Author Topic: EM Drive Developments Thread 1  (Read 763299 times)

Offline zen-in

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Re: EM Drive Developments
« Reply #2520 on: 10/24/2014 12:10 AM »
Don't want to forget that thrust has been measured in the same axial direction relative to the thruster whether the thruster was pointed up, down, left or right. This speaks strongly against outside thermal drafts.

It does not speak to thermal expansion of course.

My theory on thermally generated thrust claims the cone section transmits heat energy to the surrounding air by conduction.   The two ends do not have exposed Copper so the heat flow from each end would be much less.   FR4 (high density fiberglass as used in PCBs) is a better insulator than Copper.   The fact that March saw < 1 degree change in temperature would be expected because of the good heat transfer from the Copper cone section to the surrounding air.   There is no mention of the surrounding air temperature so I am assuming this < 1 degree change refers to just the Copper section of the device.   

...
You must have meant "transmits heat energy to the surrounding air by conduction convection" because heat transfer by convection in fluids like air occurs much faster than by conduction.  Air has very low thermal conductivity and very low thermal diffusivity, so heat does not get transferred in air by conduction, but by convection.
But at NASA Eagleworks the measured forces were in the horizontal direction.  Furthermore, the direction of the force was always oriented towards the large diameter base, even when they flipped the EM Drive to point 180 degrees in the opposite direction.  Furthermore, in the up and down test performed by Shawyer, the direction of the force should not have flipped (as reported by Shawyer) when Shawyer flipped the test article upside down, as natural convection always works such that the warmer part is on the bottom, and the air circulates from the warmer bottom part to the cooler top part of the chamber.

Further bad news for explaining the NASA Eagleworks response as natural convection from the warmer EM Drive is that the NASA Eagleworks test show a pulse response rapidly rising in 2 seconds which coincides with the inertial response of the inverted torsional pendulum, and is way too short a time compared with the Fourier dimensionless time based on the thermal diffusivity of the materials involved and the characteristic length.  So the initial time-response cannot be explained in terms of thermal natural convection.  The speed of heat transfer is restricted by the thermal diffusivity of the material.

I used the Crooke's radiometer as an example.  The rotation of the paddles is not from convection.   The higher emmissivity of the dark side of the paddles imparts more momentum to the air molecules that bump against it because that side of the paddle is hotter.   The dark side of the paddle receives an equal and opposite momentum.   Convection does not transfer momentum with whatever heated the air, unless you are talking about a hot air balloon or bouyancy effects in a closed system.   The air has left and no longer affects whatever has heated it.   The Crooke's radiometer demonstrates how very small power levels can have visible effects and like the em-drive experiments has a low friction bearing.

I just looked at the video of Shawyer's device and it does rotate in the opposite direction from what my theory describes.   However that might just be due to more heat being dissipated from the large end.   In the Eagleworks paper I have not being able to find where the direction of the force is stated.     I'll have to assume it is the same as Shawyer's experiment.     Only by performing other null tests can this possible explanation be eliminated.  eg: run it in a vacuum chamber or apply a heater strip to inner surfaces of the device.
« Last Edit: 10/24/2014 12:16 AM by zen-in »

Online Rodal

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Re: EM Drive Developments
« Reply #2521 on: 10/24/2014 12:16 AM »
.....
I used the Crooke's radiometer as an example.  The rotation of the paddles is not from convection.


Considering Crookes radiometer, eliminates both conduction and convection. 

Crooke's radiometer is contained in a partial vacuum.

None of the tested devices (NASA Eagleworks, Shawyer of Chinese) to my knowledge were tested in a partial vacuum.  To my knowledge Crooke's radiometer does not move under ambient pressure conditions. 
« Last Edit: 10/24/2014 12:18 AM by Rodal »

Offline zen-in

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Re: EM Drive Developments
« Reply #2522 on: 10/24/2014 12:34 AM »

Considering Crookes radiometer, eliminates both conduction and convection. 

Crooke's radiometer is contained in a partial vacuum.

None of the tested devices (NASA Eagleworks, Shawyer of Chinese) to my knowledge were tested in a partial vacuum.  To my knowledge Crooke's radiometer does not move under ambient pressure conditions.

