Quote from: Mulletron on 05/31/2015 04:56 PMYes and as much of early thread 2 will attest, using methods for calculating cylinders will get you close to frustums but no cigar. Also the accuracy of Eagleworks Comsol simulations has been proven accurate using physical measurement (thermal camera for example).Back then a proper Df equation did not exist nor an understanding how the SPR method of Df > length resonance > thrust (at selected mode) method hangs together.With respect to COMSOL, so far all it has been able to do is to predict thrust with dielectrics. From my reading of the past comments, COMSOL never predicted any thrust without a dielectric. So if it can't predict thrust without a dielectric, as SPR can, why is it being used to try to model what is happening inside a cavity that has no dielectric?

Yes and as much of early thread 2 will attest, using methods for calculating cylinders will get you close to frustums but no cigar. Also the accuracy of Eagleworks Comsol simulations has been proven accurate using physical measurement (thermal camera for example).

Quote from: TheTraveller on 05/31/2015 05:04 PM...With respect to COMSOL, so far all it has been able to do is to predict thrust with dielectrics. From my reading of the past comments, COMSOL never predicted any thrust without a dielectric. So if it can't predict thrust without a dielectric, as SPR can, why is it being used to try to model what is happening inside a cavity that has no dielectric?1) The NASA Eagleworks COMSOL FEA solutions being discussed in this thread are not at all thrust predictions.They are eigensolutions to the eigenvalue problem: they give the mode shape electromagnetic field distributions, the natural frequencies and the predicted Q. They are used at CERN and at major companies and academic institutions to predict natural frequencies, mode shapes and cut-off.2) The approximate cut-off equation you are using from a handbook also does not predict thrust3) The approximate natural frequency formula you are using also does not predict thrust.None of the above solutions deal (solely by themselves) with thrust predictions.Even if one were to use, for example, MEEP to try to calculate thrust based on evanescent waves, for example, the analyst must keep a clear distinction between on what basis are mode shapes, frequencies and cut-off being predicted, and what is involved in any thrust modeling calculation. Commingling these solutions together only results in confusion.

...With respect to COMSOL, so far all it has been able to do is to predict thrust with dielectrics. From my reading of the past comments, COMSOL never predicted any thrust without a dielectric. So if it can't predict thrust without a dielectric, as SPR can, why is it being used to try to model what is happening inside a cavity that has no dielectric?

Quote from: Rodal on 05/30/2015 08:54 PMQuote from: davish on 05/30/2015 08:50 PMQuote from: Rodal on 05/30/2015 08:36 PMOh Baby, here is a test stand floating on air, ready for baby EM drive ...Is this "baby" EM Drive supposed to have lower thrust according to any of the theories? Or is thrust completely based on resonance?Some theories have thrust inversely proportional to frequency (hence this one at 24 GHz should have ~10 times less thrust than the ones at 2.4 GHz so far tested, based on inverse of linear proportionality alone)McCulloch's formula F = PQl/c * (1/w_small - 1/w_big) where l is the cavity length is independent of frequency. But it is still proportional to power input.Most theories have thrust proportional to PowerInput This just has a little battery, so also have to factor out less thrust due to the lower Power Input So, yes, substantially less thrust, according to those theories.Higher frequency also means more geometrical attenuation, perhaps that's good, if it also has higher Q to go with itAnd you can put a lot of these ones together, and it looks much neater and Hi-Tech If it works, it can go right away into a CubeSatNotsosureofit's expression is also independent of frequency when the diameter and the length of the cavity are both scaled to decrease inversely proportional to increasing frequency, in order to maintain the same mode shape.When the frequency increases by a factor of 10 (24 GHz = 10 * 2.4 GHz), then the diameter needs to be decreased by a factor of 10 and the length needs to be decreased by a factor of 10, in order to keep the same mode shape and thrust, as per Notsosureofit's formula.When the diameter and the length of the cavity are both scaled to decrease inversely proportional to increasing frequency, McCulloch's thrust expression also stays invariant.So, Baby EM Drive by the guy in Aachen, Germany, at 24 GHz will be an extremely interesting test to find out whether McCulloch's and Notsosureofit equations are correct.IMHO this Baby EM Drive test is the most interesting EM Drive test !!!The ammonia molecule readily undergoes nitrogen inversion at room temperature. The resonance frequency is 23.79 GHz, corresponding to microwave radiation of a wavelength of 1.260 cm. The absorption at this frequency was the first microwave spectrum to be observed. Ammonia has been used for Masers at 24 GHz for these reasons.When using ammonia, safety precautions should be followed: https://www.health.ny.gov/environmental/emergency/chemical_terrorism/ammonia_tech.htm

