Aerial refuelling without human intervention | Hacker News Reader

Aerial refuelling without human intervention

airbus.com

69 pointsgeox84 comments

This is a procurement / funding / politics issue; not a technical one. You'd have to get the tanker, and receivers across multiple DoD branches and countries to buy into a system. The KC-46 is cutting edge, but is a minority against the backdrop of -135s and -10s. The 46 made the leap to a digital video feed instead of window, but is manually-operated.

Operational automated refueling is likely in store sometime in the next few decades, but like everything DoD-procurement-related (at least in the US), will be a slow rollout.

Hasn’t the remote vision system on the KC-46 been a bit of a disaster as well?

Yes, Just one of the many issues Boeing is eating the cost overruns for.

Taken in sum, virtually everything about the Pegasus has been a trainwreck, and you can see muted signals that virtually everyone is quietly searching for an alternative fleet. I would not be surprised if the 46 program on the whole is forecasted to run deep, deep in the red for Boeing.

BDS is, in general, having a hard time adjusting to a post-GWoT world of fixed cost, versus the oh-so-coveted cost plus glory days in the Aughts.

Then again, maybe the problem runs deeper. If anyone can name me a unqualified-no-doubt-successful new Boeing project - something that isn't someone else's IP or sucked up in an acquisition - from the last twenty years, I'm all ears. The USAF tossed them a softball project to bolt wings and a GPS on a Mark 82 iron bomb . . and they couldn't figure it out without bringing in Kratos.

> Taken in sum, virtually everything about the Pegasus has been a trainwreck, and you can see muted signals that virtually everyone is quietly searching for an alternative fleet.

And yet they are still favoured to win the KC-Y competition (the successor to the KC-X, which picked Boeing's KC-46A as the winner) either (a) by default since Lockheed Martin has left competition (with Airbus saying they're going it alone), or (b) the USAF just cancelling the competition and ordering more KC-46As.

(a) https://breakingdefense.com/2023/10/lmxt-exit-lockheed-to-sk...

(b) https://breakingdefense.com/2023/03/air-force-leans-towards-...

Meanwhile Canada (which all sort of issues with military procurement themselves) found that Airbus was the only qualified bidder for their tanker replacement program and picked the A330 MRTT (of which deliveries have already begun).

Good ol nepotism and anti-competitive practices.

The age of being too scared to speak up is nearing an end. Money, ideology, coercion and ego doesn’t actually define 100% of the population. It defines a convenient portion.

Boeing is definitely a shell of its former self. They need to get out of the news. Period. Are there any engineers left in charge, or has it all be overrun by pointy haired bosses and MBAs? I have a feeling the answer to that question has the answers to their issues.

MBAs, Accounting, Biology, Accounting, Management. . the board is almost entirely non-aerospace background, and largely nontechnical even when it is an aero degree (Sabrina Soussan being the sole exception, and I suspect she's just on the board because of Siemens). Speaking anecdotally, yes, the vast majority of leadership, also nontechnical, with very very very few aerospace backgrounds.

This all tends to flush out the go-getters, and doing good CFD work largely requires go-getters. It's very good at retaining box checkers though, and of course the serially dishonest.

This problem of nontechnical leadership[1] is bigger than Boeing, but that same JackWelchian focus on finance-uber-alles[2] is a real thorn in the side of American industry, or even just "American-Made Stuff".

[1] "I ran a shoe factory. And now I'm in charge" Late stage capitalism has so many echoes of late-stage Soviet industry that it's getting a little creepy.

[2] Again, "if you're good with money, you're good with everything" is a crappy way to make stuff, but our problem is when that matches your ideology you tend to see everything through that same lens. Ironically, this is a mental trick that gets tends to get trained out of you in hard sciences.

> The 46 made the leap to a digital video feed instead of window, but is manually-operated.

How does changing from a window to digital video improve performance? A window seems to reduce complexity, though a window + zoomed video might plausibly help. It would be too bad if a plane couldn't refuel and return to the fight (or make it home) because a connection or camera or screen failed.

The hope was to eliminate the need to have an airman lying down in the back of the plane manually flying the boom to connect to the receiver aircraft, as a step towards drone tankers. This did not pan out as hoped.

Drone tankers are already a thing. The US navy has done it. This is about drone boom tankers, something that is specific to USAF. Many countries are happy with basket aar. It has some advantages over booms.

https://en.wikipedia.org/wiki/Boeing_MQ-25_Stingray

Those other countries are generally only refueling small tactical aircraft. The USAF has to also refuel large cargo aircraft and strategic bombers, so they want higher flow rates that only a large boom can deliver.

Russia refuels the Blackjack with a basket, the world's largest combat aircraft.

