Boom Supersonic aims to fly 'anywhere in the world in four hours for $100'(cnn.com)
cnn.com
Boom Supersonic aims to fly 'anywhere in the world in four hours for $100'
https://www.cnn.com/travel/article/boom-supersonic-four-hours-100-bucks/index.html
12 comments
It’s not a matter of physics.
All things being equal, it takes a lot more energy to slice through the air at Mach 2 than at Mach 0.85. But all things are not equal: Concorde flew about twice as high as regular subsonic planes. At that altitude, the air is about half as dense, so it takes less energy to move it out of the way.
In the end what matters is the lift to drag ratio and the speed ratio. In cruise mode, a regular commercial jet has a L/D ratio of about 17, and Concorde of 7 [1], i.e. about 2.4 lower. So each minute it spends cruising, Concorde will burn 2.4 times more fuel than a subsonic jet of equal mass. But Concorde flies faster, so it spends less time to cover the same distance. How much less? About 2/0.85 = 2.35. In other words, to cover the same distance Concorde burns about the same amount of fuel as a subsonic jet, while in cruise mode. Concorde’s fuel economy was horrible at takeoff though due to a triple whammy: L/D ratio of only 4, need to use the (very inefficient) afterburners, and the tyranny of the rocket equation.
But if someone can solve these issues, there is nothing that prevents a supersonic to be as fuel efficient as a subsonic jet.
[1] https://en.wikipedia.org/wiki/Lift-to-drag_ratio#Supersonic/...
All things being equal, it takes a lot more energy to slice through the air at Mach 2 than at Mach 0.85. But all things are not equal: Concorde flew about twice as high as regular subsonic planes. At that altitude, the air is about half as dense, so it takes less energy to move it out of the way.
In the end what matters is the lift to drag ratio and the speed ratio. In cruise mode, a regular commercial jet has a L/D ratio of about 17, and Concorde of 7 [1], i.e. about 2.4 lower. So each minute it spends cruising, Concorde will burn 2.4 times more fuel than a subsonic jet of equal mass. But Concorde flies faster, so it spends less time to cover the same distance. How much less? About 2/0.85 = 2.35. In other words, to cover the same distance Concorde burns about the same amount of fuel as a subsonic jet, while in cruise mode. Concorde’s fuel economy was horrible at takeoff though due to a triple whammy: L/D ratio of only 4, need to use the (very inefficient) afterburners, and the tyranny of the rocket equation.
But if someone can solve these issues, there is nothing that prevents a supersonic to be as fuel efficient as a subsonic jet.
[1] https://en.wikipedia.org/wiki/Lift-to-drag_ratio#Supersonic/...
>It’s not a matter of physics.
It is, and you're misunderstanding some of the basics of supersonic flight.
"As speeds approach the speed of sound, the additional phenomenon of wave drag appears. This is a powerful form of drag that begins at transonic speeds (around Mach 0.88). Around Mach 1, the peak coefficient of drag is four times that of subsonic drag. Above the transonic range, the coefficient drops drastically again, although remains 20% higher by Mach 2.5 than at subsonic speeds. Supersonic aircraft must have considerably more power than subsonic aircraft require to overcome this wave drag, and although cruising performance above transonic speed is more efficient, it is still less efficient than flying subsonically."[1]
Factoring in that supersonic airplanes are significantly heavier, have lower L/D, must spend more fuel getting to higher altitudes, still have to fly subsonic a considerable amount of the flight time/path, etc. means that it's a matter of physics.
[1] https://en.m.wikipedia.org/wiki/Supersonic_transport
It is, and you're misunderstanding some of the basics of supersonic flight.
"As speeds approach the speed of sound, the additional phenomenon of wave drag appears. This is a powerful form of drag that begins at transonic speeds (around Mach 0.88). Around Mach 1, the peak coefficient of drag is four times that of subsonic drag. Above the transonic range, the coefficient drops drastically again, although remains 20% higher by Mach 2.5 than at subsonic speeds. Supersonic aircraft must have considerably more power than subsonic aircraft require to overcome this wave drag, and although cruising performance above transonic speed is more efficient, it is still less efficient than flying subsonically."[1]
Factoring in that supersonic airplanes are significantly heavier, have lower L/D, must spend more fuel getting to higher altitudes, still have to fly subsonic a considerable amount of the flight time/path, etc. means that it's a matter of physics.
[1] https://en.m.wikipedia.org/wiki/Supersonic_transport
A few lines down in your link you have this: "At about Mach 2, a typical wing design will cut its L/D ratio in half (e.g., Concorde managed a ratio of 7.14, whereas the subsonic Boeing 747 has an L/D ratio of 17)".
Sure, at trans-sonic speeds the coefficient of drag is horrible, but a supersonic commercial jet doesn't spend more than the minimum time necessary in that speed range.