I think the reason why a Crooke's radiometer requires a partial vacuum is to minimize air friction.   It also doesn't work in a hard vacuum.

From Wikipedia:
When a radiant energy source is directed at a Crookes radiometer, the radiometer becomes a heat engine. The operation of a heat engine is based on a difference in temperature that is converted to a mechanical output. In this case, the black side of the vane becomes hotter than the other side, as radiant energy from a light source warms the black side by black-body absorption faster than the silver or white side. The internal air molecules are "heated up" (i.e. experience an increase in their speed) when they touch the black side of the vane.
end quote

While this is one theory of how a Crooke's radiometer works it actually rotates in the reverse direction from what this theory would require.   The white side of the paddle trails.   This is described further in the Wikipedia page.   So direct heating of air molecules from a warm surface can have some unexpected results.

from Wikipedia:
Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.
end quote
« Last Edit: 10/24/2014 12:39 AM by zen-in »

Online Rodal

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Re: EM Drive Developments
« Reply #2523 on: 10/24/2014 12:46 AM »
...
Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.
end quote

This is an interesting effect of another nature. 

<< The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. >>

How would this work for the EM Drive? 

Would we have to posit that the "porous" part is the gap between the flat bases and the surface of the cone?

It is a fact that all the EM Drives that were tested had removable flat bases that were simply torqued into place, they were not welded or bonded without porosity, so certainly one has to admit that there is a gap through which  gas molecules can move (at the circumferential gap of the bases instead of the edges of the blade of the radiometer).
« Last Edit: 10/24/2014 12:48 AM by Rodal »

Offline JohnFornaro

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Re: EM Drive Developments
« Reply #2524 on: 10/24/2014 01:14 AM »
Thanks also to zen-in that provided the picture that motivated the discussion that motivated this insight.

And thanks also to Jack, who built the house that... never mind.
Sometimes I just flat out don't get it.

Online Rodal

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Re: EM Drive Developments
« Reply #2525 on: 10/24/2014 01:17 AM »
Thanks also to zen-in that provided the picture that motivated the discussion that motivated this insight.

And thanks also to Jack, who built the house that... never mind.
and thanks also to John  :)
« Last Edit: 10/24/2014 01:20 AM by Rodal »

Offline zen-in

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Re: EM Drive Developments
« Reply #2526 on: 10/24/2014 01:51 AM »
...
Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.
end quote

This is an interesting effect of another nature. 

<< The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. >>

How would this work for the EM Drive? 

Would we have to posit that the "porous" part is the gap between the flat bases and the surface of the cone?

It is a fact that all the EM Drives that were tested had removable flat bases that were simply torqued into place, they were not welded or bonded without porosity, so certainly one has to admit that there is a gap through which  gas molecules can move (at the circumferential gap of the bases instead of the edges of the blade of the radiometer).

Crooke's radiometer theory from Wikipedia:
On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.

Applying this to the em-drive the large end would be the cold side and the cone section the hot side.   Air moves from the cold side to the hot side and generates a tangential force.   This force is in the same direction as the theorized em force.  (opposite to what I was proposing earlier).   I don't think this requires a partial pressure; just a very low friction bearing or torsion pendulum.

Shawyer's up/down thrust plot is not symmetrical.   The up plot has a faster rise time.  I could speculate that this difference is due to convection.   But I don't know enough about how these plots were done.

Online Rodal

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Re: EM Drive Developments
« Reply #2527 on: 10/24/2014 02:04 AM »
...
Crooke's radiometer theory from Wikipedia:
On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.

Applying this to the em-drive the large end would be the cold side and the cone section the hot side.   Air moves from the cold side to the hot side and generates a tangential force.   This force is in the same direction as the theorized em force.  (opposite to what I was proposing earlier).   I don't think this requires a partial pressure; just a very low friction bearing or torsion pendulum.

Shawyer's up/down thrust plot is not symmetrical.   The up plot has a faster rise time.  I could speculate that this difference is due to convection.   But I don't know enough about how these plots were done.

