3 ms·

Performance-wise there's nothing close. You fly twice as high because hydrogen burns so lean, and you only need roughly 1/5th the equivalent mass of kerosene in

Performance-wise there's nothing close. You fly twice as high because hydrogen burns so lean, and you only need roughly 1/5th the equivalent mass of kerosene in fuel to get you the same distance. There are obvious barriers in the way (cost, certification, handling), but the potential benefits have been known for a long time.

ncmncm 4y ago
The main problem with LH2 is that it won't fit in the wing tanks like kerosene. The tanks may be very light, because the pressure is low and the LH2 weighs nothing, but they will be big! Some bet LH2 aircraft will have a wholly new shape, more like a lifting body, with a lot more inboard room for the bigger tankage. But another possibility is long underwing nacelles, alongside the engines. Those might even be retrofitted to existing airframes. Some people dislike the idea of sharing the cabin with inboard hydrogen tankage, as a safety concern. Fuel tanks shearing off with the wings in a crash has saved lives. Probably the nacelles would be rigged to be dropped in an emergency, to leave behind detonation risk.
- coderenegade 4y ago
  Yeah that's right, you need roughly twice the fuel volume, though that's easier to accommodate than needing to deal with a heavier fuel like ammonia, for example. Blended wing bodies and flying wings might make more sense with LH2. They haven't happened so far because they're harder to certify (essentially from scratch vs a standard design which uses evidence from previous designs to expedite certification), and they don't work too well with existing airport infrastructure. If you're going through the trouble of certifying LH2 anyway, that could provide justification for a new design, and working with airports to get the infrastructure going.
  - ncmncm 4y ago
    I am betting compatibility with past practice wins over incremental efficiency. But I have no way to evaluate whether retrofitting existing airframes with underslung tankage will be practical.
    - coderenegade 4y ago
      I tend to agree. Performance-wise, kerosene is "good enough". The only area where I see LH2 being worth the effort is military aircraft, especially unmanned. Of course, that's not a knock against green hydrogen itself (which I'm sure some will interpret it as) since kerosene is really just hydrogen with extra steps. But there are more factors that go into an effective propulsion system than just raw performance and efficiency.
      - eru 4y ago
        > Performance-wise, kerosene is "good enough". The only area where I see LH2 being worth the effort is military aircraft, especially unmanned. I'm not so sure. The military tends to put a premium on not exploding, even when fired up on. Even at the expense of efficiency. Case in point: TNT vs dynamite. > TNT has never been popular or widespread in civilian earthmoving, as it is considerably more expensive and less powerful by weight than dynamite,[12] as well as being slower to mix and pack into cylindrical boreholes; for its part, dynamite has never been popular in warfare because it degenerates quickly under severe conditions and can be detonated by either fire or a wayward bullet. TNT's primary asset is its remarkable insensitivity and stability: it is waterproof and incapable of detonating without the extreme shock and heat provided by a blasting cap (or a sympathetic detonation); this conveniently also allows it to be melted at 81 °C (178 °F), poured into high explosive shells and allowed to re-solidify with no extra danger or change in the TNT's characteristics.[13] Accordingly, more than 90% of the TNT produced in America was always for the military market, with most filling shells, hand grenades and aerial bombs and the remainder being packaged in brown "bricks" (not red cylinders) for use as demolition charges by combat engineers. From https://en.wikipedia.org/wiki/Dynamite https://en.wikipedia.org/wiki/Dynamite See also https://en.wikipedia.org/wiki/Multifuel#Underperformance_issues https://en.wikipedia.org/wiki/Multifuel#Underperformance_iss... and https://en.wikipedia.org/wiki/JP-8 https://en.wikipedia.org/wiki/JP-8 (they add special stuff to make military fuel auto-ignite at a higher temperature than civilian fuel). However, you might be right that in unmanned situation the military might be ok with more dangerous LH2. Though I doubt it, because the LH2 storage tanks on the ground also need to be relatively close to the front lines. And unless you make it on-site, you need to have a logistics train to get the LH2 there.

ncmncm 4y ago

The main problem with LH2 is that it won't fit in the wing tanks like kerosene. The tanks may be very light, because the pressure is low and the LH2 weighs nothing, but they will be big! Some bet LH2 aircraft will have a wholly new shape, more like a lifting body, with a lot more inboard room for the bigger tankage. But another possibility is long underwing nacelles, alongside the engines. Those might even be retrofitted to existing airframes. Some people dislike the idea of sharing the cabin with inboard hydrogen tankage, as a safety concern. Fuel tanks shearing off with the wings in a crash has saved lives. Probably the nacelles would be rigged to be dropped in an emergency, to leave behind detonation risk.

coderenegade 4y ago
Yeah that's right, you need roughly twice the fuel volume, though that's easier to accommodate than needing to deal with a heavier fuel like ammonia, for example. Blended wing bodies and flying wings might make more sense with LH2. They haven't happened so far because they're harder to certify (essentially from scratch vs a standard design which uses evidence from previous designs to expedite certification), and they don't work too well with existing airport infrastructure. If you're going through the trouble of certifying LH2 anyway, that could provide justification for a new design, and working with airports to get the infrastructure going.
- ncmncm 4y ago
  I am betting compatibility with past practice wins over incremental efficiency. But I have no way to evaluate whether retrofitting existing airframes with underslung tankage will be practical.
  - coderenegade 4y ago
    I tend to agree. Performance-wise, kerosene is "good enough". The only area where I see LH2 being worth the effort is military aircraft, especially unmanned. Of course, that's not a knock against green hydrogen itself (which I'm sure some will interpret it as) since kerosene is really just hydrogen with extra steps. But there are more factors that go into an effective propulsion system than just raw performance and efficiency.
    - eru 4y ago
      > Performance-wise, kerosene is "good enough". The only area where I see LH2 being worth the effort is military aircraft, especially unmanned. I'm not so sure. The military tends to put a premium on not exploding, even when fired up on. Even at the expense of efficiency. Case in point: TNT vs dynamite. > TNT has never been popular or widespread in civilian earthmoving, as it is considerably more expensive and less powerful by weight than dynamite,[12] as well as being slower to mix and pack into cylindrical boreholes; for its part, dynamite has never been popular in warfare because it degenerates quickly under severe conditions and can be detonated by either fire or a wayward bullet. TNT's primary asset is its remarkable insensitivity and stability: it is waterproof and incapable of detonating without the extreme shock and heat provided by a blasting cap (or a sympathetic detonation); this conveniently also allows it to be melted at 81 °C (178 °F), poured into high explosive shells and allowed to re-solidify with no extra danger or change in the TNT's characteristics.[13] Accordingly, more than 90% of the TNT produced in America was always for the military market, with most filling shells, hand grenades and aerial bombs and the remainder being packaged in brown "bricks" (not red cylinders) for use as demolition charges by combat engineers. From https://en.wikipedia.org/wiki/Dynamite https://en.wikipedia.org/wiki/Dynamite See also https://en.wikipedia.org/wiki/Multifuel#Underperformance_issues https://en.wikipedia.org/wiki/Multifuel#Underperformance_iss... and https://en.wikipedia.org/wiki/JP-8 https://en.wikipedia.org/wiki/JP-8 (they add special stuff to make military fuel auto-ignite at a higher temperature than civilian fuel). However, you might be right that in unmanned situation the military might be ok with more dangerous LH2. Though I doubt it, because the LH2 storage tanks on the ground also need to be relatively close to the front lines. And unless you make it on-site, you need to have a logistics train to get the LH2 there.