What's more, improvements are possible even for the trans-sonic range. The planned Concorde B was projected to have dramatic fuel consumption improvement of 25% at Mach 1.2 [1]. This projection was made around 1980. In the 40 years since, computers have advanced a bit, so there's a chance the Boom guys know what they are talking about.
[1] http://www.concordesst.com/concordeb.html
Sure, at trans-sonic speeds the coefficient of drag is horrible, but a supersonic commercial jet doesn't spend more than the minimum time necessary in that speed range.
What's more, improvements are possible even for the trans-sonic range. The planned Concorde B was projected to have dramatic fuel consumption improvement of 25% at Mach 1.2 [1]. This projection was made around 1980. In the 40 years since, computers have advanced a bit, so there's a chance the Boom guys know what they are talking about.
[1] http://www.concordesst.com/concordeb.html
>A few lines down in your link you have this: "At about Mach 2, a typical wing design will cut its L/D ratio in half (e.g., Concorde managed a ratio of 7.14, whereas the subsonic Boeing 747 has an L/D ratio of 17)".
That is literally proving my point. Thanks for agreeing with me?
>Sure, at trans-sonic speeds the coefficient of drag is horrible, but a supersonic commercial jet doesn't spend more than the minimum time necessary in that speed range.
And the wave drag is still bad even at supersonic speeds. The planes still have to spend a significant amount of time subsonic (take off, approach, landing, etc.) even if it's minimalized, it's still a significant amount.
>What's more, improvements are possible even for the trans-sonic range. The planned Concorde B was projected to have dramatic fuel consumption improvement of 25% at Mach 1.2 [1].
Still worse than subsonic at that time. Since then, subsonic, high bypass engine design has made that gap even wider.
So still, no, it's a matter of physics.
That is literally proving my point. Thanks for agreeing with me?
>Sure, at trans-sonic speeds the coefficient of drag is horrible, but a supersonic commercial jet doesn't spend more than the minimum time necessary in that speed range.
And the wave drag is still bad even at supersonic speeds. The planes still have to spend a significant amount of time subsonic (take off, approach, landing, etc.) even if it's minimalized, it's still a significant amount.
>What's more, improvements are possible even for the trans-sonic range. The planned Concorde B was projected to have dramatic fuel consumption improvement of 25% at Mach 1.2 [1].
Still worse than subsonic at that time. Since then, subsonic, high bypass engine design has made that gap even wider.
So still, no, it's a matter of physics.
This comes up periodically. The status does not seem to have changed in quite some time. They don't even have a scale prototype yet, much less anything like a full scale design. No place to build it, etc. At this point it's vaporware.
It's technically feasible of course but the claims are ridiculous. You obviously can't fly anywhere in the world in 4 hours at mach 2, and the $100 price tag is just stupid, which further solidifies the sentiment that it's just some kind of scammy attempt to gather funds. I bet even a simple calculation for fuel costs and zero profit margins won't give you the $100 promice even on high volume and "short" routes like NY-London.
And people overestimate how much someone's willing to pay in exchange of time. Even if you save 4 hours of flight (which is only a portion of the equation), you'd have to value your free time at least at $50/hour to pay even just $200 more. Some will, most won't. Europe is dominated by low cost airlines so I don't see the market for their product.
>"Either we fail or we change the world,"
Well this isn't a selfie filter, if you fail you kill lots of people.
And people overestimate how much someone's willing to pay in exchange of time. Even if you save 4 hours of flight (which is only a portion of the equation), you'd have to value your free time at least at $50/hour to pay even just $200 more. Some will, most won't. Europe is dominated by low cost airlines so I don't see the market for their product.
>"Either we fail or we change the world,"
Well this isn't a selfie filter, if you fail you kill lots of people.
> > "Either we fail or we change the world,"
> Well this isn't a selfie filter, if you fail you kill lots of people.
I was under the impression that by "fail" they meant "fail to create economical supersonic flight". While sending passengers to their deaths in an unsafe aircraft would also be a type of failure, I don't think that's what was implied here.
> Well this isn't a selfie filter, if you fail you kill lots of people.
I was under the impression that by "fail" they meant "fail to create economical supersonic flight". While sending passengers to their deaths in an unsafe aircraft would also be a type of failure, I don't think that's what was implied here.
The 4 hour vision is not at Mach 2. It’s their eventual aspiration, not their expected results from the current vehicle design.
An aspiration that is very, very hard to realize.
An aspiration that is very, very hard to realize.
Fast, Cheap, Safe - Chose two
“Good, fast, cheap. Choose two.”
They have picked price and fast, so “good” has to go. Couldn’t that be something other than safety?
Thinking on the shittiest of airlines, could they go lower?
https://en.m.wikipedia.org/wiki/Project_management_triangle
They have picked price and fast, so “good” has to go. Couldn’t that be something other than safety?
Thinking on the shittiest of airlines, could they go lower?
https://en.m.wikipedia.org/wiki/Project_management_triangle
It's a matter of physics; nothing we can do about it.