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He stepped on the Rudder and redefined Va

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He stepped on the Rudder and redefined Va

Old 28th Sep 2013, 09:33
  #61 (permalink)  
 
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Bubbers, read the post above.

yaw damper authority is a fraction of the full rudder travel
Meaning the yaw dampers maximum input can only mover the rudders a fraction so can't have caused violent yawing.

For example the 747 rudder can move +/-32 degrees however the yaw damper can only move the rudder +/-4 degrees.

You need a power control unit (PCU) failure like the 737 to command full and violent yaw.

Last edited by SMOC; 28th Sep 2013 at 09:52.
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Old 28th Sep 2013, 13:43
  #62 (permalink)  
 
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Originally Posted by AirRabbit

Tails of transport category airplanes do not “come off” at speeds under Va … or over Va … if the airplane is flown the way it was intended (and certificated) to be flown.
One of the things I discovered in the aftermath of AA587 was that a fair number of pilots seemed to understand Va as that speed below which ANY maneuver is ostensibly safe. That's not how I was taught. I was taught more to the effect that below Va any NORMAL maneuver is safe, and certainly dancing on the rudder stop-to-stop is not a normal maneuver, at least in my opinion.
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Old 28th Sep 2013, 15:25
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I was recently interviewed for nonTR DEC position. Questions I was asked (among the others) were:

- which scheme correctly depicts model of solar system, followed by sketches of the Sun, the Earth and the Moon circling around each other.
- if aeroplane A has twice the mass of aeroplane B, at the same speed its kinetic energy is a) half of B b) the same c) quadruple of B d) double of B
- if aeroplane A has twice the speed of aeroplane B for the same mass, its kinetic energy is a) half of B b) the same c) quadruple of B d) double of B
- pendulum of larger mass and the same length at the same free fall acceleration has a) higher b) lower c) same frequency compared to lighter one.

Thanks to PPRuNe, I wasn't bewildered by the need to ask such questions and appreciated the reason behind them.

Folks, you are welcome to ask questions, whoever knows (or thinks he knows) the correct answer will be happy to reply, we all might learn something useful from discussion, but If you insist on obstinately pushing forward theories that have nothing to do with reality, you just have no right to feel offended if your efforts are not appreciated.

No, he did not step on the rudder and redefined Va. If he did and tail separated, he would have redefined it. He rapidly cycled the rudder under conditions where no rudder input at all was necessary, thus wiping out himself, his crew and his passengers from existence and posthumously opening the can of worms:

One of the things I discovered in the aftermath of AA587 was that a fair number of pilots seemed to understand Va as that speed below which ANY maneuver is ostensibly safe.
Sadly, correct. That's why every manual I've come across in last couple of years has warning of possible airframe failure if controls are cycled even below Va.

I was taught more to the effect that below Va any NORMAL maneuver is safe, and certainly dancing on the rudder stop-to-stop is not a normal maneuver, at least in my opinion.
Opinion correct.
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Old 28th Sep 2013, 15:40
  #64 (permalink)  
 
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Originally Posted by clandestino

Folks, you are welcome to ask questions, whoever knows (or thinks he knows) the correct answer will be happy to reply, we all might learn something useful from discussion, but If you insist on obstinately pushing forward theories that have nothing to do with reality, you just have no right to feel offended if your efforts are not appreciated.
Careful now, I got banned for saying something pretty similar, albeit not as elegantly.
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Old 28th Sep 2013, 16:41
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It may be appropriate to offer just a tad more information on this specific issue… Not a lecture ... more of a plea ...

I think it quite valuable to understand the factors involved in the loads experienced on the vertical stabilizer / rudder under conditions when an airplane is “yawed” into a sideslip. A sudden rudder deflection will start a yaw, and, if the deflection is at maximum, you get the maximum rudder load. With this condition, the yaw will move the airplane tail to what is called an “over-swing” position. Once getting to that position, the airplane will experience the maximum torsion on the vertical tail. With the rudder in that position, the maximum force on the vertical stabilizer and the maximum force on the rudder surface are opposite each other. With the rudder held in this maximum deflected position, the airplane will oscillate from its “over-swing” position, and dampen down to a position known as “equilibrium yaw.” The same analysis is performed for engine failure, for rolling moments, and lateral (side-to-side) gusts. The most severe of these cases provides the design basis for the vertical stab and the rudder and is called the “limit load.” Here is where the 1.5 factor comes into play. The “ultimate load” is described as the “limit load” multiplied by 1.5. The structure must be able to support the “limit load” without permanent deformation that is detrimental to flight AND support the “ultimate load” without failure. The time for this test is 3 seconds. If either failure occurs within that 3 seconds, the test is failed. But (and it’s a VERY BIG “but”) when the airplane is in this maximum equilibrium yaw, a sudden commanded full, or nearly full, opposite rudder movement against that sideslip can generate loads that exceed the “limit loads” and possibly the “ultimate loads” and can result in structural failure. Certification limits do not consider the survivability of the structure under these extreme conditions.

