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Comment by oceanplexian | Hacker News Reader

I’m a pilot and this is… a vast oversimplification. Jet aircraft are significantly more efficient at higher speeds and at higher altitudes precisely because there’s less drag up there and the engines can operate more efficiently. They are wildly inefficient when low and slow.

A lot of the assumptions people make about efficiency don’t hold water in aerospace. There are no laws of physics preventing supersonic aircraft from being efficient provided they can fly high enough and we figure out how to build better engines.

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While true at cruise speeds/altitudes, any supersonic transport still has to climb up to those altitudes. On any american flight (not to alaska/hawaii) i doubt the greater efficiencies at 60+ thousand feet would be worth the fuel to get there with a supersonic wing. These would only be 2 or 3-hour flights at most anyway.

If we really want time savings, fix the entire airport experience. Thats where time can be most saved. When travelling domestic I ussually end up spending far more time waiting for flights/bags/security than actually flying.

If you're old enough, there was a time before the airport experience was so broken when you could show up 15-20 mins before your flight.

That would be me!

I remember the times before September 11, 2001, when I could show up at the airport about 30 minutes before my flight, get through security (which was locally operated -- no TSA), get my boarding pass at the gate, and board. It was great!

People could also meet you at the gate when you arrived, instead of outside the security area. There would always be peoples' families and loved ones there waiting for them.

Geneva, CH, recommends that you arrive less than 2 hours before your flight departs.

If you are flying within Europe, without checking a bag, and have the QR code from your boarding pass, it always takes less than 30 minutes to get to the gate. Allowing an hour is more than safe.

It’s good to assume that it heavily depends on airport, and time. I’ve been many times in the past years when just security took me more than 30 minutes. There are airports where it’s always less than 10 minutes (especially if you know some tricks), and there are airports where it depends on time. One hour is a good rule of thumb in Europe nowadays if you don’t have checked baggage. It would have been a stretch a few times, but I would have never missed a flight if I had been there only 1 hour before departure.

Last summer was crazy for popular airports in Europe, with queues lasting for multiple hours just to get _to_ security. It was said that it was due to staff shortages due to layoffs during the pandemic though.

I have flown out of there recently and this would have been terrible advice. Really bad queues for bag drop and security.

Come to Australia. These times still exist.

At the right time on a good day, you can hop off the bus at Helsinki airport and be thru self-checkin AND security in about seven minutes flat.

Me too.

The airport experience is why, even though I enjoy actually flying, I avoid doing it to the greatest degree I can. Everything that happens from the time I arrive at the airport to the time the airplane leaves the runway is awful.

TTP/Global Entry sort of fixes this. What really fixes it is flying private. Unfortunately, that's doesn't do much to help the carbon problem.

The real difference now is that flying is too affordable. It used to be, only the rich could fly.

What we need to do is make air travel much, much more expensive, out of the reach of most people except on special occasions, and we can go back to having (1) less unnecessary carbon emissions from people flying to Disneyland or whatever shitty resort they spend their vacations at, and (2) very short waits at the airport for people who need to get somewhere in a hurry and can afford it.

Environmental and efficiency problem solved.

Wow that would be very heavy handed and really assumes that the rich traveling are some how more meaningful for whatever destinations they are going to - maybe flying to some shitty meeting in Sweden that could be done over video conference. By this logic inflation happening now will fix the problems in the world bringing all prices up and forcing most people to become vegans because meat becomes too expensive and will also be for the rich only. Then cars can be for the rich too and in the end we can let the poor sit with out technology at all leaving only the rich one percent having all the carbon emissions. Finally the environmental crises is solved.

> really assumes that the rich traveling are some how more meaningful

No, it assumes you care about reducing air travel more than equality of access to it

> forcing most people to become vegans because meat becomes too expensive

Sounds...effective? It isn't what is happening, but taxing the hell out of meat would be a great lever to pull if you want to drive consumption away from it.

Outside of cost the only possible lever is rationing. Good luck with that one.

“… TTP/Global Entry sort of fixes this…”

wish that were true, but the variance of wait time, even with tsa precheck, etc defeats the purpose. needs to be reliably consistent (and short) for me to take advantage of a 30min show time.

Those problems solved but a lot of other problems created. This genie can't go back into the bottle that easily. People live in other countries or states now and want to see their families too.

I am old enough, but arriving 20min before a flight was never really a thing. You could in theory arrive that way, but you were running a risk. Any delay in security, a delay in the bus system, or just bad luck with an irrate customs person could always delay you a few minutes too long. And if you werent even checked in 20min before your flight you had a very good chance of being bumped off the flight for someone on standby. There was also zero chance of any checked bags making it onto your flight unless you were checking in at least an hour before travel.

An plane could be like a bus...

Show up, hop on, tap your credit card to pay, and the plane takes off while you're still wandering down the aisle looking for a seat.

I like where your head is at! make that the vision.

/fire suit on

The last time I flew through Dublin airport I got from my taxi to my gate in 16 minutes including checking in a bag. I had arrived 3 hours early nonetheless due to the "chaotic" queue times I had read about.

This is one reason why I prefer to take the train for work whenever possible, even it takes longer and isn't that much cheaper, the onboarding experience is awfully simple and relatively stress-free.

You are obviously on the east coast.

From the bay area, there is nowhere you might want to go that a train would make less stressful.

Want to go to LA? That's 1 hour in the air for around 100 bucks. Or it's a 10 hour ordeal involving transfers between coach bus and train in more than one location. All for the low price of 60 dollars.

Want to go to New York? That's 6 hours by air or 80+ hours by rail. Where realistically you are going to book a roomette ($$$) and not just sit in coach for 3 days straight.

