Hypersonic drag reduction with forward energy deposition.

originally posted by: mbkennel
I remember the infamous Astr0 saying something about secret craft that 'make a vacuum' in front of them and are sucked along. Plus some noise about 'ultrasonics', which I think may be intentional misinformation---that is what an insider would need to do, salt truth with invention). It really didn't make sense to me physically in its original form, but now something is coming together.

From what I can tell, the drag reduction technology you cite is very real and probably very effective. I was never quite able to reconcile using it as a mode of propulsion, though.

An aircraft creating a vacuum to be sucked into sounds too much like the inverse of a sailboat pushing its own sails with an electric fan... I'm not 100% sure on that point yet through. Maybe you can get around it by pushing the air upwards and downwards, mitigating any back-reaction against the desired direction of travel. Still, it seems like an awful lot of energy / work input to generate 1 atm * surface area worth of thrust.

From what I can tell, creating a vacuum with ultrasonic waves also seems impossible. Air pressure waves do induce zones of rarefaction, but the time-averaged behavior simply can't be that of a vacuum, as these waves are waves in a medium. Cavitation sounds attractive but it's a phenomenon of liquids, not of gases.

If there's no way to create a vaccuum with ultrasonics, then there isn't a simple generational evolution in the technology from sound emitters -> lasers and beyond, as was also claimed. Pushing the start of the breakaway tech back in time makes a breakaway civ more plausible, but in this case we're talking about things that simply shouldn't be possible, even in an incremental sense, with older tech.



Now with all that said, one doesn't need to create a vacuum in order to generate thrust, but only a pressure gradient. I still have a hard time understanding why this would be a more attractive prospect than conventional thrust, but it would explain both the geometry and size of the observed triangle craft. More surface area yields more thrust, and the (e.g.) Illinois 2000 sighting craft has flat perpendicular surfaces to push off of.