Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1882099 times)

Offline TheTraveller

What I can't understand about Tajmar's build is he could have easily duplicated Shawyer's 1st Experimental EMDrive ...This Tajmar mini EMDrive is really a very strange build.
Tajmar's paper:

Quote
We would like to thank Roger Shawyer for his assistance 

I'm sure that Shawyer helped to make sure it worked as best it could.

Still makes no sense, to an engineer, for Tajmar to build what he did.

There are heaps of real engineering issues that will really dent the Force generated.

I don't believe there was a good impedance match as the magnetron ran at 200C while the hottest the cavity got was 35C at the small end. To me that suggest the cavity was rejecting / reflecting back most of the magnetrons Rf energy.

Would like to see the peak return loss dBs Tajmar measured when doing the bandwidth and Q calculations. Knowing that would reveal the VSWR and the reflection coefficient.

To do these Force measurements, you need to know the actual forward power delivered into the cavity and not just assume the magnetrons rated 700Ws has magically turned up inside the cavity.
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
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Offline TheTraveller

Have been told the max return loss was an estimated 12.5dBs.

This is a terrible result with at best 360Ws making it into the cavity and then only if the cavity bandwidth is wide enough to handle the magnetron's power output bandwidth. If not then even less power gets inside the cavity and even more gets rejected and reflected back to the magnetron to heat it up.

Sorry but a terrible design and build.
« Last Edit: 07/26/2015 07:43 PM by TheTraveller »
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
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Offline TheTraveller

Would it be correct to say that the Shawyer construction injects the microwaves near the top or small end, rather than from the sides? There was definitely discussion of this previously but I can't seem to find it.

In the 1st Experimental EMDrive the waveguide entry was roughly centered on the side wall.

In the 2nd Demonstrator EMDrive, the waveguide entry was near the bottom end.

In the 3rd Flight Thruster EMDrive, the coax entered near the bottom end.
« Last Edit: 07/26/2015 07:54 PM by TheTraveller »
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
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Offline birchoff

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Have been told the max return loss was an estimated 12.5dBs.

This is a terrible result with at best 360Ws making it into the cavity and then only if the cavity bandwidth is wide enough to handle the magnetron's power output bandwidth. If not then even less power gets inside the cavity and even more gets rejected and reflected back to the magnetron to heat it up.

Sorry but a terrible design and build.

Given the information we have from the paper and this new information whats the Df

Offline TheTraveller

Have been told the max return loss was an estimated 12.5dBs.

This is a terrible result with at best 360Ws making it into the cavity and then only if the cavity bandwidth is wide enough to handle the magnetron's power output bandwidth. If not then even less power gets inside the cavity and even more gets rejected and reflected back to the magnetron to heat it up.

Sorry but a terrible design and build.

Given the information we have from the paper and this new information whats the Df

My calculator can't get resonance or a Df at any mode using 2.45GHz as the driven frequency other than by using the 3rd of 4th harmonic of 2.45GHz. Magnetrons are supposedly good at driving higher harmonics, so maybe that is what is happening.

As I said before, this is a very strange build to a guy who understands how to build EMDrives. It just doesn't make sense.
"As for me, I am tormented with an everlasting itch for things remote. I love to sail forbidden seas.
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Offline DrBagelBites

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Who from this forum is going to be at the AIAA conference?

I'll be attending the conference.

Offline Star One

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One thing that bothers me if as we keep hearing better drives are going to rely on super conductivity isn't that going to be an issue in itself. With one tricky technology relying on another tricky technology?
« Last Edit: 07/26/2015 08:43 PM by Star One »

Online WarpTech

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@WarpTech
was confused yesterday caused by the notification "kr". Dr Rodal posted the description of what is meaning it (namely not the radii of the cone at a given point at the z-axis, but the radius based on the cone apex).

@Rodal
Thanks for the explanation
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1409751#msg1409751


I'm not confused by this. I know that kr = k*r, is the distance from the cone apex in terms of phase. I agree the paper is confusing in the way it is written because they also use kr.

