6 ms·

Supersonic flight is easy. Efficient supersonic flight is hard. Aerodynamics, aerostructure, propulsion all of them are trying to break you. Controlling all of

Supersonic flight is easy. Efficient supersonic flight is hard. Aerodynamics, aerostructure, propulsion all of them are trying to break you. Controlling all of them would definitely be an achievement.

api 6y ago
As far as I know efficiency is what has kept civilian supersonic flight from being a thing. Even military aircraft tend to only go supersonic when needed because it guzzles fuel. My biggest skepticism about Boom is that I don't see them even talking about this issue much. If they can't get big efficiency improvements I see this being a niche toy for the super rich rather than a mainstream transport option. I'm not an expert, but I wonder: can you get large efficiency improvements by going to really extreme altitude where the air is thinner? Maybe that's the long term plan. But as far as I know that may require a novel engine design or the adaptation of military engines, and the latter is a minefield if classification and ITAR regulations. Extreme altitude also means you're dead if you get a major hull breach, but the increased risk there may be statistically mitigated by decreased overall flight time... and it's still going to be safer than driving a car.
- tim333 6y ago
  Extreme altitude also means there's less air to hold the plane up which seems to require a lot of power for level flight. I'm not sure about ballistic flight paths - a lot of fuel to get up there and then none for a while. Apparently re Musk's old Telas that he launched towards Mars: >It has achieved a fuel economy of 9,886.9 miles per gallon (4,203.4 km/liter, 0.02379 liters/100 km), assuming 126,000 gallons of fuel. https://www.whereisroadster.com/ https://www.whereisroadster.com/ But it's not on a very popular flight route. Should be kinda near Mars Oct 7th.
  - GuB-42 6y ago
    > Extreme altitude also means there's less air to hold the plane up which seems to require a lot of power for level flight. There is also less drag, and both lift and drag are calculated using the same formula: Cl * A * .5 * r * V^2 - Cl (Cx for drag, Cz for lift) is a coefficient depending on the wing shape, among other factors - A is the area (thickness for drag, wing surface for lift) - r is the air density - V is velocity If you divide the air density by 4 by going higher, you get the same lift and drag by going twice as fast. Which is great, and a good reason for fast planes to fly high. The reason it is so great is that in order to fly level, lift cancel gravity and thrust cancel drag. Because by going higher, we managed to keep the same lift and drag with higher speed, it means we got faster using the same amount of thrust. There are certainly complications somewhere. For example at supersonic speeds you get shock drag but suffice to say, high altitude is good for speed. Still there is a good reason why planes don't just get higher to get speed for free. And that's because planes are not rocket powered. Air breathing engines lose efficiency the faster you get, they are also designed to operate at specific speed ranges.
- mpweiher 6y ago
  > Even military aircraft tend to only go supersonic when needed because it guzzles fuel. Yep. In fact, this is one of many things that makes the Concorde so special: being able to cruise for a long time at Mach 2+. Supercruise has only come to fighter jets fairly recently, and there it is usually in the Mach 1.4-1.6 range. This means that if the Concorde has even a small head-start, it can outrun most fighter jets that might want to intercept it. The SR-71 could keep it company but is unarmed. Maybe the Mig-31, although its range also diminishes rapidly with increased velocity. > efficiency is what has kept civilian supersonic flight from being a thing This was an issue, but less than you might suspect, for example it didn't actually burn that much more than its contemporaries. The planned Concorde B [1] was to have more efficient engines that would have allowed the same performance without afterburners. Along with having larger fuel tanks, this would have led to a dramatic increase in range and therefore in the possible routes. Alas, the US effectively killed Concorde before that could happen by not allowing