Missing light aircraft in the NT
Moderator
An extra comment or three, if I may.
I then asked, "did you feel out of control at any point, and were loose object flying around the cabin" in all circumstances
One of the problems is that the AIP talks about levels of turbulence, driven by concern for pilot control in an airspace environment. That has naught to do with the structure and structural design considerations. The design standards prescribe pretty substantial gust profiles which would provide aircraft responses sufficient to warrant description as pretty severe thumps by the average pilot. The main thing to keep in mind is that, should you exceed the static structure capability of the aircraft for more than a few seconds, you should not be surprised if the tin bits go "bang". About the only mitigation you can throw in as the pilot is to have slowed down in advance to a speed where you have some level of protection in pitch by virtue of the Va min stall/limit load consideration. You have a modest speed margin to ultimate load but not so much as to place any reliance in your ability to slow down once you find yourself in severe conditions. You MUST be on the ball and always thinking ahead of the game.
then there's what the manufacturer actually put together, which may be stronger or even weaker than designed based on competence and quality of materials, workmanship etc
The Design Standards (for this discussion that means FAR 23 or equivalent) prescribe what the OEM needs to achieve. Sure, the OEM may choose to go for a bit more fat than required. However, I wouldn't rely on that as the end aim is to sell aircraft in a competitive marketplace. What you will see, though, is that the design generally will end up with a little bit of fat to make achieving the Design Standards requirements a bit easier. Obviously, a normal category aircraft will be quite different to an acrobatic category design - we need to constrain the discussion to like products.
Keep in mind that a lot of this stuff is subject to demonstration by an objective test so fancy sums don't cut the mustard. For a FAR 23 aircraft, you should be able to rely on the system's getting it sufficiently right that the aircraft Type does, in fact, meet (or exceed a little) the prescribed standards. That's what the Type Certification process is all about. The CofA process is how we go about giving us some assurance that the OEM's manufacturing system produces subsequent aircraft which comply with the Type Certification. We should be reasonably comfortable that the FAR 23 aircraft to which we entrust our lives are up to speed if everyone is doing their bit satisfactorily.
I mean one company could choose to make the spar double thickness and weight as they never want a wing to fold, the other guy makes it as light as possible with new untested materials to make the craft light and nimble.
Subject to the commercial reality of a competitive marketplace. All the aircraft are going to be much of a muchness when it comes to needless fat associated with some sort of altruism.
A good place to get an insight is the ATR saga,
The AD system addresses in service problems. If such problems relate to the basic certification, then there is a process (which is trotted out on occasion as necessary) where the basic certification can be reviewed and the OEM required to fix stuff which might have got through the initial soul searching. Overall, although it may not be perfect, the system works pretty well.
The problem with Va is actually too much science/physics/philosophy when it comes to explanation, hence confusion and lack of knowledge.
Actually, Stjepan, I'd go the other way and opine that the problem is associated with too little knowledge - in the main, a consequence of the theory courses at PPL/CPL/ATPL being far too light on and simplistic. Then there is the "blind leading the blind" problem where many (not all by any stretch of the imagination) instructors are only capable of passing on information from their own imperfect knowledge bases. The resulting hazard is that most pilots have a quite incorrect misunderstanding of what Va is and what it is trying to do. The same applies to other considerations - stalling comes to mind.
regular Joe Bloke pilot won't go reading any scientific material if not understood within 1 or 2 paragraphs
And that is a sad reality of modern younger folk. All fine for chaps such as yourself who have come into the system at a mature age and have an obvious thirst for knowledge. But a lot of the new chums have little, if any, interest in anything beyond the absolute minimum study they can get by on. The chap who I always cite as being at the other end of the spectrum, is our Centaurus. He pores over written stuff and has a collection of aviation history and technical information which is the envy of many of us. The result is a one very knowledgeable pilot.
For many, flying in green band on ASI is assumed safe
And that view can be quite dangerous.
When in turbulence or approaching turbulent weather, slow down to Va and your survival chances will improve.
Providing that one keeps in mind that such a view has some relevance in respect of Va min but only for limited circumstances. On the other hand, if one slows a bit further, then the dice start to be loaded in the pilot's favour by virtue of the stall line/limit load factor situation.
