But the air propelled downwards by the ion has a mass (hidden in the ion mobility parameter), that's what's matters, just like the mass of a helicopter's propeller is irrelevant. If one can speak of thrust for a helicopter, one can speak of thrust for a lifter.
BTW the momentum of the discharged+ejected ions is negligible compared to that of the neutrals they drag along, because their concentration is very small. BTW2 the derivation is elegant but admittedly it could be a little more rigorous wrt distinguishing between scalars and vectors. Michel ----- Original Message ----- From: "Harry Veeder" <[EMAIL PROTECTED]> To: <vortex-l@eskimo.com> Sent: Friday, February 16, 2007 8:14 PM Subject: Re: [Vo]: Lifters > > At the beginning of the derivation it says "ion mass is irrelevant here (no > inertia effects)". > If it is irrelevant than the derived force does not really correspond to a > thrust. > > Harry > > > Michel Jullian wrote: > >>> ...the thrust formula >>> I*d/mu where ion mobility mu... > >> Also, for you Michel, why does the ion mobility equation necessarily >> interpret as being ion wind? > ... >> Dave > > Because ion [induced] wind yields exactly the above thrust formula if you do > the maths, here is an elegant derivation by R.S. Sigmond (if the 16 kB gif > image makes it to the list) > > Michel > > > > >
