Take-Off Power - How often?

[Hidden Agenda]

The Flight Manual of the Bell 206 says:

TORQUE LIMITS
Takeoff Range 85% to 100%
(Do not exceed 5 minutes)

TEMPERATURE OUTLET TEMPERATURE (TOT)
Maximum for Takeoff 791ºC
(Do not exceed 5 minutes above 741ºC)

How often can I apply 5 minutes of power in the takeoff range? Is that 5 minutes per flight, 5 minutes per hour, or do I just reduce to less than takeoff power once my 5 minutes are up and then I am free to reapply power in the takeoff range again.

I can’t seem to get a definitive answer from the manufacturer’s representative so I would be interested to hear what other pilots reckon.

Thanks!

[206 jock]

'or do I just reduce to less than takeoff power once my 5 minutes are up and then I am free to reapply power in the takeoff range again.'

Lordy, I hope I don't buy this JR once you've finished with it!

Nothing in aviation is definitive. I regard the 5 minute ratings as a 'get out of jail' card and nothing more. Just because they're there, doesn't mean you have to use them. Once in the cruise, I'll settle at 70%/700 TOT, unless I need to knock on. The less stress you put on engine/turbine, the more likely they will last longer - not sure whether that's backed up by facts, but it seems to work for me.

Mind you, I don't fly mine hot or high, and rarely at max weight, so other operators might have a different view of these limits.

[lrose]

If you have been useing 100% TQ and max Temp for 5 minutes (a long time when sitting light in the seat)just on TAKEOFF and need more I would be buying some life insurance quick. :ok:

[Wunper]

Hidden Agenda

Read this definitive input from Nick... its all to do with beans

http://www.pprune.org/forums/showthread.php?s=&threadid=139754&highlight=limits

W:p

[Aesir]

This is how I see it!

If operating on torque limitation at low DA then I'm not close to the engines rated limit when pulling 100% Q so pulling 100% is not causing the engine harm, it's stressing the transmission.
The TOT temp limit is of course there for the engine.

See the engine only produces about 317 hp @ 100% Q which is about 75% engine power. Although most manufacturer's won't tell but its likely that the components were designed to last at least up to 150% TBO and using the 5 min power rating is not really going to make a big change in the overall life expectancy of your engine or gearbox. They are just as likely to fail before TBO if you baby them all their life.

But exceeding limits is another matter entirely, then you are really into the experimental pilot category as well as all pilots flying the machine after you, they just may not know it.

But anyway you are maybe overanalysing this a bit, it's very seldom that you have to use the takeoff limit for more than a few seconds except when slinging, then it's not uncommon that you are in the zone for maybe 2 min especially when hauling beton, usually though the customer wants quick pick-ups and drop-off's. Its expensive to have a helicopter hanging in hover and not hauling stuff around ; )

Operationally this is really not an issue, just use the 5 min power when you need it and it's probably going to be a while until you need it again.

I did my initial B206 check-out at Bell Ft-Worth (91) and this is how I remember they explained this. They would not comment on any cooldown period between periods and they were right, it's really not any issue.

Hope that helps! There is really not a definitive answer as far as I know.

[Arm out the window]

Good call, Aesir.
Anyone who interprets a 5-min takeoff power limit as something you can pull to for 4 min. 59 sec, relax for 1 sec and then go again needs a good attitude readjustment session.
Thrashing machinery isn't real smart; not only will you get caught, but it might even come back and bite you on the bum one day.

[BlenderPilot]

Our hangar located at the definition of Hot an High, today's conditions Elev. 7,340 FT, 32°C, 30.10, you figure out Density Altitude and it should come out to something above 10K,

Anyway there is a flight we do everyday at around 13:30, 50 Gal. 1 Pax, and lots of equipment, at this WT the helicopter will barely hover IGE (about 10 inches off the ground) always biting the TOT redline, if you get a little wind from the wrong place you will have to let it sink to the ground (even during taxi) to avoid going over the redline, that's the way the JR flies Hot and High, (I should say barely flies) Sometimes you have to hover to the taxiway to lineup with the wind, then start your TO run, this sometimes takes more 5 minutes to to do this so what I do is taxi in the TO range, then settle down let it "breathe a little" a couple of seconds and then begin my takeoff again of course in the yellow arc again.