Va has nothing to do with turbulence penetration
True, from the point of definition. However, one can use the definition to provide a pad for one's operation so far as structural margins might be concerned. It just needs a bit of knowledge and commonsense.
Operating at or below Va won’t make operations in turbulence ‘safe’.
But likely safer if one's operating technique is compatible with the realities of Va.
and how far are both of them from Vno ?
This is an extremely important consideration. If one is flying along merrily with not a care in the world and no thought to turbulence, a sudden encounter with severe turbulence might very well spoil one's day as there is no way the aircraft can be slowed instantaneously to a more appropriate speed for the new conditions.
many of POH's actually don't have VB listed.
Vb is more a heavy aircraft matter.
From AC 23-19A
Everyone needs to keep in mind that the ACs tell us what the FAA thinks their rules might mean. It follows that, when delving into the regs, it is important to check what AC amplification is available. In paraphrase, all we have been saying is what is embodied in the AC.
Most Pitts aircraft have Va> Vs.√n
For those who might not know who djpil is (probably not many don't know) he is quite expert in respect of the engineering which went into the Pitts and flying the models.
The design maneuvering speed (VA) is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.
I'd take issue with that statement, unless qualified. Especially for pitch, if Va is above Va min, there is the presumption of a checked manoeuvre to avoid exceeding the limit load factor. We need to keep in mind that Va is thinking about the controls, not the main airframe structure.
So, just under Va, can a pilot push fully forwards on the control column, without over stressing the aircraft?
Ah, not necessarily. The positive and negative stall lines generally are different so you need to consider that. When thinking about the general aircraft structure, you also are only looking at a Va min situation so you would need to be considering Va min for the negative stall line. One push and then relax. For structural testing, the usual approach is that the structure has to handle the prescribed loads for a minimum of three (3) seconds.
The other consideration to keep in mind for turbulence, is that the ASI starts to get a bit unreliable when everything is bouncing and bumping. If you want to use the ASI as a reference in turbulence, better to slow down a bit more to account for this problem.
Stalling is eminently preferable to inflight disintegration as you get a second bite of the cherry.
I then asked, "did you feel out of control at any point, and were loose object flying around the cabin" in all circumstances
One of the problems is that the AIP talks about levels of turbulence, driven by concern for pilot control in an airspace environment. That has naught to do with the structure and structural design considerations. The design standards prescribe pretty substantial gust profiles which would provide aircraft responses sufficient to warrant description as pretty severe thumps by the average pilot. The main thing to keep in mind is that, should you exceed the static structure capability of the aircraft for more than a few seconds, you should not be surprised if the tin bits go "bang". About the only mitigation you can throw in as the pilot is to have slowed down in advance to a speed where you have some level of protection in pitch by virtue of the Va min stall/limit load consideration. You have a modest speed margin to ultimate load but not so much as to place any reliance in your ability to slow down once you find yourself in severe conditions. You MUST be on the ball and always thinking ahead of the game.
then there's what the manufacturer actually put together, which may be stronger or even weaker than designed based on competence and quality of materials, workmanship etc
The Design Standards (for this discussion that means FAR 23 or equivalent) prescribe what the OEM needs to achieve. Sure, the OEM may choose to go for a bit more fat than required. However, I wouldn't rely on that as the end aim is to sell aircraft in a competitive marketplace. What you will see, though, is that the design generally will end up with a little bit of fat to make achieving the Design Standards requirements a bit easier. Obviously, a normal category aircraft will be quite different to an acrobatic category design - we need to constrain the discussion to like products.
Keep in mind that a lot of this stuff is subject to demonstration by an objective test so fancy sums don't cut the mustard. For a FAR 23 aircraft, you should be able to rely on the system's getting it sufficiently right that the aircraft Type does, in fact, meet (or exceed a little) the prescribed standards. That's what the Type Certification process is all about. The CofA process is how we go about giving us some assurance that the OEM's manufacturing system produces subsequent aircraft which comply with the Type Certification. We should be reasonably comfortable that the FAR 23 aircraft to which we entrust our lives are up to speed if everyone is doing their bit satisfactorily.