In my equation for the tapered cylinder using Bessel functions, I had z*w/c, which is the same thing. For a given k value based on the input frequency, k being the wavenumber of the propagating mode in the z direction, r is the distance from the apex. It is simply their way of normalizing the graph, because computing the Hankle functions is easier that way.

The graphs I posted for the Reissner-Nordstrom metric are equivalent representations for k=1, where r is the radial coordinate. It is the radial solution for a charged black hole. What is wrong with that? What we are dealing with is a frequency dependent, electromagnetic metric. It does not affect matter the way normal gravity would, but it does effect the EM waves that fall in the right bandwidth in such a way as to mimic gravity.
Todd

Is your underlying idea that the expanding photon gas give some extra thrust?
May be in such a situation you described (open horn antenna?) could be more thrust like simple photon rocket.
(expanding of the photon gas plus backreaction while radiation?)
For conical cavity thrusters who are not spitz and closed to be a resonator the situation is different? I am not sure.
Some times ago i had a similar idea...
Look at point "2."
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1382616#msg1382616

Or do you think this is at the end a pure gravity effect?

Yes, very similar to your point "2", with the inclusion of the non-linear affect of gravity. Due to this non-linearity, the momentum exchange at the small end is larger than at the big end. I'm making progress toward deriving everything, but I'm not quite there yet.

I put together a spreadsheet of the EM Drive experimental designs, and where they stand on the Impedance charts from Zeng & Fan that I posted yesterday. http://forum.nasaspaceflight.com/index.php?topic=37642.msg1409676#msg1409676

I give the kr value for small end and the big end at the input frequency. I also give the relative angle, color coded like Zeng & Fan and a little in-between. :)

What I see is, at the resonant frequency it has a minimum kr defined by the small end and therefore, does not exceed c while resonating. In all cases, it appears that the resonance is operating on nearly the same portion of the impedance curve, just outside the deepest part of the gravity well shown on the TM01 chart. However, once the waves decay and become evanescent, k->0 for those waves at a very high thrust to power ratio. I could be wrong, I'm still trying to understand this myself.
Todd

EDIT 2: Updated Tajmar's frustum dimensions X2, per @TheTraveller's observations. Now, this frustum is operating mostly on the same part of the impedance curve as the others.
« Last Edit: 07/26/2015 11:20 PM by WarpTech »

Offline X_RaY

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Tajmar Experimental results

Cavity Length(m) = 0.0686
Big Diameter(m) = 0.0541
Small Diameter(m) = 0.0385
Dielectric = None
Frequency = 2.44Ghz
Input Power = 700w (output of magnetron)

are that really the diameters used in the paper?(i dont have the paper )
Is it possible that this are the radii? if i look at the picture the height is almost equal to the a-side of the waveguide...
the a-side of WR430=109,22mm and WR340=86,36mm
the big diameter is almost equal to that ???

 ;D
http://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/

This is the  American Institute of Aeronautics and Astronautics link to Martin Tajmar's et.al. paper, that should be obtained from the American Institute of Aeronautics and Astronautics:

Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler
51st AIAA/SAE/ASEE Joint Propulsion Conference
 ;)
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

if everyone is able to share a link to the paper (without the need to pay for) please send me a PM
« Last Edit: 07/26/2015 09:17 PM by X_RaY »

Offline Rodal

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Tajmar Experimental results

Cavity Length(m) = 0.0686
Big Diameter(m) = 0.0541
Small Diameter(m) = 0.0385
Dielectric = None
Frequency = 2.44Ghz
Input Power = 700w (output of magnetron)

are that really the diameters used in the paper?(i dont have the paper )
Is it possible that this are the radii? if i look at the picture the height is almost equal to the a-side of the waveguide...
the a-side of WR430=109,22mm and WR340=86,36mm
the big diameter is almost equal to that ???

