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# I've got some questions about ionizing air and ion thrusters? Answered

I'm hoping to build an electrohydrodynamic (EHD) thruster ( see here http://blazelabs.com/l-intro.asp#peek )in the near future. Not a lifter like most, but just a thruster designed to create thrust as efficiently as possible. One of the big problems with these devices is obviously energy wasted ionizing air. The thrust of an EHD thruster is T = ID/K where I = current D = distance between anode and cathode and K = the potential needed to ionize the fluid (in this case air). Therefore, increasing the distance will increase efficiency but will decrease absolute thrust. What needs to be done is to separate ionization and acceleration.

The ionization needs to be independent of the ground and I'm not sure how to do this. I need to be able to create a constant cloud of positive ions. It seems though that not having the cathode nearby will require a much higher voltage therefore decreasing efficiency. One Idea I've had so far is to have the positive ionizer, then have a negative grid a few centimeters away and a positive grid a couple millimeters after that one. Hopefully inertia would cause most of the ions to flow through both grids without discharging, and be further propelled. Then several centimeters after that would an electromagnet that accelerates the ions. Any input on whether this will work or better ways to do this?

Finally, I don't fully understand how an ion discharges. If it is energized, the energy has to go somewhere right? So say you have your positive ionizer and a negative sheet right in front of it, when the ions hit the sheet what happens to the energy? Does it get recycled or turned into heat? I'm hoping to figure out some way to recycle the energy from the ions (minus inefficiencies), but I don't have a good enough grasp on this yet. So any ideas about this are greatly appreciated.

I would be very happy if I got this up to 10g of thrust per watt, so input/ideas are appreciated, cheers!

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## 8 Replies

Kiteman (author)2012-02-03

You cannot cut down the energy "wasted" ionising the air, since it is the ionised air that provides the thrust.

The greater the ionisation, the greater the thrust.

The ions are what complete the circuit between the high-tension sections, carrying the current across the air-gap like electrons carry it through metal.

As far as I am aware, nobody has been able to generate enough thrust for the lifter to carry more than its own mass into the air, never mind the power source. Ion drives are only useful in free-fall (ie in space), at which time their ability to generate the thrust for long periods of time makes them very useful.

sk8aseth (author)2012-02-04

I should have explained how I was planning to design it. Rather than shooting ions out of the thruster, the ions should accelerate neutral air molecules which are shot out the back. The ions should then hit the collector. What I don't understand is what happens to the energy from the ions when the hit the collector, and if it's possible to recycle that energy.

Kiteman (author)2012-02-05

How are you going to make electrically-charged ions accelerate electrically-neutral molecules?

sk8aseth (author)2012-02-05

If you look on the site I posted, you can see it in the theory of operation. As the ions are being pulled towards the collector, the run into neutral air molecules and cause them to accelerate.

iceng (author)2012-02-03
Here is a pointer to a \$100 ion gun.
1. The first pic a theoretical physicists ion device.
2. The second pic a real working thermionic gen ion gun ( TV ).
3. A hardware cloth ring with spikes as emitters sputtering to activate Oxygen = O2 into Ozone = O3 and other ions that I make.
The ions are made with an AC source of high voltage, later you add a
pulsed set of high DC voltage metal rings to accelerate particles where
you want a reaction force to push your mass.

sk8aseth (author)2012-02-04

Thank you that helps clarify things. One question though is does it matter whether an AC or DC source of HV is used if I only want to make positively charged ions?

iceng (author)2012-02-04

You generate a positive ion of oxygen (air) by stripping off a single electron
making the remainder of the atom a net positive atom.  In nature this
is accomplished by DC (lightning).

The negative electrons can be quickly pulled away by a positive charge
because of tiny mass.

There are lots of references on plasma forth state of matter on the web.
Welding plasma can be AC aluminum or DC iron maintained after an
HF high volt arc initiation.

steveastrouk (author)2012-02-03

Adding to what Kiteman says, your term "k" is not voltage, it is a constant, and its not a very small one either, so the thrust is, as the math shows, very very small.