I think that it is also important to understand that in order to begin to move any of the flight controls, there is what is known as a “break-out” force, or the force necessary to begin the controller movement - like the control wheel or rudder pedal. Once movement is started, there is a force necessary to continue to move the controller. But here we’re focused on the relevant control and control force is that necessary to move the rudder pedals. As you would probably suspect, the A300-600 rudder is hydraulically actuated – no surprise. In systems such as this, there is no direct feedback to the pilot. There is no “air load” on the control surface that the pilot can “feel,” so the system is built to provide an artificial “feel.” By way of comparison, a B767 (a similar sized airplane) at 250 knots has a breakout force of 17 pounds-feet (technical term) and the pilot would need to generate 80 pounds-feet to achieve maximum displacement – which in this airplane, is a bit over 3 and a half inches of rudder pedal travel and 8 degrees of rudder surface deflection. The A300-600 is noticeably different. Same circumstances the pilot has to use 22 pounds-feet to start the movement (breakout force) and 32 pounds-feet to get maximum rudder pedal travel (about 1.2 inches) and maximum rudder surface deflection (9.3 degrees). I don’t want to bore you with math, but the answer is that the A300 is over 7 times as sensitive as the B767; important enough to repeat … over 7 times as sensitive!! If you say this another way … the amount of rudder actually deflected for each pound of force on the rudder pedal above the breakout force is almost 9 times as much in the A300 as in the B767.

I said that the AA587 F/O was at the controls and therefore must bear at least some of the responsibility. I stand by that statement. However, I should also acknowledge that, in my opinion at least, pilots are not often enough trained on the FULL aerodynamic envelope, and how to manage that envelope, of the airplane they fly. My background and experience is heavily focused on education and training – and, no, I don’t believe that education is the fix-all remedy. However, education AND training, in combination with experience, is the basis on which being a pilot should stand. And like anything else, the content of that education, training, and experience has to be appropriate for what the person (here, the pilot) will be expected to face and handle professionally and completely.

I think that this F/O was probably one of those individuals who took a lot of pride in his airmanship – and I suspect he probably was a very good pilot. I think he was the type of person who constantly wanted to correct back to what he was trying to hold - and don’t we all, at least to some degree? I also think that he probably was a bit unsure of the proper way to deal with a wing-tip vortex encounter. I think he was not advised of, and very probably not trained on, the problems that can develop with maximum control input and repeated maximum control reversals. I think he was not aware of the sensitivity of the controls, particularly of the rudder, and how much rudder he was getting with very little force applied and how little pedal deflection generated full surface deflection.

I am also aware that the organizations that hire pilots are not interested in having their pilots spending their “on duty” time 90% in training and 10% on the line. But the question quickly becomes, do we train pilots for the minimum regulatory requirements (which all – or most anyway – airlines do today) and depend on the “good-naturedness” of the management to volunteer additional time in training … or do we increase the mandatory training requirements to an appropriate level – and what IS that appropriate level? I believe this is an important question – not just to be hashed around at the local bar at overnight stops. Serious, committed effort is necessary to determine what is required – absolutely required – and what is “nice to know” kinds of things. This is NOT an easily defined goal – but I know that as long as we continue to ignore it … we’ll never get to the answer!

Last edited by AirRabbit; 28th Sep 2013 at 21:40.
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Old 28th Sep 2013, 17:12
  #66 (permalink)  
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Rabbit - You are vastly overcomplicating the subject, where members in here think articulation substitues for knowledge.

Simply put a plane has design limitations, generally predicated on G force, as G force is a static number, given a varying airspeed. So 2 gs at 300 kts = 2 gs at 100 kts. Weight is weight. Certainly the input at 300 kts equal to the imput at 100 kts will provide more Gs.