Quote from: M. Tajmar and G. Fiedler
Our final tapered cavity design had a top diameter of 38.5 mm, a bottom diameter of 54.1 mm and a height of 68.6 mm as well as a side entrance for the microwaves as shown in Fig. 2. The cavity was made out of three copper pieces where the lower and middle part as well as the side flange were hard soldered using silver and the top part was able to adapt its position in order to optimize for a high Q factor. A standard WR340 waveguide was then used to connect the magnetron to the EMDrive. 

This is the  American Institute of Aeronautics and Astronautics link to Martin Tajmar's et.al. paper, that should be obtained from the American Institute of Aeronautics and Astronautics:

Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler
51st AIAA/SAE/ASEE Joint Propulsion Conference
 ;)
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083
« Last Edit: 07/26/2015 09:16 PM by Rodal »

Offline X_RaY

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Tajmar Experimental results

Cavity Length(m) = 0.0686
Big Diameter(m) = 0.0541
Small Diameter(m) = 0.0385
Dielectric = None
Frequency = 2.44Ghz
Input Power = 700w (output of magnetron)

are that really the diameters used in the paper?(i dont have the paper )
Is it possible that this are the radii? if i look at the picture the height is almost equal to the a-side of the waveguide...
the a-side of WR430=109,22mm and WR340=86,36mm
the big diameter is almost equal to that ???

Quote from: M. Tajmar and G. Fiedler
Our final tapered cavity design had a top diameter of 38.5 mm, a bottom diameter of 54.1 mm and a height of 68.6 mm as well as a side entrance for the microwaves as shown in Fig. 2. The cavity was made out of three copper pieces where the lower and middle part as well as the side flange were hard soldered using silver and the top part was able to adapt its position in order to optimize for a high Q factor. A standard WR340 waveguide was then used to connect the magnetron to the EMDrive. 

This is the  American Institute of Aeronautics and Astronautics link to Martin Tajmar's et.al. paper, that should be obtained from the American Institute of Aeronautics and Astronautics:

Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler
51st AIAA/SAE/ASEE Joint Propulsion Conference
 ;)
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

OK, was just a thought.
I was playing with the dimensions to get frequency match to 2.4 Ghz while looking at the pictures...
Have to go to bad now, bye

Offline TheTraveller

Interesting comment on Iulian's old forum:

http://www.masinaelectrica.com/emdrive-independent-test/#comment-12985

Quote
Third, because the cavity geometry is axisymmetric, you can use the free RF program Superfish to determine the modes in the cavity, the best place to excite each mode, and the Q of each cavity mode.

Superfish will run fine on a PC. Many accelerators far more complex than what you are doing were designed using Superfish and its support programs.

The program will allow you to see the field patterns for the different cavity modes, which is helpful.

Anybody know anything about SuperFish?

http://www.lanl.gov/projects/feynman-center/technologies/software/poisson-superfish.php
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Offline frobnicat

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Those with access to the paper can check that maybe the vertical set-up of frustum (on horizontal balance measurement) is with the waveguide axis aligned with arm : if we define a plane with both the axis of frustum and axis of waveguide, thrust would be expected only in this plane of symmetry, if this plane is parallel to vertical axis of rotation it would come as a surprise that there is some measured thrust vector orthogonal to such plane of symmetry, by symmetry argument alone, regardless of possible mechanisms unless some very strong (and strange) kind of parity breaking, i.e. naming axis of frustum is X and waveguide is (roughly orthogonal) Y it's like measuring net thrust on Z, sorry for the clumsy wording...

Thanks, I have authorized access to the paper but I had not checked that.  What figure in the paper are you referring to ? is it this one?

Yes, it appears as I say, if a thrust vector component is aligned with axis of waveguide it would be toward (or away) from axis, not tangential.