Our engines spend an incredible amount of time in the yellow arc, but never more than 5 minutes at a time, we have two JR's with engines that have more than 9000 hours on them, we have never had a problem with engines not making their TBO's or not passing their power checks, as long you use common sense and don't exceed limitations published in the books these aircraft will take care of you.

Its the only way they fly around here, I might need "attitude readjustment session", but like an old timer from a major US operator told me the other day, "we don't baby our aircraft around here, we just stick to what the manual says you can or can't do and get the max out of the aircraft"

[The Rotordog]

There are a lot of different philosophies about power. Some people believe that you should only pull as little power out of the engine as you can. But remember, component overhauls intervals are based on published power limits. You get no official extra credit or extension by babying the bird.

The reality is that you can pull up into the yellow for five minutes, push the pole down into the green, then pull up into the yellow for another five minutes. Factory instructors (being human) don't like to admit this, but it is true. Good practice? I did not say that.

I'm with Blender. Sometimes, just hovering out for departure will put you well into your five-minute limit. You're going to need another couple of minutes for the take-off...what do you do? Well, obviously, you set her back down and get the offending gauge back into the green. But you will not find any guidance as to how long you must let the engine/transmission "rest" for there is none. Pull and fly away, my son.

[Quick Release]

I think Nck's" bean explanation sums it up well, keep in mind the B206 flight manual gives us these limits and so indicate no inspection required even giving you a transient limit as well both with TQ and Tot but surley reduce its life, X amount of hrs of stress bring it to the end of its life, increase the stress and reduce the life, it may or may not fail but what may have started out a +2 or 3 rated engine reduces and only makes the pwr assurance hopfully not before time and certainly reducing that valuable performance.
The flight manual quotes limits for starts over 810* so we may say fine but the Allison maint manual says these starts are accumulative meaning must be causing unecessary stress and so reducing its life and so performance (at best). They dont clarify the limts with regards 5mins and how often is acceptable but will look forward to seeing you when you stop by for your new engine well before its due! lol
I look after our machines like i own them, only use limits when i must , dont try read between the lines and look for ways to abuse them, thats all the boss can ask for i recon.


:D

[Max Takeoff]

What if you take of low alt and then fly to a hot and high field. Can you pull into the five minute "Take off" limit on landing to save doing a limited power run on over rough ground or would that be, word wise, a technical no no as it is landing not taking off?

Ah the joys of the grey areas. Me I will just stick to looking after it with kid gloves.

After all if you are taking off in conditions that need all the power then I really hope the donkey doesn't stop at 100ft as it will be a hard arrival with little lever left. What options we accept as pilots.

[Quick Release]

well done Max TO :D yea you are right, its just a term i guess, grey it is.

[OEI and Still Flying]

I don’t have a manual to hand but.
There is also an airspeed limitation of around 80/82 knots on the 83-100 Tq range
I think this limitation is on the mast rather than the engine. (I stand to be corrected on this point)
Please don’t ask me the technical reason for the mast.
I am sure there are more educated individuals out there that myself to answer that one
But from a practical point of view if after five minutes you haven’t reached beyond 80kts! Well that’s another story.

As the book suggests it is a Take off range therefore it can be used any time you TAKE OFF.
If for example you a doing shuttle /ferry work which lasts 5mins per sector you are going to use it if required 12 times an hour.
Maybe not the best on the engine but the manual says you can do this.

[BlenderPilot]

OEI and Still Flying,

The takeoff power limitation has to do with the engine not the mast, the mast limitation you are talking about in that is related to airspeed has to do with mast bending, as I undersand the mast in the 206 will bend forward at high airspeed, I think it was about 1 or 2 inches forward!

[Arm out the window]

BlenderPilot, with 50 gal you're flying about 1.5 hrs I guess; is there an option to have a stock of, say, 25 litre fuel drums on the way, drop in for a quick hot refuel during the job (10 minutes time out, and a bit of logistical work to put the drums there) - take off lighter in the first place. The answer is money, I suppose.
With the conditions you're working in, sounds like the Jet Ranger isn't the right machine for the job considering you have to flog it to do anything much.
I know there are probably numerous reasons why the situation is as it is, and from what you say you are getting away without harming the engines; still, why would they bother putting a 5-minute limit there at all if they meant for us to pull to it for way longer than that in,say, an hour. Part of the problem is that the limit is too wishy-washy, of course - if they were more specific, there wouldn't be the option to dodge the issue.

