The weight of fuel
 

:eek:

“An airplane on a 15- or 16-hour flight uses nearly 40 percent of all its onboard fuel just to carry the weight of the fuel it takes to go that far.”

How Air Travel Will Change in 2019
https://www.cntraveler.com/story/how...change-in-2019

This is nothing compared to putting a satellite (or anything else) into orbit. The great majority of the fuel, especially but not only in the early stages, is needed to carry the fuel for later parts of the trip.

It begs the question: does it make financial sense to do a technical stop? Assume it is a route where only one carrier flies the nonstop, so there's no competitive disadvantage to 17 hours gate-to-gate vs. 16 hours. Would flying two 8-hour segments (plus reserves) burn less total fuel than a single 16-hour segment? Or do the costs associated with the 2nd take-off and climb to cruise altitude more than burn up the savings?

Airlines used to have technical stops all over the place because they were limited by aircraft range. With longer range aircraft, I assume they got rid of them for competitive reasons. But maybe they make sense on these ultra-long flights?

Some portion of passengers might actually *like* them on a 16+ hour trip.

Aircraft burn a huge amount of fuel on takeoff, compared to the amount they burn in cruise, but there IS a diminishing return at a certain point where that efficiency drops. This is largely why long hauls from SYD to LHR still do stops. It's a curve, not a straight line if you graph it out.

But from physics point of view, it's the old rocket fuel problem. To get where you need to go, you need enough fuel to move you..but fuel has weight, so you need more..but when you need more you gain weight..so you need MORE fuel. A vicious circle.

This is why massive rockets are needed to put comparatively small satellites into orbit.

But the same principle applies to planes, and to your personal car. For fun, watch your MPG go up as your fuel tank gets closer to empty. The car has to haul less weight and gets more efficient.

Another reason to exercise more often in 2019... Do it for your body and for your carbon footprint!

I saw this video on YouTube recently that goes into the issue:


At ~3:45 into the video, there's a graph showing that the lowest pounds/mile fuel burn is around 3,000nm, which would take around 5-5.5 hours to fly at Mach 0.85. Of course, as also mentioned in the video, passengers (especially business travelers) really don't want to stop all that often if they can avoid it.

The thing is you cannot stop at the north pole for your tech stop. So it would be definitely more. Assuming it takes 1 hour to stop and refuel and to do everything anyway. So 16 versus much more?
Of course it depends where you are flying to, going to Australia there isn't much point to the great circle route. But going to the Middle East you often go all the way up to the north pole, so EK cannot really do a tech stop.

There is a calculation possible of the minimum fuel including fuel burn for cruise, take off, on ground taxiing, fuel to diversion, etc to determine the most fuel efficient sector length for a long haul flight.

There is a calculation possible of the minimum cost of segments, including cost for cruise, take off, landing, fuel cost (can be different around the world), crew, aircraft maintenance (based on cycles & hours), etc to determine the most cost efficient sector length for a long haul flight.

Those 2 calculations will very likley not have the same answer. Then you need at airport at those optimum sector lengths (that's unlikely).
And then politics' come in play, as some direct routes are not possible.

https://cimg4.ibsrv.net/gimg/www.fly...dde46fea2a.gif

As Efrem said! There must be a (similar?) equation covering aircraft?

Yes, there is a system of equations to which nonlinear optimization can be applied to minimize the cost of a flight (though I don't believe calculating delta-v based on specific impulse is part of them). As noted, airport availability and marketing likely have more an effect on the decision than the physics. Singapore's direct EWR-SIN flight certainly isn't the cheapest way to get there from a fuel cost standpoint. They're selling the cost of time.

I flew to Australia one time, and I was glad that I had to stop in HNL. I guess I'm a weirdo, in that I actually like take-offs and landings. I certainly don't like sitting in one place for hours and hours and hours and hours.... :(

I enjoyed the one time I went via NAN for the same reason...

Not sure what you mean by that. The great circle route is the shortest distance between any two points on Earth. Australia is no exception.

Great Circle Mapper

I guess I mean a route that doesn't make sense on a flat versus curved world view. Like if you look at SIN to LAX vs SFO, one goes further north than the other. And if you look at SIN to JNB it is basically a straight line, not really curving. So same as if you just put a map on a table and traced the shortest distance point by point, disregarding the curvature of the earth.

Not really. This tutorial may make the concept more clear:

https://gisgeography.com/great-circl...t-flight-path/

The same issue applied to the early explorers going to the North and South Poles.

Dozens of men (and horses) would carry food for the few men that would eventually make the final push for the Pole. The food would be dropped off along the way and the the extra men would turn back way short of the Pole.

Of course, the horses were also "dropped off" along the way and supplied some of the food for the return trip.

The problem is that there is no such thing as "a map." There are dozens of ways to project a sphere onto a flat surface, none of them good for all purposes. Conclusions such as these may be correct for one projection but not for another. If you are assuming a Mercator projection, say so, though its distortion at high northern and southern latitudes makes it useless for flight paths that go into those regions or that one is comparing with other paths that go into those regions.

Aside from that, though, your earlier point about the lack of refueling stops anywhere near the middle of several long-distance great-circle routes is valid. Breaking up a long trip to refuel, thus carrying less fuel, makes sense only if such stops exist. On most polar routes they don't, though IIRC some flights from the US east coast to Asia refueled in Anchorage in the days before non-stop flights of that distance were practical. ANC may not have been in the ideal location for that purpose, but it was close enough.

Pan Am went to great lengths to build up the infrastructure for its TPAC Clipper services...including setting up the then-desolate Wake Island among other Pacific stations for refueling and resupply. It's unlikely we'll ever see an airline take, or need to take, such an initiative to build a few fuel stops from the ground up like that. But such will be necessary for various space travel needs in the future. A brief article on the early Pan Am setup days:

https://www.clipperflyingboats.com/t...irline-service

Of course the world's top air forces do have the flexibility to place an aircraft refueling point at lots of locations as needed for a given mission, thanks to air-to-air refueling! And no need to land and taxi in for the fill-up! ;)

Cargo carriers do this, like FedEx/UPS. They'll make a technical stop in Alaska before continuing on to Asia. The slight loss in time is made up with fuel savings.

They don't do it for fuel savings. They do it because the cargo load is too heavy to make it non-stop.

For the method in which the cargo is carried, it represents a fuel savings, ie 1 heavy trip with a fuel stop, lighter trip with no stop.

How is it a fuel savings when you left cargo behind that will have to be flown on an additional flight? The will certainly burn more fuel.

In terms of fuel per weight*mile, isn't a heavier plane with a fuel stop cheaper?

whoops, should have said

not sure when the energy equation will ever make sense, for there to be electric-assisted commercial passenger aircraft... just like cars. fixed weight. on-demand power delivery. limited capacity, but enough to assist on take-off phase, and then "sip" on jet fuel for the cruise....

No. Flying non-stop will use less fuel. You also save time on the aircraft which reduces maintenance and crew costs.

your course assumptions are further complicated by wind velocities. the last couple times on the western route, we flew from middle of southern europe to iAd, we used the great southern trade wind route. south of great Britain and Gurrnsey,

This is a really really good video that explains it well. It's mind blowing how much fuel it takes to move fuel.