But all things equal we are not talking about a plane flying through tops at Vmo with the pilots standing on the rudders, but a departure, slow speeds, well under Va. So a tail coming off at such slow speeds defies logic, unless, ofcourse, it's a carbon fibre/aluminum hybrid, that can't be Xrayed for fissures, but none the less, after the accident was fortified.

That said, the fallacy that one right rudder load for instance at a given acceptable load factor, then swinging the other way, at an acceptable load factor, has some mysterious exponential effect is pure baloney.

We aren't talking about building up resonance frequencies that need occilations on the order hundreds of hz, that typically happen well past Vne.

People can say all they want that test pilots can't account for every action that a pilot will possibly pull in an plane, but there is a reason why test pilots go up and slam everything up and down, back and forth, side to side, then bring it down for the engineers to see if the math was right.

Pure baloney to consider that any pilot moving the rudder three times will in any way exceed what a test pilot would do over thousands of hours, with much more rigourous flight imputs.

This is a simple case of carbon fibre mated with alluminum, resulting in Airbus fortifying the structure, after the fact, then trying to sell it to the authorties that anything can happen in a plane, at anyspeed, with any control input...effectivelly making many of your Vspeeds completly unreliable. This is just the recalibration going on in the industry right now where water isn't wet, the sky isn't blue, grass isn't green, and Va doesn't mean full deflection but rather, a worthless number, because you know, Airbus says so. The FAA has swallowed this hook line and sinker the same way they were convinced that an ATP wasn't required of prospective airline hires, putting 200 hour ab initio pilots in the cockpit 'because they have a special training program that meets or exceeds ATP requirements'.

Sure.

Last edited by Teldorserious; 28th Sep 2013 at 17:15.
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Old 28th Sep 2013, 17:20
  #67 (permalink)  
 
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Best one I read today.
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Old 28th Sep 2013, 17:52
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But all things equal we are not talking about a plane flying through tops at Vmo with the pilots standing on the rudders, but a departure, slow speeds, well under Va. So a tail coming off at such slow speeds defies logic, unless, of course, it's a carbon fibre/aluminum hybrid, that can't be Xrayed for fissures, but none the less, after the accident was fortified.

That said, the fallacy that one right rudder load for instance at a given acceptable load factor, then swinging the other way, at an acceptable load factor, has some mysterious exponential effect is pure baloney (...) and Va doesn't mean full deflection but rather, a worthless number, because you know, Airbus says so.
Boeing and IFALPA seem to differ:
A structural design manoeuvring speed or Va is defined for evaluating aircraft structural design. At or below this speed, Boeing aircraft are capable of sustaining a single maximum deflection input to any control surface – elevators, ailerons or rudders (as limited by control surface limiters, blowdown or control stops). It should be noted that these control surface inputs are to be in one axis (i.e. not in combination) and do not include control input reversal or oscillatory inputs.
(...)
Boeing aircraft are not designed to a requirement of full authority rudder reversals from an "over yaw" condition. Sequential full or nearly full authority rudder reversals may not be within the structural design limits of the aircraft, even if the airspeed is below the design manoeuvring speed. There are no Boeing Procedures that require this type of pilot input. It should also be pointed out that excessive structural loads may be generated in other areas of the aircraft, such as engine struts, from this type of control input.
Source and more on the subject: http://www.ifalpa.org/downloads/Leve...20aircraft.pdf , p. 2 & 4. They have one on rudder use in the Airbus, too: Aircraft Design & Operation Committee (ADO)

Last edited by Jetdriver; 28th Sep 2013 at 18:10.
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Old 28th Sep 2013, 18:54
  #69 (permalink)  
 
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Originally Posted by AirRabbit
I don’t want to bore you with math, but the answer is that the A300 is over 7 times as sensitive as the B767; important enough to repeat … over 7 times as sensitive!! If you say this another way … the amount of rudder actually deflected for each pound of force on the rudder pedal above the breakout force is almost 9 times as much in the A300 as in the B767.
True, but largely irrelevant unless someone provides the reference where it says a) rudder on any transport category aeroplane is normally used to control bank or b) that large, rapid and alternating control inputs have reasonable use on any aircraft. Go on, find any single circumstance on any single aeroplane where inflight rapid stop to stop movements in any axis make sense.

