long haul fuel efficiency

[icarusone]

"Raj Nangia, an aeronautical engineer who has analyzed the issue for Britain's Royal Aeronautical Society, says that flying 18 hours in one hop could double the cost of flying the same route with three stops. To fly far, a plane needs lots of fuel onboard, and to carry all that fuel, it needs even more fuel -- just as a car burns more fuel when it is heavily loaded."

Quote, Wall street journal online


Interesting concept given the price of fuel.

Try taking all of the variables out of it, i.e. remaining on the great circle route for stopovers, no ATC vector delays, all of the same passengers remain onboard and are all going to and from the same origin/destination. What do you all make of this?

Interesting to think that an airline could save fuel by having 3 hops to a destination instead of non-stop.
What tipping point is there on the amount of climbs and descents to/from altitude?

Anyone done any research along these lines?


fuel weight as a percentage of total weight charted:
500,000lb loaded without fuel,
375,000lbs fuel carried with 20,000lbs rsv, vs 125,000 carried(x3) with 20,000lbs rsv.

.............1st third........2nd third........last third of trip
direct.........44%.............34%................22%
----------395,000.......270,000...........145,000

3stop.........22%.............22%................22%
----------145,000.......145,000...........145,000


direct plane would have to climb 895,000 lbs to altitude
3 stop plane would have to climb 1,935,000 lbs to altitude (645,000 x 3)

So it is all a matter of evening out the climb fuel in cruise savings at that point.

*above chart didn't account decrease cruise burn in lighter, 3-stop aircraft

[NG_Kaptain]

Let me work that out. We do long haul flights from the UAE to North America and Australia. Is he saying we should takeoff, land in Sri Lanka, fly to Singapore then takeoff again to Sydney and that would cause us to save on fuel. Doesn't make sense to me.

[Cardinal]

I think one must consider the decreased cruise burn, that's where the savings are! 4 or 5% per hour for every extra pound on board.

[NG_Kaptain]

What about the approach and landing?
Airport fees?
The takeoff and climb to altitude?
Crew limits?

[icarusone]

4% of what, sound's too good to be true for 1 lb.

[icarusone]

Only talking about fuel burn. I see where else we can go with the other costs.

Reasonably sterile environment without zigzaging between cities or getting excessive delays.

[FE Hoppy]

probably save more than he thinks as there would be no pax on board. They would all be on the direct flights :ugh::ugh:

[Brian Abraham]

Did read a study done on this (in relation to fuel burn only), I think in AW&ST, and from memory, they came up with an optimum stage length in the order of 3 to 4,000 miles.

[icarusone]

Thanks Brian.

I've been running some numbers and it certainly seems there is a happy medium. I do mostly short-haul <2500nm and can't come up with any situations that save ANY gas using this method. In relation to long haul and ultra long haul, I can see the rationale. As we know, there are a lot of variables in this one.

[763 jock]

If you believe Wikipidia, Thai have dropped EWR to BKK and are dropping the LAX route in October. I'm no expert, but carrying fuel for 16 hours before you burn it may be a step too far in the current climate.

Interesting to see if other carriers continue with ULH ops.

[411A]

Rather extensive studies were done at one carrier, which operated the L1011-500 type.
It was found that, although quite long range flights were indeed possible (12 hours), more profits could be made by using an optimum 8 hour stage length plus one shorter sector.
More payload, better pax comfort, for about the same fuel consumed.
Of course, extra landing/handling/parking fees tend to eat into the bottom line to some degree.

[Jetjock330]

3 hops to Sydney from UAE? Some more things to consider!

In 3 hops would require 2 different sets of crew positioned at each station awaiting the arrival of the aircraft enroute. Hotels and forward planing must be counted in. 3 sets of cycles on the engines and the gear, fuselage etc...

An 18 hour sector would have double cockpit crew, allowed upto a 22 hour max duty. (bunks and single sector entry into the duty tables)

A single crew would not be able to do two 6 hours legs with an hour fifteen turn around, in order to try and do two of the sectors. Even intruducing a 3rd man might not help.

I understand there is a limit to the cost of carriage of fuel, but it all needs to be in seen context.

[icarusone]

Lots of variable costs outside fuel burn (They are becoming less of the equation though as fuel costs exceed 40% of cost):

Crew costs/duty
Taxi fuel
Ground Handling
Airframe Cycles
Engine cycles
Aircraft Utilization
ATC delays

Accidents/incidents (greater percentage in t.off/ldg phase). This is a stretch.

Variable revenue also:
If you can pick up and drop off passengers on the shorter segments, you'll generally get higher yields from the shorter distances. Adding to the bottom line of course.