> Concorde burned 52% of its fuel just taxiing and taking off
and later in the article:
> Remember, Concorde burned 52% of its fuel just taxiing down the runway.
Setting aside that these are completely different claims, the author does not cite this claim at all and it fails my personal gut check. Where is this information coming from?
The claim in the article, "Concorde burned 52% of its fuel just taxiing down the runway", is completely wrong and kind of ruins my confidence in the article. A Concorde used less than 1% of its fuel taxiing down the runway, not 52%.
Source: Air France Flight 4590 Accident Report states that the plane had 95 t of fuel on board when the aircraft started out and used 800 kilos of fuel during taxiing (page 17) and 200 kilos after taxiing before takeoff (page 159).
https://www.faa.gov/sites/faa.gov/files/2022-11/Concorde_Acc...
(Since there's a bunch of discussion about how to reduce taxiing consumption, I'll point out that one tonne of aviation fuel is about $700, so there's not much money to be saved by creating battery-powered tugs or whatnot.)
As far as takeoff, "at the start of cruise 20% of the total fuel burnoff will have been consumed while only 9% of the total distance will have been covered." From "Operation Experience on Concorde", a paper by the Design Director. While 20% is a lot, it is much less than 52%.
https://www.icas.org/icas_archive/ICAS1976/Page%20563.pdf
9% of the distance but 100% of the altitude. That statement completely ignores the hardest part of the flight (with respect to building potential energy) of getting at altitude.
> (Since there's a bunch of discussion about how to reduce taxiing consumption, I'll point out that one tonne of aviation fuel is about $700, so there's not much money to be saved by creating battery-powered tugs or whatnot.)
Probably the biggest win in aviation emissions would be converting all the ground support vehicles to electric. They’re currently classified as off-road vehicles, so don’t have to adhere to the same emission standards and normal cars and trucks. Additionally, they already spend a lot of time parked at the gate, which makes charging convenient and means that workers are never “waiting” for the vehicle to charge.
Yes, it sounds like the repetition of a mangled version of the SR71 stories. Burning 45 tonnes of fuel on the runway would be completely insane.
Checking various links on taxiing burn yields about 2 tonnes which is a lot more realistic and reasonable (a previous HN comment indicates the 767 burns about a tonne taxiing: https://news.ycombinator.com/item?id=24283386 concorde burning twice that sounds fair)
This seems incredibly inefficient. Is there a future for hybrid aircraft, which would feature both traditional turbofans and large batteries for energy storage?
Batteries would eliminate the need for an APU and power the aircraft during taxi, allowing the engines to be started just before actual takeoff, and shut down immediately after landing.
Either the batteries could power wheel motors directly during taxi, or the aircraft could mix turbofans with e-fans (which could also allow energy recovery during descent and help power the aircraft during cruise, reducing fuel consumption further).
Very inefficient but good for safety: if an engine is failing, you hopefully might discover that while taxiing rather than when you are in the death zone 25 meters up in the air.
Not an expert, but intuition suggests this probably isn’t true.
If an engine is going to fail spontaneously it’s almost certainly going to happen at high thrust, not while at idle or very low thrust values during taxi.
Fair enough. But delaying engine start-up until the aircraft has nearly finished taxiing wouldn’t have any effect on the way the engine operates during start-up. It just means it would spend less time at idle or near-idle speeds during taxi.
Electric taxiing (on APU) has been in development for over a decade, but it's mostly intended for single aisles (the shorter the flight the more the taxi overhead), and the relatively low fuel prices has led to these projects mostly dying off: L3 shuttered their effort in 2013, Honeywell and Safran's EGTS joint venture was dissolved in 2016, and wheeltug... apparently still lives (with no support from either boeing or airbus), though it was initially supposed to enter service in 2018.
Airlines would also significantly reduce engine operating hours, reducing engine wear and thus maintenance costs. I’ve been on flights out of Heathrow that seem to spend almost as much time taxiing as they do in the air (due to weather or ATC delays or whatever), so for short-haul operations this seems really significant.
Local air quality is also a concern for airports: the air in the neighbourhoods around Heathrow often stinks of jet exhaust, sometimes you can smell it from miles away. Presumably, much of those emissions come from taxiing aircraft.
The limiting factor for most turbine engines isn’t really operating hours, but “cycles”, which is to say starts and stops. From a maintenance perspective it’s not terribly important whether you start the engine at the gate or the runway.
Also, as far as maintenance goes, engine hours are weighted by operating power. So, an hour at idle doesn’t count as much as an hour at cruise power. One of the reasons airlines started using not-full power on takeoff when conditions allow it is because of “power by the hour” maintenance contracts, which incentivize that.
> This seems incredibly inefficient. Is there a future for hybrid aircraft, which would feature both traditional turbofans and large batteries for energy storage?