[John Eacott]

Many moons ago I was operating a 206 on a gravity survey out of Tom Price, W.A. Tiger country, with nowhere to go if the donk coughs. The 4 axis INS ( apparently out of a military tank!) took up the back seat, and had to be time set every 4 minutes or less, so up to 8am with the cooler temperatures we could fly about 8km between landings, then down to 4km legs when the OAT went above c.32C.

I couldn't work out why the Canuck flying opposite days to me, kept doing 8km way past 10am, until it transpired that he was using 5 minute power on every leg, since it was less than 5 minutes :eek: :mad:

I have no doubt he saved my life when he spent 6 hours one Friday flying with a broken skid tube, which couldn't be fixed when he got back on Friday PM as the welder was in t'pub ;) The engineer decided to ground the 206 on Saturday (my day) and change the compressor case halves, since the power assurance was trending down, whilst the skid tube was fixed. About 10 of the compressor stators were cracked, and bent over into the next row: without a doubt they wouldn't have lasted another day's flying.

Whether the abuse of the 5 minute power contributed, I don't know, but I was glad not to fly with that fellow again :rolleyes:

[OEI and Still Flying]

BlenderPilot

Not being able to refer to the manual
The limitation we speak of is not listed in the limitation sections under engine or airspeed (from memory)
But I suppose for the sake of “ Hidden Agendas” original post on how long he can pull 100% the following applies

Caution

Be aware Mast bending will occur in the 83-100% range above 80knts

[NickLappos]

It must be summer already, that's when this question is asked yet again! Can't wait for Lu to get better, the missing 18 degrees is next on the annual schedule.

The rating is a takeoff rating, use it for takeoff. You get to use it for up to 5 minutes each takeoff. If you are not taking off, you don't get to use it, and if you use it more that 5 minutes, you are technically (and actually) harming your machine.

The engine and transmission manufacturers assumed a few takeoffs per hour, and they calculated the overhaul on that. Use the power less, and you make TBO or beat it, use it more and you don't.

Hurry back Lu! Its almost time, and we are starting to miss you, its getting dull around here!

[eagle 86]

If the Flight Manual says "Takeoff Limit" then that's what it is!! If you have to go into this zone for a subsequent landing then this is a sign of poor performance planning. I fail to understand why some of you chaps question the manufacturers limits - they know a lot more about their machines then you probably ever will. Bear in mind it may not be you who suffers the catastrophic failure but the bloke who flies the helicopter 50 hours down the track.
GAGS E86

[Arm out the window]

This doesn't answer the question in a situation such as John E. described above - the legs were all less than 5 min, so the other pilot he mentioned kept pulling into the takeoff limit all day.
Surely the limit needs to be defined more accurately; manufacturers can nominate maximum temperatures, speeds and so on, so it must also be possible to say how much time out of the total should be allowed, or rather how long between 5 minute applications is acceptable.
Regarding landing, it is nonsense to say that this magical extra power allowance should only be used on takeoff - simple scenario, you take off heavy from a large, low DA pad and fly up a mountain to a tight pad where higher power is needed to get in. You would still only need to use the 5 minute rating once in the flight; what's the difference between using it in the landing phase rather than on takeoff?
It's our winter, Nick, but I'll still ask the question; why is such a limit made so non-specific as to be next to useless?
If they assume a few takeoffs per hour, then why not say how many are used in the assumption so everyone knows; if people can pull to 100 percent for 5 minutes, drop the lever for a second and then get stuck into it again, they may as well not waste the ink putting it in the flight manual.

[NickLappos]

Arm,

You ask a good question. Let me try and explain it this way:

Imagine that each minute at TO power extracts one bean from a big jar of beans. One minute, one bean. If you stay at low cruise power, say 65% power, then five hours takes one bean out of the jar.

There is nothing unsafe about running at TO power, it is not "beyond limits". But if there are 10,000 beans in the jar, then you only get so much life from your engine, transmission and drive train.

We manufacturers set a 5 minute limit per takeoff as a way to remind you of that. Inside the factory walls, we imagine that you make about 2 1/2 takeoffs per hour (don't try a 1/2 takeoff, it should only be done by professionals!). We calculate that if one does 2 1/2 TO's per hour, and the rest in cruise then the power systems will last 3707 hours, and you will have performed 9200 takeoffs.
If you make more TO's, plan to overhaul sooner, if you make less, your engine will last a lot longer.