I mean one company could choose to make the spar double thickness and weight as they never want a wing to fold, the other guy makes it as light as possible with new untested materials to make the craft light and nimble.
Subject to the commercial reality of a competitive marketplace. All the aircraft are going to be much of a muchness when it comes to needless fat associated with some sort of altruism.
A good place to get an insight is the ATR saga,
The AD system addresses in service problems. If such problems relate to the basic certification, then there is a process (which is trotted out on occasion as necessary) where the basic certification can be reviewed and the OEM required to fix stuff which might have got through the initial soul searching. Overall, although it may not be perfect, the system works pretty well.
The problem with Va is actually too much science/physics/philosophy when it comes to explanation, hence confusion and lack of knowledge.
Actually, Stjepan, I'd go the other way and opine that the problem is associated with too little knowledge - in the main, a consequence of the theory courses at PPL/CPL/ATPL being far too light on and simplistic. Then there is the "blind leading the blind" problem where many (not all by any stretch of the imagination) instructors are only capable of passing on information from their own imperfect knowledge bases. The resulting hazard is that most pilots have a quite incorrect misunderstanding of what Va is and what it is trying to do. The same applies to other considerations - stalling comes to mind.
regular Joe Bloke pilot won't go reading any scientific material if not understood within 1 or 2 paragraphs
And that is a sad reality of modern younger folk. All fine for chaps such as yourself who have come into the system at a mature age and have an obvious thirst for knowledge. But a lot of the new chums have little, if any, interest in anything beyond the absolute minimum study they can get by on. The chap who I always cite as being at the other end of the spectrum, is our Centaurus. He pores over written stuff and has a collection of aviation history and technical information which is the envy of many of us. The result is a one very knowledgeable pilot.
For many, flying in green band on ASI is assumed safe
And that view can be quite dangerous.
When in turbulence or approaching turbulent weather, slow down to Va and your survival chances will improve.
Providing that one keeps in mind that such a view has some relevance in respect of Va min but only for limited circumstances. On the other hand, if one slows a bit further, then the dice start to be loaded in the pilot's favour by virtue of the stall line/limit load factor situation.
Va has nothing to do with turbulence penetration
True, from the point of definition. However, one can use the definition to provide a pad for one's operation so far as structural margins might be concerned. It just needs a bit of knowledge and commonsense.
Operating at or below Va won’t make operations in turbulence ‘safe’.
But likely safer if one's operating technique is compatible with the realities of Va.
and how far are both of them from Vno ?
This is an extremely important consideration. If one is flying along merrily with not a care in the world and no thought to turbulence, a sudden encounter with severe turbulence might very well spoil one's day as there is no way the aircraft can be slowed instantaneously to a more appropriate speed for the new conditions.
many of POH's actually don't have VB listed.
Vb is more a heavy aircraft matter.
From AC 23-19A
Everyone needs to keep in mind that the ACs tell us what the FAA thinks their rules might mean. It follows that, when delving into the regs, it is important to check what AC amplification is available. In paraphrase, all we have been saying is what is embodied in the AC.
Most Pitts aircraft have Va> Vs.√n
For those who might not know who djpil is (probably not many don't know) he is quite expert in respect of the engineering which went into the Pitts and flying the models.
The design maneuvering speed (VA) is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.
I'd take issue with that statement, unless qualified. Especially for pitch, if Va is above Va min, there is the presumption of a checked manoeuvre to avoid exceeding the limit load factor. We need to keep in mind that Va is thinking about the controls, not the main airframe structure.
So, just under Va, can a pilot push fully forwards on the control column, without over stressing the aircraft?
Ah, not necessarily. The positive and negative stall lines generally are different so you need to consider that. When thinking about the general aircraft structure, you also are only looking at a Va min situation so you would need to be considering Va min for the negative stall line. One push and then relax. For structural testing, the usual approach is that the structure has to handle the prescribed loads for a minimum of three (3) seconds.
The other consideration to keep in mind for turbulence, is that the ASI starts to get a bit unreliable when everything is bouncing and bumping. If you want to use the ASI as a reference in turbulence, better to slow down a bit more to account for this problem.