Mmmm.  The person that wrote this on Wikipedia literally copied what Prof. John Baez had already explained in his blog several years ago:

http://math.ucr.edu/home/baez/physics/General/LightMill/light-mill.html

Since Prof. Baez has been one of the very outspoken critics of Dr. White's Quantum Vacuum Plasma explanation and the NASA Eagleworks tests, I find it interesting, that to my knowledge Prof. Baez has not advanced the Crook radiometer theory as an explanation for the NASA Eagleworks experiments.  Maybe this is a question that can be posed to Prof. Baez himself since the explanation quoted from Wikipedia has been taken from Baez himself.

« Last Edit: 10/24/2014 02:17 AM by Rodal »

Offline zen-in

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Re: EM Drive Developments
« Reply #2528 on: 10/24/2014 02:12 AM »
...
Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.
end quote

This is an interesting effect of another nature. 

<< The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. >>

How would this work for the EM Drive? 

Would we have to posit that the "porous" part is the gap between the flat bases and the surface of the cone?

It is a fact that all the EM Drives that were tested had removable flat bases that were simply torqued into place, they were not welded or bonded without porosity, so certainly one has to admit that there is a gap through which  gas molecules can move (at the circumferential gap of the bases instead of the edges of the blade of the radiometer).

Crooke's radiometer theory from Wikipedia:
On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.

Applying this to the em-drive the large end would be the cold side and the cone section the hot side.   Air moves from the cold side to the hot side and generates a tangential force.   This force is in the same direction as the theorized em force.  (opposite to what I was proposing earlier).   I don't think this requires a partial pressure; just a very low friction bearing or torsion pendulum.

Shawyer's up/down thrust plot is not symmetrical.   The up plot has a faster rise time.  I could speculate that this difference is due to convection.   But I don't know enough about how these plots were done.

Mmmm.  The person that wrote this on Wikipedia literally copied what Prof. John Baez had already explained in his blog several years ago:

http://math.ucr.edu/home/baez/physics/General/LightMill/light-mill.html

Since Prof. Baez has been one of the very outspoken critics of Dr. White's Quantum Vacuum Plasma explanation and the NASA Eagleworks tests, I find it interesting, that to my knowledge Prof. Baez has not advanced the Crook radiometer theory as an explanation for the NASA Eagleworks experiments.  Maybe this is a question that can be posed to Prof. Baez himself since the explanation quoted from Wikipedia has been taken from Baez himself.

Prof. Baez's explanation is a lot easier to follow.  The Wikipedia authors left a lot out.   It turns out the paddles of a Crooke's radiometer do turn as if a force was pushing against the dark side of each paddle.   This analogy does not match the results of the em-drive experiment.

Online Rodal

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Re: EM Drive Developments
« Reply #2529 on: 10/24/2014 02:17 AM »
[...

Prof. Baez's explanation is a lot easier to follow.  The Wikipedia authors left a lot out.   It turns out the paddles of a Crooke's radiometer do turn as if a force was pushing against the dark side of each paddle.   This analogy does not match the results of the em-drive experiment.
Thanks for pointing out that observation.

« Last Edit: 10/24/2014 02:28 AM by Rodal »

Offline aero

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Re: EM Drive Developments
« Reply #2530 on: 10/24/2014 05:18 AM »
I'm not happy with my understanding of Shawyer's terminology. In particular he uses the terms Lo, Lg1 and Lg2 in his derivations. (I have taken the liberty to use "L" in place of "lamda" here.) One of his derivation papers can be found here.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCQQFjAB&url=http%3A%2F%2Fwww.emdrive.com%2FCEAS2009paper.doc&ei=nsFJVIH-A6_1iQKLnoHwAw&usg=AFQjCNGgzJQ1yl_K5kVzCOBAKkv3E3U-4w&sig2=1sgg_WEjJw9rhHJ-Wla6UA

I'm reasonably confident that Lo is the RF drive wavelength. I thought that Lg1 and Lg2 were the big and small end diameters of the cavity. Shawyer gives an equation for the "Design Factor" of his thruster which is a function of those values only and I read that for his Demonstrator Thruster, the design factor = 0.844. Since I thought I knew the values for Lo and Lg1 I decided to search for the valu Lg2. I have attached a plot of my calculation of the design factor less 0.844, as a function of Lg2, with Lo and Lg1 fixed. The plot should cross zero where Lg2 gives the design factor = 0.844. (Recall that the diameter of the demonstrator thruster is 280 mm.)