The numbers above are made up, but the idea that a takeoff is several times more damaging than a cruise hour is entirely true.
No thundering limit, where 6 minutes at TO power will end your life. Just a faster draining of those beans from the jar.

[Freewheel]

Taking up the number of take-offs per hour, there's a limitation on certain components of some Bells (205/212+others?) based upon RIN. You'll find it mentioned in small type in Bell publications.

I'm not familiar enough with these types to know exactly what a RIN is or how it's calculated, but I always had the impression it was related to the number of 'high power events' the rotor system was subjected to per hour (average). Presumably these 'high power events' were within regular limits, and yet somehow impacted upon the life of some components.

Anybody got more detail?

[Sandy Toad]

Why should it be called Take Off Power?
I can use it for upto 5 Mins on Take Off without exceeding any limitation, however use it momentarily on a landing when encountering a strong downdraught in the mountains and I'm outside limits?
Exactly what difference is it to the engine? High TOT is high TOT.

[Hidden Agenda]

Thanks Gents some very interesting feedback. Most of it I have heard before…the beans explanation is a new one to me and a nice way to describe it … reminds me of life at Club-Med… and I appreciate the ‘Sunday drivers’ perspective as much as the guy who flies in the part of Mexico that is as hot as the Jalapenos.

I also understand the argument that a machine that is worked very hard will not get to TBO, and I like to think that in those cases the power assurance checks, SOAP programmes, chip lights and similar safety features and techniques will assist operators to arrange for timely premature removal of the components that have taken a hammering before the safety margin has been significantly eroded. After all we don’t tell the guy with the mallet not to hit so hard because he might have to buy a new one during his lifetime. Nor do we let Hertz tell us that we can’t drive faster than 45 mph. To many of us a helicopter is a tool to be used in business, to make money, as is deemed appropriate by the owner, not something to be taken out for a ride around the block on a Sunday morning and the view that retaining its resale value is paramount. But we do insist that the machine be operated and maintained in accordance with the manufacturer’s limits and recommendations.

I am looking at the legal considerations of pilots, that for operational and contractual reasons, are having to use power in the takeoff range for periods in any one flight that are longer than the ‘5 minute limit’ stipulated in the Flight Manual.

I am sure that there are a number of pilots who have flown military or law enforcement missions, and probably ENG missions too, where they have been required to remain in an OGE hover for extended periods of time. If these pilots use ‘take-off’ rated power in excess of the 5 minutes for a continuous period then it would seem that they are operating outside flight manual limits. If they move into forward flight and do a large orbit allowing air flow through the coolers etc. before they return to the OGE hover are they now back to operating within the flight manual limits?

If takeoff power is for takeoff purposes only why do the ‘hover ceiling’ graphs specifically state ‘takeoff power’? Why do we not have hover performance graphs to use for the maximum continuous power rating?

Does the takeoff range on the Bell 206 torque gauge, which we are told is connected with a KIAS limitation and mast moment, have any real implication with regard to hovering flight?

Why is it that if the same old questions get asked every year, come summer time, the manufacturer doesn’t do something to clarify the situation once and for all. If a flight manual amendment isn’t commercially viable there must be other ways that they could get the message across; Ski’s ‘HeliProps’ is one example that comes to mind.

Bell’s representatives, in face to face meetings, are unable / unwilling to provide the ‘party line’ answer, probably because of legal and liability issues. Is it possible that someone from Bell could use the medium of an anonymous forum such as this to clarify the issue?

[Arm out the window]

Thanks Nick; at least that gives an idea of about how many times is considered to be OK to use up to 5 min of 'Takeoff' power before starting to cut into engine life more than is ideal .
I guess the sad fact is that unless a limit is written specifically, rather than as something that can be argued about, it will be pushed to the letter rather than the spirit of it by those who choose to do so.
Given that use of the 5 minute limit more than about 2.5 times per hour will cause the engine to deteriorate more rapidly than is expected in TBO planning, I guess it follows that a machine that's been subjected to much more than about 12 - 15 minutes per hour in the T/O range for numerous hours is looking statistically worse for likelihood of an engine failure than one that's been 'babied', as some have been terming it; looking for power trends etc to catch it before it fails in that case seems a bit hopeful, to say the least.
Blender mentioned the experienced hands who advised against 'babying' aircraft; experience counts for a lot, certainly, but urban myths and dubious practices can also become accepted truth sometimes, until someone says 'hang on, is what we're doing really a good idea?'
I'm all for working to the limits, but it seems to me to go against logic to pretend that lowering the lever momentarily into the green range and going for it again somehow complies with the manufacturer's intent.