Stalling is eminently preferable to inflight disintegration as you get a second bite of the cherry.
The following 2 users liked this post by john_tullamarine:
One point has been overlooked by all and I would be interested to read djpil, john tullamarine, lead balloon, take on airframe fatigue and corrosion. I only mention these three as I know them and their qualifications.
There are many Cessna 210 here in Aus with over 18,000 hours airframe time; and that logged time in too many cases does not reflect the true total time. I know too many pilots/operators whom are less than diligent when recording flight times.
Cessna do not seem to publish much data in regards to specific airframe life limits. There was a time when the Cessna Conquest II (C441) had a grounding and time life airframe components, due to tailplane failure and subsequent events which led to SID's for this and many other types.
The poor old Nomad required a certification review and strain gauges fitted (Australian Flight Test Services, Adelaide) and airframe used was VH-SNL. Later I flew a Grumman G21 Goose and when the aircraft arrived from New Zealand, the main spars were badly corroded but after fitting strain gauges and the clever people reviewed the data it was determined there was no reduction in strength.
In the early days at Royal Vic Aero Club, the late Roy Goon was the Australian agent for Fuji Aero Subaru and DOT at the time required flight G loading equipment to be installed for a period of time.
Whilst poor airmanship and a lack of knowledge are no excuse perhaps it is time for a serious review of aging general aviation aircraft ...
.
There are many Cessna 210 here in Aus with over 18,000 hours airframe time; and that logged time in too many cases does not reflect the true total time. I know too many pilots/operators whom are less than diligent when recording flight times.
Cessna do not seem to publish much data in regards to specific airframe life limits. There was a time when the Cessna Conquest II (C441) had a grounding and time life airframe components, due to tailplane failure and subsequent events which led to SID's for this and many other types.
The poor old Nomad required a certification review and strain gauges fitted (Australian Flight Test Services, Adelaide) and airframe used was VH-SNL. Later I flew a Grumman G21 Goose and when the aircraft arrived from New Zealand, the main spars were badly corroded but after fitting strain gauges and the clever people reviewed the data it was determined there was no reduction in strength.
In the early days at Royal Vic Aero Club, the late Roy Goon was the Australian agent for Fuji Aero Subaru and DOT at the time required flight G loading equipment to be installed for a period of time.
Whilst poor airmanship and a lack of knowledge are no excuse perhaps it is time for a serious review of aging general aviation aircraft ...
.
then there's what the manufacturer actually put together, which may be stronger or even weaker than designed based on competence and quality of materials, workmanship etc
The Design Standards (for this discussion that means FAR 23 or equivalent) prescribe what the OEM needs to achieve. Sure, the OEM may choose to go for a bit more fat than required. However, I wouldn't rely on that as the end aim is to sell aircraft in a competitive marketplace. What you will see, though, is that the design generally will end up with a little bit of fat to make achieving the Design Standards requirements a bit easier. Obviously, a normal category aircraft will be quite different to an acrobatic category design - we need to constrain the discussion to like products.
Keep in mind that a lot of this stuff is subject to demonstration by an objective test so fancy sums don't cut the mustard. For a FAR 23 aircraft, you should be able to rely on the system's getting it sufficiently right that the aircraft Type does, in fact, meet (or exceed a little) the prescribed standards. That's what the Type Certification process is all about. The CofA process is how we go about giving us some assurance that the OEM's manufacturing system produces subsequent aircraft which comply with the Type Certification. We should be reasonably comfortable that the FAR 23 aircraft to which we entrust our lives are up to speed if everyone is doing their bit satisfactorily.
The Design Standards (for this discussion that means FAR 23 or equivalent) prescribe what the OEM needs to achieve. Sure, the OEM may choose to go for a bit more fat than required. However, I wouldn't rely on that as the end aim is to sell aircraft in a competitive marketplace. What you will see, though, is that the design generally will end up with a little bit of fat to make achieving the Design Standards requirements a bit easier. Obviously, a normal category aircraft will be quite different to an acrobatic category design - we need to constrain the discussion to like products.
