Will we ever fly supersonically over land? • Hacker News Board

Re: Will we ever fly supersonically over land?

#151

Post by vilhelm_s » Sun, Jul 04, 2021, 4:50 AM UTC

lazide wrote: post #135

kortex wrote: post #99

Earlier quoted context omitted.

Why wouldn't size correlate with magnitude? A whip crack breaks the sound barrier, it doesn't shatter windows. Same with a bullet, which goes even faster. You need both pressure level (voltage) and momentum (current) in order to stay strong over distances (shock waves diffuse over time) to break windows. Small, super fast things create large pressure differentials, big jets create more momentum.

Because the Mach cone produced by the leading edge/cone keeps most of the air from interacting with the aircraft behind it. It’s in the ‘wake’ as it were, though there may be multiple Mach cones or non-‘cone’ shaped ones depending on the shape of the aircraft. This does cause some stability or handling issues for the aircraft. The analogy re: voltage or amperage are spurious and just don’t apply here.

Surely the air is still interacting with the airplane.

The shockwave generated by a body shaped like an acute cone is a (somewhat less acute) cone with the same apex. Inside the shock wave, the air gradually turns around to move parallel to the body, like so [0]. Each streamline that enters the shock structure keeps turning around, so each bit of air keeps feeling a force even after it passes through the original cone-shaped shock. In the case of a cone-shaped body, the interaction happens to create a single "straight" wave, but it's still generated by the entire surface of the cone, not just the sharp point of it.

As a rule of thumb, the magnitude of the sonic boom is proportional to the weight of the plane. That is because most of the interaction between the plane and the air is from the wing, it needs to continuously deflect down enough air to generate a lifting force. So the total boom has one contribution from the cross-section of the fuselage, and another from the wings, and the latter is determined by the weight.

[0] https://www.researchgate.net/profile/Richard-Benay/publicati...

Re: Will we ever fly supersonically over land?

#152

Post by tonyedgecombe » Sun, Jul 04, 2021, 5:33 AM UTC

bronco21016 wrote: post #93

failwhaleshark wrote: post #61

Earlier quoted context omitted.

Flying, in-general, is inefficient unless it's a large, lifting body in ground effect.

I’d be interested to see a breakdown in fuel/seat-mile. I bet air travel isn’t as inefficient as the millions of people traveling alone in a car every day to work.

The thing is most people don’t drive their car 4000 miles across the Atlantic for a meeting.

Re: Will we ever fly supersonically over land?

#153

Post by tonyedgecombe » Sun, Jul 04, 2021, 5:54 AM UTC

FreeSpeech wrote: post #71

pyrale wrote: post #56

Earlier quoted context omitted.

What a rhetoric device. Is your preferred solution to let people die in droves to a mass extinction ?

So what proposal do luddites put forward then? People should travel intercontinentally by ship?

It's hard to take something away from people once they have already had it. Yet if we had never discovered flight then we wouldn't spend much time lamenting the lack of air travel. Instead we would get on with life within the limitations we have just like we do for other constraints.

Re: Will we ever fly supersonically over land?

#154

Post by tonyedgecombe » Sun, Jul 04, 2021, 6:18 AM UTC

neolog wrote: post #35

harimau777 wrote: post #9

Earlier quoted context omitted.

Unless we dramatically increase vacation time or dramatically increase rail speeds, that would mean that many people would not be able to see their families and friends or travel to events.

Most travel is business. Business events mostly don't require travel as we saw this year.

And without business travellers many or even most flights wouldn't be financially viable.

Re: Will we ever fly supersonically over land?

#155

Post by publicola1990 » Sun, Jul 04, 2021, 7:23 AM UTC

t0mas88 wrote: post #8

Ericson2314 wrote: post #6

Earlier quoted context omitted.

All overland passenger transport should be rail. Over the oceans I suppose we should strive for ships and dirigibles. That said, I find it hard to believe that plane travel can be eradicated for e.g. diplomacy. And frankly, if frequent contract between the powerful different countries is needed to avoid e.g. world wars, it's is worth it. In the short term, any carbon we can capture needs to go in back in ground and s…

Air travel has a big PR problem, because somehow a lot of people think it's the absolute worst for the environment. While on many routes a car is worse in terms of CO2 emission per trip than a small to mid sized airliner if there are less than 3 people in the car. Similar for your suggestion that we should take ships over the ocean, because cruise ships are much more polluting per passenger mile than modern airliners…

On the the other hand commercial air travel is one of the safest means of travel. If you wanted to optimize for safety you would take a scheduled flight to your destination than go by road.

Re: Will we ever fly supersonically over land?

#156

Post by jaclaz » Sun, Jul 04, 2021, 7:25 AM UTC

marcosdumay wrote: post #32

harimau777 wrote: post #9

Earlier quoted context omitted.

Unless we dramatically increase vacation time or dramatically increase rail speeds, that would mean that many people would not be able to see their families and friends or travel to events.

Well, in a plane trip you have 3 lost hours before it starts and after it ends, so a normal train, running at 130km/h will be faster than a plane at 850km/h for any trip of less than ~460km. If you make it a fast train, at 350km/h, it will beat the plane on any trip up to 1700km. Most trips are short, so no, most trips can be done by train and people still spend less time on them than by plane.

