If you're talking about the reference to the F-111 and P-51 aircraft, that's talking about the subsonic L/D, not the supersonic L/D. A bit of searching on google confirms this: http://www.hq.nasa.gov/pao/His...
I have journal access. I'd appreciate if you could give me the links to the articles you're talking about.
All that talk about form drag is completely irrelevant. For the second time, I'm just talking about a simple number: Lift/drag. Yes, it changes under different circumstances and yes, for a lot of craft it is lower at higher altitudes. I never said Lift/drag is constant across the entire flying envelope of an aircraft! That would be idiotic and insane. I'm just saying the relationship between Lift/drag and range does not depend on air density since, for a first-order analysis, you can absorb all of the dependencies into the lift/drag ratio.
> And I also explicitly said I was talking about straight and level flight, multiple times. Even in level flight, angle of attack is often non-zero. Angle of attack describes the orientation of the plane itself, not its velocity vector.
Jeezus... I did not say AoA is zero! For the third time, I'm talking about straight and level flight at cruise speed and altitude.
I didn't miss it. I'm just asking you to point to where it gives a L/D of 14. If you mean the [Anderson, 2000] graph, I'm sorry but that's just showing the Kuchemann trend, NOT an actual measured L/D. The Kuchemann trend is not accurate for low Mach numbers.
If you're pointing to somewhere else in the article, then where?
> Assuming an electric car gets twice the thermal efficiency compared to a petrol car I'll do some math
Your very starting assumption is wrong. ICE engines are, at best, 25% efficient. This is for hybrids; old-school gas cars are closer to 16 or 17% efficiency. When I said they're very inefficient, I meant it.
Electrical engines are very efficient. 90% efficiencies aren't unusual. The Tesla Model S gets 68% wall-to-wheels efficiency (from plug to battery to motor to wheels).
As I said above, until a SABRE engine is flying we might as well be talking about the efficiency of flying carpets. The intercooler has been tested and apparently it works, so I'm hopeful that the engine design will work, but you never know until you actually fly.
And even if it works, there's still a very large gap between "can struggle up to space carrying ridiculous amounts of cryogenic liquid hydrogen" and "affordable passenger aircraft."
As far as I know, the Concorde's engines are still the most efficient combustion engine to have ever been built. This is mainly due to the intake which had very good pressure recovery. Modern engine design techniques could push the efficiency still higher. Unfortuntaely, the fairly high drag at supersonic speeds more than cancel out this efficiency improvement.
> You won't get anything close to the rated range of out of something like a 747 if you stay at 3 km altitude the whole trip.
That's only because the 747 is designed to fly at that altitude and speed. It's airframe and engines have been optimized for that speed. I fail to see how this is relevant to what I'm saying.
> A characteristic L/D of 25 does not mean that lift is always equal to 25 times drag. Rather, it means that lift is always less than or equal to 25 times drag. The instantaneous L/D ratio is controlled within that range, as needed by the pilot, by adjusting the plane's angle of attack.
You're getting dumber by the minute. I explicitly said I'm talking about straight and level flight.
Nothing you said negates what I'm saying about lift/drag. You're just attempting to spin an argument around it.
I have a PhD in engineering. The mechanics of flight are obviously complicated but I'm attempting to simplify it so that we can make ballpark estimates of fuel consumption and efficiency. And I explicitly said I'm referring to straight and level flight at cruise speed. My analysis is correct.
'Ballistic suborbital hop' is a neat bait-and-switch word trick though. Sure, you can reach 'space' (above 100 km) with relatively low fuel consumption if you wanted to, but that will only get you a few hundred miles downrange. To travel clear across the world, you need a ballistic trajectory that comes pretty darned close to an orbital trajectory, and then you're looking at basically building a rocket.
Using a ballistic trajectory is far, far less fuel efficient than flying, no matter the altitude, because you aren't taking advantage of the atmosphere to provide lift. If you look at vehicles designed for ballistic trajectories (missiles, ICBMs, etc.) they all have very high fuel mass fractions and very low payload mass fractions.