Quote

Notice from the COMSOL FEA picture of the electromagnetic field in my post http://forum.nasaspaceflight.com/index.php?topic=37642.msg1409813#msg1409813

that the waveguide is NOT aligned with the center axis of axi-symmetry of the truncated cone EM Drive.


Yes, I couldn't make sense visually of that picture, but you are right, it appears the waveguide enters frustum off axis... How strange ! What could motivate that ?

On the other hand I relied on impression from pictures figure 2. b) (CAD) and c) (snapshot of assembly) that there is not this offset and waveguide is symmetric (the 2 axis are in same plane). What do you see ? It's like there is a different geometry for the Comsol model... weird.

Quote

If you were to cut the EM Drive truncated cone along a plane intersecting the axis of axi-symmetry where the electromagnetic field is shown in the COMSOL image, the waveguide enters the EM Drive completely on the 1/2 of the EM Drive.  The center axis of the waveguide is way off, away from the plane where the electromagnetic field is shown.

Thus << if we define a plane with both the axis of frustum and axis of waveguide>> is not the correct plane, because the waveguide is entering the EM Drive off-axis.

Could you envision a torque, due to the waveguide entering the EM Drive not symmetrically, resulting from two thrust vectors:  one thrust vector aligned with the axis of axi-symmetry of the EM Drive and the other axis being the axis of the waveguide?

Imagine a vertical vector (due to the EM Drive cone) and a horizontal force vector that is acting at a distance R from the vertical vector.  This seems to result in a torque.  If everything is rigid, this torque is reacted by the table, and it may show up as a torsional displacement, registering as a horizontal force (which arises from the torque produced by the waveguide acting asymmetrically).

I see. Actually even if the two axis of thrust share a same plane (as per my argument), it's not obvious such plane is not off axis of rotation of the balance, unless set up like that on purpose, and it would suffice to impart torque... albeit at a lower magnitude ratio (relative to a tangential component). But if axis of waveguide is off axis of frustum as COMSOL model seem to imply, it would be no surprise (assuming a real thrust mechanism behind all that) to see a component orthogonal to both (hence tangential for the balance) : intuitively if it were a flow of momentum pouring from waveguide to frustum it would have to "bounce" asymmetrically like a turbo injector while getting some vorticity around axis of frustum (fluid mechanics analogy, maybe irrelevant).

And we also don't know how the magnetron itself is arranged relative to waveguide axis, maybe there is another out of plane_waveguide_frustum asymmetry here...

Offline TheTraveller

Tajmar Experimental results

Cavity Length(m) = 0.0686
Big Diameter(m) = 0.0541
Small Diameter(m) = 0.0385
Dielectric = None
Frequency = 2.44Ghz
Input Power = 700w (output of magnetron)

are that really the diameters used in the paper?(i dont have the paper )
Is it possible that this are the radii? if i look at the picture the height is almost equal to the a-side of the waveguide...
the a-side of WR430=109,22mm and WR340=86,36mm
the big diameter is almost equal to that ???

 ;D
http://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/

This is the  American Institute of Aeronautics and Astronautics link to Martin Tajmar's et.al. paper, that should be obtained from the American Institute of Aeronautics and Astronautics:

Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler
51st AIAA/SAE/ASEE Joint Propulsion Conference
 ;)
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

if everyone is able to share a link to the paper (without the need to pay for) please send me a PM

Using the WR340 flange narrow dimensions I estimate the big end diameter at 110mm, which very strongly suggests the big and small end diameters are radius and not diameters as claimed.

Likewise the cavity length when compared to the flange longer length suggests it too has been half sized.

This suggests all the dimensions need to be doubled.

With those mods and assuming the length is the overall length and not the inside length with the screwed in small end plate, it is possible to get TE111 resonance at 2.45GHz. Df is 0.562. At 700W input and a Q of 48.8 the Force prediction is 128uN, which means their Df is lower than 0.562 or they have other numbers wrong.

