6 ms·

It is worse than even that: > Within the space of four seconds, the energy from the annulus gas flow accelerated the IP turbine past its critical speed, until

It is worse than even that: > Within the space of four seconds, the energy from the annulus gas flow accelerated the IP turbine past its critical speed, until centrifugal forces exceeded the ultimate strength of the nickel alloy disk. The red-hot, wildly spinning disk instantly fractured into several sections, which rocketed outward in multiple directions at incomprehensible speed.

mr_toad 14d ago
“It goes without saying that if any of the turbine fragments had entered the passenger cabin, there would have been injuries, if not fatalities, even if the plane later landed safely.” They got lucky.
gambiting 14d ago
The fact that it's assumed to have infinite energy when planning for this is crazy. Engineers saying yeah there is no material in the world that can stop it.
- bell-cot 14d ago
  Infinite is a bit poetic there. For large enough n, n inches of (say) armor steel could stop it. But that suggestion got Sales talking about "commercially viability", and Finance sided with them, and we all know how that story goes.
  - WJW 14d ago
    It's not (purely) the sales and finance people, planes need to be able to get off the ground to be useful at all. I doubt even an A380 would still be able to lift off if you strap a dozen inches of armor plating to every part of the plane that could possibly be reached by shrapnel.
    - bell-cot 14d ago
      You'd put the containment armor directly around the engine. It wouldn't take dozens of inches. Whether you use Newton's rule of thumb (penetration ends when the mass of armor displaced equals the mass of the shell that hit it) or more modern rules - a failing turbine disk is neither a precision-engineered anti-armor weapon, nor a heavy battleship shell. I'd bet the plane would still be able to take off, if it made it that far. But it never would - with the extra weight guaranteeing that no airline would buy it, Finance would never sign off on funding to even complete the design work. (Yes, the reality behind my quips about Sales and Finance is more complex:)
      - K0balt 13d ago
        Full containment is probably possible, but it would render the aircraft nearly useless, not just economically uncompetitive. A 70kg chunk of nickel alloy is very dense, and at 800m/s , that’s 20 MJ. Thats about the same as 5kg of TNT, but focused on a small area. For comparison, a modern 120mm artillery shell fired from a tank or similar field artillery has 10-20 MJ of kinetic energy. A couple thousand kg of armour could likely contain that kind of energy, but it would also translate that energy to the engine mounts, wing, spar, and fuselage if it was not going to become a projectile itself. You could easily stop a fragment and critically damage a spar attachment, rupture a wing fuel tank, or end up with translational shock damage to any number of critical systems and structures. You’d probably have to double or triple your engineering margins of the entire aircraft, probably doubling the weight of the airframe. So yeah, possible probably. But not on an aircraft designed to carry passengers or freight. It would be the biggest 6 seat aircraft ever built lol. Interestingly, if you work backwards from that cargo capacity, you can arrive at a much smaller aircraft that could possibly feature full containment, because engine diameter and energy goes way down and containment starts to look much more practical. I would not be surprised if containment could be achieved in the small biz jet scale, with just significant sacrifices in cargo or range. OTOH even the A10 warthog does not have full disk containment, and it’s probably the strongest candidate ever fielded for such a project… so, ymmv.
        bell-cot 13d ago
        > A 70kg chunk of nickel alloy is very dense, and at 800m/s , that’s 20 MJ. > For comparison, a modern 120mm artillery shell fired from a tank or similar ... Yes. But when the goal is kinetic penetration of modern armour, they don't use artillery shells. Instead - https://en.wikipedia.org/wiki/Armour-piercing_fin-stabilized_discarding_sabot https://en.wikipedia.org/wiki/Armour-piercing_fin-stabilized... - which bear no resemblance to a failed turbine disk. And have about twice the muzzle velocity, which makes huge difference in penetrating a modern armour systems. Ditto their far greater density, vs. nickel alloy. OTOH, your "A couple thousand kg of armour could likely contain..." seems too charitable. High-bypass jet engines are big. Beyond that, I'm more optimistic about mitigating shocks and such. A critical parameter here - https://en.wikipedia.org/wiki/A380#A380F https://en.wikipedia.org/wiki/A380#A380F The freight variant was to have a 6,400 mile range carrying 150t of payload. So we could squander 25t per engine on disk containment and shock mitigation, and still have a 50t payload. Or a 3-digit passenger headcount. Bottom line, there is no real-world difference between your "nearly useless" and my "disastrously uneconomical". Neither one will be designed, let alone built. For the A10, I'd say military priorities would always block full disk containment - because every pound used for that is a pound they don't have for more weapons or munitions or range or armour or fuel or runway length or electronics or whatever. And over most of the 360 which disk fragments could exit a warhog's engines, there's nothing critical which they could hit.
- cucumber3732842 14d ago
  I know we all like to hand wring about stuff like this but realistically it's "infinite" to prevent the same genius textbook engineers who cooked up the VMC procedure and the CMM procedure from cooking up equally half baked "with a plate of this thickness at this angle it will remove X energy from anything that penetrates it therefore we are good to put some super critical thing right in it's path" solution.
- wolvoleo 13d ago
  Maybe not stop it, but perhaps they can design it so that if it happens it's more likely to be directed away from the fuselage? Like with armor that does not block or absorb but deflect, which requires less energy. Perhaps even a small reactive armor strip? (dangerous as though that would be on a plane). But then again I'm sure aviation engineers would have thought of this and rejected it for good reason.

