Please review Rogers advise:QuoteThe route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve. If you aim for something like 75% of theoretical Q you will still get viable levels of thrust within a reasonable budget for a small business.
The route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve. If you aim for something like 75% of theoretical Q you will still get viable levels of thrust within a reasonable budget for a small business.
Quote from: X_RaY on 03/14/2016 09:00 pmHave to agree! As I said I did this only to get an idea of the dimension in general of the frequency shift using this linear approximation. Its much more than the few KHz TT stated about the 13µm differences of a single endplate. Does he multiply it by two for both plates or does he meant the total displacement or surface roughness? Please review Rogers advise:QuoteThe route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve. If you aim for something like 75% of theoretical Q you will still get viable levels of thrust within a reasonable budget for a small business.
Have to agree! As I said I did this only to get an idea of the dimension in general of the frequency shift using this linear approximation. Its much more than the few KHz TT stated about the 13µm differences of a single endplate. Does he multiply it by two for both plates or does he meant the total displacement or surface roughness?
Quote from: TheTraveller on 03/14/2016 09:11 pmPlease review Rogers advise:QuoteThe route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve. If you aim for something like 75% of theoretical Q you will still get viable levels of thrust within a reasonable budget for a small business.I'm still not convinced that a higher Q will automatically lead towards a higher generated force as it has yet to be established that there is a relation between them.I'm still having trouble with the concept of having almost no energetic losses (= high Q) on one side and an increased force, which means a transfer of energy, on the other side. In my mind, these to are in an apparent conflict.. no?The only possible way i can see a high Q result in a higher force, is when the force is not generated on the frustum walls, but is somehow created inside the frustum and causes it to move "somehow" (the gravity/gravity field EMtheory). The only result of a high Q is that you store more electromagnetic energy in the cavity.If the force is generated on the frustum walls (either on front/back plates or the side walls) it must come at the expense of the Q of the electromagnetic waves. Any (yet to be determined) interaction between the walls and the electromagnetic waves must come at the expense of the Q.So that's , after nearly 2 years of following this topic, i remain a skeptic of the extreme high Q pursuit and the floating car promises they hold.
Quote from: TheTraveller on 03/14/2016 09:11 pmQuote from: X_RaY on 03/14/2016 09:00 pmHave to agree! As I said I did this only to get an idea of the dimension in general of the frequency shift using this linear approximation. Its much more than the few KHz TT stated about the 13µm differences of a single endplate. Does he multiply it by two for both plates or does he meant the total displacement or surface roughness? Please review Rogers advise:QuoteThe route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve. If you aim for something like 75% of theoretical Q you will still get viable levels of thrust within a reasonable budget for a small business.This implies a surface finish of 13 microns, not a dimensional tolerance of 13 microns. Correct? A 13 micron surface finish is actually pretty crappy. As a SWAG on my part, it looks like Dave got better than 2 microns on his polished end plates (based on observation of haze and geometric distortion).
If the force is generated on the frustum walls (either on front/back plates or the side walls) it must come at the expense of the Q of the electromagnetic waves. Any (yet to be determined) interaction between the walls and the electromagnetic waves must come at the expense of the Q.
Quote from: TheTraveller on 03/14/2016 09:11 pmQuote from: X_RaY on 03/14/2016 09:00 pmHave to agree! As I said I did this only to get an idea of the dimension in general of the frequency shift using this linear approximation. Its much more than the few KHz TT stated about the 13µm differences of a single endplate. Does he multiply it by two for both plates or does he meant the total displacement or surface roughness? Please review Rogers advise:QuoteThe route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve. If you aim for something like 75% of theoretical Q you will still get viable levels of thrust within a reasonable budget for a small business.This implies a surface finish of 13 microns, not a dimensional tolerance of 13 microns. Correct? A 13 micron surface finish is actually pretty crappy. As a SWAG on my part, it looks like Dave got better than 2 microns on his polished end plates (based on observation of haze and geometric distortion).What we really need is a proper mechanical drawing, with dimensional tolerances and required flatness and surface finish, as any drafting student is taught to do.
Quote from: Flyby on 03/14/2016 11:03 pmIf the force is generated on the frustum walls (either on front/back plates or the side walls) it must come at the expense of the Q of the electromagnetic waves. Any (yet to be determined) interaction between the walls and the electromagnetic waves must come at the expense of the Q.Exactly correct. The conversion of internal cavity energy to external kinetic energy is at the expense of reduced internal cavity energy & Q as this conversions adds to cavity Q losses.No free lunches.It is all detailed in Rogers papers.
