Michel Jullian wrote: > > ----- Original Message ----- > From: "Harry Veeder" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Tuesday, February 20, 2007 7:34 AM > Subject: Re: [Vo]: Re: Lifter aerodynamics > > >> >> Yes I mean drag, but there may be other aerodynamic forces to consider. >> Also I don't think the profile is aerodynamic because the boundary is not >> crisp like a fuselage. >> >> Does gf mean g-force? If so that a percentage of the acceleration due to >> gravity or a force as in force = ma ? > > Yes, gram force, that's about 1 cN. Yes, thrust is a force. > >> The fact that a certain current coincided with lift off does not necessarily >> provide a comprehensive explanation of what makes it go. For example, the >> current drawn by spark plug does not account for the motion of the blade >> on a lawn mower. > > Ah but the ion wind force formula is not some empirical formula as you seem to > suggest -I posted Sigmond's derivation-, and it accounts for the measured lift > (=the weight since aerodynamic drag is negligible: you can see on the Excel > screenshot on the Blazelabs page that the wind speed is less than 1m/s = > 3.6km/h) within measurement errors.
I do not think it is an empirical formula. However, unless the acceleration is measured you do not really know if the formula provides an adequate account of the _acceleration_ of the lifter. > That's enough proof for me, but YMMV. On the frontiers of knowledge, unlike the urbane application of existing knowledge, the right to be wrong is as important as the desire to be right. > >> Anyway, if an accelerometer were mounted on a lifter the actual dynamic >> forces involved could be estimated more accurately. > > You can also measure acceleration on the video (if you can find a way to view > it ;-). And since the mass is known you will find the force via f=ma, a good > exercise indeed. > > Michel The method would be inaccurate unless it was recorded with a high speed video camera. harry