Russia only has 16 Blackjacks. The US flies and refuels many more than that during a single sortie. The basket is about three times slower than the boom, which multiples when refueling many aircraft.

From what Ive heard on the internet, it doesnt improve performance. But thats just anecdotal.

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.

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.

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

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

Would it be possibly to have whole fleets of constantly flying planes assuming the fuel burden wasn't too much, I can think of a few high value areas where it might be worth the deterrent capability of always having a fair few planes constantly scrambled...

You may enjoy https://en.m.wikipedia.org/wiki/Operation_Chrome_Dome.

Also: https://en.wikipedia.org/wiki/Stratovision

> Several high-profile nuclear accidents were associated with the "Chrome Dome" program, including the accidental release of nuclear weapons on foreign territory, and it was shut down in the wake of one such accident in 1968.

Wow, that's quite an accident.

One of the incidents was caused by aerial refueling: https://en.m.wikipedia.org/wiki/1966_Palomares_B-52_crash

Palomares is in Spain. Fifty years later, it's still an issue for the people living there.

Do you have a different link that talks about that? The Wikipedia article says there were no health issues.

“Despite the cost and the number of personnel involved in the cleanup, traces of contamination remained forty years later. Snails were observed with unusual levels of radioactivity.[31] Additional tracts of land were also appropriated for testing and further cleanup. However, no indication of health issues has been discovered among the local population in Palomares.[29]”

I didn't mean to imply that there were health issues.

It's kind of hard to believe that measurable affects were found among the snails but it hasn't contributed to a case of cancer here or there over the years.

Human cancer that is, although I do feel for the snails.

Also mentioned in the Watts short "Malak": https://news.ycombinator.com/item?id=38362711

Not constantly, but take a look at the refueling pattern for Operation Black Buck in the Falklands war: https://en.m.wikipedia.org/wiki/Operation_Black_Buck

There's probably a better reference for this.

Two pilots once flew a Cessna 172 for over 64 days, refueling and resupplying from a truck https://en.wikipedia.org/wiki/Flight_endurance_record#/media...

They eventually were forced to land because their engine was down on power from lack of maintenance.

Boeing previously:

https://en.wikipedia.org/wiki/Boeing_MQ-25_Stingray

Using UCLASS platform:

https://en.wikipedia.org/wiki/Unmanned_Carrier-Launched_Airb... (aka X-47B demonstrator)

Edit: (Although Airbus’ demonstration shows substantially greater capabilities than previous demonstrations) Surfaced to demonstrate advancement velocity.

Isn't this a completely different thing? This is used for manned aircraft refueling, where the job of the drone is just to fly as straight and level as possible, and the receiving aircraft that is flown by a human has the much harder job of maintaining formation.

In the Airbus system, the refueler plane takes automated control of the receiving plane, and maintains formation using controls on both planes.

eh, the process is mostly automated today. this is less of a demonstration of capability and more a demonstration of different schools of thought re: aircraft GNC.

Some prior art from 2006: https://www.flightglobal.com/darpa-and-nasa-demonstrate-worl...

Video: https://youtu.be/F-Y7fhIasjM

I wonder why it is designed so that the tanker controls the aircraft being refueled, rather than the other way around?

If one tanker is refueling multiple aircraft, coordination via the tanker would be easier, maybe?

Not a domain expert but i would imagine that the smaller an aircraft the more responsive it is.

Conversely, small aircraft are more subject to turbulence, so they also need more correction to see stay in a straight line

Think about it this way: you essentially have two different “problems” you’re trying to solve simultaneously, flying the tanker and flying the plane being refueled. As other comments have pointed out, the plane being refueled has much higher control authority and responsiveness, compared to the generally larger tanker. Also, given the two aircraft are flying in near identical environmental conditions because of their close proximity. The “easier” of the two aircraft to fly is the plane, not the tanker. So your control algorithm (or pilot) flies the tanker and the plane just matches its control inputs plus a position offset.

A single tanker can simultaneously refuel multiple aircraft: https://www.youtube.com/shorts/FSJ9Hqgz9T0

Because the tanker is less manoeuvrable than the planes being refuelled. Because the tanker can refuel more than one plane at a time.

Could this be used for longer-range electric passenger aircraft? Charging could be made safer than refueling, since you can make a long cable to keep the "battery tanker" plane far away from the plane with the passengers.

It is prohibited for passenger aircraft to fly anywhere near this close together, because it is dangerous: https://www.youtube.com/watch?v=YcLiAAVeYhk

No because it takes a lot longer to charge a battery than to refuel.

Tanker should provide all consumables - fuel, lubricants, etc.

On a 4-engined aircraft, one engine could be powered down at a time for maintenance.

