Helical engine is based on theorem of relativity that massive particles cannot be accelerated to speed of light, as it would increase their relativist mass. This mechanism is clearly inefficient and on par with effectiveness of photon rocket. But there are indicia, that speed of light limit is valid only for uncharged particles and these charged ones have this limit much lower. Under such a situation the above principle could work way better with charged particles, than the relativity theory implies.
In addition, inside superconductors and topological insulators like graphene the motion of electrons is limited to a narrow planes or stripes, which gives them very high speed, so that this limit can be further decreased and even mechanical motion could induce interaction of electrons with vacuum (Podkletnov-Poher experiments). In my opinion, the motion of electrons can be constrained by even simpler way by their attaching to surface of electrodes within capacitor (1). The high dielectric constant of ceramic capacitors would lower speed of electromagnetic wave propagation even more, therefore electrons would interact with vacuum even under much lower speed - this is IMO principle on which Woodward drive can work. On youtube we can find intriguing experiments with rotating charged capacitors or induction coils loaded with high voltage, which move even being enclosed with cover, so that ionic wind effects cannot apply there.
Therefore the principle of helical engine can be actually quite feasible once we realize, that the speed limit for light propagation can be greatly lowered in various dielectric and that instead of modulation of speed of charge carriers we can modulate their dielectric constant or relative permeability or both.
What do your posts have to do with this thread which is about Pais?