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Take-Off Power - How often?

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Take-Off Power - How often?

Old 15th Jun 2005, 07:09
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Take-Off Power - How often?

The Flight Manual of the Bell 206 says:

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

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.

Hidden Agenda is offline  
Old 15th Jun 2005, 08:25
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'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.
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Old 15th Jun 2005, 08:57
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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.
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Old 15th Jun 2005, 10:16
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Hidden Agenda

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


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Old 15th Jun 2005, 11:21
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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.
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Old 15th Jun 2005, 12:42
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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.
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Old 15th Jun 2005, 13:17
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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"
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Old 15th Jun 2005, 15:21
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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.
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Old 15th Jun 2005, 16:07
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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.

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Old 15th Jun 2005, 17:31
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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.
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Old 15th Jun 2005, 18:15
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well done Max TO yea you are right, its just a term i guess, grey it is.
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Old 15th Jun 2005, 21:14
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Limitation is on the mast

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.
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Old 15th Jun 2005, 21:52
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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!
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Old 15th Jun 2005, 23:36
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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.
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Old 15th Jun 2005, 23:37
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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

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
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Old 16th Jun 2005, 21:34
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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


Be aware Mast bending will occur in the 83-100% range above 80knts
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Old 17th Jun 2005, 00:25
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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!
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Old 17th Jun 2005, 01:30
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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.
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Old 17th Jun 2005, 03:15
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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.
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Old 17th Jun 2005, 03:46
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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.
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