Take-Off Power - How often?
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I think Gomer Pilot is taking a very sensible, pragmatic view on this issue. Nick, as I see it, the primary issue is not guaranteeing any level of reliability if detailed definitions of limits are kept to - which is clearly impossible - but providing pilots with sensible rules they can work to. Knowing rules (eg, how frequently you can use maximum contingency/take off power) and being happy to apply them means safer, less stressful flying because mental capacity is not taken up with subjective deliberation. It is comforting to know that so long as you operate within the limits you are not unreasonably stressing the aircraft.
The cynic in me would say lack of definition in frequency of using max transient limits provides manufacturers with a grey area to argue against any litigation following failure.
I believe frequency limits should be specified, or at least recommended. Depending on the environment and the operation, some acft will be less stressed by full exploitation than others, but that's the same with anything, such as max continuous power. As pilots we all know we can influence longevity of components and reliability by determing how close to limits we operate to, but at least we want to know what these are, and only the manufacturer can tell us that.
The cynic in me would say lack of definition in frequency of using max transient limits provides manufacturers with a grey area to argue against any litigation following failure.
I believe frequency limits should be specified, or at least recommended. Depending on the environment and the operation, some acft will be less stressed by full exploitation than others, but that's the same with anything, such as max continuous power. As pilots we all know we can influence longevity of components and reliability by determing how close to limits we operate to, but at least we want to know what these are, and only the manufacturer can tell us that.
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I don't think we differ on the basics, Gomer, but I must tell you that you are too simplistic when you say, "All I have to work with are the flight manual and the limitations. " Let me offer an example. If the max torque for takeoff is 100%, does that allow you to pull that torque from a ground condition in .01 second, with a collective jerk that pulls 2 g's? No, huh? How can you prove that jerk is not permitted from the entire package of flight manual and limitations available to you? It is written nowhere, yet if you did, you would harm the machine, possibly lose control and probably lose your licence.
Obviously, the skill of piloting is far deeper that the red lines. The red lines are part of a vast system of training, acceptable methods of compliance, judgements and tribal knowledge that can never be written down, let alone captured by a set of limits. The limits we use are the tip of the iceberg of how we do our jobs, and reliance on them alone is simply unacceptable.
Obviously, the skill of piloting is far deeper that the red lines. The red lines are part of a vast system of training, acceptable methods of compliance, judgements and tribal knowledge that can never be written down, let alone captured by a set of limits. The limits we use are the tip of the iceberg of how we do our jobs, and reliance on them alone is simply unacceptable.
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On the R22 I've been told that the 5min takeoff rating is an oil temperature restriction as opposed to an assumption about component life/wear. Is that the whole story, and can we therefore (as I've been told) pull it with reference to the oil temp rather than with a view to the bean jar ?
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I've always said, and believed, that I get paid mostly for my judgement. Of course judgement is always called for, and is always assumed. Good judgement comes from making bad decisions, and judgement is simply the sum of one's experience. I don't have your experience or judgement, though, and all I can expect from you is in the flight manual and on the gages. That was what I was getting at.
I'm certainly not advocating operating at limits all the time, but only as necessary, when required. And it is sometimes required. Being cavalier about limits will eventually result in exceeding them, which is why I said I am concerned about staying within them.
I'm certainly not advocating operating at limits all the time, but only as necessary, when required. And it is sometimes required. Being cavalier about limits will eventually result in exceeding them, which is why I said I am concerned about staying within them.
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Got to say I generally agree with Gomer - a limit is a limit - in my experience an exceedance of a limit is usually a result of poor planning, bad assessment of prevailing conditions, lack of experience, lack of pilotting ability or, in the worse case, continuing blatent disregard of manufacture's limits. Those of us who, on this forum, are experienced pilots should be mindful that a lot of sproggs read our posts and take what we say as gospel.
GAGS E86
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Punto - since the oil is there to cool and lubricate the engine (thus protecting it from wear) then you are still using beans and will wear out then engine earlier than if you didn't use the 5 min rating.
As to limits, I'm with gomer and eagle - if you have to exceed them to avoid crashing or to save life (in extremis not routine) then pull away, but don't plan to do it. If you do exceed a limit, then for God's sake own up to it, don't let pride get in the way of doing the right thing - it might cost someone else their life.
As to limits, I'm with gomer and eagle - if you have to exceed them to avoid crashing or to save life (in extremis not routine) then pull away, but don't plan to do it. If you do exceed a limit, then for God's sake own up to it, don't let pride get in the way of doing the right thing - it might cost someone else their life.
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Punto,
You are about to discover something we all find out sooner or later. When someone, even your instructor, tells you something, it is possibly not correct. The engine oil temp is not the reason for your takeoff power limit, get your money back from that instructor! If the engine oil temp served as the limit for the takeoff power (thus limiting the helos performance, gross weight and payload) then it would be fixed by adding a bit more cooler capacity, believe me!
