Lifters in vacuum & why they DO NOT work

Engineer Xavier Borg - Blaze Labs Research

Lifters, ionocrafts or any form of EHD thruster, may look mysterious at first glance due to the lack of moving parts. To make things worse and promote confusion, these interesting devices have also found their place on antigravity/free energy websites and have also been sold, at some science suppliers, as antigravity devices. The lift mechanism may be easily accounted for with simple conventional physics laws, which once understood, can be used to design and predict the behaviour of these devices. Those interested in mathematical detail for deriving the thrust and other parameters of an EHD thruster, may find my paper Full analysis & design solutions for saturated corona current condition very helpful.

One has to understand that the lift mechanism is provided by the well known Coulomb's law of electrostatics acting on ions, and by the law of conservation of momentum, by which it transfers momentum to neutral air molecules. EHD thrusters can be designed in various shapes & sizes but in general they all have an ion emitter in the form of a fine wire, fixed over the collector, usually in the form of either an aluminium plate of foil with smooth round edge at the top or a mesh. The positive terminal is connected to the wire and the negative to the collector, although reversing the polarity still gives the same thrust direction, but somewhat lower force. Charged air molecules and neutral air molecules can in general be assumed to have the same mass.

The high electric field intensity around the fine wire ionises the air molecules, which are in turn repelled from the same wire and attracted towards the bottom, negatively charged electrode. The forces involved are given by Coulomb's Law. As each positive ion is attracted toward the collector foil, it in turn attracts the collector toward it, pulling the lifter up. At the same time, its repulsion from the top wire also pushes the lifter upward. By Newton's laws, the momentum that the lifter gains in the upward direction is equal to the net downward momentum of all the ions (conservation of momentum). This is basically what happens if we do not consider any reaction forces with neutral molecules. Now if this were all that happened, when the ions collide with the lifter at the bottom electrode, (as they all probably do), the momentums would cancel (add up to zero) and the lifter would not move. Here is where the neutral air molecules come into play. As the ions travel "downward" toward the bottom electrode, they collide with neutral air molecules, transferring some of their downward momentum to the neutral air, driving them generally downward.

By conservation of momentum, the total momentum of the projected ion and the target neutral air molecule before collision would be the same after collision, but after the collision, the ion would have less downward momentum. The ion has now transferred some downward momentum to a neutral air molecule. After many similar collisions, the ion having speeded up and crashed many times over its path to the collector, eventually hits the collector foil, transferring any remaining or re-acquired downward momentum against the upward momentum of the lifter. But the amount of downward momentum it transfers is far less than the total amount of upward momentum it provided the lifter during its travel downward. Most of that momentum has now been transmitted to the neutral air molecules. The neutral air, since it is not attracted to the lifter by electrostatic attraction, will just blow by the sides of the lifter and can be detected as a neutral wind below it. Most of these neutral molecules do not impact the collector and hence their net thrust is not cancelled. If we add up all the downward momentum components in the vertical direction of the neutral air and the ions in flight, it will equal the "upward" momentum of the lifter. The lifter can fly in the air, because the neutral air can take away some of the downward momentum, leaving the lifter/ion combination with a net upward momentum. It has all to do with momentum transfer between ions and neutral air molecules and their flow profile, laminar or vortex flows being most efficient.

As shown in the diagram above, the fluid about the centre axis will reach a velocity much higher than the rest of the fluid. If we where using a perfect fluid with no viscosity only a very thin jet will be formed and propagate in the direction of the collector. Because of the existence of viscosity, the flow will slow down somehow in the direction of the collector and simultaneously will became a bit larger, with the surrounding parts of the flow being progressively carried by it.

If we start to increase the size of the bottom electrodes (or more generally the cross-sectional area of the lifter "presented" to the direction of flight), whether it is electrically part of the collector or not, more and more of the neutral air molecules will hit the lifter structure. If enough "neutral" air is hitting and transferring momentum back onto the collector, the lifter will be unable to fly. The Horizontal plane lifter shown above proves this point with its zero thrust.