[John Eacott]

Nick,

Maybe we need to know how many beans are in the jar to start with!

;) :ok:

[ATN]

'If takeoff power is for takeoff purposes only why do the ‘hover ceiling’ graphs specifically state ‘takeoff power’?'

The manufacturers rightly consider you will have to put the aircraft in hover before taking off.

'Why do we not have hover performance graphs to use for the maximum continuous power rating?'

Some aircraft have different graphs for hover at TO power and at MCP. For the 365 N2 the difference in MTOW is 720 kgs at 40 C.

ATN

[Arm out the window]

ATN, I'd say it's more likely that the manufacturers understandably want to make their machine look as good as possible in the specs, and there would also be defined standards that apply to the certification of aircraft and relate to the types of proving flights and documentation you must produce.
So the hover ceiling would use maximum power, because the helicopter can actually hover under the specified conditions.
You don't necessarily have to be able to hover to take off, just get light enough on the skids or wheels and you can do the old 'cushion creep' - not all that pretty but it works.

[ATN]

AOTW,

I used this trick on some occasions when there was no other options, but
I have never seen this procedure approved/certified in any RFM. So manufacturers do have to produce data and graphs for hover IGE and OGE and specify at which power settings the perfs have been obtained. IMO it does make sense to associate HOGE and T/O PWR limitations since longer periods of time are spent HOGE than HIGE. More data are available for recent and sophisticated aircraft than for their old and basic predecessors.

ATN

[Graviman]

Are there any turbine helis with "powertrain life" or "rate of powertrain damage" indicators? Reading Nick's account of the blade creep bean (and G/box tooth/bearing life), makes me wonder whether such an instrument would tell a clearer picture about heli duty usage. It would need to be part of the powertrain ECU (or is it FADEC?).

Mart

[NickLappos]

John Eacott had the right observation, and Graviman hit it,too.

There are now tools at hand to count the beans coming out, and to take good test data from the qualification tests to determine how many beans there are to start with.
I believe we are at the threshold of a new way to certify the aircraft system as a whole, instead of a collection of disconnected parts.

Turbine engines have time-temperature recorders that estimate creep life (the true limiter for turbines.) Time to extend that to allow "variable limits" within the bounds of safety, but tied to digital systems that make a red flag pop up on the displays and say "Out of Beans".

BTW, TO power is OK for landing, and a terminal hover to pick someone up is allowable at TO power. Besides, if I am down there, do NOT leave me there because the flight manual says so!!

[Gomer Pylot]

The Bell Retirement Index Number (RIN) is related to takeoffs. For most models, it's 1:1, meaning one takeoff increments one RIN. On the 212, it's different, but I haven't flown a 212 in so long I'm afraid to say exactly what the formula is, other than that it's not 1:1. Turbomeca has the same thing, but they call it cycles, and have an incredibly complicated formula that requires counting every time the N1 goes above or below 85%, and by how much. Nobody I know uses it, instead using the 'lump' calculation, basically counting one cycle per takeoff which had a start preceding it, and .15 if there was no start. It uses cycles more quickly, but better engine cycles than brain neurons. This may be different for other engines.

Personally, for takeoff and landing, all I care is that nothing goes above the redline. That's why they put red lines on the gages. Max continuous is something different, and seems to often be limited by operators to something less than what the manufacturer specifies, just to try to keep all the beans in one pile as long as possible.

[John Eacott]

Lycoming/Honeywell have a similar count for the LTS101, requiring logging of max N1 when flown, and then a fun set of calculations to derive Ng and Np cycles. Something like total number of Ng excursions (>90% to <78% to > 90%), or Np excursions (>85% - <85% - >85%). Having taken the "lump" calculation in earlier years, it's proved to be worth recording Ng and spending a bit of time calculating Ng and Np cycles, for the better life of the engine.