The take off power limit is most often set by the life reduction that comes with the stress on the engine (usually the crank or the exhaust valve temperatures) and the stress on the gears in the main transmission (tooth bending). Could be either, or both at the same time.
This thread is traveling into an interesting direction! For those who advocate limits observance, welcome to my position. For those who think, as long as they observe the limits they are doing no damage to their helicopter, welcome to the real world. You ARE damaging your helicopter by observing the limits. That is the message that I have been discussing, but that Gomer has bent into some other black and white case.
Limits are not magic lines, where below is pure and white and full of happiness, and above is awful and black and full of death and destruction.
Observe the limits, you must, but as you do, be assured, even as you do, you are damaging your machine. It is forming little tears in its metal, it is struggling to stay together. It is extracting beans from its jar.
What is the difference between above and below the limits? The difference is that the RATE of damage is more understood, and the ability to get closer to assured life is more sure.
Does that mean if you reduce TO power at 5.0 minutes per application that the engine will not fail? No, but it gives you a better chance.
All pilots are requested to observe the limits, but let all pilots be aware, there are many more limits not expressed, and just as likely to get you in trouble.
You are about to discover something we all find out sooner or later. When someone, even your instructor, tells you something, it is possibly not correct. The engine oil temp is not the reason for your takeoff power limit, get your money back from that instructor! If the engine oil temp served as the limit for the takeoff power (thus limiting the helos performance, gross weight and payload) then it would be fixed by adding a bit more cooler capacity, believe me!
The take off power limit is most often set by the life reduction that comes with the stress on the engine (usually the crank or the exhaust valve temperatures) and the stress on the gears in the main transmission (tooth bending). Could be either, or both at the same time.
This thread is traveling into an interesting direction! For those who advocate limits observance, welcome to my position. For those who think, as long as they observe the limits they are doing no damage to their helicopter, welcome to the real world. You ARE damaging your helicopter by observing the limits. That is the message that I have been discussing, but that Gomer has bent into some other black and white case.
Limits are not magic lines, where below is pure and white and full of happiness, and above is awful and black and full of death and destruction.
Observe the limits, you must, but as you do, be assured, even as you do, you are damaging your machine. It is forming little tears in its metal, it is struggling to stay together. It is extracting beans from its jar.
What is the difference between above and below the limits? The difference is that the RATE of damage is more understood, and the ability to get closer to assured life is more sure.
Does that mean if you reduce TO power at 5.0 minutes per application that the engine will not fail? No, but it gives you a better chance.
All pilots are requested to observe the limits, but let all pilots be aware, there are many more limits not expressed, and just as likely to get you in trouble.
Interestingly, Eurocopter demonstrate this concept quite well with their MGBs and overtorques; you enter the relevant numbers into a spreadsheet and it calculates a "damage calculation value" which is then subtracted from a nominal total. When this total diminishes to zerto, it is now completely damaged! In fact you would always reach TBO first, but the concept mirrors Nick's explanations.
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Better Management Tools
Nick Lappos says “You ARE damaging your helicopter by observing the limits.”
Let us not forget that the helicopter is being damaged even if we are leaving it in the hangar. How many operators take ‘short term storage’ maintenance procedures seriously? And of course we all know of calendar life limits!
Management of the rate of damage is surely the issue.
In the world of ‘aerial work’, as against the world of ‘public transport’, another dimension to the problem is the customer’s perception of value for money. This, in most cases, is seen as “The most kilos hauled between two places in the shortest possible time, and no late arrivals on the job due to ‘maintenance issues’.” The industry even encourages this view, and we all know that if our company goes out of business due to ‘cut throat’ business practices there will always be another outfit that will come over the hill to replace us at even cheaper rates.
Managing the rate of flow of the ‘beans’ is commercially important and a great challenge. Maybe Eurocopter with automatic cycle counting in their current generation helicopters, un-popular in many circles though it is, has given us a good management tool. However the majority of helicopters being operated in these environs are not so blessed. What I think we need is the best possible guidance from the manufacturers on how to manage the flow of ‘beans’ and I don’t see much evidence of this guidance being forthcoming.
Let us not forget that the helicopter is being damaged even if we are leaving it in the hangar. How many operators take ‘short term storage’ maintenance procedures seriously? And of course we all know of calendar life limits!
Management of the rate of damage is surely the issue.
In the world of ‘aerial work’, as against the world of ‘public transport’, another dimension to the problem is the customer’s perception of value for money. This, in most cases, is seen as “The most kilos hauled between two places in the shortest possible time, and no late arrivals on the job due to ‘maintenance issues’.” The industry even encourages this view, and we all know that if our company goes out of business due to ‘cut throat’ business practices there will always be another outfit that will come over the hill to replace us at even cheaper rates.
Managing the rate of flow of the ‘beans’ is commercially important and a great challenge. Maybe Eurocopter with automatic cycle counting in their current generation helicopters, un-popular in many circles though it is, has given us a good management tool. However the majority of helicopters being operated in these environs are not so blessed. What I think we need is the best possible guidance from the manufacturers on how to manage the flow of ‘beans’ and I don’t see much evidence of this guidance being forthcoming.