Until a SABRE engine is flying we might as well be talking about the efficiency of flying carpets. The intercooler has been tested and apparently it works, so I'm hopeful that the engine design will work, but you never know until you actually fly.
By the way, if it works, it will achieve an efficiency about equal to that of a conventional turbofan engine. Which is great, but still wouldn't get you from London to Sydney cheaply.
> Electric cars are not inherently "green" since a large portion of our electricity comes from coal and natural gas.
You're right about the hydrogen, but wrong about this. Electric cars ARE green because internal combustion engines are really, really, and I do mean really, inefficient. If you do the math, the typical electric car in the USA produces 2-4x times less emissions than a gas car (even taking electricity production into account). And in places where the electricity is generated cleanly, they produce zero emissions.
Nope, you're dead wrong on all points. Flight is far more efficient than a ballistic trajectory. Being in an atmosphere is actually really great because wings allow you to lift far more weight than your engines themselves are capable of. And there's no way to 'glide' in space. You fall. The only way to avoid rapidly falling to the ground is to accelerate to such a tremendous speed (orbital velocity) that your freefall trajectory is wider than the curvature of the Earth. And to get to such speeds, you need a two-stage rocket that costs an insane amount of money and, at present, has to be thrown away each time it's used (Elon Musk is planning to change this, but it's not like it would make it as cheap as air travel).
I completely agree about the feasibility of a Mach 2.0 transport in the same vein as Concorde. I never suggested anything to the contrary.
What you have to consider though, is that even though there have been a lot of technological improvements since the 70's, fuel costs have also risen enormously (as a fraction of operating cost), and airliners run on profit margins of 1% or so. It's a really lousy business to be in overall and it's no surprise that most airlines are heavily state-supported.
While reports about Concorde losing money are a bit overblown, it still didn't make nearly as much money as subsonic airliners, and an SST introduced today would have the same problem. From the perspective of the consumer, it makes far more sense to get a regular business class ticket than a ride on an SST unless you really really have to go from London to NY in 3 hours. A long-haul SST service from, say, London to LA or LA to Sydney would be far more attractive but would be technologically hard.
That's another good point that I forgot to mention: At high speed, it becomes hard to develop efficient engines. The best engine efficiency occurs at low (below Mach 2.0 or so) speeds where good pressure recovery exists and the velocity of the exhaust jet is matched with forward flight speed. At higher speeds air-breathing engines become far less efficient.
The dependence between L/D ratio and range is independent of height or air density. Assuming fixed speed, in less dense air, you have less drag, but you also produce less lift.
So that everyone can have an informed opinion about this, the laws of physics of high-speed travel are quite simple. The lower the lift-drag ratio of your craft (at cruise speed at level flight), the more fuel you have to consume per mile. The problem with supersonic travel is that at supersonic speeds, high lift-drag ratios become virtually impossible. A 747 has a L/D ratio of over 25; the Concorde had a L/D of about 7 at Mach 2 (and it was a pretty efficient, low-drag design). The best supersonic designs I'm aware of achieve a L/D of around 9 at L/D at Mach 1.5. These are incredibly optimized designs that have been fine-tuned with supercomputers and would be quite unfeasible for a passenger aircraft (weird shapes, no windows, etc.) As a result the Concorde consumed about 3x more fuel PER MILE than a comparable subsonic jet. So half the mass of the Concorde was fuel (!), it winded up being very heavy, and it carried only 100 passengers. And its maximum range was limited to 4500 miles.
And if you look at a craft like the SR-71 blackbird, it fits the same pattern. It had a L/D of about 6 at cruise speed (Mach 3.2), 60% of its mass was fuel, and it could only go about 3000 miles before requiring refuelling.
At hypersonic speeds, it's even worse, as various laws start catching up with you and limiting your theoretical L/D to about 4 or 5. If you're running on typical jet fuel, forget London to Sydney. Such a craft could barely make it from London to Athens. So because of that, they're suggesting hydrogen. Which is both hilarious and also firmly puts this idea in the realm of 'things that are never going to happen.'
