747 Takeoff and cruising power comparison
747 Takeoff and cruising power comparison
(OP)
Can anyone give me some pointers as to the power required by a 747 powered by RB211 engines for takeoff, compared to the power required for the same aircraft to maintain a typical cruising altitude/speed.
I know there are lots of varaibles but I am looking for ball park figures
thanks in advance
I know there are lots of varaibles but I am looking for ball park figures
thanks in advance





RE: 747 Takeoff and cruising power comparison
> Overcoming drag at speed
TTFN
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RE: 747 Takeoff and cruising power comparison
If the fully loaded aircraft requires 95% of available engine power for taking off, then at cruising height and speed the engines are throttled back to around X% of full power.
Any ideas of typical values of X?
RE: 747 Takeoff and cruising power comparison
Full power take off is just that. The engines are brought to full power and when the aircraft reaches a certain speed (Vto), the aircraft leaves the ground.
The crew could also elect to perform a reduced power take off. The aircraft charts would be used to determine this power setting.
Some conditions that influence take off performance would be aircraft weight, temperature, pressure altitude, wind and thrust.
RB211-524B2, 50,100# thrust.
RB211-524D4, 53,000# thrust.
RB211-524G2 with 58,000# thrust.
RB211-524H with 60,600# thrust.
RE: 747 Takeoff and cruising power comparison
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: 747 Takeoff and cruising power comparison
I work in oil and gas and look after a fleet of RB211 aeroderivative engine used in gas compression duties.
One of the company senior managers has been contacted by a 'business management consultant' who has stated with some 'justifications' that that aircraft RB211 engines are typically overhauled each 3000 take off cycles, with overhauls typically 7 years apart.
We typically overhaul our RB211s at 30k operating hours or about once each 4 years - so the
snake oil salesmans, consultants figures look as if they can make a pretty good contribution to our bottom line at first glance.The difference is that our RB211s operate all the time at or around full load and aircraft engines only pull full load at take-off.
So, an aircraft engine might only operate at full load for around 3000 hours in a 7 year period, whereas an aeroderivative engine in gas compression or power generation duty might operate close to full power for 25k hours in a 3 year period.
I have been asked why we don't overhaul our engines at 7 year intervals, since aircraft engines have to be more strictly maintained: my response is going to be based on the knowledge that the life of a GT is determined by hot end operating temperatures which are determined by load
So, in order to pacify management that we are doing the right thing I am assembling a small presentation describing the differences in operating regimes between aircraft engines and their industrial derivatives - as part of this presentation, I would like to know what percentage of full load power is required to maintain a 747 at a typical cruising height and speed.
I am not looking for precise data, just a information along the lines that "a typical 747 requires (say) 50% (or whatever a realistic value is) of take off power to maintain cruise height and speed"
RE: 747 Takeoff and cruising power comparison
Concorde took off at 38000 lbf thrust per engine, cruised on 10000 lbf thrust (at M2+)
You can hear jets throttle back when they hit cruising altitude.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: 747 Takeoff and cruising power comparison
consider a couple of points ...
1) does your maintenance show up issues ? i'm not sure what parts of the engine are most sensitive to fatigue (though the hot section would be my guess).
2) what are the consequences (and costs) of failure ? for an airplane they are pretty severe so the MTBO is shortened. what about your operation ?
3) how long have you been maintenaing the engines this way ? if for a while it would suggest that you're doing nothing particularly wrong.
maybe RR might offer some (knowledgeable) insight ? i'd expect that they'd suggest shortening your maintenance cycle !
RE: 747 Takeoff and cruising power comparison
Greg - Yes you're right, the flaps go back and the engine power drops at cruising speed
rb1957 - thanks for your insight but I already know all this.
1) No maintenance issues. The principal sources overhual cost are blade failure and combustor distress - burning away of protective coatings
2) Consequences of failure are loss of production i.e. financial. The biggest risk to safety is blade loss so, apart from performance and overhaul cost, there is a safety risk with extended running.