Originally Posted by AirRabit
However, I should also acknowledge that, in my opinion at least, pilots are not often enough trained on the FULL aerodynamic envelope, and how to manage that envelope, of the airplane they fly.
True, but largely irrelevant to case discussed as aeroplane was well within the envelope when it hit the wake and was chased out of it by inappropriate inputs on rudder pedals. It was not as if large slip oscillations was brought on by external factors so we need to teach pilots how to fight it. Better teach them how not to start it and while...

Originally Posted by AirRabbit
I don’t believe that education is the fix-all remedy
... here it would just do the work.

Originally Posted by AirRabbit
And like anything else, the content of that education, training, and experience has to be appropriate for what the person (here, the pilot) will be expected to face and handle professionally and completely.
If other aeroplanes, of the same type or different, were regularly falling out of sky with their tails torn off after hitting the wake vortex, then I might concede you have a point here and poor average line pilot is indeed ill-equipped to deal with the horrible rudder.

Originally Posted by AirRabbit
I think that this F/O was probably one of those individuals who took a lot of pride in his airmanship.
According to the report, chapter 1.5.2.1. he was regarded as above average pilot so pride would not be misplaced. However, his misunderstanding that he was instructed under AAMP to use rudder unconditionally when faced with slight upset turned out to be fatal. Should we call this "incomplete airmanship"?

Originally Posted by AirRabbit
I think he was not advised of, and very probably not trained on, the problems that can develop with maximum control input and repeated maximum control reversals.
Perchance because conventional wisdom considers such inputs completely useless and extremely dangerous so has just one thing to say about them: don't.

Originally Posted by teldorserius
Simply put a plane has design limitations, generally predicated on G force
That's just very, very small fraction of the limitations. BTW, limitations are not optional, you have to obey them all.

Originally Posted by teldorserious
But all things equal we are not talking about a plane flying through tops at Vmo with the pilots standing on the rudders, but a departure, slow speeds, well under Va.
Fin failure happened at 251 kt, Va was 270. 1 it takes a lot of subjectivity to put it under "well below Va" which is not to say it is safe to do whatever you want faar below Va. Large enough sideslip might produce extreme load thorough high Cl when rhoveesquared is lacking.

Originally Posted by teldorserious
So a tail coming off at such slow speeds defies logic
It does only if your premises include completely wrong picture of lateral dynamic stability and aircraft-pilot coupling.

Originally Posted by teldorserious
We aren't talking about building up resonance frequencies that need occilations on the order hundreds of hz, that typically happen well past Vne.
No, we are talking about dynamically unstable yaw that reached extreme amplitude at frequency below 1Hz.

Originally Posted by teldorserious
People can say all they want that test pilots can't account for every action that a pilot will possibly pull in an plane, but there is a reason why test pilots go up and slam everything up and down, back and forth, side to side, then bring it down for the engineers to see if the math was right.
They might use full displacement. They might use rapid but they would never use large, rapid and alternating. They know better than killing themselves.

Originally Posted by teldorserious
Pure baloney to consider that any pilot moving the rudder three times will in any way exceed what a test pilot would do over thousands of hours, with much more rigourous flight imputs.
One has to weigh NTSB well explained, consistent and documented report against two words: "pure baloney". Tough one, eh?

Originally Posted by teldorserious
This is just the recalibration going on in the industry right now where water isn't wet, the sky isn't blue, grass isn't green, and Va doesn't mean full deflection but rather, a worthless number, because you know, Airbus says so
No, such recalibration is just going on around anyonmous internet fora where people promote brazen falsehoods without any fear of consequences.
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Old 28th Sep 2013, 19:24
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the NTSB did not unanimously agree with blaming the copilot.


if stomping on the rudder is bad, better put a placcard in front of the pilots


or make stronger planes
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Old 28th Sep 2013, 19:54
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Blantoon, don't come in here with 4 posts and start giving the riot act. I am all ears if you have something to offer up.

If the tails of airliners come off under Va, then technically Va doesn't exist, or it needs to be lowered, or recertified with a placard that states.

'Pilots are to only use the rudder one way per episode to avoid catastrophic results'
What does anyone's number of posts have to do with anything?