overflight, due to noise, particularly the sonic boom, and one suspects also the fact the the US SSTs weren't making much progress. And of course the oil price shock. Concorde tickets were actually quite a bit cheaper than the public expected, BA (and AF, presumably) later raised prices to match public perception, with a nice boost to profitability. > extreme altitude where the air is thinner Jets in general (~35K feet) and Concorde in particular (~60K feet) already do this. IIRC, jet engines are actually not very efficient, but they continue to operate well at high altitudes where the air is so much thinner that the plane becomes more efficient overall, whereas both piston engines and the propellers they drive become significantly less efficient at altitude. [1] https://www.heritageconcorde.com/concorde-b https://www.heritageconcorde.com/concorde-b
  - rbanffy 6y ago
    > and one suspects also the fact the the US SSTs weren't making much progress. I also can't quite avoid that suspicion. The Concorde was noisy, but not that noisy and Concorde B should be quieter from the aerodynamic improvements.
- TylerE 6y ago
  Concorde already flew at 60,000ft. Go much higher than that and you're going to need to put the passengers in space suits, as any cabin depressurization would be...really bad.
  - liability 6y ago
    Would it really? Subsonic airliners already fly high-enough to kill passengers if they depressurized. The oxygen masks that drop are only a stop-gap to give the pilot time to drop down to a safer altitude (and the pilots have an independent, superior, source of bottled oxygen.) Humans can survive a hard vacuum briefly, if they're repressurized promptly. Perhaps putting the pilots in pressure suits would be sufficient. I think it's a matter of how quickly pilots could descend with the plane, which is probably a complicated question for aviation engineers to solve. This all said, only pilots getting pressure suits probably wouldn't inspire passenger confidence.
    - api 6y ago
      Also unlike Concorde today it is quite possible to make the plane fly itself if the pilots and crew all pass out. If all the meat sacks pass out, drop out of mach and drop down in altitude, send SOS, find somewhere to land. At this point ground control could start commanding the plane remotely too. We are not quite ready for pilotless passenger planes, but pilotless as a fallback is viable.
    - TylerE 6y ago
      At the 60k ft the Concorde flew at, a loss of pressure results in loss of consciousness in 10 seconds (or less). They already had unusual emergency procedures. You can't just mindlessly descend because that would overstress/overspeed the airframe.
      - liability 6y ago
        The passengers don't strictly need to stay conscious, though the pilots certainly do need to. I do wonder how likely a total and rapid loss of pressurization is to coincide with the plane remaining airworthy at all though. I'm guessing most survivable scenarios involve a less than immediate depressurization, which would buy the pilots more time to save the passengers. And of course I doubt the pilots would be doing anything mindlessly, let alone responding to an emergency.. In any event, I think the Concorde proves that operating at that altitude is feasible. It's not like 60,000 feet at supersonic speeds is survivable. The pilots would have minutes to get down before passengers were brain damaged. The chemical oxygen generators giving oxygen to the passengers don't last long, not nearly as long as the oxygen bottles for the pilot/crew, and that's assuming the passengers can get the masks on.
- Ajedi32 6y ago
  I checked their website and it does link to an article which explains the improvements they made over the Concorde in regards to fuel efficiency: https://blog.boomsupersonic.com/the-big-3-components-of-supersonic-aircraft-c1c614aeedbb https://blog.boomsupersonic.com/the-big-3-components-of-supe...
smt88 6y ago
My friend is an aerospace engineer and described the efficiency problem to me in detail. He said it's impossible to commercialize supersonic flight without breaking some laws of physics. I confess to not understanding the reasoning that got him there. It's not a controversial opinion in physics, though. I suspect Boom may end up being the uBeam of aviation.
- mpweiher 6y ago
