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#1020 by flux_capacitor on 24 Feb, 2015 21:35
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Finding pictures of shawyer's test device(s) is not that hard, but can any1 actually confirm that this is the Chinese truncated cone? or is it completely unrelated?
...
I think it's from Shawyer and improperly attributed to Juan Yang on some other web sites: http://emdrive.com/flightprogramme.html
Someone should ask Roger Shawyer directly about the Chinese version (especially the dimensions of the cavity). He knows a lot about it, since he went there to speak with Juan Yang and give her some advice.
Yes, that Shawyer's Flight Thruster development programme. A 3.85GHz thruster weighing 2.92 Kg,.
http://emdrive.com/flightprogramme.html
I don't recall estimated dimensions for it. If anybody estimated the dimensions, @aero is the most likely one to have done it.
I did not. I see nothing to use as a reference. Perhaps someone could estimate ratios. Big/small, big/height or whatever.The photo is a bit blurry and that makes estimating a bit challenging, and there are lens distortions to the photo, but nothing too major. If the concrete block happened to be the standard width of 440 mm, cited by wikipedia, then the dimensions would be roughly as estimated in the chart.
I'm an artist, not a physicist. If these dimensions seem wrong and you have a different guess for the width of the concrete block, let me know and I'll recalculate based on your width standard.
I finally found the real dimensions of this thruster test article in two reference papers from Shawyer on emdrive.com:
- Shawyer, Roger (27 October 2009). "The Emdrive Programme – Implications for the Future of the Aerospace Industry" (Word document). CEAS 2009 European Air and Space Conference. Manchester, U.K.: Royal Aeronautical Society.
- Shawyer, Roger (10 June 2010). "The EmDrive - A New Satellite Propulsion Technology" (Word document). Toulouse Space Show'10, 2nd Conference on Disruptive Technology in Space Activities (TECHNO DIS 2010). Toulouse, France: CNES.
So here are the numbers to know:Overall diameter 265 mm Overall height 164 mm Weight 2.92 kg Operating frequency 3.85 GHz Unloaded Q 60,000 Input power 150 to 450 W Max. measured thrust 174×10−3 N Average specific thrust 326×10−3 N/kW
So the max. diameter is larger (+18 mm) and the height is smaller (-22 mm) than lasoi's results based on the information in the picture. Hence the ratio of the frustum in the picture is wrong, probably due to the lens of the camera that was used to take it. I think lasoi could get the right dimension of the smaller end diameter, tweaking the image so it could fit those new numbers. -
#1021 by flux_capacitor on 24 Feb, 2015 22:03
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Secrets of Antigravity Propulsion Figure 8.4 - copy past this into the Google search. Click the first link it opens up the chapter and the figure 8.4 (interesting picture) Mr. Paul March spoke about. Very interesting reading Mr. Paul, thank you.
Here is the picture attached.
What about other sources of microwaves easily available besides the Gunn diode and the magnetron? What do you think of:
- Klystron. Bigger but with also very high power. Klystrons offer "cleaner" and narrower frequencies than magnetrons. This feature may be actually a tradeoff since Mulletron (http://forum.nasaspaceflight.com/index.php?topic=36313.msg1331792#msg1331792) and Dr. Rodal (http://forum.nasaspaceflight.com/index.php?topic=36313.msg1331838#msg1331838) showed the wideband of the noisy magnetron in Chinese experiments may compensate the detuning of the cavity due to its deformation while being heated.
- TWTA (traveling-wave tube amplifiers). Quite compact and powerful. Shawyer used two TWTAs to feed the test article I talked about in my previous post. Quoting his 2010 conference paper:QuoteA major part of the work is in the development of the frequency tracking algorithm. This is needed to ensure the input frequency matches the resonant frequency of the high Q (60,000) cavity, over the full input power range and the qualification temperature specification.
The thruster is designed to be powered from existing flight qualified TWTAs, which are driven from a dual redundant frequency generator unit (FGU) The FGU includes a frequency control loop using feedback signals from the thruster.
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#1022 by lasoi on 24 Feb, 2015 22:38
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According to those figures the frustum height is only 62% of the base diameter. But the height of the frustum in the photo is 75% of its base diameter, and that's excluding the nuts atop the small endplate. If we included those then the percentage would be even greater, closer to 80% of the base diameter. Are we sure those are the correct measures for the frustum in the photo? The distortion in the photo, which is primarily around the periphery, isn't nearly enough to account for that much discrepancy. I don't mind being wrong but I don't see how those numbers jive with the photo.