Keep in mind that a lot of this stuff is subject to demonstration by an objective test so fancy sums don't cut the mustard. For a FAR 23 aircraft, you should be able to rely on the system's getting it sufficiently right that the aircraft Type does, in fact, meet (or exceed a little) the prescribed standards. That's what the Type Certification process is all about. The CofA process is how we go about giving us some assurance that the OEM's manufacturing system produces subsequent aircraft which comply with the Type Certification. We should be reasonably comfortable that the FAR 23 aircraft to which we entrust our lives are up to speed if everyone is doing their bit satisfactorily.
A good place to get an insight is the ATR saga,
The AD system addresses in service problems. If such problems relate to the basic certification, then there is a process (which is trotted out on occasion as necessary) where the basic certification can be reviewed and the OEM required to fix stuff which might have got through the initial soul searching. Overall, although it may not be perfect, the system works pretty well.
The AD system addresses in service problems. If such problems relate to the basic certification, then there is a process (which is trotted out on occasion as necessary) where the basic certification can be reviewed and the OEM required to fix stuff which might have got through the initial soul searching. Overall, although it may not be perfect, the system works pretty well.
The recent event at VA where crew confusion almost led to ripping the tail off an ATR when the split elevator system was overpowered in opposite directions at VMo also shows the fragility of any aircraft when you place strange new twisting moments at high speed. One thing I noticed from recent transport category events is how unfamiliar some airline crews are with their own type, let alone new pilots on 210s...
One point has been overlooked by all and I would be interested to read djpil, john tullamarine, lead balloon, take on airframe fatigue and corrosion. I only mention these three as I know them and their qualifications.
With corrosion you just constantly check for that in the usual locations. The trick is how much corrosion can be removed from say a spar or such before the integrity of the certified numbers voids, that's something for an Engineer to work out. I know a few Pipers and Cessnas that have had a few layers of spar shaved back to remove corrosion and still flying 20 years later.
Last edited by 43Inches; 1st Jan 2023 at 05:15.
I think JT covered this earlier (and I'm paraphrasing): If the 'operational circumstances' - the way an aircraft is operated and maintained - differ from the designer's assumptions, 'all bets are off' when it comes to the compliance of an aircraft with its certification basis and, therefore, the various margins of safety that arise from compliance with the various 'V' speeds (assuming their real implications are understood by the writers of POHs and pilots - big assumption). Out of many, many examples, if you take a Blackhawk helicopter and operate it with long range fuel tanks strapped to it for most of the time, rather than during the much shorter percentage of operations assumed by the designers, 'unexpected' cracks start appearing in places that were not designed to bear the greater loads imposed by the long range tanks, continuously. If you jump into a Nomad and operate it close to the ground in hot and very turbulent conditions 'most of the time', rather than in the profile of flights assumed by the designer - take off, climb to altitude and cruise fat dumb and happy most of the time, then descend - your Nomad's going to break 'sooner' than expected. Nobody would have much of a clue as to what many 'old' 'GA' aircraft have been put through over decades.
If business is so tight that .1 on a few flights is going to hurt then they shouldn’t be operating.
Operators undercutting the market? Surely not with the demand in all facets of aviation. Owners wanting to increase profits?
I shudder to think what older aircraft could be costing these days, but if the charter rate is right then everything down the line is covered.
25 years ago the rate for a 210 was around $250-$350 an hour (yes a large spread as I can’t remember), ok smart cookies throw in inflation etc and what’s the going rate these days?
So is Katherine Aviation paying the award or equivalent?
You take a claim to fairwork, they'll rip into it, they're far from toothless. I have far more faith in them than the union. But as I said, they keep taking those jobs, it's a very competitive segment, it's about getting the hours and getting out.
Fairwork you say? They have no regulatory powers. It’s up to you to personally take legal action.
Fairwork you say? They have no regulatory powers. It’s up to you to personally take legal action.
Moderator
A few posts since I was here last.
I know too many pilots/operators whom are less than diligent when recording flight times.
Indeed. That is a REAL worry when it comes to continuing airworthiness matters. Keeping to the bucket of life fatigue analogy, if you don't keep the odometer working, it all turns to custard .....
Cessna do not seem to publish much data in regards to specific airframe life limits.
