What causes an airplane to stall?

[djpacro]

depends on the attitude

 

 

[Kamloops]

Djpacro.

 

How oh how did you come to that conclusion.

 

Its a stall!!!!!!!!

 

Learn to recognize that its a stall and get the damn nose down asap.

 

Obviously keeping the current attitude, or trying to pull the nose up even more is not working.

 

Did your instructor teach you this?

 

If so go find a new instructor and take extensive stall training to break your current bad habits that you were taught by some moron.

 

 

[djpacro]

I will never forget an instructor who did indeed show me that technique quite recently, after briefing me on the technique when I queried it. Just coming over the back side of a loop we were extremely slow and he stalled it then pulled the nose down and the aeroplane responded with a sudden spin entry. He was obviously well versed in this as he recovered in a neat 1/2 turn and pulled out of the dive.

 

My turn next. Same stall exercise. Small forward movement of the stick to reduce the angle of attack and we are unstalled so continue to fly the loop.

 

That instructor agreed that my technique of moving the stick forward was better than his of suddenly getting the nose down.

 

Seems to me that he had confused his own instructor's teachings on unusual attitude / stall recoveries. I wonder what key words his instructor used to describe the correct actions that work in all situations?

 

"Learn to recognise that it is a stall ..." not as easy as it sounds to many people, when I ask how they would recognise a stall they typically rattle off all those standard symptoms of an approaching stall but that doesn't answer the question.

 

 

[Garfly]

Ha, ha ... it's good to go softly into anonymous new fora lest we inadvertently teach grandma how to suck eggs ... ;-)

 

 

[aro]

The spiral you are talking about is the "graveyard spiral." The load factor occurs when the pilot attempts to pull up while still in the turn.

The load factor will increase without pilot input because the aircraft maintains the trimmed AOA as the airspeed increases. The pilot can make it worse, but it happens even without pilot input. However it is true that the aircraft will not stall without pilot input because the AOA does not increase.

 

After the wings level pull up to start the energy management turn, we bank keeping the load at 1g and allow the nose to go down as it wishes.

If you are nose up and slowing and allowing the nose to drop, you will naturally be at less than 1g. You can bank and pull to maintain 1g, but as the aircraft slows you have to add AOA to maintain the G. It becomes very much a timing thing whether you get the aircraft turned and airspeed increasing again before AOA exceeds the critical angle.

 

The problem is that height gained is the square of the airspeed, so what works in a fast aircraft might not work so well in a slower aircraft.

 

If you start at 120 knots and let speed wash off to 60 knots you get more than double the height than from 80 knots to 40 knots. Double the height gives much more time for the nose to go down and the aircraft to turn. If you add a draggier airframe you lose more energy on the way up and back down. It's easy to see how in slower draggy aircraft people could run out of energy before completing the turn.

 

 

[Garfly]

On this old, but good, subject of stalling, Aviation Safety Magazine (USA) has had this to say recently:

 

http://www.aviationsafetymagazine.com/issues/34_9/features/10757-1.html

 

http://www.aviationsafetymagazine.com/issues/35_9/features/Maneuvering-Stalls_11045-1.html

 

And just today, in another (Skyranger) forum, this was offered by Paul Dewhurst (UK):

 

"But stall spin accidents still are the most popular way to kill yourself in small aeroplanes! - usually the situation is distraction leading to approaching the stall inadvertently with aircraft out of balance. when the nose mushes down, our hapless pilot resists this with more back stick. When the wing starts to go down they try to stop it with aileron. it is unlikely in this stressed situation that they coordinate with rudder so adverse yaw develops causing the wing to drop further and the nose to drop further. the response to this is then more back stick and more opposite aileron.., it can slowly develop or reach a stage where it 'flicks' into a more defined spin entry.

 

The skyranger models I have tested are very resistant to this and need some big inputs and lots of yaw to spin. But it takes less than full control to enter a spin, and it is easier to spin with some power set - the engine provides some yaw that must be corrected.

 

Normally the Skyranger / Nynja will need full or nearly full control to sustain a spin and even so can often self recover - but it may take a few hundred feet to do this, and can often end up in a tight spiral dive - which also needs some recognition and skills to recover quickly.

 

Recovery from spin - it can be done simply by centralizing the flight controls - we tried this and it worked for us in our testing. But classically you must apply opposite rudder and then move the stick forwards. Due to low inertia the spin stops very quickly.