Android updates almost always cause significant system slow-down, often on purpose. This leaves people with the tough choice of either not updating - which results in a potentially vulnerable system - or having to play the updating Russian roulette. Some people choose not to update and I can't say I blame them. The android vendors need to get their shit together and stop dishing out crippling updates.
But seriously, there's only one possible reason aliens would ever want to come here and stay, and that's resources (energy, building materials). And if that's what they want, they would simply set up shop and start mining the solar system and, in all likelihood, probably just ignore us. It's not like we could stop them anyway.
But I think it's very unlikely that aliens will visit us any time soon. For a simple reason. If they are conquering solar systems for resources, the night sky wouldn't look anything like it does now. It would look like a gigantic industrial operation. It would be a fucking impressive sight! There's nothing special about OUR solar system.
It's perfectly possible - based on what we know about the formation of planets and life - that there isn't any intelligent life within a few hundred light years of Earth. Right now, it looks like we won't be contacting aliens within the next few centuries at least.
What other theory is there? Honestly, what other theory than evolution comes even close to explaining the evidence? I'm not aware of one.
> So until we've gotten it 100% figured out
That's an absurd and impossible goal.
Look, I get what you're saying. Our knowledge isn't perfect. I agree with that. We should never allow ourselves to fall into hubris. There are plenty of scientific theories that have gained 'mass acceptance' but really haven't been proven in any satisfactory way yet. So just because something has gained mass acceptance doesn't mean it's definitely true.
But the theory of evolution has been 'proven' beyond any reasonable doubt. If this were a court room, the suspect would have been convicted and executed long ago. The people who deny evolution are like the people who think Elvis is still alive. You shouldn't tell them, "You have a point, but..." They don't have a point. They are wrong and need to understand this.
I don't think it's unreasonable at all to consider that some form of EM communication will be used by advanced civilizations. EM radiation is just too easy to produce and detect and it enables very high bandwidths. The other technologies that the author is talking about - like gravitational wave communications or physical probes - have very very low bandwidths by nature of their design. General relativity dictates that it requires HUGE amounts of energy/mass to produce even feeble amounts of gravitational waves.
The point about detecting neutrinos from fusion reactors is interesting but I don't think there's any way we could separate those neutrinos from background radiation.
EM is likely to remain the most promising method for detecting ETI. Of course there's no reason that the EM radiation would be limited to the radio/microwave band. It could be based on light, or IR, or UV, or even X rays.
I think all this philosophizing about being well-rounded is bogus. But, anyway, as a scientist who also plays the guitar, the study makes me feel better about myself at least, even though I know I will definitely never get the nobel prize.
It takes a lot of intelligence to repeatedly hit a small ball with a stick.
Golf is the most pointless 'sport' in existence. You can't even compare it with low-level sports like baseball and ping pong, let alone sports that require actual skill and are moderately fun to watch, like basketball and football and soccer. And when people consider basketball players and football players to be dumb, imagine how dumb the average golf player must be.
All it takes to play golf is good motor coordination. Some people are naturally more talented at this, some aren't. That's ALL golf is. You know a sport is idiotic when a simple mechanical machine is better at it than any human could ever dream to be.
And about correlation, no it's not a coincidence that the majority of golf players seem to be those who are rapidly falling down the hill of age-related brain decay. And when their brain decays to the point where even playing golf becomes too hard, it's off to the bingo hall.
You might say I'm being too hard on golf. Actually I think I'm being too lenient. Golf shouldn't even be mentioned in the same sentence as real sports. Golfers deserve constant 24/7 ridicule until they finally pack their shit and we can repurpose the huge amounts of land devoted to that useless 'sport' for useful purposes, like landfills.
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If you're talking about the reference to the F-111 and P-51 aircraft, that's talking about the subsonic L/D, not the supersonic L/D. A bit of searching on google confirms this: http://www.hq.nasa.gov/pao/His...