Edit 1: I see what he's done. He has excluded the height of the base of the frustum and the height of the top of the frustum from the frustum's overall height. If we exclude these in the photo, then the frustum height is almost exactly 62% of the base diameter. So it works out perfectly. (Sorry for the misunderstanding. I'm an artist, not a scientist, lol.)
And the diameter of the top cap is 189mm, give or take a mm or two.
Edit 2: If by "overall diameter", Shawyer meant the diameter of the widest part of the frustum excluding the base, then we again have a discrepancy between his given numbers and the photo. But I'm assuming he includes the diameter of the base in "overall", since the photo and his given numbers fit perfectly that way.
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#1023 by Rodal on 24 Feb, 2015 23:39
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According to those figures the frustum height is only 62% of the base diameter. But the height of the frustum in the photo is 75% of its base diameter, and that's excluding the nuts atop the small endplate. If we included those then the percentage would be even greater, closer to 80% of the base diameter. Are we sure those are the correct measures for the frustum in the photo? The distortion in the photo, which is primarily around the periphery, isn't nearly enough to account for that much discrepancy. I don't mind being wrong but I don't see how those numbers jive with the photo.
For clarity, could you please let us know what you think are the best estimates?
Edit, I see what he's done. He has excluded the height of the base of the frustum and the height of the top of the frustum from the frustum's overall height. If we exclude these in the photo, then the frustum height is almost exactly 62% of the base diameter. So it works out perfectly. (Sorry for the misunderstanding. I'm an artist, not a scientist, lol.)
And the diameter of the top cap is 189mm, give or take a mm or two.
Yes, what matters are the interior dimensions, so the thickness of both end plates should be subtracted from the axial length (height), and the diameters should be measured at the intersections of the cone with the interior surfaces of the flat plates.
Big Diameter = 265 mm ?
Small Diameter = ?
Height = 164 mm ?
Thanks !
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#1024 by lasoi on 24 Feb, 2015 23:41
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Big diameter is 265 mm
Small diameter is 189 mm
Height is 164 mm.
If the diameter of the base and top are measured from where the frustum meets the base and top caps, then Shawyer's numbers (265mm base and 164mm height) don't fit the photo. But if the diameter of the base and top are measured from the widest parts of the end caps, then they fit perfectly with the photo.
If you like I'll make another chart to show you what I mean but it'd take twenty minutes or so. -
#1025 by Rodal on 24 Feb, 2015 23:45
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Big diameter is 265 mm
Small diameter is 189 mm
Height is 164 mm.
So, for Shawyer's Flight Thruster,
Cone Half-Angle:
ArcTan[(BigDiameter - SmallDiameter)/(2*Length)] = ArcTan[0.2317] = 13.05 degrees
Thanks to @flux_capacitor and to @lasoi, we can update the table below
For reference. the tangent of the cone's half angle thetaw and the cone's half angle thetaw, in ascending order, for the following cases are:
(Notice how Shawyer progressively increased the cone's half-angle, with time, in his experimental designs, by a factor of 7 in the tangent of the half-angle)
Example (and geometry) { Tan[thetaw],thetaw (degrees) }
Shawyer Experimental {0.104019, 5.93851}
Shawyer Demo {0.219054, 12.3557}
Shawyer Fligth Thruster {0.231707, 13.04564}
NASA Eagleworks frustum {0.263889, 14.7827}
Egan's example {0.36397 , 20}
Prof. Juan Yang (2014) {0.4538, 24.4 }
Shawyer Superconducting 2014 {0.7002, 35}
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#1026 by Notsosureofit on 25 Feb, 2015 00:31
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Big diameter is 265 mm
Small diameter is 189 mm
Height is 164 mm.
If the diameter of the base and top are measured from where the frustum meets the base and top caps, then Shawyer's numbers (265mm base and 164mm height) don't fit the photo. But if the diameter of the base and top are measured from the widest parts of the end caps, then they fit perfectly with the photo.
If you like I'll make another chart to show you what I mean but it'd take twenty minutes or so.