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This is all quite thought provoking. I can firmly see the logic of these arguments, and I have in mind a 'wear curve' which is like an exponential graph, and these 5 minute/takeoff ratings are on the inflection before things go off to very large numbers and shake to bits.
However there may be an argument whereby the Robbo is simply lower down on this curve behind the inflection. I do appreciate that we're not just talking about the engine here but it's possible there's a connection to the fact that the engine is so derated.
More in hope than expectation I've dropped RHC a note to ask if they are prepared to share their view on the matter. I'm not really expecting a black or white reply (or even a reply at all !) but if anything meaningful comes up I'll post the gist of it.
However there may be an argument whereby the Robbo is simply lower down on this curve behind the inflection. I do appreciate that we're not just talking about the engine here but it's possible there's a connection to the fact that the engine is so derated.
More in hope than expectation I've dropped RHC a note to ask if they are prepared to share their view on the matter. I'm not really expecting a black or white reply (or even a reply at all !) but if anything meaningful comes up I'll post the gist of it.
Having just returned from a five-day kidney dissolving ear splitting session in Le Mans, I opened PPRuNe with the usual expectation and have spent most of the morning digesting this interesting and often alarming thread on the use of engine power.
Performance limitations are not written by lawyers but by engineers who through design and testing are able to set safe operating limitations for the airworthiness authorities to approve and operators to work to.
I would hazard a guess that none of the engine maintenance manuals will offer a guarantee that any of their engines will make TBO. Why not? Well they don’t manage them and therefore cannot guarantee that they have been operated and maintained as the manufacturer stipulates.
It was always my understanding that the type of flight profile likely to be undertaken would allow the manufacturer to offer safe cycle and time limitations, this being start, taxi, climb, cruise, descent, land, taxi and shutdown etc..
However, for those operators looking at non standard flight profiles like pilot training which would include high circuits and bumps per flight hour or EMS operations where engine start to takeoff times could be very quick and therefore inducing added thermal stresses to the lifed components, the engine life limitations could be varied to take into account the higher than usual thermal stresses that the engine may undergo per flight hour/cycle and therefore LCF / IRN life is varied accordingly.
Overtemping an engine has obvious safety implications not to mention financial considerations. Using an electron microscope, the manufacturer is able to identify very accurately (evidence of solutioning of the gamma-prime precipitate) what temperature the turbine blade has been subject too.
Even with the incorporation of more modern nickel-based super-alloy components, evidence clearly shows that continued operations with reduced temperature margins greatly accelerates engines degradation and in a worst case scenario may even result in the separation of a turbine blade even though no exceedance of maximum limits was observed.
The higher the temperature, the greater the repair bill and for a small outfit, this could spell bankruptcy. As has been pointed out so well, you have a set number of beans and the way you use your engine effects the rate of bean usage and therefore the cost of overhaul, even if you do make TBO.
I do not mean to preach and neither do I work for any manufacturer, but if you are not sure then ask your relevant engine field rep for clarification on temperature limitations and possibly what might be non standard flight profiles.
Performance limitations are not written by lawyers but by engineers who through design and testing are able to set safe operating limitations for the airworthiness authorities to approve and operators to work to.
I would hazard a guess that none of the engine maintenance manuals will offer a guarantee that any of their engines will make TBO. Why not? Well they don’t manage them and therefore cannot guarantee that they have been operated and maintained as the manufacturer stipulates.
It was always my understanding that the type of flight profile likely to be undertaken would allow the manufacturer to offer safe cycle and time limitations, this being start, taxi, climb, cruise, descent, land, taxi and shutdown etc..
However, for those operators looking at non standard flight profiles like pilot training which would include high circuits and bumps per flight hour or EMS operations where engine start to takeoff times could be very quick and therefore inducing added thermal stresses to the lifed components, the engine life limitations could be varied to take into account the higher than usual thermal stresses that the engine may undergo per flight hour/cycle and therefore LCF / IRN life is varied accordingly.
Overtemping an engine has obvious safety implications not to mention financial considerations. Using an electron microscope, the manufacturer is able to identify very accurately (evidence of solutioning of the gamma-prime precipitate) what temperature the turbine blade has been subject too.
Even with the incorporation of more modern nickel-based super-alloy components, evidence clearly shows that continued operations with reduced temperature margins greatly accelerates engines degradation and in a worst case scenario may even result in the separation of a turbine blade even though no exceedance of maximum limits was observed.
The higher the temperature, the greater the repair bill and for a small outfit, this could spell bankruptcy. As has been pointed out so well, you have a set number of beans and the way you use your engine effects the rate of bean usage and therefore the cost of overhaul, even if you do make TBO.
I do not mean to preach and neither do I work for any manufacturer, but if you are not sure then ask your relevant engine field rep for clarification on temperature limitations and possibly what might be non standard flight profiles.