Although things have changed over the years, in the earlier days, light aircraft didn't get much worry spent on their longer term service history and fatigue considerations. More effort was directed to heavier aircraft. Interestingly, Australia's DCA was a leading light in fatigue work going back quite some years and ran some very valuable Industry monitoring programs with specific aircraft. We had some very expert structural folk in DCA - Max, Col, Martin, Bruce and others.
the finite limits even two mass produced planes may snap at slightly different tolerances,
Absolutely. Fatigue work is a very rubbery, statistically driven area of engineering. The published numbers are based on pretty conservative work up data and, in reality, the aircraft shouldn't go "bang" anywhere near those figures. However, if the engineering workup is flawed (usually due to imperfect state of the art understanding - think Comet), or if the recorded history (or usage patterns) is substantially in error, then it becomes a case of all bets might be off or, at the least, things become a bit suspect.
so you can only go by what it's certified to do and act accordingly.
Every pilot should read this bit several times over. The whole thing depends on the certification's getting things pretty right, then the history's bearing a reasonable validity compared to what the OEM presumed might be the case or, if it doesn't, having that information fed back through the airworthiness authorities to the OEM, or directly. Much of the problem is that the pilot training programs don't get anywhere near this stuff, so the average pilot knows schmick about it. This is why we put effort into these sorts of threads in PPRuNe.
Problem is when you have ice and other things involved
Aircraft design and operation is based on a lot of statistical presumptions which work, pretty well, overall. However, it certainly is more than possible to get into awkward situations where you are getting out on a limb. Planning, monitoring, etc., is the best defence a pilot has against this sort of problem.
The point with the ATR saga
Conspiracy aside, one of the problems is that the folk involved throughout are human and humans make mistakes. The aim of the system's safeguards is for such mistakes to be detected and corrected where appropriate. Sometimes this takes some lessons learned in blood along the way.
One thing I noticed from recent transport category events
Which is why I despair when I see new folks who have nil interest in learning more than the absolute bare minimum to get through exams and endorsements ....... It's a bit like poverty - unless you do something to break the cycle it just perpetuates and stays down in the mud.
Metal fatigue and corrosion are two different things.
Yes, but related in that corrosion can accelerate fatigue problems greatly, quite apart from having the potential to affect, adversely and directly, static strength by eating away at the tin bits.
'unexpected' cracks start appearing in places that were not designed to bear the greater loads imposed
That's one of the worries with fatigue if the OEM doesn't have the out-there-in-Industry usage data.
For those who might like to read up further, search the net for "static structural loads", "dynamic structural loads", and "structural fatigue".
We do have a few structures experts in the sandpit. Hopefully, one or more might be motivated to wade into the discussion.
I know too many pilots/operators whom are less than diligent when recording flight times.
Indeed. That is a REAL worry when it comes to continuing airworthiness matters. Keeping to the bucket of life fatigue analogy, if you don't keep the odometer working, it all turns to custard .....
Cessna do not seem to publish much data in regards to specific airframe life limits.
Although things have changed over the years, in the earlier days, light aircraft didn't get much worry spent on their longer term service history and fatigue considerations. More effort was directed to heavier aircraft. Interestingly, Australia's DCA was a leading light in fatigue work going back quite some years and ran some very valuable Industry monitoring programs with specific aircraft. We had some very expert structural folk in DCA - Max, Col, Martin, Bruce and others.
the finite limits even two mass produced planes may snap at slightly different tolerances,
Absolutely. Fatigue work is a very rubbery, statistically driven area of engineering. The published numbers are based on pretty conservative work up data and, in reality, the aircraft shouldn't go "bang" anywhere near those figures. However, if the engineering workup is flawed (usually due to imperfect state of the art understanding - think Comet), or if the recorded history (or usage patterns) is substantially in error, then it becomes a case of all bets might be off or, at the least, things become a bit suspect.
so you can only go by what it's certified to do and act accordingly.
Every pilot should read this bit several times over. The whole thing depends on the certification's getting things pretty right, then the history's bearing a reasonable validity compared to what the OEM presumed might be the case or, if it doesn't, having that information fed back through the airworthiness authorities to the OEM, or directly. Much of the problem is that the pilot training programs don't get anywhere near this stuff, so the average pilot knows schmick about it. This is why we put effort into these sorts of threads in PPRuNe.