 

Best defense is to practice stalling and slow flight regularly - and play with the edge of the stall. I like to practice thermalling and best results are at the lowest speeds, so I constantly play the edge of the stall, sometimes just tripping into the stall buffet. This is excellent practice at really feeling the aircraft state and developing an instinctive affinity, and automatic reflexes in the correct way. But also practice in all configurations. Traditionally instructors put emphasis on turning to final - so turning stalls with low power and flaps down. But for microlights this sort of accident is rare. Stalling on a go around is more common - so with power and flap and out of trim. Or circling some feature for photographs - so normal configuration, low to medium power and in a turn. Or when gliding - perhaps with engine failure after takeoff or in the cruise - so practice recoveries with just the stick, returning to the glide, as well as with power trying to minimize height loss and finishing in a climb."

 

 

[Kamloops]

Djpacro, I concur that inverted in a loop is a special circumstance.

 

I had no idea from your original statement that we (you) were not talking about normal flight.

 

So for that my apologies sir.

 

 

[Contact Flying]

Aro,

 

I don't think I am going to be able to convince you of the energy savings and safety of the energy management turn. If you know of a more effective and safer way to make very steep turns very close to the ground, crop dusters, pipeline patrol pilots, gunship pilots, and pilots needing to turn back in box canyons need to know.

 

Would you be willing to go up high and try it? I know you would like it. If just doesn't load the airplane up and bleed energy like the steep, level turn. It doesn't hurt your back so much after a hundred turns a day. The airplane likes it. It is the best thing since beer in cans.

 

Contact

 

 

[facthunter]

A full spin surely would not be a common development, but at low height a dropped wing , followed by an attempt to pick it up with aileron on a plane without exaggerated washout is going to result in a vertical dive into the deck at anything below 500 feet There are ways to recover , but our method of stall and incipient spin recovery teaching doesn't cover it. Nor are minimum height loss course reversals or power off steep turns. Nev

 

 

[Aldo]

Aro

 

I think you are missing the point being made by Contact, this is not about having an instructor/examiner sitting beside you having you complete a 180/360 degree turn maintaining +-50 feet this is about conserving and using energy to the optimum (if you continually try to do level turns at low level you will eventually end up nose first into the dirt).

 

The point (I believe) that Contact is trying to make is that you can't stall an unloaded wing, if during the turn you allow the nose to fall away naturally (you will not end up in a spiral dive) once the turn is completed level the wings, at this point you will have max energy available, yes you will be in a shallow dive (but you will have airspeed and airspeed is your friend) you then commence pulling the nose back up to maintain level flight.

 

Key points, start the turn from straight and level (I know croppies don't always do this and there are other situations where you can't always do this, e.g. Box canyon turns, 180 deg turns without loosing altitude and being on the reciprocal track) complete the turn nose down and wings level then regain straight and level flight.

 

I'm no expert and you can take my opinions with a grain of salt, Dutch may have some comments about what I have said above and he has way more experience than me.

 

Aldo

 

 

[facthunter]

Aldo, I'm not mentioning LEVEL turns. It's a minimum energy loss manoeuver. Probably used to be called a "stall" turn because some of it is at below the normal stall speed. Bit of a misleading term as it doesn't HAVE to be. I'm not too keen putting this stuff up as some misunderstandings are inevitably going to occur. Nev

 

 

[Aldo]

Aldo, I'm not mentioning LEVEL turns. It's a minimum energy loss manoeuver. Probably used to be called a "stall" turn because some of it is at below the normal stall speed. Bit of a misleading term as it doesn't HAVE to be. I'm not too keen putting this stuff up as some misunderstandings are inevitably going to occur. Nev

Nev

 

I understand what you are saying

 

Aldo

 

 

[Garfly]

This 13 sec video of a departure stall-spin-crash doesn't explain much - it's hard to figure out why it happened.

 

But it's such a graphic - unforgettable - illustration of what the theory discussed here can come down to; in seconds flat.

 

 

 

[facthunter]

Well there is no wind on the windsock and no use of rudder that I could detect. Nev

 

 

[kaz3g]

Aldo, I'm not mentioning LEVEL turns. It's a minimum energy loss manoeuver. Probably used to be called a "stall" turn because some of it is at below the normal stall speed. Bit of a misleading term as it doesn't HAVE to be. I'm not too keen putting this stuff up as some misunderstandings are inevitably going to occur. Nev

My mustering pilot used the same technique to do his runs across in front of a galloping mob of scrubbers back in the Gascoyne years ago. Not quite a stall turn, rather a Chandelle at very low speed so there was still movement of airflow over the rudder apart from prop wash.

 

Kaz

 

 

[dutchroll]

Dutch may have some comments about what I have said above and he has way more experience than me.Aldo

I'm still trying to figure out who the "3 clueless airline morons who were hired because they could tie a windsor knot" were.