In quoting 700W as the cavity input power, it would seem Tajmar doesn't understand what a return loss dB of 12.5 means and that it drops his 700Ws to 360Ws at best. Any person who understands VSWR would know what a 69:1 VSWR means, which is your Rf generator is gonna get very HOT from the reflected power.

Using 360Ws as the cavity input power, the Force prediction drops to 66uNs and at an oxidised Q of 20.2 it drops further to 27uNs.
« Last Edit: 07/26/2015 11:13 PM by TheTraveller »
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Online WarpTech

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Tajmar Experimental results

Cavity Length(m) = 0.0686
Big Diameter(m) = 0.0541
Small Diameter(m) = 0.0385
Dielectric = None
Frequency = 2.44Ghz
Input Power = 700w (output of magnetron)

are that really the diameters used in the paper?(i dont have the paper )
Is it possible that this are the radii? if i look at the picture the height is almost equal to the a-side of the waveguide...
the a-side of WR430=109,22mm and WR340=86,36mm
the big diameter is almost equal to that ???

 ;D
http://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/

This is the  American Institute of Aeronautics and Astronautics link to Martin Tajmar's et.al. paper, that should be obtained from the American Institute of Aeronautics and Astronautics:

Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler
51st AIAA/SAE/ASEE Joint Propulsion Conference
 ;)
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

if everyone is able to share a link to the paper (without the need to pay for) please send me a PM

Using the WR340 flange narrow dimensions I estimate the big end diameter at 110mm, which very strongly suggests the big and small end diameters are radius and not diameters as claimed.

Likewise the cavity length when compared to the flange longer length suggests it too has been half sized.

This suggests all the dimensions need to be doubled.

With those mods and assuming the length is the overall length and not the inside length with the screwed in small end plate, it is possible to get TE111 resonance at 2.45GHz. Df is 0.562. At 700W input and a Q of 48.8 the Force prediction is 128uN, which means their Df is lower than 0.562 or they have other numbers wrong.

Ha, I would have to agree with you there. The reported length is only 2.7". Just going by the size of the bolts, I can see it is much larger than that.
Todd

Online demofsky

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Regarding the dimensions the paper was explicit.  (Maybe wrong but explicit.)

Quote

We started by designing a model optimized for a frequency of 2.45 GHz using COMSOL in order to be able to use commercial magnetrons used in standard microwave ovens. We iterated our design several times by consulting with R. Shawyer to be as representative as possible. Our final tapered cavity design had a top diameter of 38.5 mm, a bottom diameter of 54.1 mm and a height of 68.6 mm as well as a side entrance for the microwaves as shown in Fig. 2. The cavity was made out of three copper pieces where the lower and middle part as well as the side flange were hard soldered using silver and the top part was able to adapt its position in order to optimize for a high Q factor. A standard WR340 waveguide was then used to connect the magnetron to the EMDrive.


From "Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler"

51st AIAA/SAE/ASEE Joint Propulsion Conference

http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

Online WarpTech

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Regarding the dimensions the paper was explicit.  (Maybe wrong but explicit.)

Quote

We started by designing a model optimized for a frequency of 2.45 GHz using COMSOL in order to be able to use commercial magnetrons used in standard microwave ovens. We iterated our design several times by consulting with R. Shawyer to be as representative as possible. Our final tapered cavity design had a top diameter of 38.5 mm, a bottom diameter of 54.1 mm and a height of 68.6 mm as well as a side entrance for the microwaves as shown in Fig. 2. The cavity was made out of three copper pieces where the lower and middle part as well as the side flange were hard soldered using silver and the top part was able to adapt its position in order to optimize for a high Q factor. A standard WR340 waveguide was then used to connect the magnetron to the EMDrive.


From "Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler"

51st AIAA/SAE/ASEE Joint Propulsion Conference

http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

When working in CAD, I'll wager that they mistakenly took their dimensions relative to the origin of coordinates, not end to end and not diameters. Assuming the origin of coordinates was at the center of the frustum, everything should be multiplied by 2.