I would assume the extra weight would make it not really worth the added cost and complexity.
Honestly it sounds like the "right" way to do it would be electric ground vehicles pulling the planes into position, as with tugboats in water. Plane never need carry batteries into the sky and saves a literal ton of fuel.
IIRC towing to and from the runway has two major issues:
- standard towing tractors are really slow when towing, nowhere near taxiing speed, so you need a fleet of heavier duty "fast tow", possibly dedicated (depending on price)
- more traffic around the runway, which creates more airport complexity
Taxibot does exist tho, and is certified, and used in a few airports. Though I think it's only hybrid not electric.
Bigger issue is that the engines need to be idled for a while anyway to get up to proper temps, etc. you don’t want to start the engines and jam them into full takeoff thrust 5 seconds later.
True, the engines need to be warmed up and the hydraulics need to be pressurised, but given e.g. airbus recommends single engine taxi without APU (SETWA) warming up the engines probably doesn't take that long in the grand scheme of things. Definitely not the 15~25mn of taxi. From the sources I can find, "normal" warmup takes 2~5mn depending how long ago the engine was shut down, unless outside temps are exceptionally low, and you can do that while reaching the end of your taxi.
The software in modern engines wouldn’t let you do that anyway. The engine startup process can be quite long - several minutes in a 737 MAX - while the engine’s ECU brings things to proper temperatures etc.
But with e-taxi, the startup cycle could be performed while taxiing, potentially saving airlines time on pushback as well as fuel/maintenance cost savings.
I think they've looked at that kind of thing but not found if practical so far. One innovation has been airbus jets taxiing with just one engine which cuts fuel use a lot as it mostly goes to just spinning the engines.
> .. my recent trip from Abu Dhabi to LA. 24 hours door-to-door. We have the technology to reduce that to under 10.
The direct flight (by Emirates) takes 16h15 mins, so that leaves 7h45 mins not in flight. If we want to bring that down to 10 hours just by making the flight supersonic then that would require a flight time of 2h15, corresponding to a (ridiculous) speed well over Mach 4.
In fairness, Astro Mechanica and Hermeus claim to have a pathway to Mach 5. Not saying I expect to see it, particularly not for regular people flights to the Middle East, but believing in it is kind of the premise of the article.
(I must admit I was more curious about Astro Mechanica's engine tech before they also threw in the intention to operate Uber for business jets...)
Not ridiculous if you’re flying above the atmosphere. SpaceX has proposed point-to-point rocket-powered hypersonic flights that connect New York to Paris in around 30 minutes.
Obviously the real problem with this idea is environmental: emissions would be substantial and nobody wants an extremely noisy rocket port near their city.
How do you imagine that? First thing coming to mind is the loudness of rocket starts and powered landings. Even for airports that would be too loud. At least with current regulations. So you'd probably waste time getting to some dedicated facility, far out in the midst of nowhere to care about, and getting out of a similar hole on the other side of the trip. And again regulations regarding the closure of airspaces and seas for starts and landings, as it's currently done. Which seems rather incompatible with the current system of commercial flight ops, as it's currently done. Other relevant regulations coming to mind are evacution procedures/general survivability provisions for conventional commercial flights, which are mandatory by law.
However I turn that idea, no matter from which point I'm looking at it, I'm not seeing it going anywhere.
Whenever I hear people talk about rocket flights I think of the Stephen King short story "The Jaunt". Humans develop near-instant transportation but you have to be unconscious while travelling. A kid avoids being sedated and is driven insane by whatever interdimensional stuff he sees in transit.
Likewise for every fit 20-something being launched at Mach 5 you'd have 10 octogenarians dying of cardiovascular complications.
And furthermore you would be able to start only in good weather window for takeoff and landing and Gs on Gemini flights (which were doing the same thing) weren't comfortable either.
Roughly that figure (45%) was used to get to Mach 2.0 at 60,000 feet, about 45 minutes after takeoff from LHR (normally over the Bristol channel) to JFK.
Takeoff and climb / accel to Mach 1.7 was done with re-heat (afterburners), which did use a lot of fuel. After that, normal power (no re-heat) was used to get to Mach 2.0 and cruising (supercruise).
It used about half of its fuel for taxiing, takeoff, climb, and acceleration to cruising speed. Maybe that's where the number came from originally and it got mangled in translation.
When I looked into this in another context (not supersonic jets), while "a lot" of fuel was used just getting the jet up to speed going down the runway, "most" of the fuel was going from 1 foot off the ground to N0,000 feet.
(I was curious if there was any opportunity for some sort of system to power take-off from the ground, be it catapults like on air craft carriers or just power-transmission for electric planes, and the numbers I found were that while a surprising amount of fuel was used by the time the plane lifted off, it was more like 5% than 50%.)