I have journal access. I'd appreciate if you could give me the links to the articles you're talking about.
All that talk about form drag is completely irrelevant. For the second time, I'm just talking about a simple number: Lift/drag. Yes, it changes under different circumstances and yes, for a lot of craft it is lower at higher altitudes. I never said Lift/drag is constant across the entire flying envelope of an aircraft! That would be idiotic and insane. I'm just saying the relationship between Lift/drag and range does not depend on air density since, for a first-order analysis, you can absorb all of the dependencies into the lift/drag ratio.
> And I also explicitly said I was talking about straight and level flight, multiple times. Even in level flight, angle of attack is often non-zero. Angle of attack describes the orientation of the plane itself, not its velocity vector.
Jeezus... I did not say AoA is zero! For the third time, I'm talking about straight and level flight at cruise speed and altitude.
I didn't miss it. I'm just asking you to point to where it gives a L/D of 14. If you mean the [Anderson, 2000] graph, I'm sorry but that's just showing the Kuchemann trend, NOT an actual measured L/D. The Kuchemann trend is not accurate for low Mach numbers.
If you're pointing to somewhere else in the article, then where?
> Assuming an electric car gets twice the thermal efficiency compared to a petrol car I'll do some math
Your very starting assumption is wrong. ICE engines are, at best, 25% efficient. This is for hybrids; old-school gas cars are closer to 16 or 17% efficiency. When I said they're very inefficient, I meant it.
Electrical engines are very efficient. 90% efficiencies aren't unusual. The Tesla Model S gets 68% wall-to-wheels efficiency (from plug to battery to motor to wheels).
So adjust your math from 2x to 4x.
As I said above, until a SABRE engine is flying we might as well be talking about the efficiency of flying carpets. The intercooler has been tested and apparently it works, so I'm hopeful that the engine design will work, but you never know until you actually fly.
And even if it works, there's still a very large gap between "can struggle up to space carrying ridiculous amounts of cryogenic liquid hydrogen" and "affordable passenger aircraft."
As far as I know, the Concorde's engines are still the most efficient combustion engine to have ever been built. This is mainly due to the intake which had very good pressure recovery. Modern engine design techniques could push the efficiency still higher. Unfortuntaely, the fairly high drag at supersonic speeds more than cancel out this efficiency improvement.
> You won't get anything close to the rated range of out of something like a 747 if you stay at 3 km altitude the whole trip.
That's only because the 747 is designed to fly at that altitude and speed. It's airframe and engines have been optimized for that speed. I fail to see how this is relevant to what I'm saying.
> A characteristic L/D of 25 does not mean that lift is always equal to 25 times drag. Rather, it means that lift is always less than or equal to 25 times drag. The instantaneous L/D ratio is controlled within that range, as needed by the pilot, by adjusting the plane's angle of attack.
You're getting dumber by the minute. I explicitly said I'm talking about straight and level flight.
Nothing you said negates what I'm saying about lift/drag. You're just attempting to spin an argument around it.
I have a PhD in engineering. The mechanics of flight are obviously complicated but I'm attempting to simplify it so that we can make ballpark estimates of fuel consumption and efficiency. And I explicitly said I'm referring to straight and level flight at cruise speed. My analysis is correct.
'Ballistic suborbital hop' is a neat bait-and-switch word trick though. Sure, you can reach 'space' (above 100 km) with relatively low fuel consumption if you wanted to, but that will only get you a few hundred miles downrange. To travel clear across the world, you need a ballistic trajectory that comes pretty darned close to an orbital trajectory, and then you're looking at basically building a rocket.
Using a ballistic trajectory is far, far less fuel efficient than flying, no matter the altitude, because you aren't taking advantage of the atmosphere to provide lift. If you look at vehicles designed for ballistic trajectories (missiles, ICBMs, etc.) they all have very high fuel mass fractions and very low payload mass fractions.