3)For ever - just like everyone else - but with experience, and using condition monitoring, oil analysis, performance and borescope inspection, we can extend overhaul intervals from the OEM recommended 25khr to 32khr. The longer we run between overhauls, the more of the hot end needs to be replaced and the greater the cost of overhaul. However, the cost of overhaul divided by the hours since last overhaul is fairly constant.
As I tried to explain earlier, a business consultant has turned up and asked our management why we don't have RB211 overhauls at 7 year intervals like the aviation industry - with a typical overhaul costing US$2 million, spinning the overhaul intervals out to 7 years is an attractive proposition, but its not an 'apples with apples' comparison, hence my request for approximate power consumption during cruising. I would like to be able to quantify the differences in power consumption
RE: 747 Takeoff and cruising power comparison
Your "forever" statistics of existing overhauls should give you an idea of how often you need to do serious repair/replacement vs. interval between overhauls. It sounds on the face of it, you're at the edge of where you need to be do prevent in-use failures, which is the whole point of doing maintenance. Clearly, at double the interval, you should be able to show that there'll be X% of engines that will require $Y repair, and Z% of catastrophic failures, with, perhaps a ZZ probability of death or injury to personnel/equipment.
TTFN
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RE: 747 Takeoff and cruising power comparison
I am obviously framing this request for information very poorly.
There is nothing fundamentally wrong with the way we maintain operate and overhaul our RB211 engines each 4 years or so (based on operating hours and condition).
An alleged 'business consultant' has sown the seeds of doubt in senior management by saying that the aviation industry operate their engines in a far more severe environment but only need to overhaul their engines each 7 years. The implication here is that oil and gas operators should be able to achieve the same 7 year overhaul intervals: management have come back and said that if the aviation industry can overhaul their RB211s each 7 years then what are we doing wrong?
I could just say that a 747 on long haul duty operates most of its time in cruising mode. This means that its engines spend most time in low power regime, with consequent low working temperatures so that the hot end does not burn up as quickly as working at fullpower, but I would like to try and add some numbers, even crude ball park figures.
RE: 747 Takeoff and cruising power comparison
"1) No maintenance issues. The principal sources overhual cost are blade failure and combustor distress - burning away of protective coatings" ... doesn't quite jive with "The longer we run between overhauls, the more of the hot end needs to be replaced and the greater the cost of overhaul."
"2) Consequences of failure are loss of production i.e. financial." ... would that be huge (shuting down the plant for a day, a week?) or reasonably minor (momentary production fall whilst you switch in the reserve engine) ?
"The biggest risk to safety is blade loss so, apart from performance and overhaul cost, there is a safety risk with extended running." ... uh? if a HP disc broke and spread it's components (with inifinite energy) across your plant would something (or someone) get hit ?
"3)For ever" ... ok let's say you have lots of experience that what you're doing protects the engines nicely
"but with experience, and using condition monitoring, oil analysis, performance and borescope inspection, we can extend overhaul intervals from the OEM recommended 25khr to 32khr. The longer we run between overhauls, the more of the hot end needs to be replaced and the greater the cost of overhaul. However, the cost of overhaul divided by the hours since last overhaul is fairly constant." ... so you can extraploate the cost to opening this up to 7 years and add in the increased possibiliy of having a disc rupture.
i think you wish you could tell the "consultant" to eff off (and maybe your boss for listening to them??), that your operation doesn't compare to a jet (der) so your maintenance is difference, and you've already stretched to industrial maintenance recommended (25k to 32k). actually it sounds as though you have lots of good data ... the OEM is recommending one thing for industrial apps and another of planes, and i suspect that most planes are limited by 3000 hrs rather than 7 years.
RE: 747 Takeoff and cruising power comparison
I'd stick to the RR recommendations for industrial apps and your "tribal knowledge."
RE: 747 Takeoff and cruising power comparison
"I think you wish you could tell the "consultant" to eff off" - spot on, but his stance is seductive to the bean counters and I would like some numbers to support my position.
"1) No maintenance issues. The principal sources overhaul cost are blade failure and combustor distress - burning away of protective coatings" ... doesn't quite jive with "The longer we run between overhauls, the more of the hot end needs to be replaced and the greater the cost of overhaul."