Just consider, 68.6 mm = 2.7". Those appear to be ~1/4" or ~5mm bolts with 7/16" hex-heads. If that frustum were 2.7" tall, that would be the smallest magnetron transformer seen yet. Someone goofed.
Todd

Offline birchoff

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Tajmar Experimental results

Cavity Length(m) = 0.0686
Big Diameter(m) = 0.0541
Small Diameter(m) = 0.0385
Dielectric = None
Frequency = 2.44Ghz
Input Power = 700w (output of magnetron)

are that really the diameters used in the paper?(i dont have the paper )
Is it possible that this are the radii? if i look at the picture the height is almost equal to the a-side of the waveguide...
the a-side of WR430=109,22mm and WR340=86,36mm
the big diameter is almost equal to that ???

 ;D
http://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/

This is the  American Institute of Aeronautics and Astronautics link to Martin Tajmar's et.al. paper, that should be obtained from the American Institute of Aeronautics and Astronautics:

Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects  M. Tajmar and G. Fiedler
51st AIAA/SAE/ASEE Joint Propulsion Conference
 ;)
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083

if everyone is able to share a link to the paper (without the need to pay for) please send me a PM

Using the WR340 flange narrow dimensions I estimate the big end diameter at 110mm, which very strongly suggests the big and small end diameters are radius and not diameters as claimed.

Likewise the cavity length when compared to the flange longer length suggests it too has been half sized.

This suggests all the dimensions need to be doubled.

With those mods and assuming the length is the overall length and not the inside length with the screwed in small end plate, it is possible to get TE111 resonance at 2.45GHz. Df is 0.562. At 700W input and a Q of 48.8 the Force prediction is 128uN, which means their Df is lower than 0.562 or they have other numbers wrong.

In quoting 700W as the cavity input power, it would seem Tajmar doesn't understand what a return loss dB of 12.5 means and that it drops his 700Ws to 360Ws at best. Any person who understands VSWR would know what a 69:1 VSWR means, which is your Rf generator is gonna get very HOT from the reflected power.

Using 360Ws as the cavity input power, the Force prediction drops to 66uNs and at an oxidised Q of 20.2 it drops further to 27uNs.

Whats the predicted thrust if you drop the 700W to 360W using the initial Q of 48.8? Also what do the numbers look like if you assume the model that was used was the one in equation 1 of

The Development of a Microwave Engine for Spacecraft Propulsion

Offline TheTraveller

Quote from: birchoff
Whats the predicted thrust if you drop the 700W to 360W using the initial Q of 48.8? Also what do the numbers look like if you assume the model that was used was the one in equation 1 of The Development of a Microwave Engine for Spacecraft Propulsion

66uN is the Force prediction at a Q of 48.8.

Equation 1 in the 2005 Brighton paper is obsolete. My spreadsheet uses the Force equation in the current theory paper as attached.
« Last Edit: 07/26/2015 11:54 PM by TheTraveller »
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Offline Rodal

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Actually, I forgot that Tajmar had a screw-driven reduction in length.  The length given must be the external length, the maximum length possible.

The COMSOL FEA image from Tajmar shows an internal length which is SMALLER than the big diameter. 
If I use this aspect ratio, and doubling the diameters I can get a natural frequency for TE111 around 2.45 GHz

So, yes it makes sense that:

The diameters given are actually the radii.  The diameters are twice as big as given

The internal length is actually less than 2 times the length given (the length is given by the aspect ratio in the COMSOL FEA )

There is an uncertainty from these two factors:

1) We don't quite know the internal length with the screw-modified length
2) We don't quite know the effect of the big opening from the waveguide

I pressume that the actual internal diameters are also smaller than 2 times the given diameter, but I presume this difference, due to the copper thickness is smaller than the above two effects.



See in this image that the actual internal length is smaller than the big diameter:

« Last Edit: 07/27/2015 12:05 AM by Rodal »

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