Tedious, though........and hard to really keep an eye on the N1 gauge when sling loading/fire fighting :rolleyes: And don't bother to tell me that I could spend c$50k on an automatic bit of kit that will do it all for me, thanks :ok:

[[email protected]]

Maybe the manufcaturers should stop calling it take-off power and call it contingency or some similar term. I know it will still mean the same thing but it will stop pilots arguing whether it can be used for landing or hovering.

It is very unhelpful to say it is a five minute rating and then not specify the frequency it may be used or more importantly the frequency of use the manufacturer has assumed.

It certainly gives the manufacturer a legal get out when the engine fails and the investigation shows that the 5 minute power was being used almost continuously - they then say 'we only expected it to be used 2 1/2 times an hour - we just didn't tell anyone that"

I like Nicks bean analogy but if the number of beans is known at the start and the rate of bean usage the manufacturers have calculated to make the zero bean count happen at the expected engine change hours - then operators can at least give guidance to their pilots and you won't have one guy using 50 beans and the next 500 beans to do the same job.

[Aesir]

I think crab@SAAvn got it right there : )

The manuals are more or less written by lawyer´s and it´s easiest for the manufacturer to use the "Take off power" reference in the manual so that when you come in for landing and run out of power, altitude and ideas all at once then they can say that you were only supposed to calculate on maximum continious power for the landing!

At least it´s a good argument in court and they need to protect themselves in overly litigious US of A..

But in real life of course the engine really doesn´t care if it´s taking off or landing when you use the 5 min rating.

And somebody mentioned that the manual includes hover tables calculated on "Take-off power" and he´s right, not likely that you are really just using that power for take off when hovering out of ground effect at 6.000' !

Nick´s bean counting system is pretty good, but for those asking about how many beans are there in the jar in the first place, then it´s not that simple really, because it´s a variable depending on the conditions the engine is operated in.

An engine operated in cold climate free of dust and salt & always started with GPU and always treated right are going to have more beans in the jar than an engine that started out life in the Sahara desert! Even if both were always operated well within any limits!

And those with ideas about some kind of health monitoring system for engine and/or gearbox.. please spare me.. the costs would be prohibitive for small helicopters and I´m in bad enough mood as it is after reading the latest AD issued on my engine :\

In regard to the discussion about RIN. On the 206 you have to figure one RIN for take-off, another for landing when throttling down to idle. So one trip with takeoff and landing is 2 RIN´s. Also one sling cycle is one RIN.

John Eacott..

Gotta love that cycle system for the LTS 101 add to it sling work and then it gets really complicated ;)

edited to add RIN talk!

[anjouan]

Maybe some of these helicopters ought to have the same system as the Dauphin N3. With that, the cycle count is done for you by the FADEC. It's just a matter of having a look on the overhead panel after flight and logging the N1 and N2 cycles from the computer for entry into the tech log.

[Graviman]

Aesir,

"And those with ideas about some kind of health monitoring system for engine and/or gearbox.. please spare me.. the costs would be prohibitive for small helicopters..."

The main time limited component in a turbine powered heli is the turbine blade. The hot temperature and centrifugal force slowly but inevitably cause the blades to stretch, or "creep". At some critical value of stretch the creep becomes exponentially worse with usage, at which point the engine is destined for a rebuild (or used as an aero engineering college demo ;) ). Turbine monitoring system would indicate when blades were about to wear out the shroud, or suffer catastrophic failure. Engine life could then be pushed (safely) to the limit of the design - even better if a proximity sensor actually detected the blade creep. Naturally this system is best supplied as part of the powertrain.

Piston powertrains have time limited components, generally limited by mechanical wear since the steel components will be designed to stay below fatigue limits (non ferrous components do have a fatigue life, but it is not generally severe). Bearings and gear teeth will eventually "spall" (basically spit out little bits of the hardened surface) when the wear causes localised stresses. Good oils will go a long way to protecting a piston engine powertrain, especially the crankshaft & camshaft bearing shells. Temperature management is required only to avoid thermal stess fatigue on the block, but if done sensibly prolongs life indefinately. Again, an OEM time-life monitor would allow the engine (with specified oils and componentry) to reach the maximum time between overhauls.

I'm frankly amazed that Continental or Lycombing don't consider developing a 500SHP turbo piston plant for (say) 206 and similar installation, for precisely these reasons. Improved fuel usage would counter inevitable weight increase. Maybe the next gen of Av-Jet piston engines will change all this...