Yes, and for longer trips, besides the high speed trains, there are (were) also night trains, but for some reasons most of them were canceled (and/or the prices became less and less competitive), an old thread about this:

https://news.ycombinator.com/item?id=19557848

Maybe they will start to organize a few more of these trains, the level of stress was so much lower on (overnight) trains when compared to planes when moving in Europe.

Re: Will we ever fly supersonically over land?

#157

Post by jaclaz » Sun, Jul 04, 2021, 7:32 AM UTC

sokoloff wrote: post #98

marcosdumay wrote: post #32

Earlier quoted context omitted.

Well, in a plane trip you have 3 lost hours before it starts and after it ends, so a normal train, running at 130km/h will be faster than a plane at 850km/h for any trip of less than ~460km. If you make it a fast train, at 350km/h, it will beat the plane on any trip up to 1700km. Most trips are short, so no, most trips can be done by train and people still spend less time on them than by plane.

I don’t lose 6 hours on a typical airline trip. Domestic, I tend to arrive around an hour before gate close time. International from the US, about 90 minutes. For a train, I’d still plan on a 30 minute safety buffer (to protect against en route delays to the station). Add another 30 minutes over the train for boarding, push, and taxi. So, I’m probably giving up an hour plus/minus however closer the train station is v…

Of course it depends, but train stations tend to be in the center of a city, so you start from the center of A and arrive to the center of B.

With planes, airports are way off the city centre, I think that there are few airports (here in Europe) serving large cities that can be reached in less than 1 hour from the city centre, and that applies to both A and B, to this you add, unless you use a private means of transportation (car-taxi), a half an hour for the timetable of the bus or train you need to take to/from the airport, as it won't necessarily be synchronized with your flight departure/arrival.

Re: Will we ever fly supersonically over land?

#158

Post by inglor_cz » Sun, Jul 04, 2021, 7:35 AM UTC

jltsiren wrote: post #128

beerandt wrote: post #109

Earlier quoted context omitted.

Yea, which is why trains costs are so sensitive to distance- it's massive up front cost is a function of that distance. It's not the stations, it's the rails and right-of-way. The problem most people ignore is that train marginal-increases max-out at some number of trains per day, before you need an additional set of tracks. And that happens at a much lower number than most people assume, especially if you're plannin…

Train costs are sensitive to sparsely populated regions. As long as there is a sufficiently large city every hour or so, distances don't really matter. Multi-track railways are common near major cities. They are not that expensive, because adding another set of tracks increases the width of the corridor only marginally. The airline equivalent of a new set of tracks is building a new runway. Because that's often impos…

"Multi-track railways are common near major cities. They are not that expensive, because adding another set of tracks increases the width of the corridor only marginally."

About a quarter of all railway passengers in Czechia take the suburban trains around Prague.

We sorely need extra sets of tracks from all directions, because the current tracks are overloaded. Especially the faster trains from other regions do not mix well with the regional trains that stop every 2 km or so.

But it is almost impossible to build those extra sets of tracks in a densely populated major city like Prague. Lots of NIMBYs, the needed land would be very expensive, many buildings would have to be torn down, plus the centre is a protected zone (historical buildings) and the protecting authorities fight tooth and nail against anything that changes the look and feel of the inner city.

As a result, we are stuck with old infrastructure even if new one is sorely needed. There might be a way, namely, to build all the new tracks underground - but that would be very, very expensive.

Re: Will we ever fly supersonically over land?

#159

Post by inglor_cz » Sun, Jul 04, 2021, 7:40 AM UTC

ClumsyPilot wrote: post #126

sokoloff wrote: post #100

Earlier quoted context omitted.

6 PM to 10 AM is only 16 hours. Even with 3 time zones, you’d only be at 19 hours. 250kph straight line equivalent is unlikely given the terrain in the way (Rocky Mountains, primarily).

Tonnels, we are made massive ones through the alps in europe https://en.m.wikipedia.org/wiki/Gotthard_Base_Tunnel

Gotthard is impressive, but it took the Swiss 17 years to build it. Nearby, Brenner Base Tunnel is under construction between Italy and Austria, and it is expected to take 25 years to complete.

I can't imagine how long would it take to tunnel through the Rockies. Look at the map, they are far wider than the Alps. Getting through the Rockies is like getting from Denmark to Croatia.

Re: Will we ever fly supersonically over land?

#160

Post by inglor_cz » Sun, Jul 04, 2021, 7:44 AM UTC

ClumsyPilot wrote: post #119

beerandt wrote: post #102

Earlier quoted context omitted.

It was covered in a sustainable engineering class I took. There's not much generic into about it because every rail route proposal is different, even between the same destinations. Depends a lot on geography and what's already there. You basically need to do a full Life Cycle Analysis (LCA) for each route. Sometimes they're included in the EIS for a proposed project. That's prob the best place to start. But there's a…

China has more high-speed than the rest of the world combined, with even remote parts of China hooked up to the rail network. And when you compare energy, you have to take into account that Rail is already electric, powered directly by grid without batteries or any other efficiency loss in between. Airplanes use fuel that takes a lot of energy to refine and deliver, and will at best use hydrogen in 15 years which is…

One of the reasons why China built such a network so fast is the top-down structure of the state. If the authorities decide to build something just across your neighbourhood, you are in no position to challenge them.

Although I like trains, I wouldn't want to live in such society.