  > it's impossible to commercialize supersonic flight without breaking some laws of physics Then those "laws" have been duly broken. https://en.wikipedia.org/wiki/Concorde https://en.wikipedia.org/wiki/Concorde
  - ThisIsTheWay 6y ago
    Those laws were temporarily broken, then they shut down due to soaring maintenance costs and low ridership... hardly a success story.
    - mpweiher 6y ago
      Research revealed that passengers thought that the fare was higher than it actually was, so the airline raised ticket prices to match these perceptions. It is reported that British Airways then ran Concorde at a profit. https://en.wikipedia.org/wiki/Concorde https://en.wikipedia.org/wiki/Concorde "Laws" that can be broken hardly seem to qualify as "laws of physics". An increase in maintenance costs due to the planes being very old and out of production also doesn't qualify: British Airways and Air France were able to operate Concorde at a profit, in spite of very high maintenance costs, because the aircraft was able to sustain a high ticket price. Its estimated operating costs were $3,800 per block hour in 1972, compared to actual 1971 operating costs of $1,835 for a 707 and $3,500 for a 747; for a 3,050 nmi London–New York sector, a 707 cost $13,750 or 3.04c per seat/nmi, a 747 $26,200 or 2.4c per seat/nmi and the Concorde $14,250 or 4.5c per seat/nmi. So 50% more expensive per seat/mile than a 707 and twice as expensive as a 747.
      - 6y ago
willyt 6y ago
Supposedly Concorde used more fuel taxiing from the stand to line up on the runway than a 737 flying London-Paris, but the fuel consumption PPM was comparable with a 747 once the plane was at super cruise. The problem is an building an engine that is efficient throughout the entire flight envelope. Engine efficiency improvements have come from gradually increasing the bypass ratio while solving some tricky problems with the tips of the blades approaching supersonic speeds, but, as I understand it, you can't use high bypass engines at supersonic speeds, so it will be interesting to see what technological advancements Rolls Royce have made over the original Olympus engines that powered the Concorde.
- EForEndeavour 6y ago
  > Supposedly Concorde used more fuel taxiing from the stand to line up on the runway than a 737 flying London-Paris This sounded ludicrous to me, so I tried to check it. Still not entirely convinced. The closest source I could find was a Vice article [1]: > A Concorde’s taxi to the end of a runway used as much fuel as a 737’s flight from London to Amsterdam. The article links to a now-defunct 2012 story on "scotsman.com", which I found on the Wayback Machine [2]. This story interviews Jim O'Sullivan, the former general manager and chief engineer of British Airways' supersonic fleet, but does not explicitly attribute this taxi fuel consumption claim to him or anyone else. A simulation-based fuel calculator I found says that the 737-800 would use 94,000 lb of fuel flying LHR-AMS [3]. The Concorde's fuel capacity was 211,000 lb [4]. Could any aviation nerds weigh in on how plausible it is to claim that the Concorde would somehow burn through HALF of its entire fuel load just by taxiing? Maybe "taxiing" here includes takeoff? [1] https://www.vice.com/en_us/article/ezz8q7/concorde https://www.vice.com/en_us/article/ezz8q7/concorde [2] https://web.archive.org/web/20170626124207/http://www.scotsman.com/news/transport/supersonic-the-enduring-allure-of-concorde-1-2415088 https://web.archive.org/web/20170626124207/http://www.scotsm... [3] http://fuelplanner.com/index.php http://fuelplanner.com/index.php [4] https://en.wikipedia.org/wiki/Concorde#Specifications https://en.wikipedia.org/wiki/Concorde#Specifications
  - willyt 6y ago
    Thanks, I read it in a newspaper article once and I should probably have checked but I was lazy and I knew someone else would do it for me! So I just wrote 'supposedly' and waited... I just remembered that this is a great site for Concorde facts http://www.concordesst.com http://www.concordesst.com. Also this OmegaTau podcast episode is pretty fantastic, it's so detailed you could almost jump in a Concorde and fly off after you've listed to it. http://traffic.libsyn.com/omegataupodcast/omegatau-166-flyingTheConcorde.mp3 http://traffic.libsyn.com/omegataupodcast/omegatau-166-flyin...

