ULH flights burn much more fuel

[JammedStab]

As much as 20% more according to a simple comment I read.

Is it really that much?

Example....Perth-London versus Perth-Dubai-London.

[TURIN]

I think BOAC would agree, I mean 6 fuel stops down to Joburg is obviously the right thing to do. Non-stop would be a ridiculous idea.

[FlightDetent]

Not ULH, but for illustration: a quick look into integrated planning tables for A333 suggests 11% difference in favour of 2x 4000 NM instead of 8000. (how niche is 8k with 333 I do not know)

[tdracer]

There is a rule of thumb that says ~13% penalty for 'tankering' fuel - I'd assume ULH would be similar or perhaps a bit less.

[stilton]

Hang on a minute, you're saying longer flights use more fuel ?

[megan]

There was a thread hereabouts, and from memory the optimum stage distance was about 4,000 miles.

[mutt]

3% per hour for the tankered fuel, in this case the tankered fuel would be fuel for 4000-8000 nms, so lets say 8 hours x3 = 24% of the fuel.

[Gauges and Dials]

Hang on a minute, you're saying longer flights use more fuel ?
umm... I believe he's saying that longer flights use more fuel per mile.... but then again what do I know.

Related news: Shipping the kerosene needed for the second half of the flight, to the midway point, is more efficiently done by truck or boat than by airplane. Or so I've been told.

[Intruder]

But you also have to add in the fuel for terminal operations, taxi, and climbout form the stopover point.

Unless you have detailed fuel plans for each scenario under identical conditions, I don't think you can generalize.

[DaveReidUK]

There was a thread hereabouts, and from memory the optimum stage distance was about 4,000 miles.

This one ?

http://www.pprune.org/tech-log/148577-fuel-tankering-formula.html

[CCA]

It's exponential, There's no fixed %.

The longer the flight the higher the average percentage.

[FullWings]

Yes.

Depending on the efficiency of the airframe, there will be a point where adding more fuel has mathematically virtually no effect on range. We don’t (can’t) operate in this area but the curve is beginning to steepen in the latter half of ULH sectors, so the increase in total fuel burn to go an extra hour at the end is considerably more than you might expect assuming linear behaviour.

[Dairyground]

I haven't done the sums, but it seems likely that there is a point where adding more fuel actually reduces the range. That assumes sufficient fuel tank capacity, of course.

[DaveReidUK]

I'd be fascinated to see any calculations that show that.

[jtt]

Well, if you load an infinite amount of fuel the airplane becomes infinitely heavy. So you need infinite thrust just to get it to move. And for that you need an infinite amount of fuel - all the fuel you loaded will be gone the moment you attempt to start taxiing;-)

[Gauges and Dials]

I'd be fascinated to see any calculations that show that.
The devil is, of course, in the details, and this doesn't take into account taxi, climb, terminal ops, etc. but....

If for a given airplane the cost of tankering fuel is x% per hour (say f'rinstance 3%), meaning that it takes 3 lbs per hour incremental burn to carry 100 incremental lbs of fuel, then a hard theoretical limit of flight duration is going to be 1.0/x hours (say f'rinstance 33 hours).

Fuel your aircraft for 33 hours endurance. Add 1,000 lbs of fuel, and, at the end of 33 hours you'll still be bingo fuel because you will have burned the whole 1,000 lbs carrying the extra fuel.

Mumble, mumble, double integrals, diffe-q, mumble mumble this is, as is the "x% per hour for tankering" rule of thumb, an oversimplification.

Will you ever get to the point that adding fuel reduces your range? I dunno, the only experience I have with Calculus these days is that recurring dream in which you show up for the final exam, only to realize that you didn't go to any of the lectures, didn't read the book, are stark naked, and forgot to bring a pencil....

[Gauges and Dials]

Well, if you load an infinite amount of fuel the airplane becomes infinitely heavy. So you need infinite thrust just to get it to move. And for that you need an infinite amount of fuel - all the fuel you loaded will be gone the moment you attempt to start taxiing;-)
Conversation years ago with a mathematically-inclined 12 year old who was enthusiastically learning the concepts of infinity:

Q: "If you had a pie, and an infinite number of people lined up, and each person in line, when it was his turn, took half the remaining pie, when would the pie be gone?"

A: "When the whole line had had their turn!"

[DaveReidUK]

Will you ever get to the point that adding fuel reduces your range?

No, as a simple thought experiment will show.

Hopefully I can leave that to the interested reader.

[FE Hoppy]

Tankering fuel means arriving with the extra weight. That is not the same as arriving having burned it.

You need to add the fuel to the start of the flight not the end.

However, every aircraft will have a sweet design spot and simply adding more fuel tanks and reducing traffic for the same weight will of course use more fuel per passenger mile.

[OMAAbound]

Funnily enough I was talking about this the other day. On some (extremely rough) calculations on the DXB-AKL vs DXB-SYD-AKL

DXB-AKL- 231T
DXB-SYD-AKL 225T

Like I said, rough calculations, but the 6T of fuel saved is roughly 30 minutes of flying.

Perhaps someone could give more accurate figures

[FlightDetent]

Which type, if I may ask?

[galaxy flyer]

I did a request to analyze the hourly fuel burns for the Global Express using s common flight planning engine. For each additional hour, the overall fuel burn declined, as expected, the "fixed cost" of start, taxi and climb was spread over loner time. At around the seven hour mark, the unexpected happened, the hourly burn increased.

As the added fuel equaling less distance, yes, I've seen, but it wasn't the fuel it was the added drag of external tanks. The early A-10s were ferried with three tanks, then some bright spark, put two ranks, widely spread on the pylons reduced drag and the less weight equaled slightly better range with less fuel.

[OMAAbound]

Which type, if I may ask?