But look at the shape of the curve. Its going to cross zero in about the same place for any value of the design factor. I calculated the zero value region with a much finer grid and the curve doesn't really cross zero at all. It appears to have a vertical asymptote at the zero crossing so I don't know what that means.

I wonder, could someone help me out here? Here is my Excel if that helps.

c=   2.99792E+08   f =    2.45E+09   Hz
   for Shawyer b", Lamda = Lo =    1.22364E-01   m   
   Lg1 =    0.280   m   
Df = 0.844,   Df=S_o*Lo((1/Lg1) - (1/lg2))  where S_o = (1-(Lo^2/(Lg1*Lg2)))^-1         
Combining   Df = Lo*( 1 - (Lo^2/(Lg1*Lg2)))^-1 *((1/Lg1)-(1/Lg2))
Or actual code:=($L$311*(1-($L$311^2/($L$312*K318)))^-1)*((1/$L$312)-(1/K318))-J318

like this:
0.844   0.04   6.939544594
0.844   0.05   28.08032721
0.844   0.06   -15.57872833
0.844   0.07   -6.397614737
0.844   0.08   -4.13912597
0.844   0.09   -3.117319973
0.844   0.1   -2.534764749
0.844   0.11   -2.158332745

I think my code is right and the equations are copied fairly but the zero value of Lg2 ~0.052 m, is not close to what we measured and looks to be too small even if the cone tapers all the way to the front end of the cylinder. I am misunderstanding Shawyer's paper is what I think.      
      


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Offline frobnicat

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Re: EM Drive Developments
« Reply #2531 on: 10/24/2014 12:00 PM »
...
Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.
end quote

This is an interesting effect of another nature. 

<< The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. >>

How would this work for the EM Drive? 

Would we have to posit that the "porous" part is the gap between the flat bases and the surface of the cone?

It is a fact that all the EM Drives that were tested had removable flat bases that were simply torqued into place, they were not welded or bonded without porosity, so certainly one has to admit that there is a gap through which  gas molecules can move (at the circumferential gap of the bases instead of the edges of the blade of the radiometer).

"The space past their edges behaves like the pores in Reynolds's plate" implies the mean free path is a required condition for both to work : the edges thickness and temperature gradients have to be on the order of mean free path length for the effect to be of any significant magnitude. I didn't know the condition between temperature and pressure, but it is well known that the reason why a Crookes radiometer don't turn at ambient pressure is not viscosity (it would turn slower but it would turn) but much smaller mean free path. At STP mean free path is 68nm, much lower any edge/temp. differential. Crookes radiometer works at medium vacuum with mean free path around 1mm, same ballpark as vanes thickness.
This paper page 2 : "Radiometric forces depend on the mean free path of gas molecules" ... rest of the paper fascinating but no time to read it at the moment.

I don't see any "radiometric" force being detectable at STP even with very sensitive experiments unless devising a geometry with significant temp. differentials at sub Ám scales.

On the other hand if there is a gap between the cavity and exterior, the heating of air inside could be very quick (low thermal inertia), and the dilated air would rush through this gap (jet). Me think this could do a small time constant effect, that is compatible with the step observed. But I'm not sure this could go for the magnitude. More on that later (no time right now), want to see the kick one can get from a few litres of air heated a few degrees and expelled through a small aperture ( an involuntary "nozzle" ).
« Last Edit: 10/24/2014 12:10 PM by frobnicat »

Online Rodal

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Re: EM Drive Developments
« Reply #2532 on: 10/24/2014 12:16 PM »
......

I'm reasonably confident that Lo is the RF drive wavelength. .......
I think my code is right and the equations are copied fairly but the zero value of Lg2 ~0.052 m, is not close to what we measured and looks to be too small even if the cone tapers all the way to the front end of the cylinder. I am misunderstanding Shawyer's paper is what I think.

Please take a look at this message:  (  http://forum.nasaspaceflight.com/index.php?topic=29276.msg1271695#msg1271695  )

One problem is in assuming that <<that Lo is the RF drive wavelength >>

Shawyer's Lambdag is the RF drive wavelength instead of Shawyer's Lambda0 (Lo).

Shawyer defines Lambda0  (Lo) as the "free-space propagation wavelength" and makes a difference between the wavelength inside the microwave cavity (which he calls Lambdag) and the wavelength propagation in free space Lambda0 (Lo).

