DIY Lifter – An Electrohydrodynamic Thruster (EHDT)
The diagram below shows a EHDT in its most basic form. It consists of a fine wire, suspended above a sheet of Aluminium 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 dielectric (insulating) fluid around the device, as described below.
WARNING: This project requires the use of dangerous high voltage electricity!
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.
EHDT Construction Details
Gently fold over the top a long edge so you are left with a long rounded edge, and a long sharp edge opposite. The rounded edge will be closest to the corona wire.
Fold the strip into three equal sections, plus a little extra for sticking the ends together.
Using a small amount of glue, attach three lightweight balsa wood supports, and stick the two short edges of the foil together to form a triangle.
Loop a thin wire around the supports so that it is a few centimeters from the foil, and leave a long wire for connection to the power supply.
Connect another long wire to the foil, in a position away from the other trailing wire.
Flying the Lifter
The voltage required to power the lifter will depend upon its size but it is usually above 10kV. By moving the top corona wire closer to the foil, more thrust can be produced. If it is too close arcs will jump between the electrodes, causing it not to fly.
Place the thruster on an insulating surface (a table), and away from any metal objects.
Attach the two wires to the table so that the thruster can hover, whilst being held down by the wires.
Making a HV DC power supply for the lifter
The picture on the left is of the inside of the plasma globe, and you can make the output of this DC by connecting it to a HV diode.
For larger lifters, a simple adjustable supply can be made by driving an high voltage coil with a power pulse modulator and then rectifying the output with a high voltage diode and capacitor as shown here. The diode D1 should be rated for high voltage such as 20kV, 100mA as to withstand current pulses from accidental shorts. The capacitor C1 should also be rated for 20kV. The capacitor is not essential but it can help improve performance and add some protection for the diode. The capacitance can be any value, but bigger is better.
The pulse modulator allows you to vary the output voltage very easily so that you can get more control over the performance of the lifter.