A380 mate which operates the 2 flights I've used

[msbbarratt]

Funnily enough I was talking about this the other day. On some (extremely rough) calculations on the DXB-AKL vs DXB-SYD-AKL

DXB-AKL- 231T
DXB-SYD-AKL 225T

Like I said, rough calculations, but the 6T of fuel saved is roughly 30 minutes of flying.

Perhaps someone could give more accurate figures

And stopping off in Sydney is an excellent idea anyway, nice place to be, no need to hurry on by :)

[johnpilot]

But once you add the landing fees, handling fees, extra crew required over the year to operate one additional stop, hotels, per diems, catering and delays, 6 tonnes * US$ 550 is negligible.

Expect around US$ 30,000 to turn around a 380 in a major airport and once you include the extra crew salaries, per diems and hotel bills you are closer to $ 60,000.

The flight plans have a formula. On a 13 hour flight for every extra tonne of fuel / load you carry you burn around 500 KGS extra on the 380.

[LH777]

Same on the B777. Routes I use to fly between 12-14 hours and the delta burn for 1 tonne was 450-500 kgs.

[megan]

How the money men figure it.

http://catsr.ite.gmu.edu/SYST660/aircraft_payload_range_analysis_for_financiers___v1.pdf

[Gauges and Dials]

No, as a simple thought experiment will show.

Hopefully I can leave that to the interested reader.
D'oh...

Tunnel vision or something on my part. Missing that was embarrassing.

[Derfred]

A 747 guru once told me that the theoretical range limit of a 747 was 29 hours (close to the 33 hours quoted above for 3%/hr). If you had unlimited fuel capacity, the longest you could fly for was 29 hours. Any fuel added above that would be burned by the time you reached 29 hours. (For G&D's son's benefit, flying 29 hours in a 747 would require "infinity fuel")...

It would be interesting if someone could post the kg cost of carriage for a 787-9 or A350 at max range (full tanks) and MTOW. I'm guessing it would be at least 500 kg per tonne but these aircraft are obviously more efficient than the 747.

I recall once reading the cost of carriage for a Saturn V rocket. I don't recall the figure but it was so close to 100% the fact that it could actually escape the planet is staggering. If Earth was a few percent larger than it is we would never have made it to the moon. It would have become theoretically impossible from a single launch. Of course an orbital re-fuelling stop enroute would still have been a possibility.

Which begs an amusing question. If Qantas wanted to fly Sydney to London direct (probably around 21-22 hours), what would be the cost of launching an airborne refuelling tanker out of Singapore en-route (Air Force 1 style)?

I'm sure someone's suggested it before, just prior to being laughed out of the bar... :)

[DaveReidUK]

Which begs an amusing question. If Qantas wanted to fly Sydney to London direct (probably around 21-22 hours), what would be the cost of launching an airborne refuelling tanker out of Singapore en-route (Air Force 1 style)?

You need to think more laterally than that.

http://pix.avaxnews.com/avaxnews/e5/a8/0002a8e5_medium.jpeg

[FlightDetent]

A380 mate which operates the 2 flights I've used Thanks, maybe the FCOM provides similar tables to these for A333?

PER-FPL-FLP-QFP Quick Determination of flight planning.

https://s19.postimg.org/g97duphdb/333_QFP_a.png (https://postimg.org/image/g97duphdb/)

With max capacity of 76.561 kg, let's take away -261 of taxi out fuel and -5300 leftover after landing (my best educated guess)
= 71000 kg left to burn.

then

https://s19.postimg.org/bol7frxnz/333_QFP_b.png (https://postimg.org/image/bol7frxnz/)
Reading: at most efficient FL410 (with stepped climb) the aircraft would burn 68928 kg over 13°26' stage of 6200 NM air-distance. Any 1000+ kg in mass (payload, fuel) would increase fuel required by 389 kg (a.k.a. burning 38,9 per cent of any fuel tankered).

in comparison, half distance

https://s19.postimg.org/wa4klf4mn/333_QFP_c.png (https://postimg.org/image/wa4klf4mn/)
burns 32446 kilograms.

Conclusion: 2x 32446 kg = 64.892 kg for equivalent air distance, plus 500 kg on ground for the half-way turnaround (reversers, taxi in, APU, taxi out) -> (71000/64892 - 1)*100 => 5,4% disadvantage without the stop.

The above pencil excercise is based on LW 140t (table definition), rather emptish?

[megan]

I'm sure someone's suggested it beforeSure have, not only suggested, but trialled, pre WWII mail runs across the Atlantic by Imperial Airways using Empire flying boats, and British South American Airways using Lancasters London to Bermuda non-stop. Nothing new under the sun.

[B772]

OMAAbound

Just for interest sake do you have a burn DXB-PER for the A380.

[Monarch Man]

@B772, 132T on a 10.15 sector, give or take.

[OMAAbound]

OMAAbound

Just for interest sake do you have a burn DXB-PER for the A380.

I'd go slightly higher at around 139T on 10hr30.

[donpizmeov]

Flight plan shows 129.5t, flight time 10.03 for DXB to PER. Carrying 56.4t revenue. And as Monach said 132.9 when winds make it 10.15. Both flights carrying 25.7t fuel for ALTN YPAD.

[OMAAbound]

Thanks Don, my very rough calculations were based on the block times used by EK.

How about the DXB-AKL/DXB-SYD-AKL calculations I made earlier on in the thread?

[donpizmeov]

OMAA, it's 198t direct, TOW 13t below max. 207.9t via Syd, TOW out of DXB 20t below max, but carrying more revenue. Total flight time is only 1hr 30min different to direct SYD, so probably not the best example.
AKL via MEL takes 14 min longer than direct, and total burn is 202.1t. It was carrying more revenue out of DXB.