A one-dimensional waveguide restricts the three dimensional "free space" propagation of the electromagnetic wave to a single dimension.  Therefore, the 3-D free-space wavelength is shorter than the wavelength in the microwave guide.

I would expect that, the wavelength in the guide, Lambdag=  Lambda0/cos(phi), where phi is  the angle between the crest lines and the waveguide longitudinal axis.  Since cosine is always less than unity, Lambdag is always greater than Lambda0.  In other words, "RF wavelength" is greater than Lambda0.

Lambdag = RF drive wavelength

Lambdag > Lo

(RF drive wavelength) > Lo

So basically, I don't agree with replacing Lambda0 (Lo) by RF wavelength without taking into account the fact that RF wavelength must be longer than Lambda0 (Lo).
« Last Edit: 10/24/2014 02:09 PM by Rodal »

Online Rodal

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Re: EM Drive Developments
« Reply #2533 on: 10/24/2014 12:34 PM »
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 air inside microwaves is not heated appreciably by microwaves because air molecules aren't as polar as water molecules. Even though the total charge on a molecule is zero, the nature of chemical bonds is such that the positive and negative charges do not completely overlap in most molecules. Such molecules are said to be polar because they possess a permanent dipole moment. Many plastics, glasses and ceramics are labeled "microwave safe" because their molecules are not very polar. 






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
and
2) 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.

« Last Edit: 10/24/2014 02:40 PM by Rodal »

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Re: EM Drive Developments
« Reply #2534 on: 10/24/2014 02:50 PM »
......
I'm reasonably confident that Lo is the RF drive wavelength. .......
I think my code is right and the equations are copied fairly but the zero value of Lg2 ~0.052 m, is not close to what we measured and looks to be too small even if the cone tapers all the way to the front end of the cylinder. I am misunderstanding Shawyer's paper is what I think.
....
Shawyer's Lambdag is the RF drive wavelength instead of Shawyer's Lambda0 (Lo)....

I don't understand why Shawyer's equations are written in terms of the unknown Lambda0 (Lo) instead of the known Lambdag =RF drive wavelength

Shawyer quotes Cullen

"The force on the plate closing the end of the waveguide is": 2* ((PowerInput) / c ) * (Lo / Lambdag)

Since in general

(Lo / Lambdag ) < 1

the force on the plate closing the end of the waveguide  < 2* ((PowerInput) / c )

(Notice the factor of 2 characterizing perfect reflection for the case that all photons bounce of the wall as a perfect mirror and that no photon is absorbed)

Unless one knows Lo, that's all we know: that the force on the plate closing the end of the waveguide  is less than twice the Power Input divided by the speed of light.

Why doesn't Shawyer remove the unknown Lo from the equation ?

Is the unknown Lo left on purpose as a fudge factor (to account for the few photons that do not bounce off the wall but instead dissipate inside the copper as a phonon)?

Isn't the ratio Lo / Lambdag involved in the design factor ? (= 0.844 for the example you gave)

It is actually very close to what is used for solar sails (~90 %)

Perhaps this is another thing Shawyer could answer in addition to what are the actual dimensions of the different EM Drives Shawyer actually used.
« Last Edit: 10/24/2014 03:50 PM by Rodal »

Offline aero

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Re: EM Drive Developments
« Reply #2535 on: 10/24/2014 04:19 PM »
Quoting from the linked paper above:

Quote
We now suppose that the beam enters a vacuum-filled waveguide.  The waveguide tapers from free-space propagation, with wavelength L0, to dimensions that give a waveguide wavelength of Lg and propagation velocity vg.

This statement led me to think that L0 was the RF drive wavelength. Or maybe L0 is the diameter of the small end?
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Online Rodal

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Re: EM Drive Developments
« Reply #2536 on: 10/24/2014 04:24 PM »
Quoting from the linked paper above:

Quote
We now suppose that the beam enters a vacuum-filled waveguide.  The waveguide tapers from free-space propagation, with wavelength L0, to dimensions that give a waveguide wavelength of Lg and propagation velocity vg.

This statement led me to think that L0 was the RF drive wavelength. Or maybe L0 is the diameter of the small end?
That statement says that Lo is the wavelength in free-space propagation and that Lg is the wavelength in the waveguide.   