api 6y ago

As far as I know efficiency is what has kept civilian supersonic flight from being a thing. Even military aircraft tend to only go supersonic when needed because it guzzles fuel. My biggest skepticism about Boom is that I don't see them even talking about this issue much. If they can't get big efficiency improvements I see this being a niche toy for the super rich rather than a mainstream transport option. I'm not an expert, but I wonder: can you get large efficiency improvements by going to really extreme altitude where the air is thinner? Maybe that's the long term plan. But as far as I know that may require a novel engine design or the adaptation of military engines, and the latter is a minefield if classification and ITAR regulations. Extreme altitude also means you're dead if you get a major hull breach, but the increased risk there may be statistically mitigated by decreased overall flight time... and it's still going to be safer than driving a car.

tim333 6y ago
Extreme altitude also means there's less air to hold the plane up which seems to require a lot of power for level flight. I'm not sure about ballistic flight paths - a lot of fuel to get up there and then none for a while. Apparently re Musk's old Telas that he launched towards Mars: >It has achieved a fuel economy of 9,886.9 miles per gallon (4,203.4 km/liter, 0.02379 liters/100 km), assuming 126,000 gallons of fuel. https://www.whereisroadster.com/ https://www.whereisroadster.com/ But it's not on a very popular flight route. Should be kinda near Mars Oct 7th.
- GuB-42 6y ago
  > Extreme altitude also means there's less air to hold the plane up which seems to require a lot of power for level flight. There is also less drag, and both lift and drag are calculated using the same formula: Cl * A * .5 * r * V^2 - Cl (Cx for drag, Cz for lift) is a coefficient depending on the wing shape, among other factors - A is the area (thickness for drag, wing surface for lift) - r is the air density - V is velocity If you divide the air density by 4 by going higher, you get the same lift and drag by going twice as fast. Which is great, and a good reason for fast planes to fly high. The reason it is so great is that in order to fly level, lift cancel gravity and thrust cancel drag. Because by going higher, we managed to keep the same lift and drag with higher speed, it means we got faster using the same amount of thrust. There are certainly complications somewhere. For example at supersonic speeds you get shock drag but suffice to say, high altitude is good for speed. Still there is a good reason why planes don't just get higher to get speed for free. And that's because planes are not rocket powered. Air breathing engines lose efficiency the faster you get, they are also designed to operate at specific speed ranges.
mpweiher 6y ago
> Even military aircraft tend to only go supersonic when needed because it guzzles fuel. Yep. In fact, this is one of many things that makes the Concorde so special: being able to cruise for a long time at Mach 2+. Supercruise has only come to fighter jets fairly recently, and there it is usually in the Mach 1.4-1.6 range. This means that if the Concorde has even a small head-start, it can outrun most fighter jets that might want to intercept it. The SR-71 could keep it company but is unarmed. Maybe the Mig-31, although its range also diminishes rapidly with increased velocity. > efficiency is what has kept civilian supersonic flight from being a thing This was an issue, but less than you might suspect, for example it didn't actually burn that much more than its contemporaries. The planned Concorde B [1] was to have more efficient engines that would have allowed the same performance without afterburners. Along with having larger fuel tanks, this would have led to a dramatic increase in range and therefore in the possible routes. Alas, the US effectively killed Concorde before that could happen by not allowing overflight, due to noise, particularly the sonic boom, and one suspects also the fact the the US SSTs weren't making much progress. And of course the oil price shock. Concorde tickets were actually quite a bit cheaper than the public expected, BA (and AF, presumably) later raised prices to match public perception, with a nice boost to profitability. > extreme altitude where the air is thinner Jets in general (~35K feet) and Concorde in particular (~60K feet) already do this. IIRC, jet engines are actually not very efficient, but they continue to operate well at high altitudes where the air is so much thinner that the plane becomes more efficient overall, whereas both piston engines and the propellers they drive become significantly less efficient at altitude. [1] https://www.heritageconcorde.com/concorde-b https://www.heritageconcorde.com/concorde-b
- rbanffy 6y ago
  > and one suspects also the fact the the US SSTs weren't making much progress. I also can't quite avoid that suspicion. The Concorde was noisy, but not that noisy and Concorde B should be quieter from the aerodynamic improvements.
TylerE 6y ago
Concorde already flew at 60,000ft. Go much higher than that and you're going to need to put the passengers in space suits, as any cabin depressurization would be...really bad.
- liability 6y ago
  Would it really? Subsonic airliners already fly high-enough to kill passengers if they depressurized. The oxygen masks that drop are only a stop-gap to give the pilot time to drop down to a safer altitude (and the pilots have an independent, superior, source of bottled oxygen.) Humans can survive a hard vacuum briefly, if they're repressurized promptly. Perhaps putting the pilots in pressure suits would be sufficient. I think it's a matter of how quickly pilots could descend with the plane, which is probably a complicated question for aviation engineers to solve. This all said, only pilots getting pressure suits probably wouldn't inspire passenger confidence.
  - api 6y ago
    Also unlike Concorde today it is quite possible to make the plane fly itself if the pilots and crew all pass out. If all the meat sacks pass out, drop out of mach and drop down in altitude, send SOS, find somewhere to land. At this point ground control could start commanding the plane remotely too. We are not quite ready for pilotless passenger planes, but pilotless as a fallback is viable.
  - TylerE 6y ago
    At the 60k ft the Concorde flew at, a loss of pressure results in loss of consciousness in 10 seconds (or less). They already had unusual emergency procedures. You can't just mindlessly descend because that would overstress/overspeed the airframe.
    - liability 6y ago
      The passengers don't strictly need to stay conscious, though the pilots certainly do need to. I do wonder how likely a total and rapid loss of pressurization is to coincide with the plane remaining airworthy at all though. I'm guessing most survivable scenarios involve a less than immediate depressurization, which would buy the pilots more time to save the passengers. And of course I doubt the pilots would be doing anything mindlessly, let alone responding to an emergency.. In any event, I think the Concorde proves that operating at that altitude is feasible. It's not like 60,000 feet at supersonic speeds is survivable. The pilots would have minutes to get down before passengers were brain damaged. The chemical oxygen generators giving oxygen to the passengers don't last long, not nearly as long as the oxygen bottles for the pilot/crew, and that's assuming the passengers can get the masks on.
Ajedi32 6y ago
I checked their website and it does link to an article which explains the improvements they made over the Concorde in regards to fuel efficiency: https://blog.boomsupersonic.com/the-big-3-components-of-supersonic-aircraft-c1c614aeedbb https://blog.boomsupersonic.com/the-big-3-components-of-supe...

