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maddog888
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SQ A380 Fuel Saving Departure From LHR

Sun Mar 28, 2010 2:54 pm

Partial extract from news page on BAA's LHR website:

"Heathrow, NATS, Singapore Airlines and Airbus have launched an improved departure procedure for the Airbus A380, saving even more fuel, emitting even less CO2 and remaining within the airport’s strict noise procedures.

This new procedure saves an additional 300kg of fuel per flight, equating to one metric tonne of emissions of CO2 on a flight to Singapore, as well as reducing NOx emissions.

The companies worked together over the last year to develop the new airline procedure, which has been put into place immediately. Singapore Airlines A380s departing Heathrow now use less power when taking off, saving fuel and reducing NOx emissions. Once a height of 1,500 feet has been reached, the aircraft uses flexible acceleration up to 4,000 feet, before continuing its journey."



I read the above on the BAA website for Heathrow and wondered what exactly is meant by "flexible acceleration". Is it just a euphemism for reduced acceleration? It talks of savings of 300kg of fuel on a flight to Singapore. I don't know how significant this is as a percentage of total fuel burn. I am always skeptical of press releases.

Anybody able to enlighten me?

Julian
 
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Starlionblue
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RE: SQ A380 Fuel Saving Departure From LHR

Mon Mar 29, 2010 12:05 am

I'm guessing they mean flex thrust, which is reduced acceleration as you surmise.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
thegeek
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RE: SQ A380 Fuel Saving Departure From LHR

Mon Mar 29, 2010 1:49 am

So, does this mean that they stop using flex thrust at 4000ft altitude, and that's why they save fuel? I thought flex thrust resulted in more fuel being used in general.
 
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Starlionblue
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RE: SQ A380 Fuel Saving Departure From LHR

Mon Mar 29, 2010 2:13 am

Ah yes good point. Forgot about that. Flex thrust uses more fuel.

I live how the press release is so uninformative. Not that I expected better.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
411A
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RE: SQ A380 Fuel Saving Departure From LHR

Mon Mar 29, 2010 4:42 am

Quoting Starlionblue (Reply 3):
Flex thrust uses more fuel.

Not on all airplanes, it doesn't.
L1011, for example
 
cobra27
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RE: SQ A380 Fuel Saving Departure From LHR

Mon Mar 29, 2010 5:00 pm

If you read Getting to grips on fuel consumption, flex increases consumption around 100kg depenending on size of the plane, but it significantly prolongs lifetime of the engine
 
prebennorholm
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RE: SQ A380 Fuel Saving Departure From LHR

Mon Mar 29, 2010 10:52 pm

We will have to know a lot more details to be able to evaluate this. Climb profiles out of LHR are very complex due to both traffic and noise.

But obviously a new profile has been agreed for SQ 380s, a profile which saves a little fuel compared to the previously agreed profile.

There is no information whether the new profile then gives a slightly increased noise footprint. It's not necessarily so, but very likely. And BTW, it is hard to hear a 380, so....

At all busy airports the climb profiles are compromises or tradeoffs between:
- safety
- traffic management
- noise
- fuel economy.

You pull one of those four strings and the whole pattern moves.
Always keep your number of landings equal to your number of take-offs
 
cobra27
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RE: SQ A380 Fuel Saving Departure From LHR

Tue Mar 30, 2010 10:31 am

Noise abatement increases consumption, compared to regular T/O
It is harder to optimise dep/arrvilas at LHR because there is tons of traffic.
 
411A
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RE: SQ A380 Fuel Saving Departure From LHR

Tue Mar 30, 2010 2:29 pm

Quoting cobra27 (Reply 5):
If you read Getting to grips on fuel consumption,

Don't need to read 'Getting a Grip', I already have one, thank you, and on the type I specified, flex thrust does not normally increase fuel consumption.

As in many subjects in airline/large jet aircraft operation, it very much depends on the specific type and/or specific operational procedures.
 
musang
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RE: SQ A380 Fuel Saving Departure From LHR

Tue Mar 30, 2010 4:29 pm

Quoting Starlionblue (Reply 3):
Flex thrust uses more fuel
Quoting cobra27 (Reply 5):
flex increases consumption around 100kg depenending on size
Quoting cobra27 (Reply 7):
Noise abatement increases consumption, compared to regular T/O

although the press release says it saves 300 kg. Why would BAA say that if it weren't true?

I too have never heard of "reduced acceleration" or "flexible acceleration". Assuming the automatics are doing it, and a speed increase is dialled in, acceleration happens as a result of a programmed pitch reduction so will be a constant unless complicated by a simultaneous thrust change. One knot per second is representative.

The old SQ 380 launch sequence was TOGA thrust to 1500 feet, reduce to Managed Climb thrust with no speed increase, to 4000 feet, where acceleration/flap retraction commenced.