For blade failure, I should have written blade rejection - at overhaul, a selection of blades is destructively tested for creep and life assessment - nearly all hot end components (blades, combustors) are coated with thermal barrier material - this does not have an infinite life and any breach of these coatings (hot gas erosion, fod, corrosion etc) means loss of base material and component rejection/replacement. The longer we run, the more components we have to replace - rather than remove and reapply the coating.
"so you can extrapolate the cost to opening this up to 7 years and add in the increased possibiliy of having a disc rupture" - the disc cycle life is monitored by the OEM (using our operating data) and we would not authorise reinstallation of a disc that did not comfortably exceed OEM life requirements.
"i suspect that most planes are limited by 3000 hrs rather than 7 years" - its effectively 3000 cycles which can take as long as 7 years to achieve.
"so why are you trying to compare to a 747 (or a 757 for that matter)?" - I wish I wasn't but some slimeball sales rep who probably wouldn't know a gas turbine if he was hit on the head with one has been taking this approach to drum up work.
RE: 747 Takeoff and cruising power comparison
there really is no point to comparing your usage to an airplane's when you have OEM data supporting your usage.
you could ask RR what their calendar time limit is.
you can extraploate your costs so that a 7 years MTBO would correspond to >60k hrs. curve fit what you know, maybe linear, maybe parabolic (nudge, nudge ... you can adjust the future to suit your conclusion !). sounds like you've never had a disc rupture, and probably don't want one ... the longer you run between overhaul the greater the chance of something going amiss. you can probably paint a pretty nasty picture of this.
at the end of the day, you can only recommend a course of action, and someone else is making the decision; just make sure that that someone else can't pin the blame on you later when things go awry. (CYA?)
RE: 747 Takeoff and cruising power comparison
Working for XXX and flying one or two cycles a day, we were able to extend the calendar Mx tasks. What American would have to do every 18 months, we were able to "escalate" (never did like that term) to 30 or 36 months. And the FAA bought into it.
The green eyeshade types were so locked into the immediate cost savings, that they didn't notice that we were flying the things more than the two cycles per day due to volume increase and aircraft retirement. So we ended up with a Mx plan that would have been valid 2 years prior. Lo and behold, things were failing on the line long before they were due to be checked under the cheaper plan. Of course, all of those involved in the escalation were rewarded and moved on to bigger and better things. The rest of us slobs were left to mop up the mess.
Sounds like you are in a similar sit, so be highly protective of your posterior.
RE: 747 Takeoff and cruising power comparison
Your consultant is making an academic comparison, he has nothing more than some industry practice. YOU have actual data on YOUR equipment. The statistics of your operation is what's important. Use YOUR data to refute the arguments, if it supports your position. Whatever the consultant could say cannot supplant actual data from your own operations.
TTFN
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RE: 747 Takeoff and cruising power comparison
Maybe MIL-HDBK-1783 can give you something as a reference for your case.
RE: 747 Takeoff and cruising power comparison
The answer to the accountant's arguement ("why can't we go 7 years?") is "we should be overhauling at 3,000 hours, not 30,000 hours". Damn spin doctors.
RE: 747 Takeoff and cruising power comparison
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: 747 Takeoff and cruising power comparison
Take a look at this link: http://ww
The RB211-22C engine will generate 41,030 lb of thrust on takeoff (5 minute maximum) and 36,900 lb of thrust on continous duty.
I can't say how much the 747 airplane actually requires but that is how much the engines can generate in flight. Since weight is a huge issue on airplanes, you can bet the engines aren't sized any larger than necessary, so they probably can use the full take off and crusing thrust if flying under worst case scenarios.
RE: 747 Takeoff and cruising power comparison
NB: cruise isn't necessarily "max continuous".
RE: 747 Takeoff and cruising power comparison
94% takeoff power
96% climbout power
87% cruise power
He said the power settings do vary depending on flight load, but he said he wouldn't see below about 80% power at cruise.
Naturally, for noise abatement over certain cities, the climbout power will be less until they get over 10,000ft.
I stand corrected on my first post, but the point is that aircraft jet engines do not get throttled to a much lower position while at cruise.
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: 747 Takeoff and cruising power comparison
Correct me if I'm wrong but I'd guess 100% of max power at ground level is going to be more that 100% max at 30000ft due to air density.