Mart


[Edit: To correct for understanding that Nick's "beans" actually refer to all time limited components, and not just turbine blades.]

[NickLappos]

No Mart, the beans refer especially to all time-limited components.

Regarding the cost, I would bet dollars to donuts that the electronics and computation in the cell phone that all ppruners carry are more complex and expensive than those needed to count beans. The difference is tyhe number of units sold to cover the development. I do promise you that the list of R22 costs for components would demonstrate to normal people how economically imperitive it is (let alone safety concerns) that we move toward accounting directly the remaining life.

Gomer Pylot, your wish to have simple red lines is like my wish as a boy to have all the cream chees and jelly sandwiches in the world available, it is a dream. Do yoy actually think we put the lines where things break? Do you actually think there is such a relationship, where a red line marks the danger point, and all things less are wonderful, and .001% beyond that red line is death and destruction?

I give a class on where the red lines come from (having painted more than my fair share of them on gages) and I can assure you, almost none of the red lines you see are due to an actual "it will break right now if you exceed this" limit. Alomost all red lines carry with them an assumed life, an assumed operating philosophy, and an assumed degree of inspection.

The science of determining safe limits and life is the essence of engineering, and is fraught with ethical decisions like "safer" and "enough" and "practical".

Let me ask you, in driving your family, does a traffic light signal safety? If you travel the speed limit, are you truly assured that nothing unsafe can happen to you? If you inflate your tires to 33 psi, will they never blow out?

Gomer Pylot, wish for Mother Helicopter God to paint lines in places so you are always covered, but if we painted them to assure you Nothing Ever would Happen, your payload would be 10% of what it is now, your cost to operate 10 times higher, and your actual safety would be hardly different, since odds are you would take that assuredly safe machine, and CFIT yourself with it just as easily, or misjudge that distance, or overload it unintentionally. When we fix the real cause of helicopter accidents, we can spread our knowledge to the rest of human endevors. The enemy is usually us, not our machines.

[Gomer Pylot]

Nick, I know very well that redlines don't represent an "It will break above here" point, nor that nothing will ever break below them. Engines can fail while at idle - anything mechanical can break any time. My comment simply meant that as long as I stay below the redlines I'm legal, I don't have to shut down and write up an exceedance, and probably nothing bad will happen. I just don't want to have to read charts while flying with something close to the redline, and the N1 bias system on the S76A++ represents what I'm talking about. Just keep the N1 below the painted red line, and you're below the limits, regardless of the temperature and altitude.

As long as no red lines are exceeded, I don't have to make an entry in the logbook, and that's my main concern. I'm always prepared for something to fail, but so far, after 37 years, nothing has, and a large percentage of the 20,000+ takeoffs I've done have been at one redline or another, or at least very close to one. I keep my fingers crossed while knocking on my head, and stay ready for something to surprise me.

[NickLappos]

Gomer Pilot,
Let me extrapolate your comment (a very apt one, IMHO) to say:

All limits and procedures must be realized in the hands of the pilot and crew. They are not engineering abstracts nor are they legalisms, they are the best guidance we have to aid the crew.

[Gomer Pylot]

Yes, Nick, but you're speaking as a test pilot, not as a chief pilot nor as an FAA inspector. I appreciate what you do as a test pilot, but once the aircraft gets a type certificate and is in my hands, your contribution wanes, and the contributions of the others becomes paramount. Logic and common sense have little to do with enforcement actions. As a pilot, I have no idea what you've done during testing. All I have to work with are the flight manual and the limitations. You supposedly guarantee that staying below the redlines won't cause any immediate catastrophes, and that implies that going above them slightly won't either. There is no way that an increase of 1% torque, or one knot, or whatever, will result in immediate destruction, but it can result in immediate certificate or employment action. That's the distinction we have to make. Thus, I try to always stay within limits, not just for my own physical safety, but for the safety of my job and certificate.

[rotorspeed]

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.

[NickLappos]

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.

[puntosaurus]

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 ?

[Gomer Pylot]

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.

[eagle 86]

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

[[email protected]]

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.

[NickLappos]

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.

[212man]

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.

[Hidden Agenda]

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.

[puntosaurus]

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.

[NickLappos]

Remember there is a transmission and rotor in there somewhere....

[Hilife]

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.