I would gladly offer something up, but since other people have already said anything I'd say far more eloquently than I could and you still won't put down that shovel; I think I'll refrain from wasting my time.
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Old 28th Sep 2013, 20:33
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Mr. Teldorserious – as I said earlier in this thread, throughout my tenure on this forum (and others) I’ve attempted to maintain at least some decorum in what I consider to be a rather professional discussion – as is typical of this forum. I don’t know your level of education – or the level of understanding you have – with regard to airplane construction and/or certification issues and, neither do you know mine. I have attempted to point you toward the regulatory requirements for the use of rudder in transport category airplanes. Yet you seem to be enamored with the concept of relying on what you “know” about airplane structures issues. With no attempt to insult you, I sincerely believe that regardless of the proficiency you now have in an airplane, if you were to broaden your knowledge of aircraft certification requirements and flight testing procedures, you would probably elevate that proficiency by a substantial margin. Of course, I have only the option of recommending that you do so … and, as to your comment on the rest of the participants on this forum “…thinking that articulation substitutes for knowledge…” I do not believe that to be true – even to the smallest level. Additionally, the “baloney” you believe I’m trying to force you to eat, may just be the “meat ‘n potatoes” on which you rely each time you say or hear “gear up.” In an attempt to get you to recognize the accuracy of your position, without causing you any potential embarrassment, I would humbly suggest you find an aeronautical engineer in whom you have substantial confidence and ask him/her to explain to you the potential results of applying rudder in the way the FDR assuredly shows was applied aboard AA587. Simplistically, if you ask this engineer his/her opinion of the results of a transport category airplane experiencing 7 control wheel reversals and 5 rudder pedal reversals, to the same magnitudes and at the same altitudes and airspeeds experienced by AA587 (which I presume you recognize to be well below Vne), all within 7 seconds, as recorded on the AA587 FDR, perhaps this engineer can explain the results better than I have apparently been able to explain. AND, should it be that you are, indeed, correct, I would you suggest you run, not walk, to the FAA and secure a consulting gig with them to rewrite their regulations for certification of transport category airplanes – as that would surely put some substantial coin in your pocket due to the significant amount of errors that must surely exist in those documents.
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Old 28th Sep 2013, 20:39
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Come on Clandestino – you know there is no one here saying that rudder should be normally used to control bank or that large, rapid, alternating control inputs have any reasonable use on any airplane, and certainly not me. The point is that such control applications make NO sense. And I agree that this particular airplane was well within the normal operations envelope and would warrant normal control inputs to control the airplane … in fact, this specific pilot did just that, and did so a mere 9 seconds previously to his initiating these obviously out-of-bounds over-control applications, when this encounter was no more serious than the one he had just transitioned quite successfully. How do I know that? Take a look at the FDR readouts and see for yourself. And, of course, teaching pilots the way to control an airplane throughout the entire envelope is entirely appropriate – and had that been accomplished, this might not have happened.

Also, I’m not sure what “horrible rudder” you are referencing … the one on the A-300-600? I have yet to see anyone say that this is a “horrible rudder.” Attempting to fix something that isn’t broken is like believing that gun control will stop killings due to guns. Guns don’t kill people. People using guns kill other people. But that’s a whole different issue. It wasn’t the rudder that came off the airplane … it was the entire vertical fin that was ripped off … and it was ripped off because of the misuse of the rudder control, accompanying the misuse of the lateral controls – don’t forget that when the ailerons are deployed, so are the roll-control spoilers – which add their own substantial influence into the mix.

I agree that airplanes around the globe are not falling out of the sky because of a loss of the vertical fin. I would love to think that this is due to the superb training received by the pilot groups. However, I tend to believe that at least to the same level of satisfaction you have for the training that currently exists, I believe it is uncommon to see encounters with wing-tip vortices that are handled the way this pilot did the second time. Rather, I believe most pilots deal with those encounters the way this pilot did on his first encounter with the vortex. The question should be – why didn’t he do the same thing he did previously?