Until a SABRE engine is flying we might as well be talking about the efficiency of flying carpets. The intercooler has been tested and apparently it works, so I'm hopeful that the engine design will work, but you never know until you actually fly.
By the way, if it works, it will achieve an efficiency about equal to that of a conventional turbofan engine. Which is great, but still wouldn't get you from London to Sydney cheaply.
> Electric cars are not inherently "green" since a large portion of our electricity comes from coal and natural gas.
You're right about the hydrogen, but wrong about this. Electric cars ARE green because internal combustion engines are really, really, and I do mean really, inefficient. If you do the math, the typical electric car in the USA produces 2-4x times less emissions than a gas car (even taking electricity production into account). And in places where the electricity is generated cleanly, they produce zero emissions.
Nope, you're dead wrong on all points. Flight is far more efficient than a ballistic trajectory. Being in an atmosphere is actually really great because wings allow you to lift far more weight than your engines themselves are capable of. And there's no way to 'glide' in space. You fall. The only way to avoid rapidly falling to the ground is to accelerate to such a tremendous speed (orbital velocity) that your freefall trajectory is wider than the curvature of the Earth. And to get to such speeds, you need a two-stage rocket that costs an insane amount of money and, at present, has to be thrown away each time it's used (Elon Musk is planning to change this, but it's not like it would make it as cheap as air travel).
I completely agree about the feasibility of a Mach 2.0 transport in the same vein as Concorde. I never suggested anything to the contrary.
What you have to consider though, is that even though there have been a lot of technological improvements since the 70's, fuel costs have also risen enormously (as a fraction of operating cost), and airliners run on profit margins of 1% or so. It's a really lousy business to be in overall and it's no surprise that most airlines are heavily state-supported.
While reports about Concorde losing money are a bit overblown, it still didn't make nearly as much money as subsonic airliners, and an SST introduced today would have the same problem. From the perspective of the consumer, it makes far more sense to get a regular business class ticket than a ride on an SST unless you really really have to go from London to NY in 3 hours. A long-haul SST service from, say, London to LA or LA to Sydney would be far more attractive but would be technologically hard.
> and a Miele design will hit an L/D ratio of ~14 at low Mach numbers
Link?
That's another good point that I forgot to mention: At high speed, it becomes hard to develop efficient engines. The best engine efficiency occurs at low (below Mach 2.0 or so) speeds where good pressure recovery exists and the velocity of the exhaust jet is matched with forward flight speed. At higher speeds air-breathing engines become far less efficient.
The dependence between L/D ratio and range is independent of height or air density. Assuming fixed speed, in less dense air, you have less drag, but you also produce less lift.
Minor correction: The HIGHER the L/D, the more fuel you have to consume per mile.
So that everyone can have an informed opinion about this, the laws of physics of high-speed travel are quite simple. The lower the lift-drag ratio of your craft (at cruise speed at level flight), the more fuel you have to consume per mile. The problem with supersonic travel is that at supersonic speeds, high lift-drag ratios become virtually impossible. A 747 has a L/D ratio of over 25; the Concorde had a L/D of about 7 at Mach 2 (and it was a pretty efficient, low-drag design). The best supersonic designs I'm aware of achieve a L/D of around 9 at L/D at Mach 1.5. These are incredibly optimized designs that have been fine-tuned with supercomputers and would be quite unfeasible for a passenger aircraft (weird shapes, no windows, etc.) As a result the Concorde consumed about 3x more fuel PER MILE than a comparable subsonic jet. So half the mass of the Concorde was fuel (!), it winded up being very heavy, and it carried only 100 passengers. And its maximum range was limited to 4500 miles.
And if you look at a craft like the SR-71 blackbird, it fits the same pattern. It had a L/D of about 6 at cruise speed (Mach 3.2), 60% of its mass was fuel, and it could only go about 3000 miles before requiring refuelling.
At hypersonic speeds, it's even worse, as various laws start catching up with you and limiting your theoretical L/D to about 4 or 5. If you're running on typical jet fuel, forget London to Sydney. Such a craft could barely make it from London to Athens. So because of that, they're suggesting hydrogen. Which is both hilarious and also firmly puts this idea in the realm of 'things that are never going to happen.'