smt88 6y ago

My friend is an aerospace engineer and described the efficiency problem to me in detail. He said it's impossible to commercialize supersonic flight without breaking some laws of physics. I confess to not understanding the reasoning that got him there. It's not a controversial opinion in physics, though. I suspect Boom may end up being the uBeam of aviation.

mpweiher 6y ago
> it's impossible to commercialize supersonic flight without breaking some laws of physics Then those "laws" have been duly broken. https://en.wikipedia.org/wiki/Concorde https://en.wikipedia.org/wiki/Concorde
- ThisIsTheWay 6y ago
  Those laws were temporarily broken, then they shut down due to soaring maintenance costs and low ridership... hardly a success story.
  - mpweiher 6y ago
    Research revealed that passengers thought that the fare was higher than it actually was, so the airline raised ticket prices to match these perceptions. It is reported that British Airways then ran Concorde at a profit. https://en.wikipedia.org/wiki/Concorde https://en.wikipedia.org/wiki/Concorde "Laws" that can be broken hardly seem to qualify as "laws of physics". An increase in maintenance costs due to the planes being very old and out of production also doesn't qualify: British Airways and Air France were able to operate Concorde at a profit, in spite of very high maintenance costs, because the aircraft was able to sustain a high ticket price. Its estimated operating costs were $3,800 per block hour in 1972, compared to actual 1971 operating costs of $1,835 for a 707 and $3,500 for a 747; for a 3,050 nmi London–New York sector, a 707 cost $13,750 or 3.04c per seat/nmi, a 747 $26,200 or 2.4c per seat/nmi and the Concorde $14,250 or 4.5c per seat/nmi. So 50% more expensive per seat/mile than a 707 and twice as expensive as a 747.
    - 6y ago

willyt 6y ago

Supposedly Concorde used more fuel taxiing from the stand to line up on the runway than a 737 flying London-Paris, but the fuel consumption PPM was comparable with a 747 once the plane was at super cruise. The problem is an building an engine that is efficient throughout the entire flight envelope. Engine efficiency improvements have come from gradually increasing the bypass ratio while solving some tricky problems with the tips of the blades approaching supersonic speeds, but, as I understand it, you can't use high bypass engines at supersonic speeds, so it will be interesting to see what technological advancements Rolls Royce have made over the original Olympus engines that powered the Concorde.

EForEndeavour 6y ago
> Supposedly Concorde used more fuel taxiing from the stand to line up on the runway than a 737 flying London-Paris This sounded ludicrous to me, so I tried to check it. Still not entirely convinced. The closest source I could find was a Vice article [1]: > A Concorde’s taxi to the end of a runway used as much fuel as a 737’s flight from London to Amsterdam. The article links to a now-defunct 2012 story on "scotsman.com", which I found on the Wayback Machine [2]. This story interviews Jim O'Sullivan, the former general manager and chief engineer of British Airways' supersonic fleet, but does not explicitly attribute this taxi fuel consumption claim to him or anyone else. A simulation-based fuel calculator I found says that the 737-800 would use 94,000 lb of fuel flying LHR-AMS [3]. The Concorde's fuel capacity was 211,000 lb [4]. Could any aviation nerds weigh in on how plausible it is to claim that the Concorde would somehow burn through HALF of its entire fuel load just by taxiing? Maybe "taxiing" here includes takeoff? [1] https://www.vice.com/en_us/article/ezz8q7/concorde https://www.vice.com/en_us/article/ezz8q7/concorde [2] https://web.archive.org/web/20170626124207/http://www.scotsman.com/news/transport/supersonic-the-enduring-allure-of-concorde-1-2415088 https://web.archive.org/web/20170626124207/http://www.scotsm... [3] http://fuelplanner.com/index.php http://fuelplanner.com/index.php [4] https://en.wikipedia.org/wiki/Concorde#Specifications https://en.wikipedia.org/wiki/Concorde#Specifications
- willyt 6y ago
  Thanks, I read it in a newspaper article once and I should probably have checked but I was lazy and I knew someone else would do it for me! So I just wrote 'supposedly' and waited... I just remembered that this is a great site for Concorde facts http://www.concordesst.com http://www.concordesst.com. Also this OmegaTau podcast episode is pretty fantastic, it's so detailed you could almost jump in a Concorde and fly off after you've listed to it. http://traffic.libsyn.com/omegataupodcast/omegatau-166-flyingTheConcorde.mp3 http://traffic.libsyn.com/omegataupodcast/omegatau-166-flyin...