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Comment by amelius | Hacker News Reader

Is it more economical to carry all that weight in fuel versus having stopovers?

Or is this a tradeoff of time versus climate, where time won?

That becomes the main issue, the Concorde as it was had 26,400 gallons <=> 95,680 kgs of fuel, and would need more than double that (likely) to do the flight in one go (bar major improvements to efficiency, and counting that more weight at takeoff needs more weight of fuel to fly that extra weight).

A quick search says about 40 minutes to refuel a jet, so a stopover is going to add at least an hour, probably more because they have to come out of supersonic, etc.

And how are these numbers in subsonic flights?

A flight from London to Singapore. How much fuel would it need without stops, versus how much fuel in the least-fuel case (but more-stops case)?

One thing to take into account is that landing and taking off is very wasteful with fuel - jet engines use significantly more fuel when running in dense air and that doesn't include increased power for climbing.

I'm sure there's someone who can plug in numbers into a flight planner here, I'm interested in actual numbers.

OK, sure, I plugged this into a sim flight planner (http://onlineflightplanner.org/). This is on a Dreamliner.

    Heathrow - Changi: 63933 kgs
    
    Heathrow - Tehran: 26957 kgs
    Tehran - Changi: 39580 kgs

So at least based on this it's not too much of a difference, only 4% more with a stop. (Tehran looked to be roughly in the middle on the flight plan between London and Singapore.)

Interesting, I'd expect it to be a larger difference considering how much the carriers avoid stopovers.

Maybe the fees and organization of refueling tips the balance?

Carriers don't want to do a stop unless they're offloading and onboarding passengers, so they'd rather run one flight to the intermediary, and another direct.

Well yeah, we're talking a about WHY it's a problem for them to stop.

IIRC airframe lifetime is rated in pressurization cycles.

It adds a surprising amount of time. You have to descend, land, taxi to a fueling area, refuel, taxi, take off, climb. And that's if the local regulations allow fueling with passengers on board.

That's probably around 2 hours extra. And this in turn can require the plane to carry additional pilots and flight attendants.

Refueling is very wasteful - that's why so many flights are direct today - because it's much cheaper.

I'm sure that's true although I don't know how the numbers pencil out. That said, people also much prefer non-stop flights because of time, hassle, and reduced likelihood of something going wrong.

That's not quite true AFAIK at least a couple of years ago the super long routes (18+h) were served in business class only because not enough customers wanted to do such a long flight in economy.

That's mostly not true as far as I've seen because most trans-pacific flyers are not willing/able to spend thousands of additional $ to fly in business class.

Another factor besides comfort is that they can extend the flight time 1-2 hours by having fewer passengers and bags onboard, which of course means premium seats like SQ23/24.

Qantas is planning to launch 18–21 hour routes in 2026 with economy class, using modified A350-1000 with an extra fuel tank in the hold.

Are you talking about "Project Sunrise"?

https://en.wikipedia.org/wiki/Kangaroo_Route#Project_Sunrise

The Singapore Airlines Singapore to New York flight is 19 hours and only has premium economy and business. I have to make this trip fairly often and I prefer to take the direct flight as it’s simpler, faster and I have to pay extra for leg room either way. That said, if I had the means I would take business each time, because 19 hours in even the nicest economy seat can be tough.

It's also riskier to do fuel stops en route. Most accidents happen on takeoff or landing.

Accidents, and maintenance - much maintenance is predicated on cycle times, i.e. how many take offs and landings (and others are based on operational hours).

Depends on distance, cargo is best way to look at the ranges. As they optimize for cost per nautical mile. Not passenger demand or comfort or speed. At certain point refuelling saves in cost.

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