Problem is when you have ice and other things involved
Aircraft design and operation is based on a lot of statistical presumptions which work, pretty well, overall. However, it certainly is more than possible to get into awkward situations where you are getting out on a limb. Planning, monitoring, etc., is the best defence a pilot has against this sort of problem.
The point with the ATR saga
Conspiracy aside, one of the problems is that the folk involved throughout are human and humans make mistakes. The aim of the system's safeguards is for such mistakes to be detected and corrected where appropriate. Sometimes this takes some lessons learned in blood along the way.
One thing I noticed from recent transport category events
Which is why I despair when I see new folks who have nil interest in learning more than the absolute bare minimum to get through exams and endorsements ....... It's a bit like poverty - unless you do something to break the cycle it just perpetuates and stays down in the mud.
Metal fatigue and corrosion are two different things.
Yes, but related in that corrosion can accelerate fatigue problems greatly, quite apart from having the potential to affect, adversely and directly, static strength by eating away at the tin bits.
'unexpected' cracks start appearing in places that were not designed to bear the greater loads imposed
That's one of the worries with fatigue if the OEM doesn't have the out-there-in-Industry usage data.
For those who might like to read up further, search the net for "static structural loads", "dynamic structural loads", and "structural fatigue".
We do have a few structures experts in the sandpit. Hopefully, one or more might be motivated to wade into the discussion.
JT, to expand on the subject a little could you give a run down on rolling "g", that is rolling whilst pitching the nose up. Only ever flew one aircraft where a rolling "g" limit was mentioned, had a 6g normal limit which was reduced to 4g if pulling the nose up simultaneously while rolling, had a "g" meter of course. Wonder if rolling "g" has a role in these accidents.
Moderator
a run down on rolling "g"
The story runs along the following lines.
Consider the symmetrical pitch up manoeuvre. If we are at whatever g load, that is a symmetrically (spanwise across the wing) distributed load. Va min and limit load factor (or g) is relevant as it is the speed where we can ask the aircraft for all it can give us in symmetrical pitch manoeuvring - "corner speed" as the military folk would have it - without too much risk that it will bite us on the tail and require us to explain why stuff is bent and twisted when we give it back to maintenance. As the maintenance boss in a previous life, that sort of thing would have concentrated my attention somewhat with ASORs going on forever and a day.
So, here we are pulling say, somewhere near limit load somewhere near Va min for whatever reason, and then Captain Speaking applies a significant aileron input. What happens ? The aircraft will roll. What causes it to roll ? For our very conventional bugsmashers, one aileron goes down while the other goes up, providing a rolling moment. If we have a think about things, what this is doing, is increasing the wing up load at the aileron going down (wing side going up) as well as giving us a twisting load out along the wing as the aileron is back at the trailing edge. End result is that the upgoing wing is being asked to do more work (effectively the load now is more than limit load for that side of the wing) so we need either to have slowed down a bit or backed off the symmetrical g load intentionally so that we stay below limit load and don't cause too many problems. This is much the same as the situation with Va vs reducing weight to get us onto a more appropriate stall characteristic line.
End result for those aircraft whose operating rules so require is that the pilot will be given either a reduced speed limit or reduced symmetrical g load limit prior to conducting significant pitching manoeuvres with a concurrrent significant rolling manouevre. The most obvious example of this at play, as I can recall, is the F16 when doing those wonderful airshow display manoeuvres for us envious folk consigned to the ground. Roars in, checks the pitch up g with a very obvious bunt, and then rolls aggressively into a steeply banked turn manoeuvre.
I vaguely recall reading somewhere that this all started to be a concern back in WW2 when the Corsair drivers, during ground attack runs, would roll while pulling up after doing their thing to put the aircraft's armoured bits between their soft, pink bits and the pointy stuff which the (now thoroughly unimpressed folks on the ground) would be throwing at them. End result was the aircraft came back with bent bits and pieces and the boffins had to go back to the certification drawing board.
Only ever flew one aircraft where a rolling "g" limit was mentioned, had a 6g normal limit which was reduced to 4g if pulling the nose up simultaneously while rolling
Which helo was that, good sir ?
