What is the "DesignFactor" you compute for smallDiameter=0.17 m, bigDiameter=0.28 m and length=0.345 mFor DesignFactor = 0.844 and bigDiameter=0.28 m and length=0.345 mI get smallDiameter = 0.1289 m which is much larger than the values you showed, and not so far off from 0.17 m

I like the value you calculate for the small diameter. But can that length be right? I suppose so. Using that length, big diameter and the taper from the photo I calculate small diameter about 0.1 meter. Close enough considering the uncertainty in just exactly where Shawyer is measuring when he tells us the diameter of the thruster and we don't know the wall thickness either. The equations are all related to the internal dimensions while photos show external dimensions and it's all based on assuming we know what Shawyer measured to get the published number.Oh. Would you post your design factor equation in it's normal form? I'd like to put it into my spreadsheet to see what the curve looks like and to confirm your number.

I mean in the form Design factor = expression.

#define Nrec 6t_data data_in[Nrec] ={ // w_big w_small lambda Q power force {"Shawyer (2008) a", 1.0 , 16 , 8 , C/2.45 , 5900 , 850 , 16 }, {"Shawyer (2008) b", 1.0 , 28 , 4 , C/2.45 , 45000 , 1000 , 214 }, {"Juan (2012) TE011", 1.0 , 28 , 4 , C/2.5 , 32000 , 1000 , 214 }, {"Juan (2012) TE012", 1.0 , 28 , 4 , C/2.45 , 50000 , 1000 , 315 }, {"Brady et al. (2014) a", 1.0 , 24.75 , 16.5 , C/1.933 , 7320 , 16.9 , 0.0912 }, {"Brady et al. (2014) c", 1.0 , 24.75 , 16.5 , C/1.88 , 22000 , 2.6 , 0.0554 },};

.....I'm trying to build a case for Brady a with thermal air jet : do we agree on inner volume approx. that of a truncated cone length 0.33 big diameter .4 small diameter .24 (I'm not into a few %) that is approximately 27 litres (27000 cm^3), equivalent to a cube of 30cm side ?

I will do what you ask (unless somebody else wants to do it), but I think that it would be better to wait until we settle on dimensions, there are still issues to be discussed with John (both beams) and aero.

Ok - What dimensions are we currently questioning?

Quote from: aero on 10/24/2014 10:11 pmOk - What dimensions are we currently questioning?All of them. Take a look at my table above. The predictions are closest for the Shayer demo when using the AutoCad drawing from JohnFornaro.They are off by more than a factor of 2 if we estimate the Shawyer demo small diameter based on the other Fornaro dimensions and the 0.844 designFactor.John Fornaro based his dimensioning for the NASA Eagleworks on the back beam cross section, and not the front one, so the NASA Eagleworks dimensions should be reviewed.

...I hope your records are better than mine because I don't have lengths recorded, (or the other dimensions, for that matter.)

I use the microwave at home and I have never noticed the air getting warm inside it, unlike the air inside my oven. That's why to get a crust on a pie, I use the oven.

The quality factor of an empty microwave oven (30 × 30 × 20 cm^3), with penetration depth of the walls δ≈1μm, is of the order of 10^4, while when we put a glass of water inside the chamber the quality factor is of the order of 10^2. If we put more water in the chamber, the quality factor would be lower and the absorption would be greater.

.../...So, the air inside the EM Drive would have to get heated by convection heat transfer, and the same considerations as in the message http://forum.nasaspaceflight.com/index.php?topic=29276.msg1275630#msg1275630 hold: the copper temperature increases only 1 deg F, and the air needs to get heated by convection from this tiny temperature differential.

The different consideration, is that rather than relying on natural convection circulation, considering the gas law P V=n R T, and since the volume inside the cavity stays the same, as the temperature of the air increases, the pressure increases, and this may produce an air jet at the gap between the bases and the cone. This would have the advantage of explaining the force always being directed axially regarding of orientation of the EM Drive.

However:1) it still would not explain the impulsive response in 2 seconds (at NASA Eagleworks) since heating of air inside the cavity due to convection heat transfer is much slower than that

and2) the temperature rise of only 1 deg F is so tiny, that, without doing any calculation my intuition would be that this would produce a very small change in pressure and probably not enough to have the EM Drive act as a jet. On the other hand, the forces measured at NASA Eagleworks are also extremely small (50 microNewtons)

However, although molecules with mirror symmetry like oxygen, and nitrogen have no permanent dipole moments, it is possible to induce a dipole moment by the application of a strong external electric field. This is called polarization and the magnitude of the dipole moment induced is a measure of the polarizability of the molecular species. One would have to calculate whether the Electric Fields could be strong enough to produce polarization of the air molecules inside the cavity to the extent that the microwave can heat the air molecules so that a pressure would be generated enough to produce a jet with the measured microNewton forces. Also whether the air inside the cavity could be humid enough to contain enough water molecules for microwave heating to produce this effect.

Just for giggles I calculated the sensitivity (numerically) of Force to the dimensional parameters. I used Prof. M's new equation on Shawyer a" to calculate force. I used delta X = 2%. dF/dX dF/dXfor X mN/meter mN/cm =s 47.523 0.475 =w-big 101.979 1.020 =w-small 215.756 2.158 No real surprise but in general centimeter sized errors in dimensions are noticeable.