I wrote the other day: > BTW2 the derivation is elegant but admittedly it could be a little more > rigorous wrt distinguishing between scalars and vectors.
For more clarity in this respect, I enclose an annotated version of Sigmond's derivation for the lifter thrust (or rather it's opposite namely the force exerted by the ions on the air), where I have added arrow signs to the vector variables plus a few words of explanations. I hope it helps. Corrections welcome. Michel P.S. For those not familiar with the ion mobility concept, the fine zig zag trajectory due to the multiple collisions of an ion ploughing through the medium's neutrals under the effect of an electric field distribution is commonly modeled by a smooth path along the local electric field line (which, as may not be obvious, can have any odd shape in Sigmond's derivation including a forwards and then backwards path as is the case for ions emitted from the front part of the wire), with ion velocity vi equal to the "ion mobility" ยต (ion and medium specific statistical parameter) times the local electric field modulus E (which is not assumed to be constant along the path in the derivation, which is a good thing since it isn't!). ----- Original Message ----- From: "Michel Jullian" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, February 16, 2007 9:38 PM Subject: Re: [Vo]: Lifters ... > BTW2 the derivation is elegant but admittedly it could be a little more > rigorous wrt distinguishing between scalars and vectors. ... >> 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
IonWindThrustDerivationAnnotated.gif
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