The subscript "g" stand for waveguide.  The subscript "o" stands for free-space in standard nomenclature.

Lo/Lg < 1

Lg = Lo / Sqrt [1 -( Lo/LcutOff )^2]

where LcutOff  is the upper cutoff wavelength (= c/( lower cutoff frequency ))

Therefore:

Lo =( LcutOff *Lg ) / Sqrt[LcutOff ^2 + Lg ^2 ]


Lo =LcutOff *(RF drive wavelength) / Sqrt[LcutOff ^2 + (RF drive wavelength)^2 ]

For TE01 in a waveguide

LcutOff = 2 * LengthDimension

We have a truncated cone subject to TE0nm modes instead of a simple waveguide subject to TE0n modes, but in absence of a better defined cut-off frequency, and from the writing in Shawyer's, I suggest to adopt the TE01 waveguide cutoff frequency (unless we come up with a better definition for cutoff frequency), giving:

Lo =(2 * LengthDimension)*(RF drive wavelength) / Sqrt[(2 * LengthDimension)^2 + (RF drive wavelength)^2 ]

which is:

Lo =(RF drive wavelength) / Sqrt[1 + ((RF drive wavelength)/(2 * LengthDimension))^2 ]

Lo =(c/(RF drive frequency)) / Sqrt[1 + (c/(2 * LengthDimension * (RF drive frequency)))^2 ]

So only for  RF drive wavelength < <(2 * LengthDimension) , would the equality Lo =(RF drive wavelength) hold in the limit as  ((RF drive wavelength)/(2 * LengthDimension)) -> 0


For example, for RF drive wavelength ~ LengthDimension we have instead:

Lo =0.894 * (RF drive wavelength)
« Last Edit: 10/24/2014 05:39 PM by Rodal »

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Re: EM Drive Developments
« Reply #2537 on: 10/24/2014 05:53 PM »

Quote
Lo =0.894 * (RF drive wavelength)

Ok. I'll try that.
---------------------------------------
Now, while reading the above linked paper in detail, I found some Flight Thruster dimensions.

Base plate diameter = 265 mm,
Height = 164 mm.

If those dimensions are consistent with the photograph, then we should be able to extract the small end dimension.
---------------------------------------
I plugged in Rodel's value of Lo. It moved the zero crossing slightly, but to the left.
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Re: EM Drive Developments
« Reply #2538 on: 10/24/2014 06:18 PM »

Quote
Lo =0.894 * (RF drive wavelength)

Ok. I'll try that.
---------------------------------------
Now, while reading the above linked paper in detail, I found some Flight Thruster dimensions.

Base plate diameter = 265 mm,
Height = 164 mm.

If those dimensions are consistent with the photograph, then we should be able to extract the small end dimension.
---------------------------------------
I plugged in Rodel's value of Lo. It moved the zero crossing slightly, but to the left.

What is the "DesignFactor" you compute for smallDiameter=0.17 m, bigDiameter=0.28 m and length=0.345 m ?

I get a DesignFactor = 0.401



For DesignFactor = 0.844  and bigDiameter=0.28 m and length=0.345 m

I get smallDiameter = 0.1289 m which is much larger than the values you showed, and not so far off from 0.17 m

« Last Edit: 10/24/2014 06:28 PM by Rodal »

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Re: EM Drive Developments
« Reply #2539 on: 10/24/2014 06:27 PM »
Quote
Now, while reading the above linked paper in detail, I found some Flight Thruster dimensions.

Base plate diameter = 265 mm,
Height = 164 mm.

If those dimensions are consistent with the photograph, then we should be able to extract the small end dimension.

The paper also gives the mass of the thruster as 2.92 kg.

If we assume that the base plate is that bottom plate in contact with the table top, and that the height is the distance from the table top to the top surface (where you'd set your coffee cup) then maybe we can estimate the internal dimensions to calculate the thickness of the sidewalls of the thruster. But is it aluminum or stainless? Either way I speculate that the inner surface is plated with silver, gold or maybe copper. The internal plating shouldn't detectably affect the mass though or having rough internal dimensions, we could also estimate the plating mass using the skin thickness at 3.86 GHz.

And in this, by "we" I mean, "you."  :)
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