Quote from: davish on 05/30/2015 08:50 PMQuote from: Rodal on 05/30/2015 08:36 PMOh Baby, here is a test stand floating on air, ready for baby EM drive ...Is this "baby" EM Drive supposed to have lower thrust according to any of the theories? Or is thrust completely based on resonance?Some theories have thrust inversely proportional to frequency (hence this one at 24 GHz should have ~10 times less thrust than the ones at 2.4 GHz so far tested, based on inverse of linear proportionality alone)McCulloch's formula F = PQl/c * (1/w_small - 1/w_big) where l is the cavity length is independent of frequency. But it is still proportional to power input.Most theories have thrust proportional to PowerInput This just has a little battery, so also have to factor out less thrust due to the lower Power Input So, yes, substantially less thrust, according to those theories.Higher frequency also means more geometrical attenuation, perhaps that's good, if it also has higher Q to go with itAnd you can put a lot of these ones together, and it looks much neater and Hi-Tech If it works, it can go right away into a CubeSat

Quote from: Rodal on 05/30/2015 08:36 PMOh Baby, here is a test stand floating on air, ready for baby EM drive ...Is this "baby" EM Drive supposed to have lower thrust according to any of the theories? Or is thrust completely based on resonance?

Oh Baby, here is a test stand floating on air, ready for baby EM drive ...

Quote from: TheTraveller on 05/31/2015 05:04 PMQuote from: Mulletron on 05/31/2015 04:56 PMYes and as much of early thread 2 will attest, using methods for calculating cylinders will get you close to frustums but no cigar. Also the accuracy of Eagleworks Comsol simulations has been proven accurate using physical measurement (thermal camera for example).Back then a proper Df equation did not exist nor an understanding how the SPR method of Df > length resonance > thrust (at selected mode) method hangs together.With respect to COMSOL, so far all it has been able to do is to predict thrust with dielectrics. From my reading of the past comments, COMSOL never predicted any thrust without a dielectric. So if it can't predict thrust without a dielectric, as SPR can, why is it being used to try to model what is happening inside a cavity that has no dielectric?All this testo engineer argument stuff is not productive. Now this old gal engineer states that over 40 years in engineering I've seen design calculations ( I don't care what or who does them) fall a little short time and time again. Bottom line, build the test bed, but be a smart engineer knowing we can't know all and design the flexibility to fine tune it. Simple. This is what I'm doing.We're dealing with something here that nobody quite knows how it works.

...We really do need both.10 years before the Wright brothers flew the first airplane, there were tables compiled (I forget by whom) that showed lift vs drag coefs for a variety of wing shapes. People had been trying for years to build airplanes from those tables.Those tables were wrong.The genius of the Wrights was not really in building the first airplane, it was in building the first wind tunnel so they could test wing shapes and figure out how this stuff REALLY worked.I feel like that's where we are. And we need both physical and virtual models so we figure out where the equations are 'Wright' and wrong by building physical devices to test the theories.This work would progress WAY faster if we had access to a 3D metal printer - I'm guessing bronze would work almost the same as pure copper and you could build a new device in about a day. Imagine if you could iterate a device every 2-3 days!!!

An equally simple and related question: what Shawyer Design Factor does COMSOL, MEEP or some other tool predict?

Quote from: Rodal on 05/31/2015 06:00 PMAn equally simple and related question: what Shawyer Design Factor does COMSOL, MEEP or some other tool predict?I think what you are saying is COMSOL can't predict the small and big end cutoff wavelength, guide wavelength and group velocity values?If it can't, then for sure it is a nice tool but virtually useless in predicting EMDrive cavity dynamics and related thrust.

Quote from: Blaine on 05/31/2015 04:21 PMOkay, seriously can we get past this back and forth arguing between the traveler and rodal. Its giving me a headache and its deluding the conversation for us all.I think it is important to know why my EM Drive Calculator, which is based on microwave industry & SPR equations for Df, shows the EW frustum was in cutoff and not capable of generating thrust, while COMSOL says it was not in cutoff and should. Note here the actual result was no thrust as predicted by the Calculator.I'm an engineer, I need the numbers to stack up and it they don't, I need to know why. If my Calculator is in error, then I need to fix it. But so far it is predicting what SPR is measuring.Please understand the small end being in cutoff to the guide wavelength only involves TE01 mode. It does not involve TE012 as that is about 2 x 1/2 waves fitting in between the end plate spacing. So the length mode is not involved in small end cutoff. Only diameter, BesselJ cutoff function at the TE01 excitation mode and external Rf frequency are involved.Here is the test:Show where a 0.1588m diameter circular waveguide can propagate a 2.168GHz signal at TE01 mode. All the microwave industry equations say it can't, so why does COMSOL say it can??If I have this wrong, then the basis of the Df equation is wrong.Cutoff and guide wavelengths from here:http://www.tuks.nl/pdf/Reference_Material/Circular_Waveguides.pdf

Okay, seriously can we get past this back and forth arguing between the traveler and rodal. Its giving me a headache and its deluding the conversation for us all.