Quote from: X_RaY on 03/14/2016 05:44 pmAt the moment and in general there are much bigger problems (thermal expansion, How much will a ~20cm copper frustum expand due to heating? If it is less than 1/2 a cm or so, then it shouldn't be too much of a concern. Best to have a tunable frustum IMHO. And from what I've learned today, it might be best to have the big end be the side that is tuned.
At the moment and in general there are much bigger problems (thermal expansion,
Quote from: TheTraveller on 03/14/2016 11:43 pmQuote from: Flyby on 03/14/2016 11:03 pmIf the force is generated on the frustum walls (either on front/back plates or the side walls) it must come at the expense of the Q of the electromagnetic waves. Any (yet to be determined) interaction between the walls and the electromagnetic waves must come at the expense of the Q.Exactly correct. The conversion of internal cavity energy to external kinetic energy is at the expense of reduced internal cavity energy & Q as this conversions adds to cavity Q losses.No free lunches.It is all detailed in Rogers papers.I am fairly sure that a force in itself won't use up energy until the cavity actually begins to free accelerate by F.dx = Energy (if it does accelerate purely via light) . This should be similar to two mirrors accelerated away from each other and the light between them red-shifts when the mirrors actually start to accelerate. If the mirrors are held stationary and are perfectly reflective no red-shifting of the light between the mirrors should happen but a force will still be present. (While the two systems [cavity or mirrors] are different, I am assuming if there were a force purely by the pressure of light inside the cavity that we could parallel between the two systems.)On the other hand if the light is accelerating something other than the cavity as a propellant that passes through the walls then there is a chance of seeing Q or energy content drop even when the cavity isn't accelerating because the light is accelerating something else via F.dx=E . If there is some anomalous force the difference between these two scenarios might be a way to narrowing down where it is coming from.
Note that the reaction is either the acceleration a, or a force equal to Ma, but not both.
Quote from: dustinthewind on 03/15/2016 02:11 amQuote from: TheTraveller on 03/14/2016 11:43 pmQuote from: Flyby on 03/14/2016 11:03 pmIf the force is generated on the frustum walls (either on front/back plates or the side walls) it must come at the expense of the Q of the electromagnetic waves. Any (yet to be determined) interaction between the walls and the electromagnetic waves must come at the expense of the Q.Exactly correct. The conversion of internal cavity energy to external kinetic energy is at the expense of reduced internal cavity energy & Q as this conversions adds to cavity Q losses.No free lunches.It is all detailed in Rogers papers.I am fairly sure that a force in itself won't use up energy until the cavity actually begins to free accelerate by F.dx = Energy (if it does accelerate purely via light) . This should be similar to two mirrors accelerated away from each other and the light between them red-shifts when the mirrors actually start to accelerate. If the mirrors are held stationary and are perfectly reflective no red-shifting of the light between the mirrors should happen but a force will still be present. (While the two systems [cavity or mirrors] are different, I am assuming if there were a force purely by the pressure of light inside the cavity that we could parallel between the two systems.)On the other hand if the light is accelerating something other than the cavity as a propellant that passes through the walls then there is a chance of seeing Q or energy content drop even when the cavity isn't accelerating because the light is accelerating something else via F.dx=E . If there is some anomalous force the difference between these two scenarios might be a way to narrowing down where it is coming from. As per attached.QuoteNote that the reaction is either the acceleration a, or a force equal to Ma, but not both.EmDrive Force Measurement:http://www.emdrive.com/EmDriveForceMeasurement.pdfThe EmDrive is not a rocket. It does not generate acceleration unless it is free to move. When constrained there is no external Force generated.
Quote from: TheTraveller on 03/15/2016 11:20 amQuote from: dustinthewind on 03/15/2016 02:11 amQuote from: TheTraveller on 03/14/2016 11:43 pmQuote from: Flyby on 03/14/2016 11:03 pmIf the force is generated on the frustum walls (either on front/back plates or the side walls) it must come at the expense of the Q of the electromagnetic waves. Any (yet to be determined) interaction between the walls and the electromagnetic waves must come at the expense of the Q.Exactly correct. The conversion of internal cavity energy to external kinetic energy is at the expense of reduced internal cavity energy & Q as this conversions adds to cavity Q losses.No free lunches.It is all detailed in Rogers papers.I am fairly sure that a force in itself won't use up energy until the cavity actually begins to free accelerate by F.dx = Energy (if it does accelerate purely via light) . This should be similar to two mirrors accelerated away from each other and the light between them red-shifts when the mirrors actually start to accelerate. If the mirrors are held stationary and are perfectly reflective no red-shifting of the light between the mirrors should happen but a force will still be present. (While the two systems [cavity or mirrors] are different, I am assuming if there were a force purely by the pressure of light inside the cavity that we could parallel between the two systems.)On the other hand if the light is accelerating something other than the cavity as a propellant that passes through the walls then there is a chance of seeing Q or energy content drop even when the cavity isn't accelerating because the light is accelerating something else via F.dx=E . If there is some anomalous force the difference between these two scenarios might be a way to narrowing down where it is coming from. As per attached.QuoteNote that the reaction is either the acceleration a, or a force equal to Ma, but not both.EmDrive Force Measurement:http://www.emdrive.com/EmDriveForceMeasurement.pdfThe EmDrive is not a rocket. It does not generate acceleration unless it is free to move. When constrained there is no external Force generated."Clearly, in a static situation, where T and R both exist as forces , they will cancel out."Not clear, and not proven, and only if Fg1=Fg2, an assertion I do not believe is accurate.I have not read the whole paper, but will do so soon and comment further.