Also, I believe you are jumping on the Advanced Maneuver Training that the airline was using. As I said some years ago, I have had the opportunity to see and fly a good share of that same training program – and I saw nothing that could be even remotely interpreted to be permission to use the rudder unconditionally when encountering the slightest upset. It is true that this program discussed the use of rudder – and it was introduced with no more fanfare or encouragement than were the elevator and ailerons. And, as I recall, the times when it made sense to use the rudder were those cases where the nose was uncontrollably pitched up, and the rudder could be used to bring the nose of the airplane back down toward the horizon. That is still true and still makes sense. In my experience with that particular program there was no hint that pilots were encouraged to use the rudder to address the recovery of a “slight upset.” However, the rudder is on the airplane for a specific reason – just as are the elevators and ailerons (including the spoilers). Recall the video of the B747 crash in the middle-east recently? The nose of the airplane was uncontrollably high – and it was apparent to me that the pilot was struggling to get it down … very likely on the rudder to help him do just that. Unfortunately, there was insufficient time and altitude for it to work.
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Old 28th Sep 2013, 20:59
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In respect of the questions/comment about all planes being unable to withstand the rudder being pedaled back and fro......or of it never being done.....and that no plane is tested for rapid reversals etc etc.

Take glider winch launches
If the speed goes too high on the launch you indeed do just that and pedal the rudder left and right. The a/c yaws significantly back and fro and the winch driver sees it as a signal to reduce the speed of the winch cable.
This is the official "too fast" signal on a winch launch.
So here you have substantial rapid alternating rudder deflections being regularly introduced when the a/c is flying near to the max manoeveing speed. Probably not stop to stop but certainly most of the way there.

I am quite well aware that transport aircraft are not in the same category as gliders but I'm just pointing out such movements are commonly used in one such class of aircraft.
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Old 29th Sep 2013, 04:50
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That is still in use in the UK? It is expressively forbidden in Germany for the last 20 years or so. It resulted more than once in unsafe situations and accidents. If the speed is too high simply disconnect, but it might help of course to tell the winch driver beforehand that the speed is increasing, that's why we have mandatory radio communications, right?
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Old 29th Sep 2013, 07:00
  #76 (permalink)  
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Must be fun to get an Airbus type...

'So what's the recomended rudder technique?'

'Well, um, you only push the rudder one way, for x amount of time, not too hard, not too fast, gently allowing it to come back to center. Set your timer...then when it dings, you are allowed to push it the other way, only so fast and hard.'

'How hard and how fast?'

'Well, you know, not too hard, or too fast. And just remember, your tail can come off at any speed. Yeah and forget about a higher Va with more weight..that doesn't apply either, especially on take off. By the way, the FAA says pigs can fly now, hell has just frozen over, girls are boys, red is blue, horses are really cows...are you taking notes?'
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Old 29th Sep 2013, 07:43
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@Denti
As listed in the UK's BGA's laws and rules: Part 9 - Signals
Page 3 of the Part 9 pdf file dealing with signals controlling a winch launch
"RP11: If the glider is being launched too fast, the pilot should yaw the glider from side to side with the rudder"
https://www.gliding.co.uk/bgainfo/lawsandrules.htm

Pilots are warned during training that before doing this they should ensure that they have 'unloaded the glider' by reducing the amount of back pressure they have on the stick if they are pulling back very hard at this point.

There is no radio communication that I have ever seen used between the glider and the winch during the launch. The only radio communication used is between between the launch point and the winch during the setting up of and the inititiation of the launch.
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Old 29th Sep 2013, 07:50
  #78 (permalink)  
 
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Teledor(lessthan)serious

Must be fun to get an Airbus type...
Have you even read the Boeing contributions on this problem? you can find them here:http://www.ifalpa.org/downloads/Leve...20aircraft.pdf

I would draw your attention to this extract:

The FAA/EASA have three rudder manoeuvre structural load design requirements, which the rudder and vertical fin must
meet in order to be certified3. These requirements are met for all airspeeds up to the design manoeuvring speed. In addition, newer
aircraft designs meet these requirements up to the design dive speed.
At a zero sideslip condition; the aircraft must be able to withstand a rapid rudder input to full rudder deflection. A Safety
Factor of 1.5 is then applied. This means the structure must have at least a 50% safety margin over the maximum load
generated by this manoeuvre.
Starting from a zero sideslip condition, the aircraft must be able to withstand a rapid rudder input to full deflection that is
held at full deflection until the maximum sideslip angle (over yaw) is achieved. The aircraft will exceed the maximum
steady state sideslip due to the dynamic response characteristics of the aircraft. A Safety Factor of 1.5 is then applied.
Starting from a maximum steady heading sideslip condition, the rudder is rapidly returned to neutral while maintaining
the sideslip angle. A Safety Factor of 1.5 is then applied.
During certification, Boeing does not flight test these exact conditions, but gathers flight test data to validate structural loads analysis.
This analysis, combined with ground structural load testing, ensures that the structure meets design requirements.

