Thrust
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Rolls Royce Engines On Qantas A380s

Fri Dec 24, 2010 5:16 pm

Hi there. I had a question on the thrust restrictions RR has imposed on Qantas, mainly because I read in an article that with the new thrust restrictions, Qantas would have to fly the A380s with only 80 passengers if it were to operate SYD-LAX efficiently. I wanted to know how long these restrictions are expected to last, and if RR is working on a solution to allow Qantas to continue flying SYD-LAX at full capacity.
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Stealthz
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RE: Rolls Royce Engines On Qantas A380s

Sat Dec 25, 2010 8:38 am

Quoting Thrust (Thread starter):
Qantas would have to fly the A380s with only 80 passengers if it were to operate SYD-LAX efficiently.

I am not sure SYD-LAX, 80 passengers, A380 and efficiently go together in one sentence.

Quoting Thrust (Thread starter):
RR is working on a solution to allow Qantas to continue flying SYD-LAX at full capacity.

I would be reasonably certain they are!
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Stitch
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RE: Rolls Royce Engines On Qantas A380s

Sun Dec 26, 2010 1:51 am

As I understand it from posts, the main issue is that take-off thrust is significantly restricted so out of LAX they have to really dial back the TOW.

Once Rolls corrects the issue and full take-off thrust can be restored, no more payload restrictions will be necessary.
 
rendezvous
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RE: Rolls Royce Engines On Qantas A380s

Sun Dec 26, 2010 9:28 pm

Why does a couple of thousand pounds of thrust make such a huge difference to takeoff performance?
 
tdscanuck
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RE: Rolls Royce Engines On Qantas A380s

Sun Dec 26, 2010 10:19 pm

Quoting Rendezvous (Reply 3):
Why does a couple of thousand pounds of thrust make such a huge difference to takeoff performance?

If you're close to the performance limits for the runway, which these flights are, a couple of thousand pounds of thrust is the difference between being able to stop on the runway in the case of a rejected takeoff, and an overrun. If your thrust is capped, and the runway is fixed, the only way to bring the numbers back into a legal takeoff is to shed payload.

Tom.
 
prebennorholm
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 1:08 am

Quoting Rendezvous (Reply 3):
Why does a couple of thousand pounds of thrust make such a huge difference to takeoff performance?

Do we know that it is only "a couple of thousand pounds"? I think not.

What we know is:

1. QF is operating their T900s at a cap below 72klbs

2. SQ and LH at least before the mishap had a 70klbs cap on their T900s.

3. SQ and LH have not changed their A380 schedules.

Maybe all three T900 operators have them capped at 60 or 65klbs, or something like that?

If SQ and LH also have them reduced somewhat, but that doesn't do any (serious) harm to their schedule, then their PR department for sure would find no reason to brag about that reduction to the world press.

I don't think I have missed one single post about the T900 mishap, but I haven't seen any hard number to which it is temporarily capped. The absense of "noise" from SQ and LH easily leads to the assumption that they haven't had their engines reduced below 70klbs, but that's only an assumption until we see hard numbers, which we probably never will.
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Qantas744er
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 1:39 am

Quoting prebennorholm (Reply 5):
Do we know that it is only "a couple of thousand pounds"? I think not.

What we know is:

1. QF is operating their T900s at a cap below 72klbs

2. SQ and LH at least before the mishap had a 70klbs cap on their T900s.

3. SQ and LH have not changed their A380 schedules.

Maybe all three T900 operators have them capped at 60 or 65klbs, or something like that?

If SQ and LH also have them reduced somewhat, but that doesn't do any (serious) harm to their schedule, then their PR department for sure would find no reason to brag about that reduction to the world press.

I don't think I have missed one single post about the T900 mishap, but I haven't seen any hard number to which it is temporarily capped. The absense of "noise" from SQ and LH easily leads to the assumption that they haven't had their engines reduced below 70klbs, but that's only an assumption until we see hard numbers, which we probably never will.