EM propulsion study for USAF written in 1989 contains a lot about some of the theories and speculations similar to emdrive. 169 pages...5 D math...I suspect theory people will find this old paper interesting:https://drive.google.com/file/d/0B4Ez9NDUxpYLZThJTy15TUdPVnM/view
...QuoteNote that the reaction is either the acceleration a, or a force equal to Ma, but not both.EmDrive Force Measurement:http://www.emdrive.com/EmDriveForceMeasurement.pdfThe EmDrive is not a rocket. It does not generate acceleration unless it is free to move. When constrained there is no external Force generated.
This internal force F is measured by an outside observer as the Thrust T, a force acting against the observer in the direction shown.
In free space, the thruster will simply accelerate at a m/s/s, and R will not be measurable.
Quote from: Monomorphic on 03/14/2016 06:12 pmQuote from: X_RaY on 03/14/2016 05:44 pmAt the moment and in general there are much bigger problems (thermal expansion, How much will a ~20cm copper frustum expand due to heating? If it is less than 1/2 a cm or so, then it shouldn't be too much of a concern. Best to have a tunable frustum IMHO. And from what I've learned today, it might be best to have the big end be the side that is tuned. I would design it in a way, that the frustum reaches its final (resonance-optimized) dimensions, when the final average operational temperature of the cavity metal walls is reached. I do not know, whether the EM drive designers are doing this already. So I thought it can not hurt to point this out. It's better to have the frustum expand into its perfect dimensions and work WITH nature, instead of trying to compensate for expansion and work AGAINST nature. Also, if the sought after effect is reproducible and we can go to space with it, we better design this thing mechanically in a self-calibrating/adjusting way.
(...)1) Concerning <<I do not know, whether the EM drive designers are doing this already>> they are certainly not conducting their experiments so that <<the frustum reaches its final (resonance-optimized) dimensions, when the final average operational temperature of the cavity metal walls is reached>>.2) As to whether what you propose is feasible, and whether such a test would be representative of space propulsion, consider the following:a) whether a "final steady state" will be reached is a function of the amount of cooling provided. As long as the RF feed is on you have a constant source of induction heat (all EM Drive experiments have been conducted with either the RF feed constantly on, or with the RF feed pulsating on and off) .b) Cooling only takes place by:b1) thermal conductivity: this is limited by the amount of metal "sink" available. For constructions such as for example, those of rfmwguy who has only 1 mm thickness on the side walls, this is very limited. EM Drive constructions with thick walls have substantially more heat sink available. The time at which a given temperature is reached is inversely proportional to the square of the thickness. This follows from the Fourier number: b2) convection: all EM Drive experiments have been conducted without any forced air convection (and certainly without fluid convection like water, or any other fluids that have substantially more cooling capability). They rely on natural convection. It is known that the amount of convection provided by natural air convection is very limited due to the very small coefficient of heat transfer due to natural air convection. Natural convection - air ~0.5 to 20 (W/(m^2K))Forced Convection - air ~ 10 to 1000 (W/(m^2K))Forced Convection - water and liquids up to 10000 (W/(m^2K))Most importantly, natural air convection is not available in space and hence tests relying on natural convection would be very unrepresentative of what would happen in space.b3) radiation: the amount of heat radiation is proportional to the temperature to the fourth power. Hence it is very nonlinear. It would take a very large temperature increase for radiation to be effective and to be able to equal the amount of heat produced by induction heating. Hence if you are counting on radiation, the "final temperature" would be high, and it would take place at a late time, considerably longer than what EM Drive experiments have been conducted for.