80% max at cruise altitude might be significantly lower than 80% max at ground level.
RE: 747 Takeoff and cruising power comparison
80% max EGT
80% max fuel flow
80% max rpm
I'm sure there are others.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: 747 Takeoff and cruising power comparison
There are plenty of aircraft pilots and mechanics on that forum who could discuss operation and maintenance.
RE: 747 Takeoff and cruising power comparison
Good luck.
j79 guy
RE: 747 Takeoff and cruising power comparison
RE: 747 Takeoff and cruising power comparison
for industrial apps, i don't know ...
RE: 747 Takeoff and cruising power comparison
In NG compression, any pipeline 20" or bigger, or requiring 2000+ Hp, a turbine will be usually be spec'ed. When varying gas flows are the norm, aeroderivitive turbines will be used.
If an engine fails, an aeroderivitive turbine can be replaced with a fresh unit within 8 hours on-site, give or take.
A 32,000 Hp. recip would take how long to repair/replace?
rb1957 is bang on. Power density.
j79 guy
RE: 747 Takeoff and cruising power comparison
Any more most airlines have the crews collect a few minutes of engine performance data every flight. If you have a connection, maybe somebody will share the continuous health data on a couple engines.
RE: 747 Takeoff and cruising power comparison
To speech about power under operational point of view is not
practical. We use EPR a relation between exhaust pressure vs.inlet pressure ( pt2/pt1). This relation will give you an idea of "power" and was used by RR, P&w, GE.
Suppose you are taking off with MTOW and the real value of EPR for the engines will be 1.66 for RR 211-524-D4X. As OP Manual indicate,the needed EPR at the optimum initial cruise level,will be 1.64. The value is very similar to take off EPR.
Suppose you are taking off with 330 tons, your TO EPR will be aprox 1.58, the needed EPR at the optimum initial cruise level will be 1.68. This value is nearly the same to all maximum cruise EPR for the optimum initial cruise level.
Conclusion: You can expect nearly the same EPR at the opti-
mum initial cruse EPR ( at M=.84 and LRC )for all T.O. weights ( 1.66 to 1.68 ).
The comparison of T.O, EPR and Cruise EPR and is from 0%
( 370 tons ) to 10% ( 280 tons, reduced T.O. EPR ).
Those values are for B-747-287 series, with Rolls Royce
R 211-524-D4X.( the best airplane ever made !! )
Cheers
RE: 747 Takeoff and cruising power comparison
On the face of it, any engine that has to be run at steady state (here they mean at a steady load configuration) will last longer than an engine that is cycled hot/cold, high/low load.
BUT
The usage of your engines is completely different. Your situation is different. A lot of engines on rigs are sucking in seawater as spray - you get very little sea spray at 36,000'! Trying to make comparisons is really futile.
Speak to RR at East Kilbride. They know; they are experts. They make them, service them, research them.
Bean counters are dumb. Hit thm with every fact you can find - they once told us that, at 16 students per class, we only needed three instructors! For several disciplines of avionics, airframe specialists, propulsion specialists, maths and physics.... This is not to mention that some people were doing Aeroplanes 1 and others were doing Aeroplanes 2.
Go for safety in numbers - flock together like small birds confusing an Eagle. Then dump everything on them and say "when this all comes to a complete clusterf*** it will be you fault. Put it in writing.
RE: 747 Takeoff and cruising power comparison
Although it's been a while since I did A/C ops I (think I) remember that a long hauler such as 747 is only flying for about 13 hours a day on average. Obviously the engines runs a little on the ground but simplistically the engines are running maybe 60% of that 7 years.
.6*24*365*7=36792
Then so about 20% longer than your service interval.
I believe operating hours are more significant in your operation than calander days.
So now the question of why not at least extend out your servicing 20% more.
This is where your differeng service conditions etc come in.
At the end of the day what others say about following RR guidelines etc. is the real answer but I appreciate that the combined intelligence of management & consultants might struggle with this.
Something you may be able to strong arm management, does exceeding the servicing intervals invalidate any warranties or safety regs etc?
I thought this might be useful but on closer examination I'm not sure http:/
KENAT,
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