Hmm, just playing "guess the mode"...the results look reasonably close, but for Micro not Milli Newtons
??
Are those internal numbers ?
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#1027 by lasoi on 25 Feb, 2015 00:39
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Sorry to keep harping on this, I'll soon be done and out of the way. But I just wanna make sure I get this right. Can someone answer the question on the chart?
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#1028 by frobnicat on 25 Feb, 2015 00:49
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...
NASA Eagleworks has not used a hanging pendulum for their measurements.
I take it that this is a hanging Pendulum? ...
They have used a low thrust torsion pendulum. See the report for further details: http://www.libertariannews.org/wp-content/uploads/2014/07/AnomalousThrustProductionFromanRFTestDevice-BradyEtAl.pdf
Makes me musing around pendulum considerations again...
Both the pivotal movement (around vertical axis) and the active position restoring torque (around the vertical axis of rotation of the arm) is given by flexural pivots of this kind :
There are two of them mounted (on the same vertical axis obviously) for added rigidity along the two others (horizontal) axis. The role of this tandem flexural pivot is, well, pivotal in the experiment and deserve careful consideration. While those pivots can exert a torque on the arm (restoring : 0 at equilibrium), they are by definition close to the axis, and it would be hard for them to impose a fast action to the rotation of arm (high "apparent inertia" from their place). It's difficult to see a scheme that would make them the source of a "step" response in position (fast rise and fast fall of displacement of arm at on and off power as observed)
It was explained by Paul March in thread one that the IR heating of those bearings by the microwave amplifier (just behind them) would slowly (due to thermal inertia) alter the temperature of their spring and therefore their rest (equilibrium) position and was the reason of the systematic "drift" (slowly moving baseline) seen on the records. Only partially successful attempts at mitigating the problem was reported in this post.
Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal would 1) not explain a sustained force for ~40s and 2) would make a (short) thrust in opposite direction to the one observed by the pendulum, March added 3) that the "baseline slope" (observed systematic drift) was a consequence of the continued thermal expansion of the frustum (displacement of centre of mass) :...
And you can see this negative longer term frustum thermal drift by noting the downward going baseline slope of the thrust trace even after the RF power is removed from the copper frustum.
...
I vaguely remember it was made mention between the two posts of a better management of the IR induced pivots heating drift but can't find that (is it my imagination ?)
In this post I find arguments for points 1) and 2) convincing but 3) counter intuitive : would the frustum continue to increase at accelerated rate in bulk temperature after power off for more than 40s to explain the observed overall regular slope as a result of displacement of centre of mass ? Anyone with an intuition on the thermal dynamics of the frustum in vacuum to rule that out, or should we try a quantitative assessment ? This drifting baseline is annoying, maybe not important because slow, but still better to have a better understanding of the whole system. It looks like it is still due to IR heating of flexure pivots.
Argument :
Apart from constrained dynamics (buckling), displacement of centre of mass y(t) is roughly proportional to temperature T(t). Apparent thrust F(t) due to such a displacement is proportional to second derivative of y(t). To get an apparent thrust with a constant down rate would need a displacement to the left (temperature) rising in t^3. Can't see that happening long after power-off. The other way around, any "reasonable" bulk temperature curve would show at least an inflexion point between power on and power off (or soon after power off), that would imply an added apparent thrust first to the right then to the left. Any bound part that accelerates (reverse) has to stop accelerating (forward) and has to regain it's original place in the long run (forward then reverse). Where forward is the thrust toward the small end.
Sorry incomplete and confuse thoughts, to be continued...
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#1029 by Notsosureofit on 25 Feb, 2015 00:58
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Sorry to keep harping on this, I'll soon be done and out of the way. But I just wanna make sure I get this right. Can someone answer the question on the chart?
At least for the internal height, the junction between the plates is the place to measure from.
The internal diameters need to know the wall thickness of the cone etc.
That whole thing looks like he used (standard ?) heavy duty vacuum/pressure components. They look to be wire seal flanges, but need to know the manufacturer to find the exact sizes. Could be CF also, a bit more standard. They make size transition sections which could well be the cone.
20 bolts implies 202.4mm OD 148.2mm ID
24 bolts 253.2mm OD 198.9mm ID
32 implies 304.0 OD 247.6mm ID
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#1030 by Rodal on 25 Feb, 2015 01:00
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That's incorrect.
Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...
The buckling analysis (thermal instability) gives a force precisely in the same direction as measured.
It was the thermal expansion explanation (advanced by Oak Ridge Labs in another context) that gives a force in the completely opposite direction.
Please refer back to the original image to see that the thermal expansion force (of the dielectric, which is what thermally expands the most, as per Oak Ridge) is the one in the wrong direction.
The buckling on the end plate is in the opposite direction to the thermal expansion of the dielectric.
Buckling movement of the large diameter end is towards the left, and the buckling force is towards the left. (Paul indicates it as "oil canning" of the flat plate).
Thermal expansion of the HD PE dielectric is towards the right.
Movement of the EM Drive is towards the left, exactly the same direction as the buckling movement, and the same as the buckling force.
The buckling force is analogous to somebody pushing (actually bending) the center of the end plate towards the left, which will deflect the plate inwards. If the structure (the EM Drive) is free to move, it will move to the left, as a consequence of the plate being pushed inwards towards the left.
The buckling force perfectly explains the initial impulse magnitude, time duration of the impulse, and direction of travel. The buckling force cannot explain the sustained 40 sec force, hence the buckling force explanation is rejected on the grounds that it cannot explain the 40 sec duration of the force.
The thermal expansion explanation is rejected, upon inspection, on several grounds that the thermal expansion movement (of the HD PE) is in the opposite direction as the movement of the EM Drive, rejected on the basis that the HD PE has a free surface, hence free to expand, and therefore there should be no force arising from an unrestrained isothermal homogeneous thermal expansion. Thermal stresses arise in restrained materials or those under a temperature gradient or those with anisotropic coefficients of thermal expansion. This follows from the equations of thermoelasticity. The equations presented in the Oak Ridge report do not abide by the equations of thermoelasticity (Boley and Wiener). -
#1031 by lasoi on 25 Feb, 2015 01:07
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Thanks. I'll assume the interior walls are the same thickness as the frustum walls where they flare out and attach to the plate. We can see their thickness there.Sorry to keep harping on this, I'll soon be done and out of the way. But I just wanna make sure I get this right. Can someone answer the question on the chart?
At least for the internal height, the junction between the plates is the place to measure from.
The internal diameters need to know the wall thickness of the cone etc.
That whole thing looks like he used (standard ?) heavy duty vacuum/pressure components. -
#1032 by aero on 25 Feb, 2015 01:31
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An interesting bit of information over on TP, here:
http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=5830
I would post to the link but for some reason my computer is forbidden to access the arxiv web site. Anyone know why that might be?
Anyway, seems that in looking at the Juno fly-by anomaly they have came up with a "new" force relating angular and linear momentum. Seemingly would also work for electrical phenomenon and it might even be of the right order of magnitude to be of interest to us here. -
#1033 by Notsosureofit on 25 Feb, 2015 01:39
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Check the Edits above for some "standard" dimensions
That whole thing looks like he used (standard ?) heavy duty vacuum/pressure components. They look to be wire seal flanges, but need to know the manufacturer to find the exact sizes. Could be CF also, a bit more standard. They make size transition sections which could well be the cone.
20 bolts implies 202.4mm OD 148.2mm ID
24 bolts 253.2mm OD 198.9mm ID
32 implies 304.0 OD 247.6mm ID -
#1034 by aero on 25 Feb, 2015 01:46
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In the past we have been interested in the dielectric constant of the disks in the thruster. I made some meep runs showing force over a range of gap sizes with different values of the dielectric constant. Gaps are at the metal/metal contact between the end copper sheet and the cone body as a fraction of thruster height.
The value, 1.76, is the one I've used since I first looked for resonance at the frequency of 1880.4 MHz. It is clear that the dielectric constant has a strong effect of the meep force/power, but I speculate that it may be simply moving the resonance frequency so that the cavity is out of resonance for the other values of dielectric constant. Anyway, the data is attached.
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#1035 by lasoi on 25 Feb, 2015 01:57
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I've probably got the thickness of the frustum walls wrong but it's difficult to gauge because where the frustum walls flare out at the bottom and attach to the base cap they appear to be thinner than where they flare out at the top and attach to the top cap. I wish the photo was from a lower point of view so we could see beneath the top rim of the thing.
