# Could we use flowing air as a capacitor dielectric?

1. Apr 1, 2006

### RGClark

I wanted to use air as the dielectric for a capacitor for energy storage for aircraft. My thinking was that we could charge the capacitor on the ground and leave the capicitor open to the flowing air in flight. As long as the density of the flowing air remained the same, the capacitance would stay the same.
Capacitors usually don't offer significant advantages over chemical batteries per weight because you have to consider the weight of the dielectric that must be carried along. This is true even when the dielectric is air that is enclosed and must be carried along. But I thought an open air dielectric wouldn't have this problem as you're just using the surrounding air as the dielectric.
The question is would the flowing air cause the capacitor to discharge?
Would the leakage be unacceptably high in this case?

- Bob Clark

2. Apr 1, 2006

### pallidin

There are open-air capacitors. Old-style radios used a set of aluminum(I think) plates that would variably mesh in between a set of non-moving plates, with ambient air as the dielectric.
At the time, I think they were called "variable capacitors" and are probably still available today.

But, I don't think that "flowing air" would work well, if at all, because the flowing air would not retain a dielectric constant necessary for a capacitor to work properly But that's just my quess.

3. Apr 1, 2006

### chroot

Staff Emeritus
It'd be an incredibly tiny (read: insignificant) energy source.

- Warren

4. Apr 2, 2006

### RGClark

Yeah, you're right. I did a rough calculation that led me to believe I could store significant energy in an air capacitor if the plates and distance between them were at the ten's of meters scale.
Unfortunately I left out the factor 8.85 x 10 ^-12 out of the calculation for capacitance. So my calculation was nearly 10^11 too big!

- Bob Clark