It turns out that, typically, a symmetrical g reduction by around a third seems to be the rule so that would account for your 6g reducing to 4g observation. For speed reduction considerations, something in the order of 15-20 knots probably would be typical.
Wonder if rolling "g" has a role in these accidents.
We can only engage in conjecture but, were one to do so, one might opine that such could be the case.
The story runs along the following lines.
Consider the symmetrical pitch up manoeuvre. If we are at whatever g load, that is a symmetrically (spanwise across the wing) distributed load. Va min and limit load factor (or g) is relevant as it is the speed where we can ask the aircraft for all it can give us in symmetrical pitch manoeuvring - "corner speed" as the military folk would have it - without too much risk that it will bite us on the tail and require us to explain why stuff is bent and twisted when we give it back to maintenance. As the maintenance boss in a previous life, that sort of thing would have concentrated my attention somewhat with ASORs going on forever and a day.
So, here we are pulling say, somewhere near limit load somewhere near Va min for whatever reason, and then Captain Speaking applies a significant aileron input. What happens ? The aircraft will roll. What causes it to roll ? For our very conventional bugsmashers, one aileron goes down while the other goes up, providing a rolling moment. If we have a think about things, what this is doing, is increasing the wing up load at the aileron going down (wing side going up) as well as giving us a twisting load out along the wing as the aileron is back at the trailing edge. End result is that the upgoing wing is being asked to do more work (effectively the load now is more than limit load for that side of the wing) so we need either to have slowed down a bit or backed off the symmetrical g load intentionally so that we stay below limit load and don't cause too many problems. This is much the same as the situation with Va vs reducing weight to get us onto a more appropriate stall characteristic line.
End result for those aircraft whose operating rules so require is that the pilot will be given either a reduced speed limit or reduced symmetrical g load limit prior to conducting significant pitching manoeuvres with a concurrrent significant rolling manouevre. The most obvious example of this at play, as I can recall, is the F16 when doing those wonderful airshow display manoeuvres for us envious folk consigned to the ground. Roars in, checks the pitch up g with a very obvious bunt, and then rolls aggressively into a steeply banked turn manoeuvre.
I vaguely recall reading somewhere that this all started to be a concern back in WW2 when the Corsair drivers, during ground attack runs, would roll while pulling up after doing their thing to put the aircraft's armoured bits between their soft, pink bits and the pointy stuff which the (now thoroughly unimpressed folks on the ground) would be throwing at them. End result was the aircraft came back with bent bits and pieces and the boffins had to go back to the certification drawing board.
Only ever flew one aircraft where a rolling "g" limit was mentioned, had a 6g normal limit which was reduced to 4g if pulling the nose up simultaneously while rolling
Which helo was that, good sir ?
It turns out that, typically, a symmetrical g reduction by around a third seems to be the rule so that would account for your 6g reducing to 4g observation. For speed reduction considerations, something in the order of 15-20 knots probably would be typical.
Wonder if rolling "g" has a role in these accidents.
We can only engage in conjecture but, were one to do so, one might opine that such could be the case.
... Only ever flew one aircraft where a rolling "g" limit was mentioned, had a 6g normal limit which was reduced to 4g if pulling the nose up simultaneously while rolling
.....
It turns out that, typically, a symmetrical g reduction by around a third seems to be the rule so that would account for your 6g reducing to 4g observation. For speed reduction considerations, something in the order of 15-20 knots probably would be typical.
.....
It turns out that, typically, a symmetrical g reduction by around a third seems to be the rule so that would account for your 6g reducing to 4g observation. For speed reduction considerations, something in the order of 15-20 knots probably would be typical.
However the same rolling G limit of 2/3 of the limit load factor really applies to all fixed wing aircraft. The Part 61 MOS for BAK should cover it "6.3.2 Describe situations which may result in an aircraft exceeding speed limits and load factor limits." ... but .... such few words associated with a fairly big subject.
JT - some simple arithmetic helps with consideration of speed reduction. eg for that aerobatic airplane with a 6 G limit load factor and a rolling G limit of 4 - that is double the stall speed - a number which is as useful to remember as Va.