But if perpetual flying became a real need, indirect cycle nuclear aero engines would quickly be developed.

They made quite a lot of progress during the cold war.

https://en.m.wikipedia.org/wiki/Aircraft_Nuclear_Propulsion

As far as I'm aware, the engines ground tested well, but there never was a nuclear-powered flight.

Then ballistic missiles made the need for such a thing disappear...

This is pretty cool technology. If fuel were not an issue, and no other recharges (water, food, etc.) were available, how long could a plane with passengers stay in the air?

Until the next maintenance period? I'm probably completely wrong, but I think on some planes that might be 100's of hours before some maintenance is due.

This is often talked about in the case of Air Force One (which is supposed to be able to keep flying in case of a nuclear war, so that the president can survive and order the military). The limiting factor is probably engine oil, e.g. this article suggests 2-3 days. https://executiveflyers.com/how-long-can-air-force-one-stay-...

Thanks for sharing. I never realized engine cycle times were so short on planes!

> It’s generally recommended that aircraft engine oil should be replaced every 50 hours, otherwise the oil would turn to sludge and get contaminated, which would damage the engine.

This sounds like piston engine advice. I’d be surprised if jet airliners are going in for oil changes twice a week.

Jet engines constantly pump oil under pressure between the stator and rotors to provide lubricant for the radial bearings while sealing and cleaning them. It’s a completely different kind of oil to the kind you’d find in a piston engine and operates at a much higher temperature.

Agreed but what’s the service interval on that oil? Does it get changed regularly or just topped off?

It’s a piston plane but my understanding of the DC-3 is that it runs out of fuel around the same time it runs out of oil.

Hybrid-electric propulsion systems can enhance flight endurance by separating propulsion and power generation tasks, individually optimizing each for specific stress levels aligned with mission requirements.

Does the marginal efficiency make up for the added weight? Aircraft engines already operate in a very narrow envelope so they can be optimized for cruise.

Hyllion Karno is a good example for power generation unit required ultra-low maintenance.

The new VC-25B aren’t going to have aerial refueling capability as cost saving measure. They do have longer range.

> The new VC-25B aren’t going to have aerial refueling capability as cost saving measure.

Also: the old VC-25A did/does have it, but it was never used in ~30 years of flying.

Until its next forced reboot. Rebooting a plane mid flight is suboptimal.

There was plans in the 50s/60s to have a fleet of nuclear aircraft staying airborne for 2 months. That job ended up being taken by submarines, some staying in mission for 6 months. So the logistic of keeping people and a few ICBM in a metal tube for months is pretty much sorted out. With the hypersonic craze, the money is back to fund scramjets tech too. Nuclear planes are a terrible idea, don't get me wrong, but it's not impossible to build them, it has never been. The problem is radioactive exhaust for the direct cycles ones (the easy one) or reliability for the indirect cycle (the "good" ones).

They are pretty heavy due to radiation shield material requirements.

I am pretty sure material science went a long way. No need to put a foot of lead behind the reactor. The space race provided quite a bit of funding toward lightweight protection. It was too late for those plane project as they were already ramping down in the mid 60's.

Neither that or the plane powerplant are unsolavle problem, it's more of a "why would we invest this much to solve something this silly". Apparently the russians are trying to resurrect their SLAM clone and tested one. How much of this is a realistic military project versus propaganda isn't super clear to me. It's up there along with the manned military space stations in the scale of pointless deterrent PR.

Well, the record is 64 days. They did oil changes inflight on the running engine.

https://simpleflying.com/robert-timm-john-cook-endurace-reco....

Well a passenger plane needs at most 20,000 km (20 Mm) of range, since that is the furthest distance 2 points on the surface of the Earth can be apart. Most large jet airliners cruise at around 900 km/h, which gives a maximum useful endurance of around 22 hours. There's no point having an endurance much longer than that.

AFAIK, no airliners can do that yet, though some are getting close. Some of the business jet variants can (e.g. BBJ 777-8, BBJ 777-9).

The longest duration 'scheduled' airline flights to date were the Qantas 'double sunrise' flights during WWII, which were ~32 hours long [0], though the Graf Zeppelin (airship) made passenger flights longer than this [1].

0. https://en.wikipedia.org/wiki/The_Double_Sunrise

1. https://en.wikipedia.org/wiki/LZ_127_Graf_Zeppelin

Light robotankers are definitely needed for a war in the Pacific eh. Smaller, relatively "disposable" tanker units to gas up one or two manned aircraft and then zip back to base (or back to a mothertanker safely far from the theater) for another round of quick-fuel-up-and-go. With good luck and good engineering, get high rendezvous+transfer reliability and a very high duty cycle.

Spelled revolutionize wrong

Airbus isn't American

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