4 ms·

I hope they have anti-sloshing-baffles in their design, because liquid hydrogen has low viscosity, and you really do not want it sloshing around without energy

by phkamp 4y ago

I hope they have anti-sloshing-baffles in their design, because liquid hydrogen has low viscosity, and you really do not want it sloshing around without energy dissipation, in particular not during take-of or landing.

netsharc 4y ago
I'm sure they don't need an Internet comment to tell them what they already know...
namibj 4y ago
Maybe a piston pressurized on the "empty" side with gaseous cryogenic hydrogen? The forces shouldn't be an issue, at least for cylindrical tanks where adding an atmosphere or 5 in internal overpressure capability (relative to outside) is quite cheap once you already have to stay in shape filled or not.
- dotancohen 4y ago
  How would you actuate that piston? Drill through the hydrogen tank to run hydraulic lines? That's a nice place for hydrogen leaks. Electric? In a hydrogen tank?
  - namibj 4y ago
    Gaseous hydrogen. The initial idea was for ensuring feed in case of negative G's, as some high-efficiency subsonic airfoils are unstable in the high-lift orientation, so recovery from malfunction/turbulence would start with flipping to negative G's followed by rolling over into inverted cruise. That would of course only be possible if the tank can be made to reliably feed independent of gravity, and the otherwise-typical bladder (AFAIK pressurized by gas/air between the bladder and the structural tank) doesn't work for LH2, due to cryogenic temperatures making all remotely normal materials very brittle. But a low-speed piston seal that only has notable pressure across it during active roll maneuvers (centripetal force from the roll-rotation) and uncoordinated turns, between LH2 and gaseous H2 with the latter slightly warmer than the former... it's not like you'd want the empty part of the cryogenic tank to be at non-cryogenic temperatures or filled with something that'd contaminate your LH2.
ZeroGravitas 4y ago
Existing jets have both anti-sloshing baffles and active pumps to redistribute the jet fuel between tanks: http://www.b737.org.uk/fuel.htm http://www.b737.org.uk/fuel.htm

by phkamp 4y ago

netsharc 4y ago

I'm sure they don't need an Internet comment to tell them what they already know...

namibj 4y ago

Maybe a piston pressurized on the "empty" side with gaseous cryogenic hydrogen? The forces shouldn't be an issue, at least for cylindrical tanks where adding an atmosphere or 5 in internal overpressure capability (relative to outside) is quite cheap once you already have to stay in shape filled or not.

dotancohen 4y ago
How would you actuate that piston? Drill through the hydrogen tank to run hydraulic lines? That's a nice place for hydrogen leaks. Electric? In a hydrogen tank?
- namibj 4y ago
  Gaseous hydrogen. The initial idea was for ensuring feed in case of negative G's, as some high-efficiency subsonic airfoils are unstable in the high-lift orientation, so recovery from malfunction/turbulence would start with flipping to negative G's followed by rolling over into inverted cruise. That would of course only be possible if the tank can be made to reliably feed independent of gravity, and the otherwise-typical bladder (AFAIK pressurized by gas/air between the bladder and the structural tank) doesn't work for LH2, due to cryogenic temperatures making all remotely normal materials very brittle. But a low-speed piston seal that only has notable pressure across it during active roll maneuvers (centripetal force from the roll-rotation) and uncoordinated turns, between LH2 and gaseous H2 with the latter slightly warmer than the former... it's not like you'd want the empty part of the cryogenic tank to be at non-cryogenic temperatures or filled with something that'd contaminate your LH2.

ZeroGravitas 4y ago

Existing jets have both anti-sloshing baffles and active pumps to redistribute the jet fuel between tanks: http://www.b737.org.uk/fuel.htm http://www.b737.org.uk/fuel.htm