Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The Race to Build the First Sustainable Supersonic Jet

worth.com

Post reply on HN
Print view View original

51–60 of 97 posts

Re: The Race to Build the First Sustainable Supersonic Jet

#51

Post by mrpopo »

melling wrote: post #48
perl4ever wrote: post #40

Earlier quoted context omitted.

"It's the difference between able to go for the day or not" Which points to how increases in capability and efficiency can stimulate demand, which could be a bad thing from an environmental perspective.

And in the meantime, enough emissions from fossil fuels to generate electricity is emitted every year to cover a couple decades of flying.

This comment makes no sense because it doesn't state how many people get electricity and how many people fly.

The carbon footprint of one transatlantic flight is on the same order of magnitude as one person's yearly electricity consumption.

People who fly every year can substantially reduce their carbon footprint by not flying, people who already don't fly every year (the majority of the population) can't.

Re: The Race to Build the First Sustainable Supersonic Jet

#52

Post by [deleted] »

mrpopo wrote: post #50
melling wrote: post #26

Earlier quoted context omitted.

Nope, air transportation is not a major contributor to CO2. There are over 100,000 flights daily. They account for about 2.5% of CO2 emissions yearly. You know what is? Coal power plants that generate electricity. Maybe we should focus on electricity generation from coal. I’m a little surprised that more hasn’t been done. https://www.carbonbrief.org/mapped-worlds-coal-power-plants 13 years ago Google attempted their…

Air transportation is a major contributor to CO2, if you limit the scope to the people who use it. It is estimated that about 80% of the world's adults have never taken a flight, and 94% of the world's adults have not taken a flight in over a year. So, the real picture is that this 2.5% of global CO2 emissions are caused by as few as 6% of the population, who also are incidentally the richest and bear a high personal…

[deleted]

Re: The Race to Build the First Sustainable Supersonic Jet

#53

Post by syntaxing »

I think contrary to what people think, Supersonic jets is actually sustainable from a physics perspective. One of the things I'm most excited about is active flow controls on planes. The whole idea is to dynamically create laminar seperation at strategic locations. The effects of this is pretty astounding. It can drastically minimize the drag of the plane and can be also used as flight controls. I can't remember the exact year but NASA did a presentation about this and project the technology to become more prevalent by 2035. Another thing NASA is working on is to use the same jet technology to create perturbations in the wake of the plane to minimize the noise from the Sonic boom.

Re: The Race to Build the First Sustainable Supersonic Jet

#54

Post by pengaru »

melling wrote: post #26
jpeanuts wrote: post #24

In my opinion it is disingenuous to call any supersonic aircraft sustainable. Independently of any clever aerodynamic design to moderate the drag coefficient, aerodynamic drag always increases like the velocity squared. Doubling the speed will mean applying 4x the force for 1/2 the time, so all propulsive efficiencies being equal, you will expend twice the fuel to go the same distance - at an absolute minimum. In rea…

Nope, air transportation is not a major contributor to CO2. There are over 100,000 flights daily. They account for about 2.5% of CO2 emissions yearly. You know what is? Coal power plants that generate electricity. Maybe we should focus on electricity generation from coal. I’m a little surprised that more hasn’t been done. https://www.carbonbrief.org/mapped-worlds-coal-power-plants 13 years ago Google attempted their…

> There are over 100,000 flights daily. They account for about 2.5% of CO2 emissions yearly.

The generally accepted emissions weighting factor for aviation co2 emissions is ~2.6. So it's more like 6.5%, and growing fast.

Re: The Race to Build the First Sustainable Supersonic Jet

#55

Post by revax »

melling wrote: post #26
jpeanuts wrote: post #24

In my opinion it is disingenuous to call any supersonic aircraft sustainable. Independently of any clever aerodynamic design to moderate the drag coefficient, aerodynamic drag always increases like the velocity squared. Doubling the speed will mean applying 4x the force for 1/2 the time, so all propulsive efficiencies being equal, you will expend twice the fuel to go the same distance - at an absolute minimum. In rea…

Nope, air transportation is not a major contributor to CO2. There are over 100,000 flights daily. They account for about 2.5% of CO2 emissions yearly. You know what is? Coal power plants that generate electricity. Maybe we should focus on electricity generation from coal. I’m a little surprised that more hasn’t been done. https://www.carbonbrief.org/mapped-worlds-coal-power-plants 13 years ago Google attempted their…

Almost the entirety of emissions are made up of 5% when you decompose by sector.

