Pushing on solid wall is more effective than pushing on air. Shockwaves are effectively momentarily solid air that you could push on. RDE basically uses shockwa

Pushing on solid wall is more effective than pushing on air. Shockwaves are effectively momentarily solid air that you could push on. RDE basically uses shockwaves as turbine blades. (technically I should say "incompressible vs compressible" but you get the imagery)