The tl;dr for this is that Woodward proposed (based, AFAICT, on actual science) that rapid internal energy changes cause transient mass fluctuations. His device used a capacitor on a piezoelectric effector so that the effector would only push while the capacitor was charging or discharging, and only pull while the capacitor was _not_ charging or discharging, so producing an assymetric effect and, therefore, thrust.
There have been a number of attempts to verify this experimentally, all of which have been inconclusive; turns out the measuring very small forces when your test equipment is vibrating is very, very hard (see the Dean Drive).
My feeble understanding is that the underlying theory is at least plausible; it doesn't seem to violate anything we know about the universe. The last report I've seen of work on this is this (rather good) BoingBoing article from 2014:
One of the things that keeps me intrigued about this is that this is not the first time someone has claimed anomalous thrust from an asymmetrical EM device of some kind.
It could be measurement error combined with a little wishful thinking, or it could be that there's some undiscovered physics there and we're tip-toeing around the edge of the parameter space where it manifests. If that's the case, all these "X effect" systems could be working according to the same principle.
There are other cases in science (e.g. early transistor efforts and superconductors) where tinkerers and engineers hit on effects that were not understood and were ignored for a long time until we had some kind of theory that explained them and much more importantly told us how we might optimize for the effect.
The McCullough prediction that a dielectric should increase the effect seems easy to test.
There seems to be something that catches the imagination, but I suspect it's closer to that whole class of perpetual motion machines which consist of moveable weights on a wheel, than to a revolution in physics.
There's lots of unbalancing wheels, and none of them work.
https://en.wikipedia.org/wiki/Woodward_effect
The tl;dr for this is that Woodward proposed (based, AFAICT, on actual science) that rapid internal energy changes cause transient mass fluctuations. His device used a capacitor on a piezoelectric effector so that the effector would only push while the capacitor was charging or discharging, and only pull while the capacitor was _not_ charging or discharging, so producing an assymetric effect and, therefore, thrust.
There have been a number of attempts to verify this experimentally, all of which have been inconclusive; turns out the measuring very small forces when your test equipment is vibrating is very, very hard (see the Dean Drive).
My feeble understanding is that the underlying theory is at least plausible; it doesn't seem to violate anything we know about the universe. The last report I've seen of work on this is this (rather good) BoingBoing article from 2014:
http://boingboing.net/2014/11/24/the-quest-for-a-reactionles...