You got this wrong.

1. QF's T972 has 72,000Lbs of thrust. And up to the accident pushing TOGA would result in this thrust.

Now pushing TOGA gives 70,000Lbs as they changed the software to match the T970. Because in the end the 972 is a 970 with a higher thrust plug.

2. LH and SQ have the T970 and have 70,000Lbs at TOGA.

Your "capped" thrust idea is wrong. The only time they do not operate at their TOGA thrust is when they are at a FLEX thrust setting (assumed temp) which just happens to be 99% of takeoffs. However, TOGA and thus max. available thrust is always available if necessary.
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prebennorholm
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 3:02 am

Quoting qantas744ER (Reply 6):
Now pushing TOGA gives 70,000Lbs as they changed the software to match the T970.

That's the "assumption" I was mentioned. But there is more to it.

QF says that their A380 can handle the SYD-LAX route only with 80 pax instead of 470 pax. That means that TOW has to be reduced by some 90,000 lbs - or 7.2% of certified MTOW.

Going from 72 to 70klbs TOGA is a 2.8% reduction.

On no transport plane at any condition do you sacrifise 7.2% TOW for a TOGA reduction of 2.8%.

So the thread starter is correct when indicating that something in the numbers doesn't fit. There is something more to it which neither you nor I know about.

The numbers above assume that with 470 pax QF's SYD-LAX flights were operated at MTOW. I do not know if that was true. But if they did it at slightly less than MTOW, or if they could carry any additional cargo, then the unexplained "gap" in the numbers just becomes bigger.
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Aesma
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 3:43 am

Personally I wonder if the numbers are not just BS from QF, and in reality they just don't want to risk another engine blowing up, but in the middle of the Pacific. So the route is on hold until they get revised engines.
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Qantas744er
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 4:29 am

Quoting prebennorholm (Reply 7):
That's the "assumption" I was mentioned. But there is more to it.

QF says that their A380 can handle the SYD-LAX route only with 80 pax instead of 470 pax. That means that TOW has to be reduced by some 90,000 lbs - or 7.2% of certified MTOW.

Going from 72 to 70klbs TOGA is a 2.8% reduction.

On no transport plane at any condition do you sacrifise 7.2% TOW for a TOGA reduction of 2.8%.

So the thread starter is correct when indicating that something in the numbers doesn't fit. There is something more to it which neither you nor I know about.

The numbers above assume that with 470 pax QF's SYD-LAX flights were operated at MTOW. I do not know if that was true. But if they did it at slightly less than MTOW, or if they could carry any additional cargo, then the unexplained "gap" in the numbers just becomes bigger.

I see what your saying as clearly that TOGA reduction could not cause such a MTOW reduction, however like you said its all "assumptions" even though I seriously doubt there would be a reason to cap under 70K since LH and SQ have been operating the aircraft normally for a while now.

And would they really be able to do LHR-SIN-LHR at some 510-520k kgs with 60k lbs of thrust? I dont have RTOW numbers for the A380 to check takeoff performance.

Also keep in mind that for QF at LHR SOP is TOGA to 1000' Accel. 4000' to meet the noise/climb requirements. No way they can achieve that on 65k...thats for sure.

I believe that the statement by QF regarding '80 pax.' on SYD/MEL-LAX is a little over the top and probably based of the worst possible conditions at takeoff etc.
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Stitch
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 5:10 pm

LH and SQ are operating their A380s on shorter stage lengths than QF was SYD/MEL-LAX, though. It's been stated that all of QF's A388's are now operating on SYD-LHR, so with the stopover, they're now running the same stage lengths SQ and LH are so they should be able to work with the same 70k thrust settings.
 
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RE: Rolls Royce Engines On Qantas A380s

Tue Dec 28, 2010 10:50 pm

Quoting qantas744ER (Reply 9):
I see what your saying as clearly that TOGA reduction could not cause such a MTOW reduction...