At any rate I can't get the dimensions of the inner cavity in the photo to jive with Shawyer's numbers. So I'm at a loss. I will say that it's a pretty remarkable coincidence that his numbers work precisely with the measurements in the photo if we use the diameters of the base and top caps, rather than the estimated diameters of the inner cavity, whatever they may be.
I'll post the chart just for the sake of having it visible. Like I said, the two diameter scales must be incorrect. My best guess for "overall" diameter of the top, would be 189mm.
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#1036 by Rodal on 25 Feb, 2015 02:20
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An interesting bit of information over on TP, here:
http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=5830
I would post to the link but for some reason my computer is forbidden to access the arxiv web site. Anyone know why that might be?
Anyway, seems that in looking at the Juno fly-by anomaly they have came up with a "new" force relating angular and linear momentum. Seemingly would also work for electrical phenomenon and it might even be of the right order of magnitude to be of interest to us here.
http://www.sciencedirect.com/science/article/pii/S0273117714004153
http://phys.org/news/2014-09-anomaly-satellite-flybys-confounds-scientists.html
http://en.wikipedia.org/wiki/Flyby_anomaly -
#1037 by frobnicat on 25 Feb, 2015 10:15
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....
That's incorrect.
Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...
Maybe, but it appears Paul March in this post says that it is opposite, and I don't see that this disagreement was acknowledged or settled. I understand his argument, not yours (on this particular point).Quote from: RodalThe buckling analysis (thermal instability) gives a force precisely in the same direction as measured.
It was the thermal expansion explanation (advanced by Oak Ridge Labs in another context) that gives a force in the completely opposite direction.
Please refer back to the original image to see that the thermal expansion force (of the dielectric, which is what thermally expands the most, as per Oak Ridge) is the one in the wrong direction.
The buckling on the end plate is in the opposite direction to the thermal expansion of the dielectric.
Buckling movement of the large diameter end is towards the left, and the buckling force is towards the left. (Paul indicates it as "oil canning" of the flat plate).
If we leave aside thermal expansion of the dielectric at small end (admittedly I forgot to take that one into account in my post...) the point made by March is that a movement to the left will first appear as a thrust to the right (action/reaction).Now Newton's third law still states that for every action there is an equal and opposite reaction. So when the copper frustum's large OD end-cap's prompt and inward oil canning action, followed by the slower frustum cone thermal expansions, they both push the copper frustum's Center of Mass (CoM) to the left as viewed from the front of the Eagleworks' vacuum chamber looking back at the test article and torque pendulum, while noting how the copper frustum is bolted on to the T.P.. These thermally induced actions to the left requires the torque pendulum's arm to move to the right to maintain the balance of the torque pendulum's arm in the lab's 1.0 gee gravity field, since we also use the Earth's g-field to help null the pendulum's movements.
The last part " in the lab's 1.0 gee gravity field, since we also use the Earth's g-field to help null the pendulum's movements." remains obscure, are we to understand that the system is not adjusted to keep the balance arm's rotation axis as vertical as possible and that a small bias is introduced so that the heavier end of arm rests at a lower position than the lighter one (rotation not on horizontal plane but slightly inclined one) ?
Anyhow, if a centre of mass displacement induced thrust signature is to be understood as an action/reaction effect, the thrust would indeed be to the right, at least initially during a phase of acceleration of CoM to the left. Or are you considering that the buckling induces another apparent thrust than an action/reaction effect ?Quote from: RodalThermal expansion of the HD PE dielectric is towards the right.
Movement of the EM Drive is towards the left, exactly the same direction as the buckling movement, and the same as the buckling force.
That's paradoxical, why a displacement to the right of CoM of dielectric (relative to frustum cone) would induce a thrust signature in the same direction as a displacement to the left of CoM of end plate (relative to frustum cone) ?Quote from: RodalThe buckling force is analogous to somebody pushing (actually bending) the center of the end plate towards the left, which will deflect the plate inwards. If the structure (the EM Drive) is free to move, it will move to the left, as a consequence of the plate being pushed inwards towards the left.
That's I don't get. The forces that induce the inward deflection can't reciprocally push on anything fixed (vacuum chamber rest frame). The reciprocal push (first radial but then with an axial component as soon as buckling occurs) is on the rim of the cone, in the moving frame of pendulum's arm.