Still a thing at LCY

> On any american flight (not to alaska/hawaii) i doubt the greater efficiencies at 60+ thousand feet would be worth the fuel to get there with a supersonic wing. These would only be 2 or 3-hour flights at most anyway.

Hi! There are many of us who exist outside of the US and would be open to planes flying faster because the world is super big. Thanks for listening

> Hi! There are many of us who exist outside of the US and would be open to planes flying faster because the world is super big.

Sure, but that isn’t particularly affected by restrictions on supersonic flight over the US.

Yes it is.

(London-LA semi-frequent flyer).

Los Angeles is not "outside of the US". Besides, less than 20% of that trip is in USA airspace. Slow down when you hit North Dakota...

https://www.greatcirclemapper.net/en/great-circle-mapper.htm...

Canadian regulations invariable follows US regulations. So in this case yes the FAA would have to make the change too.

Suggestions about how Canada could improve really ought to be directed to the Canadians. They might be amenable to different policies in sparsely populated regions like Hudson Bay. Continental USA has no analogous areas.

Non-Americans who wish to complain about USA have a broad range of topics from which to choose; there's really no need to complain that USA regulates the operation of airlines in USA airspace.

I only commented on what is the current dynamic. Your thoughts on why there ought to be a different dynamic is interesting, but it doesn't seem like something anyone could predict.

Only a recreational pilot but I agree, when we calculate fuel usage (because people want you to pay your share this is a serious topic) there’s so many more ‘real’ variables

Yes, from basic principles, energy is force times distance. This force on an airplane is drag. Since on an airplane, both the drag and lift are proportional to the square of velocity, if (thought experiment) you assume a fixed lift to drag ratio, speed cancels out. It doesn't affect energy usage.

Basically a faster airplane can have smaller wings which produce less lift and less drag. If we in spherical cow tradition ignore body drag, you can halve wing size, increase speed by 44% and have the same drag. You need more power but for a shorter duration, for the same energy usage per trip.

You're ignoring the efficiency of the jet engine itself. You have to basically pick an altitude, temperature, and speed at which the engine is most efficient. Modern airliners are most efficient at a certain speed and altitude because they're designed to stay under the supersonic regime.

It's been a long time since I've touched compressible fluid mechanics or turbomachinery design, but if I recall correctly the theoretical "sweet spot" for overall aircraft efficiency is something like Mach 1.3. I'd have to dig though my textbooks to remind myself why, but the number stuck with me.

Definitely! I remember seeing an old picture of a physical three dimensional plot about theoretical airliner efficiency. X axis was speed, Y axis was something else and Z axis was efficiency. I think it was made of wooden shapes. There were two local maxima there, one subsonic and one supersonic. Probably it was related to the US SST project.

Can't find the picture anymore...

Most commercial aircraft take off and land well below their cruise speed. My understanding is that this limitation applies to supersonic aircraft as well. Applied power is typically restricted due to noise control requirements near airports.

That wing lift/drag relationship may be less fungible than you're supposing in order to address lower-speed flight segments.

Yes, it was just a thought experiment from first principles to get a feel for the problem.

In reality, planes fly higher where the air is less dense, and faster to keep the lift and drag equal.

In a car, lift is not needed. Higher speed doesn't have compensating effects. Higher speed more clearly causes more fuel burn for the distance.

Fair enough.

If anything, automobiles frequently utilise negative lift, as with a Formula 1 or Indy Car's inverted wing which generates increased downforces. On street cars you'll find spoilers and similar factors.

Aircraft can fly low and fast, though that's typically associated with combat aircraft evading radar or air-defence systems. Such missions are known as fuel-burners precisely because of the greatly increased drag.

I don’t think people will believe you even though you’re right. Pure math has a strange way of swaying one’s opinions; ML in particular suffers from this.

But thank you for trying to point out that engineering efficiencies matter a great deal. Hopefully the message will get through.

I thought you were saying that Marxism-Leninism suffers from naivety of pure math and I was really twisting my brain working that one out

Economic theory isn’t free from this phenomenon either. :) Though I wonder if it’s possible to model the probability of a communist revolution.

Ah finally I understand why everybody is so worked up about Anarchist Ideology lately

>Jet aircraft are significantly more efficient at higher speeds and at higher altitudes precisely because there’s less drag up there and the engines can operate more efficiently.

This is true, but isn't the flip side of this that the high altitude emissions are much more damaging?

Please unsimplify this then? Can you give a scenario where flying faster would be more economical fuel-wise?

This should enlighten you: https://aviation.stackexchange.com/questions/1609/why-do-jet...

It’s not a linear relationship but unless you’re flying in space, you’re going to deal with the fuel vs speed trade off.

If you fly too slow the wing will start to stall, so you have to pull the nose up to raise the angle of attack…. Which vastly increases drag.

It's an oversimplification but as far I understand it's not wrong at least with past/current projects.

Efficiency for a given aircraft is nice but it's not the point. I believe Concord was most efficient at cruising speed (~Mach 2) but it does not change the fact that it burned like 4x more per seat/km than a b737 (Cf: https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft). Of course Concorde was only first class but that's part of the point of the parent.

As for boom, some guesstimate are around at least 4x too (https://theicct.org/new-supersonic-transport-aircraft-fuel-b...). No idea how biased this is but I believe it's quite telling that there is only mention of SAF on https://boomsupersonic.com/sustainability. At best in some 2017 article they compare themself to a lay-flat bed in subsonic business class, but since they only manage to secure an engine maker last year it was firmly in the guesstimate too.

New York to London round trip ticket price was $14,522 in 2023 dollars...

Ok, then limit airspeed and not true airspeed. Done.

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