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Comment by credit_guy | Hacker News Reader

Why not use this technology for civilian aircraft? In particular, the envisioned supersonic Boom has too little range to be able to service enough routes to be profitable. With refueling the economics might change dramatically.

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I don't think aerial refuelling could ever be described as "economical".

Edit: Maybe if the alternative is building and maintaining an airbase for refuelling stops.

Concorde burned by far the most fuel during takeoff: 450 liters per minute. Of course, once at cruising altitude, it needed to have enough fuel to finish the trip, which was about 60 tons. The empty mass of Concorde was 75 tons, plus passengers and cargo, let's say about 110-120 tons. Imagine now that instead of pushing from the ground 180 tons, you only push 120 tons and refuel once you get there. That means you burn one third less fuel during takeoff. Not only that, you can have smaller engines, which means lighter construction in general, so less weight, etc. It's a virtuous cycle.

Aerial refueling, if it can be fully automated, and made routine, and supersafe, could be revolutionary for civilian aircraft.

I am sorry but automated or not, I don't see how aerial refueling could ever be made as safe as on-ground refueling by just the nature of two moving planes in the air rather than sitting immovable on the ground with just a hose or hose/small tanker vehicle attached.

It will never be as safe. But we always accept various tradeoffs. Traveling in a car is less safe than sitting on the couch in front of the TV, yet people do it all the time.

Actually, sitting in front of tv is pretty safe. Once you do other sports at home, like taking drugs or climbing a ladder, then it can compete with travelling in cars.

"Actually, sitting in front of tv is pretty safe."

For injuries, yes. For general health, no. Sedentary lifestyle is a silent killer.

The "this flight has significantly more risk of accident but it gets to your destination an hour earlier than a regular flight without a refuel stop" tradeoff isn't obviously one a significant proportion of consumers will take though, especially not at prices geared towards the "very important" set

And even if they were willing to, it's entirely possible regulators wouldn't let them

These analyses always seem incomplete to me. You need a whole second plane, and that plane needs to take off and land, and carry and elevate significant extra fuel during its takeoff.

I feel like the fuel economy savings are probably technically there because of the different aircraft characteristics, but again, you need to circuit an entire second plane and crew to “save” that fuel.

I’m sure someone’s done the analysis.

Plus, you can fly non-stop half way, and then some, across the globe in existing planes today. More range ain't needed. Supersonic civilian aircraft are dead for a reason.

But my understanding is that the Concorde was inneficient during takeoff because it was flying slower than the optimal speed dictated by its airframe and engines.

Are you proposing to refuel it at cruise speed? If not, one would think that the refueling would use up a lot of fuel in itself.

It was inefficient at takeoff because it was using afterburners to get the thrust needed.

Which was required due the huge amounts of aerodynamic drag produced by aircraft designed for supersonic flight while flying subsonic. These design are very aerodynamically inefficient outside their cruise speeds, and thus require a lot of thrust. This phase of flight extends all the way from take-off, and climb out. Not just while barreling down the runway.

Having an extended subsonic flight period to do a mid-air refuelling would be brutal to the financial viability of a supersonic passenger aircraft. And that's even before we consider the operational costs of the tanker aircraft

If it goes wrong, they crash and you lose two planes and several hundred people.

https://www.youtube.com/watch?v=vbQ9LXZwJ78

This is a bit skewed though. If there was no mid-air refueling and the plane was lost, you still loose several hundred people and a plane, but wouldn't be out the second plane. The second plane is autonomous so no additional people are lost. It's really not making the stat of losing a passenger plane more consequential.

Presumably GP was implying that adding a second plane increases the chance of a crash, not claiming that it increases the conseuqences should it happen

> It's really not making the stat of losing a passenger plane more consequential.

It makes it more likely, not more consequential.

You know how on the ground they sometimes tell you to not wear your safety belts while they refuel the plane? It is because every refueling has a risk of fire. An inflight refueling probably even more so.

> The second plane is autonomous so no additional people are lost.

Worth noting that in these experiments the tanker plane was not uncrewed. It is the act of connecting the hose which is automated here. (And they also tested with autonomous receiver planes.)

To be fair, spills or leaks during refuelling on land risks forming a pool of burning liquid around the aircraft. Aerial refuelling leaks would go overboard so probably not the same fire risk.

It's more a risk of collision, I think.

> Aerial refuelling leaks would go overboard

That assumes it is not an internal leak of course. Where would the receiver probe be? Probably on the nose or on the forward section of the cabin roof and you have to pipe that back to the fuel tanks (mostly in or around the wings). If maintenance ever does a shoddy job on connecting those pipes the time you will realise it is when jet-a is firehosing out of the galley.

Now obviously that involves maintenance problems and a bit of bad luck too, but that is not an unheard of combination.

Sure, but it's still hard and unsafe. Use military as a testing ground to develop the technology to a more mature status first and make it economical. Have patience. This isn't going to be a practical technology for commercial flights until it gets cheap and fueling can be done efficiently

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