...Thanks for your great reply, because it should remind all here of the fact that this 'propulsion system' is eventually supposed to work in free space with its absence of convective cooling. I don't think, that the sort of testing that's going on right now, has any real merit, because the test articles never reach e.g. their thermodynamical operating point, which is, by the way, not even defined yet. The test articles not being in thermodynamical equilibrium can certainly cause readings that seem to indicate force production. But is it so?Let me just say, that at my old workplace, we had 300+k€ high-end oscilloscopes, which needed to reach their operational temperature within about an hour after switching on, just to be able to make reliable measurements. Defining and keeping points of operation is vital in any engineering, which seems to have happily been forgone. At least it seems to me like this, with the information accessible to me. If the hitherto undertaken experiments have not run long enough for the frustum to even closely reach their stable operating points, then that is a problem of the hitherto taken approaches, not of me stating the fact. I think that I would never dare making any assumptions about any experimental setup without it having reached its operating point.Just think LIGO, e.g. does anyone seriously think that they did not heavily control environmental conditions until the point where they could be practically 100% confidential, that the measurement apparatus had reached its stable operating point and could hopefully produce expected results? The EM drive contraptions are all in fact measuring apparatuses that hope to measure a hitherto elusive way of producing propulsive forces in the low µN range. Don't you think we should apply similarly rigid considerations like in LIGO (although much simpler to achieve in this case) for trying to find out, whether there is really something going on, or whether there is some curious transitional effect emulating what is looked for?BR,CW
Quote from: Rodal on 03/15/2016 01:09 pm(...)1) Concerning <<I do not know, whether the EM drive designers are doing this already>> they are certainly not conducting their experiments so that <<the frustum reaches its final (resonance-optimized) dimensions, when the final average operational temperature of the cavity metal walls is reached>>.2) As to whether what you propose is feasible, and whether such a test would be representative of space propulsion, consider the following:a) whether a "final steady state" will be reached is a function of the amount of cooling provided. As long as the RF feed is on you have a constant source of induction heat (all EM Drive experiments have been conducted with either the RF feed constantly on, or with the RF feed pulsating on and off) .b) Cooling only takes place by:b1) thermal conductivity: this is limited by the amount of metal "sink" available. For constructions such as for example, those of rfmwguy who has only 1 mm thickness on the side walls, this is very limited. EM Drive constructions with thick walls have substantially more heat sink available. The time at which a given temperature is reached is inversely proportional to the square of the thickness. This follows from the Fourier number: b2) convection: all EM Drive experiments have been conducted without any forced air convection (and certainly without fluid convection like water, or any other fluids that have substantially more cooling capability). They rely on natural convection. It is known that the amount of convection provided by natural air convection is very limited due to the very small coefficient of heat transfer due to natural air convection. Natural convection - air ~0.5 to 20 (W/(m^2K))Forced Convection - air ~ 10 to 1000 (W/(m^2K))Forced Convection - water and liquids up to 10000 (W/(m^2K))Most importantly, natural air convection is not available in space and hence tests relying on natural convection would be very unrepresentative of what would happen in space.b3) radiation: the amount of heat radiation is proportional to the temperature to the fourth power. Hence it is very nonlinear. It would take a very large temperature increase for radiation to be effective and to be able to equal the amount of heat produced by induction heating. Hence if you are counting on radiation, the "final temperature" would be high, and it would take place at a late time, considerably longer than what EM Drive experiments have been conducted for.Thanks for your great reply, because it should remind all here of the fact that this 'propulsion system' is eventually supposed to work in free space with its absence of convective cooling. I don't think, that the sort of testing that's going on right now, has any real merit, because the test articles never reach e.g. their thermodynamical operating point, which is, by the way, not even defined yet. The test articles not being in thermodynamical equilibrium can certainly cause readings that seem to indicate force production. But is it so?Let me just say, that at my old workplace, we had 300+k€ high-end oscilloscopes, which needed to reach their operational temperature within about an hour after switching on, just to be able to make reliable measurements. Defining and keeping points of operation is vital in any engineering, which seems to have happily been forgone. At least it seems to me like this, with the information accessible to me. If the hitherto undertaken experiments have not run long enough for the frustum to even closely reach their stable operating points, then that is a problem of the hitherto taken approaches, not of me stating the fact. I think that I would never dare making any assumptions about any experimental setup without it having reached its operating point.Just think LIGO, e.g. does anyone seriously think that they did not heavily control environmental conditions to the point where they could be practically 100% confidential, that the measurement apparatus had reached its stable operating point and could hopefully produce expected results? The EM drive contraptions are all in fact measuring apparatuses that hope to measure a hitherto elusive way of producing propulsive forces in the low µN range. Don't you think we should apply similarly rigid considerations like in LIGO (although much simpler to achieve in this case) for trying to find out, whether there is really something going on, or whether there is some curious transitional thermodynamical effect emulating what is looked for? Since the EM drive seeks noting less than to overthrow centuries of confirmed physical experimental results so far, it is the greatest duty of experimenters to rigidly make sure that not only confirmed physical knowledge so far is applied correctly, but that especially the physical implementation and measurement setups in the form of test articles is made with prudent and known to be correct engineering approaches. BR,CW