The FAA/EASA impose structural load design requirements in addition to these rudder manoeuvre requirements. These include
requirements for loads due to gusts, engine failure dynamics, and lateral control induced rolling conditions. Boeing aircraft vertical
fins can also sustain loads if the rudder is rapidly returned to neutral from the over yaw sideslip or the rudder is fully reversed from
a full steady state sideslip.
Note 3: These conditions are engineering design conditions that may be physically impossible to fly.
Also to Fig.3 which shows the sideslip response to cyclic rudder movements and Fig.4 that shows the torque on the vertical stabiliser due to cyclic application of rudder.

Now you may think it amusing to slag off Airbus with cheap shots, but there are folks on this forum that actually take things more seriously than that. Let me remind you that the extract quoted above comes from Boeing. Note the careful wording that their vertical fins can sustain loads if the rudder is rapidly returned from over yaw sideslip or the rudder is fully reversed from a full steady state sideslip. No mention of the fin being able to carry the torque if the rudder is fully reversed at peak over swing sideslip. And all that relates to a single application and reverse of rudder. Look at the effect of cyclic rudder application on sideslip and you will (or should be able to) see that applying full reverse rudder at a peak of an enhanced overswing sidslip is going to produce loads well in excess of the structural capability. And that is for a Boeing aircraft!

In their equivalent document Airbus do not specifically mention an ability to withstand loads if the rudder is rapidly returned to neutral from the over yaw sideslip or the rudder is fully reversed from a full steady state sideslip, but the fact that the AA587 fin failed at about 2.2 times the limit load (as against the statutory 1.5 times) shows that their design has similar structural reserves to Boeing. [And that was the fin with the factory repair that you suggest might have been faulty - don't you realise that any aircraft repair has to be designed to be at least as strong as the original structure!]

I can only concur with Air Rabbit that you might benefit from some serious study of aircraft design and construction.

BTW, you did not respond to my request for identification of the source of your original remark re FAA changes to Va. There was a long debate about the definition of Va in an earlier thread. Perhaps you should also read Keith William's contribution in #21 of the Va Manoeuvring thread

Last edited by Owain Glyndwr; 29th Sep 2013 at 07:56. Reason: editorial
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Old 29th Sep 2013, 08:23
  #79 (permalink)  
 
Join Date: Mar 2001
Location: I wouldn't know.
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@dsc810 quite off topic now, but yes, in times gone past the same signal was used over here, but it was discontinued as it was deemed extremely unsafe and isn't allowed anymore (although some of the older crowd might still use it, if somethings happens insurance won't pay a thing then). Radio communications are required between winch and launch point as well as between launch point and glider, however every club i flew with had an additional radio on the winch to monitor the glider fields frequency for exactly that kind of command as it is of course faster than communication via the launch point. Current requirement for overspeed is to disconnect and depending on height land back or straight ahead.

And of course certification requirements between gliders and airlines are vastly different, so on the rudder issue, which is used much more often in gliders, it is probably something about apples and oranges.
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Old 29th Sep 2013, 08:54
  #80 (permalink)  
BBK
 
Join Date: Feb 2001
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It seems some posters on here have been drinking from the fountain of knowledge and some only gargled!

Air rabbit, Owain G et al

Some interesting info so thanks for posting. My vague recollection, from reading Flight International, was that the problem was largely due to the large rudder input and then the REVERSAL afterwards.

From a line pilot's point of view I cannot envisage why the FO would have thought that such inputs were necessary. No criticism implied- there but for the grace of God etc. Apart from an engine out condition one doesn't touch the rudder in normal ops. In an extreme attitude then of course it may help to use rudder eg high bank angle with the nose yawing below the horizon. I believe that was an example described in the American Airlines training video that I watched many years ago. That video was withdrawn from use after this crash.

The other point I have had drummed into me is that with powered flying controls one has to treat such controls with more than a little respect. With the rudder in particular it is a large control surface and and so, for example, when cycling the rudder on the pre take off checks one must do so SLOWLY!

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