If someone stands on a bank and pushes to the left a heavy chain that hangs from the mast of a boat, the chain will be deflected to the left and the boat will move to the left. Yes. But if someone stands on the deck of the boat, and pushes the same chain to the left, the chain is deflected to the left and the boat will recoil to the right. And buckling a large "oil canning" plate would show same effects as a freely hanging chain : depending on whether one is pushing from the bank or from the boat.Quote from: Rodal
The buckling force perfectly explains the initial impulse magnitude, time duration of the impulse, and direction of travel. The buckling force cannot explain the sustained 40 sec force, hence the buckling force explanation is rejected on the grounds that it cannot explain the 40 sec duration of the force.
The thermal expansion explanation is rejected, upon inspection, on several grounds that the thermal expansion movement (of the HD PE) is in the opposite direction as the movement of the EM Drive, rejected on the basis that the HD PE has a free surface, hence free to expand, and therefore there should be no force arising from an unrestrained isothermal homogeneous thermal expansion. Thermal stresses arise in restrained materials or those under a temperature gradient or those with anisotropic coefficients of thermal expansion. This follows from the equations of thermoelasticity. The equations presented in the Oak Ridge report do not abide by the equations of thermoelasticity (Boley and Wiener).
I have to think again about all that. You seem to make a difference whether thermal expansion is "restrained" or not on how to account for forces as seen from the outside, while it seems to me that, when all stresses and buckling have been taken into account within the system to predict a given displacement (of one part relative to another), then "recoil force" as seen from the outside depends only on those displacements of CoM (no memory if such displacement where due to constrained dynamics or not, the constraints forces "stay" inside the system). I understand March's statements as having the same difficulty to understand your take on that.
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#1038 by Notsosureofit on 25 Feb, 2015 11:43
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An interesting bit of information over on TP, here:
http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=5830
I would post to the link but for some reason my computer is forbidden to access the arxiv web site. Anyone know why that might be?
Anyway, seems that in looking at the Juno fly-by anomaly they have came up with a "new" force relating angular and linear momentum. Seemingly would also work for electrical phenomenon and it might even be of the right order of magnitude to be of interest to us here.
Don't really see a "new" force there (not up on flybys) but FYI, there is an "old force" interaction between angular momentum and a gravitational gradient that is "always" forgotten ......
This is the "Geezer" in me talking (Ya young pups) feel free to ignore ... did some of those calculations in the '60s
In those days it was thought to be able to help lift from the earths surface,...needed a source of coherent angular momentum (he he, like Hafnium which wasn't considered as I recall) -
#1039 by Rodal on 25 Feb, 2015 11:50
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(Bold added for emphasis)....
That's incorrect.
Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...
Maybe, but it appears Paul March in this post says that it is opposite, and I don't see that this disagreement was acknowledged ...
The fact that the thermal instability (buckling force) cannot be used to nullify the EM Drive thrust, was explicitly acknowledged by me and explained here http://forum.nasaspaceflight.com/index.php?topic=36313.msg1336196#msg1336196:QuoteDr. Rodal analyzed possible thermal instability (thermal buckling of the flat ends) as a cause for the measured thrust and reported this at NSF and at ResearchGate (https://www.researchgate.net/publication/268804028_NASA%27S_MICROWAVE_PROPELLANT-LESS_THRUSTER_ANOMALOUS_RESULTS_CONSIDERATION_OF_A_THERMO-MECHANICAL_EFFECT). A thermo-mechanical effect (thermal buckling) is shown that occurs in less than 1 second (for the copper thickness employed for the microwave cavity), with a temperature increase of a degree C or less and that results in forces of the same magnitude as reportedly measured by NASA. Moreover, this thermal instability produces forces in the same direction as measured, and it will occur in a vacuum (since the heating can be due either to induction heating from the axial magnetic field in a TE mode or resistive heating due to the axial electric field in a TM mode). However, this effect can only explain the initial impulsive force and cannot explain the longer 30 to 40 second measured force. Thus the thrust force measured for up to 40 second is not nullified by this explanation either.
(Bold and color added for emphasis)
Thermal expansion effect as posited by a team from Oak Ridge National Labs for another propellant-less set of experiments was also eliminated as a possible source by the NSF contributors because it would result in forces in the complete opposite direction as the forces measured by NASA.
??