If we start to reduce the air pressure, i.e. taking away some of the neutral air, the ions (which arestill being created to a lesser extent), can transfer less and less momentum to the neutral air. There are less and less air molecules to hit. Instead, they carry more and more momentum all the way to the lifter collector, in a narrow vertical path, and transfer it when they hit the upper edge of the foil. At some reduced pressure (nowhere near a vacuum) not enough momentum gets transferred to the neutral air, it is all getting transferred back to the lifter, and the lifter will fall. The ions now are hitting it with enough momentum to cancel any upward momentum and gravity will pull the lifter down. The vacuum experiments that have been done confirm this.

At the time of writing, lifters do not seem to violate any known "conventional" science. The main mechanism is just a transfer of momentum to the neutral air, and if we do not have enough neutral air the lifter simply cannot fly.

The amount of force that can actually be generated by this process depends on the accelerating voltage gradient, which accelerates the positive ions between each impact, and the volume of neutral molecules, which get a momentum exchange in the downward vertical direction. It is also understood that the volume of neutral molecules effected will depend upon both EHD thruster's size and shape as well as on the actual flow profile of the neutral molecules. The main parameters involved are electrode shape and size, and voltage, and parameters defining the neutral air molecules. Once you work out the correct values, the EHD thruster may become autonomous, with both payload and power supply on-board.

Lifters in hard vacuum

Curve showing air dielectric strength vs air pressure.

At a glance, this curve explains why lifters do not work in the pressure region shown as glow discharge area, since the airgap virtually represents a short circuit. It also explains the fact why lifters work better at sea levels (760 Torr) than at very high altitude levels. Atmospheric pressure is much lower at high altitudes.

Referring to the curve shown above:

The green point is at 760 Torr (STP), tested as the normal atmospheric pressure at which EHD thrusters lift.
The 3 purple points give a lot of air ionisation with much reduced thrust.
The blue band, shows the glow discharge region, where ionisation and spark-overs are the main results, with zero thrust.

Below is a photo of the lifter operating at 4E-2 Torr, just under the glow discharge area, with lots of glow discharge and no thrust.

Pressures above the green point give better lift and less chance of ionisation. The big question, which will totally disprove any other theory (especially antigravity), is whether or not the EHD thruster works at much lower pressures, where the air dielectric strength recovers again to its STP (760 Torr) value, which is approximately from 6E-3 Torr down. For this purpose an experiment in high vacuum has been set up as shown below:

The following equipment is used in the setup shown above:

PFEIFFER oil pump type AMEB 80FY4R3N1, 0.55 kW /1400 rpm, combined (serial) with a
PFEIFFER type TPH 330, pumping speed 330 l/s
Cylindrical vacuum chamber, height 24 cm, diameter 24 cm
Pressure detectors: PIRANI-cold cathode gauge control, Balzers 1KR020, TRR010 and RKG020.

The lowest pressure that the system can achieve is of 6E-6 mbar.


Close up view of the cylindrical vacuum chamber used during the test

During this experiment, the lifter in the chamber was not flying but was set hanging down on a very weak spring. The position of the lifter could be easily observed from the exterior. As the pressure was diminished below 8 to 15 Torr, thrust was no longer observed. The pressure was then diminished further to go far below the glow discharge area into the hard vacuum region. Air was pumped out to a pressure of 3.75E-5 Torr, indicated by the big red dot on the dielectric strength plot shown above. At this pressure, the 30 kV potential across the lifter element can easily be handled and no arcing or glow discharge occurs. The result of this experiment was zero thrust, or at least no thrust that could change the position of our very weakly spring loaded lifter. This definitely confirms that the main lifters' thrust is of an ElectroHydroDynamic form, due to ion interaction with neutral air particles, and disproves once for all any antigravity theory.

I would like to thank Willy Oscar Guns for making this experiment possible, and for all other members at Blaze Labs Research group, in particular to Rolland Swank, for their contributions to this page.