mr_toad 14d ago

“It goes without saying that if any of the turbine fragments had entered the passenger cabin, there would have been injuries, if not fatalities, even if the plane later landed safely.” They got lucky.

gambiting 14d ago

The fact that it's assumed to have infinite energy when planning for this is crazy. Engineers saying yeah there is no material in the world that can stop it.

bell-cot 14d ago
Infinite is a bit poetic there. For large enough n, n inches of (say) armor steel could stop it. But that suggestion got Sales talking about "commercially viability", and Finance sided with them, and we all know how that story goes.
- WJW 14d ago
  It's not (purely) the sales and finance people, planes need to be able to get off the ground to be useful at all. I doubt even an A380 would still be able to lift off if you strap a dozen inches of armor plating to every part of the plane that could possibly be reached by shrapnel.
  - bell-cot 14d ago
    You'd put the containment armor directly around the engine. It wouldn't take dozens of inches. Whether you use Newton's rule of thumb (penetration ends when the mass of armor displaced equals the mass of the shell that hit it) or more modern rules - a failing turbine disk is neither a precision-engineered anti-armor weapon, nor a heavy battleship shell. I'd bet the plane would still be able to take off, if it made it that far. But it never would - with the extra weight guaranteeing that no airline would buy it, Finance would never sign off on funding to even complete the design work. (Yes, the reality behind my quips about Sales and Finance is more complex:)
    - K0balt 13d ago
      Full containment is probably possible, but it would render the aircraft nearly useless, not just economically uncompetitive. A 70kg chunk of nickel alloy is very dense, and at 800m/s , that’s 20 MJ. Thats about the same as 5kg of TNT, but focused on a small area. For comparison, a modern 120mm artillery shell fired from a tank or similar field artillery has 10-20 MJ of kinetic energy. A couple thousand kg of armour could likely contain that kind of energy, but it would also translate that energy to the engine mounts, wing, spar, and fuselage if it was not going to become a projectile itself. You could easily stop a fragment and critically damage a spar attachment, rupture a wing fuel tank, or end up with translational shock damage to any number of critical systems and structures. You’d probably have to double or triple your engineering margins of the entire aircraft, probably doubling the weight of the airframe. So yeah, possible probably. But not on an aircraft designed to carry passengers or freight. It would be the biggest 6 seat aircraft ever built lol. Interestingly, if you work backwards from that cargo capacity, you can arrive at a much smaller aircraft that could possibly feature full containment, because engine diameter and energy goes way down and containment starts to look much more practical. I would not be surprised if containment could be achieved in the small biz jet scale, with just significant sacrifices in cargo or range. OTOH even the A10 warthog does not have full disk containment, and it’s probably the strongest candidate ever fielded for such a project… so, ymmv.
      - bell-cot 13d ago
        > A 70kg chunk of nickel alloy is very dense, and at 800m/s , that’s 20 MJ. > For comparison, a modern 120mm artillery shell fired from a tank or similar ... Yes. But when the goal is kinetic penetration of modern armour, they don't use artillery shells. Instead - https://en.wikipedia.org/wiki/Armour-piercing_fin-stabilized_discarding_sabot https://en.wikipedia.org/wiki/Armour-piercing_fin-stabilized... - which bear no resemblance to a failed turbine disk. And have about twice the muzzle velocity, which makes huge difference in penetrating a modern armour systems. Ditto their far greater density, vs. nickel alloy. OTOH, your "A couple thousand kg of armour could likely contain..." seems too charitable. High-bypass jet engines are big. Beyond that, I'm more optimistic about mitigating shocks and such. A critical parameter here - https://en.wikipedia.org/wiki/A380#A380F https://en.wikipedia.org/wiki/A380#A380F The freight variant was to have a 6,400 mile range carrying 150t of payload. So we could squander 25t per engine on disk containment and shock mitigation, and still have a 50t payload. Or a 3-digit passenger headcount. Bottom line, there is no real-world difference between your "nearly useless" and my "disastrously uneconomical". Neither one will be designed, let alone built. For the A10, I'd say military priorities would always block full disk containment - because every pound used for that is a pound they don't have for more weapons or munitions or range or armour or fuel or runway length or electronics or whatever. And over most of the 360 which disk fragments could exit a warhog's engines, there's nothing critical which they could hit.
cucumber3732842 14d ago
I know we all like to hand wring about stuff like this but realistically it's "infinite" to prevent the same genius textbook engineers who cooked up the VMC procedure and the CMM procedure from cooking up equally half baked "with a plate of this thickness at this angle it will remove X energy from anything that penetrates it therefore we are good to put some super critical thing right in it's path" solution.
wolvoleo 13d ago
Maybe not stop it, but perhaps they can design it so that if it happens it's more likely to be directed away from the fuselage? Like with armor that does not block or absorb but deflect, which requires less energy. Perhaps even a small reactive armor strip? (dangerous as though that would be on a plane). But then again I'm sure aviation engineers would have thought of this and rejected it for good reason.