 

 

[Kamloops]

Dutchroll, I thought I had posted the link to the Air France Heavy that stalled at well over flight level 300, and yet despite the captain and 2 copilots in the cockpit, and stall warning horns blaring, and stick shakers. They kept pulling back, when they just had to ease the nose down.

 

When i get home later today I will google the crash report and repost the link.

 

Those were the 3 morons I was referring to.

 

 

[Garfly]

Are these wingovers the kind of energy management turns you're talking about Jim?

 

 

 

[Bennyboy320]

Search youtube "Airbus stall training" excellent video. the same rules apply to RAA a/c, well maybe the the high Mach stuff.

 

 

[Kamloops]

Dutchroll, I am late posting it, but here is the story link I thought I posted before.

 

It is just one example of many hundreds where a stall in regular flight is met by pulling nose up.....until the crash....instead of pitching nose down to regain airspeed and fly away safley.

 

http://www.flyingmag.com/news/air-france-447-stalled-high-altitude-official-bea-report-confirms

 

 

[facthunter]

You don't have much speed and the stick is not held back and the rudder does the turning. Don't teach yourself at low height for heavens sake.Nev

 

 

[facthunter]

Kamloops "just one of many hundreds" Really? Whilst that accident appeared to be a rather basic misapplication of the controls and in that plane one pilot can not feel what input the other one was putting in The FMS on those aircraft does not have the sort of logic that might seem basic to flyers of our type of stuff. There was failure of one Pitot system and they were in an Inter Tropic Convergence zone, which is grim icing and turbulent weather. Normally functioning A 320 or whatever it was have stall protection etc and I don't have the details and intricacies in front of me, to unravel.. With the known unserviceability the Skipper should have been in the cockpit it the critical weather event time in my view, and it's always important to know who is actually flying an aircraft. You do it when some one says "Your plane" and you reply "I've got it", or something to that effect. Nev

 

 

[aro]

the Air France Heavy that stalled at well over flight level 300, and yet despite the captain and 2 copilots in the cockpit, and stall warning horns blaring, and stick shakers. They kept pulling back, when they just had to ease the nose down.

I think you'll find it's a bit more complicated than that.

 

For example, they exceeded the valid range of the stall warning, which meant that the stall warning sounded when they pushed forward, and stopped when they pulled back. They were not sure whether the noise and buffeting was because they were over or under speed - at one point they tried reducing thrust to idle and speed brakes to recover.

 

The full report makes interesting reading, and has a lot of information that wasn't in the media reports.

 

When they lost the airspeed the aircraft switched to alternate law, which not only removed the stall protection, but also removed speed stability. In alternate law the pitch control was based on load factor, which meant that with no input the aircraft would maintain 1 G. If the thrust was too low for the flight path it would pitch up as it slowed until it stalled, without any pilot input required. This is the opposite to normal aircraft, which pitch down to regain trimmed speed as they slow. Yes, the pilot made additional pitch up inputs, but speed instability would not have helped. The alternate laws in pitch and roll were very different which resulted in very different inputs being required.

 

So the situation the pilots were dealing with:

 

• IMC, at night
   
   
  
• Loss of airspeed indication
   
   
  
• A switch to alternate law which meant that the flight controls had different feel to what they were used to, and the aircraft was not speed stable
   
   
  
• A change from an aircraft that could not be stalled to an aircraft that would stall without pilot input
   
   
  
• Power and attitude: 10 degrees nose up with full thrust
   
   
  
• A high rate of descent
   
   
  
• Multiple alarms, including a stall warning that sounded when they pushed forward, and stopped when they pulled back.
   
   
  

 

 

It doesn't surprise me that they couldn't figure that out in the limited time available. For example, what if the loss of airspeed and rate of descent indicated a problem with the static system - how would the indications and recovery actions differ?

 

It's easy to say it was obviously a stall after the fact, but one thing I have found: everything is obvious after you know the answer.

 

Certainly the pilots didn't handle the situation well, but aircraft features e.g. the alternate law lack of stability and stall warning limitations made the situation worse.

 

 

[dutchroll]

Dutchroll, I am late posting it, but here is the story link I thought I posted before.It is just one example of many hundreds where a stall in regular flight is met by pulling nose up.....until the crash....instead of pitching nose down to regain airspeed and fly away safley.

http://www.flyingmag.com/news/air-france-447-stalled-high-altitude-official-bea-report-confirms

Yeah I've been desperately trying not to comment on this Kamloops because I've felt I needed a sanity break. For info, I'm a current operational A330 pilot in my day job (however my training was Air Force, as was 16 years of my flying career). But here goes:

Your contention that the 3 pilots were clueless morons and that's why it ended up at the bottom of the Atlantic is unjustified.