Who downloads apps from outside the app store? That's practically begging for trouble.
Android updates almost always cause significant system slow-down, often on purpose. This leaves people with the tough choice of either not updating - which results in a potentially vulnerable system - or having to play the updating Russian roulette. Some people choose not to update and I can't say I blame them. The android vendors need to get their shit together and stop dishing out crippling updates.
We need a WALL around the Earth! A BIG wall!
But seriously, there's only one possible reason aliens would ever want to come here and stay, and that's resources (energy, building materials). And if that's what they want, they would simply set up shop and start mining the solar system and, in all likelihood, probably just ignore us. It's not like we could stop them anyway.
But I think it's very unlikely that aliens will visit us any time soon. For a simple reason. If they are conquering solar systems for resources, the night sky wouldn't look anything like it does now. It would look like a gigantic industrial operation. It would be a fucking impressive sight! There's nothing special about OUR solar system.
It's perfectly possible - based on what we know about the formation of planets and life - that there isn't any intelligent life within a few hundred light years of Earth. Right now, it looks like we won't be contacting aliens within the next few centuries at least.
A mechanical device can play soccer?
What other theory is there? Honestly, what other theory than evolution comes even close to explaining the evidence? I'm not aware of one.
> So until we've gotten it 100% figured out
That's an absurd and impossible goal.
Look, I get what you're saying. Our knowledge isn't perfect. I agree with that. We should never allow ourselves to fall into hubris. There are plenty of scientific theories that have gained 'mass acceptance' but really haven't been proven in any satisfactory way yet. So just because something has gained mass acceptance doesn't mean it's definitely true.
But the theory of evolution has been 'proven' beyond any reasonable doubt. If this were a court room, the suspect would have been convicted and executed long ago. The people who deny evolution are like the people who think Elvis is still alive. You shouldn't tell them, "You have a point, but..." They don't have a point. They are wrong and need to understand this.
I don't think it's unreasonable at all to consider that some form of EM communication will be used by advanced civilizations. EM radiation is just too easy to produce and detect and it enables very high bandwidths. The other technologies that the author is talking about - like gravitational wave communications or physical probes - have very very low bandwidths by nature of their design. General relativity dictates that it requires HUGE amounts of energy/mass to produce even feeble amounts of gravitational waves.
The point about detecting neutrinos from fusion reactors is interesting but I don't think there's any way we could separate those neutrinos from background radiation.
EM is likely to remain the most promising method for detecting ETI. Of course there's no reason that the EM radiation would be limited to the radio/microwave band. It could be based on light, or IR, or UV, or even X rays.
I think all this philosophizing about being well-rounded is bogus. But, anyway, as a scientist who also plays the guitar, the study makes me feel better about myself at least, even though I know I will definitely never get the nobel prize.
It takes a lot of intelligence to repeatedly hit a small ball with a stick.
Golf is the most pointless 'sport' in existence. You can't even compare it with low-level sports like baseball and ping pong, let alone sports that require actual skill and are moderately fun to watch, like basketball and football and soccer. And when people consider basketball players and football players to be dumb, imagine how dumb the average golf player must be.
All it takes to play golf is good motor coordination. Some people are naturally more talented at this, some aren't. That's ALL golf is. You know a sport is idiotic when a simple mechanical machine is better at it than any human could ever dream to be.
And about correlation, no it's not a coincidence that the majority of golf players seem to be those who are rapidly falling down the hill of age-related brain decay. And when their brain decays to the point where even playing golf becomes too hard, it's off to the bingo hall.
You might say I'm being too hard on golf. Actually I think I'm being too lenient. Golf shouldn't even be mentioned in the same sentence as real sports. Golfers deserve constant 24/7 ridicule until they finally pack their shit and we can repurpose the huge amounts of land devoted to that useless 'sport' for useful purposes, like landfills.