New sequence is Flex thrust for take-off to 1500 feet, then Climb thrust and accelerate to "Green Dot Speed", which I believe is Airbus-speak for best rate of climb in clean configuration. Through 4000 feet, normal climb speed/profile.

The early acceleration allows flap retraction therefore reduces drag, noise and fuel per unit distance.

Its been evaluated for a year and EK + QF are aware.

The above from Flight international.

Regards - musang
 
cobra27
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RE: SQ A380 Fuel Saving Departure From LHR

Tue Mar 30, 2010 5:54 pm

Quoting musang (Reply 9):
Why would BAA say that if it weren't true?

Media thing, probably for publictiy or something
 
thegeek
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RE: SQ A380 Fuel Saving Departure From LHR

Wed Mar 31, 2010 1:32 am

Quoting musang (Reply 9):
The old SQ 380 launch sequence was TOGA thrust to 1500 feet, reduce to Managed Climb thrust with no speed increase, to 4000 feet, where acceleration/flap retraction commenced.

New sequence is Flex thrust for take-off to 1500 feet, then Climb thrust and accelerate to "Green Dot Speed", which I believe is Airbus-speak for best rate of climb in clean configuration. Through 4000 feet, normal climb speed/profile.

Just to clarify, this means reduced thrust to 1500ft, then reduced climb angle to 4000ft at the same thrust? I assume the savings come from the part between 1500ft & 4000ft? I would also assume that the new regime results in flap retraction sooner.
 
musang
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RE: SQ A380 Fuel Saving Departure From LHR

Wed Mar 31, 2010 9:56 am

Not quite.

Flex thrust to 1500' then select Climb thrust (a reduction*) and accelerate by selecting a higher speed. Retract flaps as appropriate as speed increases. The climb angle (and rate) reduce during the accel phase, but once clean at Green Dot Speed, its at the optimum climb rate speed for the weight.

* it will be a reduction at heavy weight. Sometimes in low weight/long runway situations we see an increase in thrust on selecting Climb thrust (737 classics). This is because the runway is long enough to allow a low T/O thrust, but the climb thrust calculations (by the FMC) come up with a figure based on a different set of parameters. Which I don't claim to fully understand, as Boeing manuals are written on a "need to know" basis!

Regards - musang
 
thegeek
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RE: SQ A380 Fuel Saving Departure From LHR

Thu Apr 01, 2010 12:45 am

So is Climb Thrust lower than maximum continuous thrust, or can flex thrust be higher than maximum continuous thrust? I'm a bit confused as to how come thrust would be reduced when climb thrust is selected when TOGA power is not used on take off.
 
tdscanuck
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RE: SQ A380 Fuel Saving Departure From LHR

Thu Apr 01, 2010 3:56 am

Quoting thegeek (Reply 13):
So is Climb Thrust lower than maximum continuous thrust, or can flex thrust be higher than maximum continuous thrust?

It can be. Just like on takeoff, you can have various climb thrust derates. In general, max takeoff thrust is greater than max climb thrust, which is greater than max continuous thrust.

Max continuous is, as the name suggests, certified for operation for arbitrarily long lengths of time (up to the engine maintenance limits, in theory). Max takeoff and max climb are time limited.

Quoting thegeek (Reply 13):
I'm a bit confused as to how come thrust would be reduced when climb thrust is selected when TOGA power is not used on take off.

Takeoff power and climb power are two different settings...depending on the derates/ATM/flex selected, climb thrust could be lower, equal, or higher than takeoff thrust.

Tom.
 
thegeek
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RE: SQ A380 Fuel Saving Departure From LHR

Thu Apr 01, 2010 4:44 am

Thanks for the replies. Sounds like the some or all of the savings are coming from getting to what you are calling a "clean" config sooner.
 
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Starlionblue
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RE: SQ A380 Fuel Saving Departure From LHR

Thu Apr 01, 2010 5:59 am

Quoting tdscanuck (Reply 14):

Max continuous is, as the name suggests, certified for operation for arbitrarily long lengths of time (up to the engine maintenance limits, in theory)

Up to the time when you need to fill up on oil? That's what restricts the VC-25A.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: SQ A380 Fuel Saving Departure From LHR

Thu Apr 01, 2010 6:03 am

Quoting Starlionblue (Reply 16):
Up to the time when you need to fill up on oil?

That's the most likely practical limit. That's why I put "in theory" in there. From a purist point-of-view, the engine can run at max continuous thrust until the life-limited parts give out, but that's assuming you've got enough fuel, oil, filter media, etc. to "feed" the engine for that long (for example, on a thrust stand). In a real-world on-aircraft scenario, you'll run out of fuel (with non-aerial refueling) or oil first.

Tom.

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