state will result (eventually, though in a relatively short span of time) in a new equilibrium state with a higher AoA and a lower airspeed. What happens in between is that the higher AoA (caused by pulling back) causes the drag to be greater and as a result (given no change in thrust) the airspeed starts to decay, the drop in airspeed will lower the drag again until thrust and drag are once again equal. (Ignoring complicating factors like changes in the direction of the velocity vector effecting the AoA). The drop in airspeed is a consequence of the increased AoA, rather than something that happens at the same time (though for a pilot it might very well be sufficient to assume that they do happen at the same time).

 

That's actually pretty much exactly how I explained it to my students while standing in front of the drag curve. I'm not too sure I understand what we are disagreeing about. If it is because I chopped off the middle parts about the microseconds it takes to cause and effect the aoa and airspeed in my post straight into simply 'equating' the movement of that stick to the movement they will see on the airspeed needle, then yes, I'm guilty of chopping off the entire middle process for the sake of relevancy and wordiness. If you pull out my old posts alluded to by fencer where I've explained the drag curve, you will see it explained exactly as you just did. But I've done that too many times here for LAdamson, so I apologise for skipping it in this thread.

There's been more than one thread before.

Kevin, I was referring to another thread when, among other outlandish statements, you were claiming that :

 

- in an airliner, speed is always controlled by the stick, especially during the landing phase (fortunately, after a few pages, Rónán came to my help and set you - and a few others in that thread - straight).

 

- the US Air Force doesn't know how to fly, contrarily to the US Navy (nobody bothered to argue this point with you...)

 

and, if I remember well, you also claimed at one point to be an airline pilot. So you'll understand that I am leery about getting in a long discussion, even though I may agree with some of the points you mention.

 

Japascoe, a fighter jet is just like any airplane. A plane is a plane. These rules apply to the F-18 just as well as the A340. When you pull back the stick on an F-18, you tell the plane that you want to increase the G loading just the same as on an A340.

 

Kevin, if you care to re-read my post above, you'll read again that, on the same Airbus depending on the mode, an action on the stick will either :

 

a- set directly the load factor

or

b- merely set the stabilator and of course, change angle of attack and load factor as a consequence (but this time, the load factor is not the controlled variable - or feedback - in the control loop).

 

Granted, in both cases, one can argue that the controlled device is the same (ie the horizontal stabilizer) and that (fortunately) the final result is similar (ie : the plane goes where the pilot wants it to go) but, please understand my point that the control logic between stick action and plane reaction (ie the way the plane is piloted) is different. End of discussion ?

 

One could make an analogy with the fact that there are two different control modes possible in a Boeing : normal and CWS (Control Wheel Steering I think the name is).

 

I'd contend that the stick on an Airbus still merely controls elevator deflection, with the caveat that there is a computer in between so that a given stick deflection will not always result in the same elevator deflection. Rather the computer will process the stick position to generate an elevator deflection that will produce a certain G loading. Though from a pilot's perspective yes, the stick effectively controls G-loading.

Same comment as above. We may be splitting hair here. But another way to say it is that on an Airbus in normal law, the stick controls directly G-loading while in direct law, the stick controls directly stabilator deflection (and hence, indirectly G-loading).

 

Bruno

The stick / control column, what you will, does not "control" angle of attack. It controls incidence. Angle of attack is a resultant of incidence, thrust, drag and weight. If I can maintain a high enough airspeed with my nose fully up then my "angle of attack" will stay within the safe part of the flight envelope. This is not too difficult at low altitudes but becomes increasingly more difficult the higher one flies.

Again one should not compare a jet fighter with an airliner. In one sense they follow the same rules but their performance parameters are quite different. I can take off and fly with my nose vertical to 50,000ft in an English Electric Lightning. Getting the nose vertical in an A330 would likely result in a stall at any altitude!

A stall indicates that airspeed, drag, incidence and the resultant AoA are not balanced by the thrust. If the a/c is already at maximum incidence (nose up) and maximum thrust (TOGA) when the stall occurs one's only option is to change the incidence downwards until equilibrium returns. Therefore flying is a balancing act between all these forces.

From the Captain dowards these three pilots acted as if they had never ever had any actual flying lessons. They threw out every rule in the book. Reacting to certain events like the stall must be an instinctive sub-concious reaction. The crew were never thinking beyond their noses for the entire flight. They were not monitoring their instruments, they were not planning or thinking ahead. At all times you must be thinking "What if?". For example what do you do in a light a/c as a pilot? Your passengers are admiring the view. Are you? No! Your looking for that perfect field to land in if your engine cuts out. And so should the aircrew of a commercial jet display their airmanship and be ready for any eventuality. Even on loooong booooring flights!

vololiberista

That's actually pretty much exactly how I explained it to my students while standing in front of the drag curve. I'm not too sure I understand what we are disagreeing about. If it is because I chopped off the middle parts about the microseconds it takes to cause and effect the aoa and airspeed in my post straight into simply 'equating' the movement of that stick to the movement they will see on the airspeed needle, then yes, I'm guilty of chopping off the entire middle process for the sake of relevancy and wordiness. If you pull out my old posts alluded to by fencer where I've explained the drag curve, you will see it explained exactly as you just did. But I've done that too many times here for LAdamson, so I apologise for skipping it in this thread.

 

Pretty much what my inner nitpicker was disagreeing with, yes :P. I can understand not wanting to write out the entire explanation several times.

 

 

Same comment as above. We may be splitting hair here. But another way to say it is that on an Airbus in normal law, the stick controls directly G-loading while in direct law, the stick controls directly stabilator deflection (and hence, indirectly G-loading).

 

Bruno

 

Eh, yeah pretty much a difference of semantics here and the same issue of pilot vs. engineer perspective. From a pilot's point of view the stick directly controls G-loading in normal law. From an engineer's point of view, there is no such thing as 'directly controlling G-load', the only thing you can control are your control surfaces, which will produce a pitch moment, which changes the angle of attack, which changes the G-loading. The pilot's point of view is better for understanding what happens when you pull on the stick, the engineer's point of view is a more accurate description of the physics that is happening.

Kevin, I was referring to another thread when, among other outlandish statements, you were claiming that :

 

- in an airliner, speed is always controlled by the stick, especially during the landing phase (fortunately, after a few pages, Rónán came to my help and set you - and a few others in that thread - straight).

 

- the US Air Force doesn't know how to fly, contrarily to the US Navy (nobody bothered to argue this point with you...)

 

and, if I remember well, you also claimed at one point to be an airline pilot. So you'll understand that I am leery about getting in a long discussion, even though I may agree with some of the points you mention.

 

Bruno

 

That thread was just one of many that LAdamson and I have been in about that topic. There's been many more before the one you saw. They're all the same anyways. None of those ideas are original to me, they're concepts already desseminated widely by aviation authors like Wolfgang Langsweiche, Barry Schiff and the US Navy. I found during the course of my CFI training that they were pretty good and explained some things in such ways that would be beneficial for a student. I just like defending them on this flightsim message board from people that attack it because they don't understand it, that's all. Ronan actually kind of spoke in a middle of the road kind of way as to be agreeable to everybody, he's a gentleman that always seems to write that way. I really couldn't find anyhting to disagree with in his post either. I don't think I claimed to be anything, just spoke from some personal experiences, that's all. If you disagree with those ideas, just present your own and your reasons. And I will present mine and my reasons. That's all any of us should do. There's no need to switch it to something personal.