American coverage of the Concorde has to try and make out that it was technically bad, otherwise they would have to face up to the fact that their country squashed the possibility of supersonic travel, through political bullying and protectionism of their own aircraft industry
Though, given the investment into the Concorde led to Airbus and all of their planes, disrupting Boeings dominance of that industry, I think they might have gotten the last laugh.
Might be harder to track but what about CFR or some other metric to measure how many bugs are getting through review before versus after the introduction of your product?
You might respond that ultimately, developers need to stay in charge of the review process, but tracking that kind of thing reflects how the product is actually getting used. If you can prove it helps to ship features faster as opposed to just allowing more LOC to get past review (these are not the same thing!) then your product has a much stronger demonstrable value.
Despite worries about creeping prices, coffee in Italy averages around €1.20 for an espresso or €1.50 for a cappuccino [1]. Way different than in a major American city.
Another personal suggestion in this vein: The Queue by Vladimir Sorokin (trans. Sally Laird), which consists entirely of unattributed dialogue. It's challenging at first but once you get a feel for the rhythm and start recognizing characters by how they speak, it becomes a really charming read.
Let me add also Blindness by José Saramago, it has pages-long paragraphs and sentences, characters have no names just descriptions… it’s surprising at first but not hard to get into. Amazing book!
I also recommend "Death with Interruptions" by the same author. I too was blindsided by how it was written but once you get used to the style it just flows.
Much of the dialogue is between father and son, so the dialogue is easy to keep track of. It is a great book for the bleak days of winter. Easily one of the most devastating endings to a book.
> Extremely difficult for no reason whatsoever. Terrible book.
Many people believe this is the mythical "Great American Novel" we've been arguing about and/or anticipating forever. Strong argument for that because it's actually very Hollywood, isn't it? It's an absurdly action-packed cowboy-horror mashup that's full of gratuitous violence and manifest destiny.
I know several people that thought it was "extremely gory for no reason whatsoever" and did not finish for that reason, but none that thought it was difficult. I was surprised TFA mentioned it in that light, because I remember Child of God being more of a slog and BM being a page-turner.
I just finished Blood Meridian and consulted AI as-needed to cover the many, many metaphors. The funny thing was that Google AI got a lot of the book wrong, getting the fate of some characters mixed up as well as confusing some faceless deaths with others. Too much wanton violence to keep track of.
The book definitely covers evil and nihilism thoroughly, so why would you want to read something like that? Well, for every bad decision someone makes in the book, the reader has the opposite response of, "oh crap, don't do that!" So reading about nihilism doesn't make you more nihilistic. While I thought it was a great book it isn't something you should just read without consulting outside sources.
Last time I read it, I did not find it challenging outside of some of the more obscure words used (particularly things like names of types of buildings and similar mundane objects), and my Kindle's built-in dictionary was able to define all of those in one tap.
As far as "for no reason", I would say that McCarthy's impressionist prose that meanders, leaves out some details while focusing on others, etc., is some of the best English language prose ever written. It's beautiful and conveys affect better than almost anything else I've encountered. All the "reason" I needed.
Different strokes for different folks. I'm a fashion lover but a fan of cheap cars, and I could equally say something similar about people who drive new luxury cars when there's plenty of reliable functionality to be had under $10k. There's a lot of craftsmanship that goes into nice clothes, and you can get way more expensive than $500. And fashion is a form of art in a way. What makes a painting worth thousands of dollars?
For clothes as a rule of thumb if you're not interested in doing a lot of research, items made in Portugal or Japan are more often than not priced fine enough, yes you'll pay some markup for a designer, but on average should last if you look after them.
The giveaway is almost always an over-dependence on "Not 'x' but 'y'" structure. Even when the author changes the wording so that the phrase doesn't read exactly like that, they tend to leave the structure intact, and the bots really like to lead with the inverse of what the author wants to say to create contrast.
A human author might have used this technique once to really emphasize a strong point, but today's LLMs use it so often that it loses its emphasis, and instead becomes a distinct stylistic fingerprint.
As a human who's written like that for decades, this witch-hunt makes it really hard to participate online anymore. This was a standard expository device taught in school, some of us latched onto it, and now it's impossible to argue that we're human because someone's conviction that we're AI is just an opinion and there is no evidence that will convince them, nor do they deserve the effort it would take even if it were possible.
Keep using that structure. The bots use it so much, and in ways that human authors wouldn't, that it becomes self-parodying. As long as you're not using the same device over and over again in the same piece you'll be fine.
yeah it's a crazy trend. suspicion that everything is AI is a poison to forums. have no idea how this moves forward. secretly hoping it destroys the entire internet, and rapidly. so we can go back to conspiring in smoke-filled rooms.
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