Electrohydrodynamic Thrusters (aka Lifters)
Courtesy of Blaze Labs Research
EHD stands for Electro Hydro Dynamics which is the study of the flow of a fluid under the effect of an electric field. The principle of ionic air propulsion with corona generated charged particles has been known as from the earliest days of the discovery of electricity. One of the first reference to sensing moving air near a charged tube appeared in year 1709 in a book titled 'Physico-Mechanical Experiments on Various Subjects' by F.Hauksbee. Many other pioneers of electricity, including Newton, Faraday, and Maxwell, studied this phenomenon. Unfortunately, EHD is not a common topic in most high school syllabus, which is the main reason why most of the general public get confused when seeing such devices in action.
An EHD thruster is an electrohydrodynamic device which ionises air and moves the charged ion cloud in a way and direction to transfer momentum to neutral air molecules. By Newton's third law of motion, action is equal and opposite to reaction, and the EHD thruster will move in the opposite direction of the ion cloud. Ionocrafts was the name given to the first kind of vertical takeoff EHD thrusters designed during the early 60's, and form part of the EHD thrusters family. Recently, this effect has gained popularity under the less appropriately titled 'lifter' which due to the lack of knowledge of EHD by most people, has been related to some sort of antigravity effect. It is a well known fact that these devices produce thrust along their own axis, and not against the force of gravity as would be expected from an antigravity device. An EHD thruster in its simplest form is made up of two electrodes, one with a sharp edge, the ioniser and one with a smooth edge, the collector, which when powered by a high dc voltage (a few kV ) produces thrust against the surrounding medium, normally air.
For construction details, see the DIY Devices section.
The diagram below shows a EHDT in its most basic form. It consists of a fine wire, suspended above a sheet of aliminium foil, by a lightweight insulating support such as balsa wood. If a high voltage DC source is connected as shown, a thrust will be produced, propelling the device in the direction of the positive wire. This thrust is due the motion of air, or any other dieletric (insulating) fluid around the device, as described below.
The top sharp electrode ionises the air. If the electrode is positive, free electrons in the vicinity will accelerate towards it, and strip off other electrons from the air molecules around the sharp wire.
A cloud of heavy positive charges is thus formed, and the avalanche of electrons approaching the sharp electrode account for the corona & ionisation current. In their mad rush from the ion emitter to the smooth negative electrode, the positive ions bump into neutral air molecules-air particles without electric charge. The force exerted on them by the electric field is offset by the force of friction caused by collisions of the ions with the neutral air molecules. As a result, ions drift through the air gap with an approximately constant velocity Vd, that is proportional to the electric field given by Vd=kE, where the proportionality constant K is called the ion mobility, the highest the value the more mobile (faster) and the less friction is offered.
The terrific wallop in these collisions hurls a mass of neutral air downward along with the ions. The distance in cm travelled by an ionised air molecule until it hits a neutral air molecule is given by the mean free path and is equal to 5E-3/P, where P=760 Torr at sea level. The larger the air gap relative to the mean free path, which works out to be equal to 6.6E-6cm, the more probability there is of an ion repeatedly hitting neutral molecules, and therefore the more impacts and thus effective thrust we get. During these collisions, the ion charge is not transferred to the neutrals. When they reach the lower smooth electrode, the ions, still being positive, hit it and neutralise themselves. But the grid has no attraction for the neutral air particles that got bumped along. So the air flows right along the sides of the lower electrode, making a downdraft of neutral air beneath the EHD device. The fact that most ions are neutralised at the collector explains why the reading we get from ion measuring meters setup below such devices does not account for the measured thrust. In fact for a good EHD thruster, such a reading should be close to zero. If however, one accurately measures the force exerted by the air exiting the collector side over a flat surface, it is found that this force is equal and opposite to the thrust of the device.
An EHD thruster works without moving parts, flies silently, uses only electrical energy and when immersed in a fluid (air, oil, etc..) is able to lift its own weight together with additional payload. The basic design of the simple lifter has been fully described in the TT Brown US Patent N°2949550 filed in 1957 and titled "Elektrokinetic Apparatus". Even though T.T.Brown was fully aware that the thrust from his devices was due to ion interactions, lack of EHD knowledge at that time, resulted in very low efficiency operation of these first EHD thrusters. Shown below is one of Brown & Bahnson's designs described in US Patent #3,223,038, and an ultra simple EHDT made from aliminium foil, balsa wood and a fine copper wire.
While extensive research was performed in the 1950's and 1960's on the use of electric propulsion for interplanetary spaceflight, many promising concepts had to be abandoned due to the technological limitations of the power conditioning systems in use at the time. It is also understood that the research & development of ionic thrusters by NASA at those days was aimed mainly for interplanetary space flights, and the fact that ionocrafts need a fluid medium to work has led these fantastic devices to be largely abandoned by the scientific community since the late 1960's.
To date no consistent effort has been made to reevaluate these approaches in light of modern power processing technologies and develop flying machines to operate within the atmosphere. During the 1960's a lot of work on EHD technology had been accomplished by Major De Seversky (pictured below). De Seversky noticed an air flow developing between the two electrodes of an air ioniser commonly used to clean air. "To an old flyer like me," said the major, "anything that stirs up a wind is a flying machine. So I began to develop the idea." In fact a few years later, he patented The Ionocraft patent no:US3130945 in April 28, 1964. The major seemed concerned that the Ionocraft might be mistaken for a kind of space vehicle. "This is not a spacecraft," he explained emphatically to forestall any possible misunderstanding. "It's an airplane, designed to operate within the atmosphere. But it will be able to do things that no present type of aircraft can accomplish." Indeed, this misunderstanding still prevails in the present days, but Blaze Labs research clearly shows that EHD thrusters & lifters do not work in vacuum.
End of Blaze Labs Article
Note that the Bifield Brown Effect is an effect aparently produced by capacitors or electrodes that are asymmetrical (of different sizes). This is what causes the mojority of confusion around the "Lifter" devices. You can see from the images that one electrode is sigificantly larger then the other. Most Lifters or EHD thrusters are powered with voltages below 30kV. It is said that the Bifield Brown effect would become more apparent at more extreme voltages such as above the 50kV mark. The vacuum tests performed by Blaze Labs were performed with a Lifter powered at 30kV. NASA have also perfomed vacuum tests on a rotational lifter setup powered at 50kV. These tests are not 100% conclusive but it seems unlikley that a device based on the design of a Lifter will have any significant implications for propulsion technology.
For construction details, see the DIY Devices section.