Okay, we agree that the numbers 470 pax / 72klbs and 80 pax / 70klbs don't add up. That there is simply more to it.

Quoting qantas744ER (Reply 9):
I believe that the statement by QF regarding '80 pax.' on SYD/MEL-LAX is a little over the top and probably based of the worst possible conditions at takeoff etc.

That is one valid assumption. But then you must also accept that under the same "worst possible conditions" with 72klbs engines they could carry only some 200 pax, not 470.

Of those four figures (470, 72, 80 and 70) QF has told us only three of them, the three first mentioned. They have never told us the figure 70. The only thing we know about that last figure is that AESA and RR has told us that it is less than 72.

Assuming that QF didn't lie to us with the three figures provided, then we can in fact ourselves calculate the fourth figure. and it becomes 65-ish when assuming that the A380 with 72klbs was pretty much stretched to the limits on SYD-LAX with full pax load. And somewhat lower than 65 in case it wasn't really stretched to the limits.

Quoting qantas744ER (Reply 9):
Also keep in mind that for QF at LHR SOP is TOGA to 1000' Accel. 4000' to meet the noise/climb requirements. No way they can achieve that on 65k...thats for sure.

When limiting capabilities, then there will be noise abatement profiles which cannot be made any longer. But since the A380 making a little more noise on the ground will still be more quiet than a vintage B744, then I think that will be tolerated by the authorities.

If QF's T900s are limited to something in the 60'es instead of 70klbs, then it would make no sense if SQ and LH haven't got the same limitation. And in that case they will just fly happily around on their sufficiently short sectors and long runways, just like QF does these days on their SYD-SIN-LHR route. Everything becomes a lot easier when you don't need to fill the last 100 or 200,000 lbs of fuel tank capacity.
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Aesma
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RE: Rolls Royce Engines On Qantas A380s

Wed Dec 29, 2010 2:16 am

I have heard a theory that QF has a tendency to abuse its engines (backed by the other recent uncontained failure they had, on a 744ER last summer), so it's possible RR has slapped a lower limit on them than on SQ and LH.

BTW, I think the problem is LAX-SYD, and not the other way around, because they can't use the longest runway at LAX.
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zeke
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RE: Rolls Royce Engines On Qantas A380s

Wed Dec 29, 2010 5:00 am

Quoting Thrust (Thread starter):
I wanted to know how long these restrictions are expected to last,

I believe they have already been lifted, they were brought in by EASA, and removed by EASA.

Quoting prebennorholm (Reply 7):
So the thread starter is correct when indicating that something in the numbers doesn't fit. There is something more to it which neither you nor I know about.

It would be the one engine out climb gradients. The aircraft could takeoff with the normal passenger payload and suffer an engine failure and still climb away, however their climb gradient would not meet the gradients required of a quad.

The ways to improve climb gradients is by either accelerating along the runway more to get more energy before rotating (known as V2 over speed), or if your runway length is limited, is to have more excess thrust available.

The amount of excess thrust does not need to be that significant, just significant enough to cause vertical acceleration beyond equilibrium that would meet the required climb gradient.

Anyone flown a C150 and C152 on a hot day would understand the improvement in climb gradient the C152 has with the extra 4 hp.
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rendezvous
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RE: Rolls Royce Engines On Qantas A380s

Wed Dec 29, 2010 5:21 am

Does the A380 have any valid performance data available to fly with say 60,000lb thrust?


I'm not sure I agree with the engine out climb gradient. Surely at MTOW the A380 can meet engine out climb gradients with the 'regular' 70,000lb thrust engines? While I completely agree that a little extra power can make a significant difference to the climb gradient, I don't think this is limiting. Really what is being said is that A380's with the 70,000lb engines can never take off at MTOW in case they have an engine failure.

I apologize if I have misunderstood what you were saying.

LAX MEL and SYD don't really have high terrain around them that would be limiting?

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