There is no silver bullet for reducing your carbon footprint. You should lower emissions for all industries at the same time.

Re: The Race to Build the First Sustainable Supersonic Jet

#56

Post by choeger »

mrpopo wrote: post #51
melling wrote: post #48

Earlier quoted context omitted.

And in the meantime, enough emissions from fossil fuels to generate electricity is emitted every year to cover a couple decades of flying.

This comment makes no sense because it doesn't state how many people get electricity and how many people fly. The carbon footprint of one transatlantic flight is on the same order of magnitude as one person's yearly electricity consumption. People who fly every year can substantially reduce their carbon footprint by not flying, people who already don't fly every year (the majority of the population) can't.

The climate does not care how many people caused the co2 emissions.

Re: The Race to Build the First Sustainable Supersonic Jet

#57

Post by nradov »

jpeanuts wrote: post #24

In my opinion it is disingenuous to call any supersonic aircraft sustainable. Independently of any clever aerodynamic design to moderate the drag coefficient, aerodynamic drag always increases like the velocity squared. Doubling the speed will mean applying 4x the force for 1/2 the time, so all propulsive efficiencies being equal, you will expend twice the fuel to go the same distance - at an absolute minimum. In rea…

In theory we could use renewable energy sources to manufacture synthetic jet fuel in a carbon neutral loop. It would be more expensive, but sustainable. Hopefully costs will come down enough to make this economically viable.

Re: The Race to Build the First Sustainable Supersonic Jet

#58

Post by freepor »

namirez wrote: post #34
mrfusion wrote: post #31

Earlier quoted context omitted.

You’re not factoring in the ability of supersonic planes to fly at higher altitudes lowering air resistance. Also these planes could entice the rich to forgo flying on private jets. I’m sure 50 folks on a supersonic jet is still more efficient than 50 gulf streams.

This is a common misconception. Flying at higher altitudes doesn't mean just lower air resistance; it means lower lift as well. As a result you have to fly faster for compensating lower air density. If you do the math, you realize the overall effect would be higher energy consumption.

Come again? The drag is proportional to the lift, but if you’re flying higher, and thus faster, to get the same lift, you’re getting to your destination faster.

Re: The Race to Build the First Sustainable Supersonic Jet

#59

Post by jpeanuts »

namirez wrote: post #25
jpeanuts wrote: post #24

In my opinion it is disingenuous to call any supersonic aircraft sustainable. Independently of any clever aerodynamic design to moderate the drag coefficient, aerodynamic drag always increases like the velocity squared. Doubling the speed will mean applying 4x the force for 1/2 the time, so all propulsive efficiencies being equal, you will expend twice the fuel to go the same distance - at an absolute minimum. In rea…

You are right but the reality is even worse. Fuel consumption is proportional to power (velocity * drag) rather than drag itself. When you go twice as fast, the travel time is halved, so the total fuel consumption quadruples. And as you said, supersonic drag coefficients are typically larger than subsonic ones, which makes things even worse.

Thanks for correcting my embarrassing error! It's too late to edit my comment, but indeed x4 is the lower bound.

Re: The Race to Build the First Sustainable Supersonic Jet

#60

Post by jabl »

ncmncm wrote: post #42

The only way this thing could be honestly sustainable would be if it were hydrogen-powered. That might also be a prerequisite for profitability. But the airframe would need to be quite different from current designs because hydrogen tankage needs a lot more room than kerosene fuel would. Extra space on an aircraft is fairly cheap to provide. What is difficult is more weight, including extra fuel needed to get enough…

I'm sceptical. You'd need a lot of insulation and possibly refrigeration to prevent excessive boil off on long flights, adding weight. Also you'd want the tanks to be, if not spherical, at least cylindrical. Where would you put them?

Rockets make do with minimal insulation since they can top off the tanks just before liftoff and the flight itself takes only minutes.

And then there's also the thing that the climate forcing of flights is roughly a factor of 2.6 worse than the CO2 emissions alone, largely due to high altitude water vapor emissions. Switching to hydrogen would obviously not fix this.

Post reply on HN