 

For a start the Captain wasn't even in the cockpit when the aircraft was stalled by the mishandling of the junior flying pilot, after being faced with a number of confusing system warnings and cautions pertaining to air data and airspeed. He was asleep in the crew rest. He had 2 minutes after having been awoken and greeted with a totally unexpected and confusing situation, to try to analyse and understand what these 2 guys were doing. In fact he did eventually realise what had happened but it was all too late. They were at 2000ft with a 10,000ft/min rate of descent. Even when he instructed the pilots how to correctly recover, the junior pilot pulled full back on the stick while the other pilot was trying to push forward and recover, negating any probability of doing so. In the Airbus, the flight control system "averages" the inputs of both sidesticks.

 

The Air France training system shouldered a lot of blame for the accident. It wasn't that the pilots didn't know how to recover from a stall. It was that they didn't realise that they were in one. Their training system, approved by Airbus itself, emphasised that the aircraft is not possible to stall in normal operations. This is actually quite true as the aircraft has angle of attack protection which will simply not let it stall no matter what you do with the stick......in normal operations.

 

For example, if we get a "pull up" warning from the ground proximity system, what do you think our trained immediate checklist actions are? It might surprise you that they are to pull fully back on the stick and hold it there, irrespective of anything else including airspeed. In a windshear recovery, it specifically states "up to full backstick if necessary". A colleague of mine recounted how a few years back they were cruising along and suddenly went into a substantial temperature gradient, which caused the speed to decay rapidly and with traffic below them. He ended up with full backstick, the aircraft sitting there at max angle of attack, protected by the stall protection system, before finally being able to descend to a lower altitude. So there has been a mentality around for a long time that the Airbus just can't be stalled. Unfortunately this isn't true. The stall protection is lost when certain computer failures occur, and that happened to AF447.

 

There was never any proper handover/takeover of control either. The junior pilot who stalled it in the first place was poorly trained and most likely out of his depth. The other guy tried to takeover but was clearly also confused about what was happening and allowed the junior pilot to still be attempting to pull back on the stick to arrest the rate of descent. The A330 does tell you when both pilots are making inputs on the stick, but as I mentioned before, it just averages them out unless you push and hold the takeover button. If you've got a christmas tree of warning messages and other alerts going off, it's quite possible to not notice (and indeed in the accident report, there are occasions where some aural alerts are overridden by others).

 

So it makes for a complicated analysis of what happened in an electric jet which had a number of system faults occur, design and human interface problems which have been there from the beginning, and compounded by poor training and procedures.

 

http://www.bea.aero/en/enquetes/flight.af.447/rapport.final.en.php

 

 

[aro]

I don't think I am going to be able to convince you of the energy savings and safety of the energy management turn. If you know of a more effective and safer way to make very steep turns very close to the ground, crop dusters, pipeline patrol pilots, gunship pilots, and pilots needing to turn back in box canyons need to know.Would you be willing to go up high and try it? I know you would like it. If just doesn't load the airplane up and bleed energy like the steep, level turn. It doesn't hurt your back so much after a hundred turns a day. The airplane likes it. It is the best thing since beer in cans.

I have no issue with crop dusters, pipeline patrol pilots, gunship pilots etc. doing this type of turn. I understand the reasons they do it, and I assume they train for it. But we aren't (generally) crop dusters or gunship pilots.

 

My problem is the suggestion that recreational pilots should try it after reading about it on the internet. I believe that if we are to do them we need to be trained to do them properly by someone with experience. However, the situations where we should be doing high performance turns close to the ground are very limited anyway.

 

Maybe it's a terminology problem. When you talk about a no load factor turn I think load factor 1 = 1 G, no load factor = 0 G, so you are talking about a turn where you reach 0 G (or at least significantly reduced G). Something similar to a wingover, stall turn, hammerhead etc. Certainly, you won't stall an aircraft at 0 G, but the danger with any energy management maneuver is that you run out of kinetic energy with the aircraft pointing in the wrong direction - particularly in slow aircraft which don't have an excess of kinetic energy to start with.

 

However, I downloaded your ebook to try to understand better what you are suggesting and watched the video you link to. The energy management turns shown in the video look fairly gentle and I don't have an issue with them (although I don't think they would reduce the load factor significantly). But then in the text you talk of using rudder to roll level etc. because ailerons may not respond normally, which does seem like an extreme maneuver to be performing close to the ground.

 

I'm not particularly a fan of beer in cans either :-)