...I think it is important to know why my EM Drive Calculator, which is based on microwave industry & SPR equations for Df, shows the EW frustum was in cutoff and not capable of generating thrust, while COMSOL says it was not in cutoff and should. Note here the actual result was no thrust as predicted by the Calculator.I'm an engineer, I need the numbers to stack up and it they don't, I need to know why. If my Calculator is in error, then I need to fix it. But so far it is predicting what SPR is measuring.Please understand the small end being in cutoff to the guide wavelength only involves TE01 mode. It does not involve TE012 as that is about 2 x 1/2 waves fitting in between the end plate spacing. So the length mode is not involved in small end cutoff. Only diameter, BesselJ cutoff function at the TE01 excitation mode and external Rf frequency are involved.Here is the test:Show where a 0.1588m diameter circular waveguide can propagate a 2.168GHz signal at TE01 mode. All the microwave industry equations say it can't, so why does COMSOL say it can??If I have this wrong, then the basis of the Df equation is wrong.Cutoff and guide wavelengths from here:http://www.tuks.nl/pdf/Reference_Material/Circular_Waveguides.pdf

This gold plated Emdrive was a bust:http://forum.nasaspaceflight.com/index.php?topic=36313.msg1338971#msg1338971I wonder how the baby Emdrive will do, is it made of steel or aluminum???http://forum.nasaspaceflight.com/index.php?topic=37642.msg1382129#msg1382129Edit:What in the world was the inside of this one made of, and did it have a dielectric insert?http://forum.nasaspaceflight.com/index.php?topic=37642.msg1380043#msg1380043Aluminum??Steel?And why I'm wondering...http://forum.nasaspaceflight.com/index.php?topic=29276.msg1275985#msg1275985http://forum.nasaspaceflight.com/index.php?topic=36313.msg1369555#msg1369555

Quote from: TheTraveller on 05/31/2015 04:35 PM...If I have this wrong, then the basis of the Df equation is wrong.......The EM Drive is not a cylinder, it is a truncated cone., that is the reason why the equation you are using is inexact....1) Your equation is based on the cut-off frequency for a cylinder, instead of the cut-off frequency for a truncated cone. Your equation is off by only 6% (it is really not that bad, when considering you are modeling a different geometry).....

...If I have this wrong, then the basis of the Df equation is wrong....

Quote from: TheTraveller on 05/31/2015 04:35 PM...I think it is important to know why my EM Drive Calculator, which is based on microwave industry & SPR equations for Df, shows the EW frustum was in cutoff and not capable of generating thrust, while COMSOL says it was not in cutoff and should. Note here the actual result was no thrust as predicted by the Calculator.I'm an engineer, I need the numbers to stack up and it they don't, I need to know why. If my Calculator is in error, then I need to fix it. But so far it is predicting what SPR is measuring.Please understand the small end being in cutoff to the guide wavelength only involves TE01 mode. It does not involve TE012 as that is about 2 x 1/2 waves fitting in between the end plate spacing. So the length mode is not involved in small end cutoff. Only diameter, BesselJ cutoff function at the TE01 excitation mode and external Rf frequency are involved.Here is the test:Show where a 0.1588m diameter circular waveguide can propagate a 2.168GHz signal at TE01 mode. All the microwave industry equations say it can't, so why does COMSOL say it can??If I have this wrong, then the basis of the Df equation is wrong.Cutoff and guide wavelengths from here:http://www.tuks.nl/pdf/Reference_Material/Circular_Waveguides.pdfTheTraveller, I completely agree with you that it is important to understand where this difference between your calculations and the Finite Element and the exact solutions lies, and you are owed an answer (anyone that gets a headache from reading this doesn't need to read this. This is what the EM Drives threads are all about: to discuss technical issues). In these exchanges, we are all pushed to understand what is the accuracy of mathematical models to model the real world. Once we are done with the discussion, we are both better off because we have understood the mathematical models and the real world a little better. I thank you for displaying the equation you are using for cut-off frequency because it shows the problem:the equation you are using is based on the solution for a cylindrical waveguide It is based on the zeros X_{mn} of the cylindrical Bessel and the zeros X'_{mn} of the derivative of the cylindrical Bessel functions.The EM Drive is not a cylinder, it is a truncated cone., that is the reason why the equation you are using is inexact.The cut-off frequency for a truncated cone is not based on cylindrical Bessel functions (that you are using).The cut-off frequency for a truncated cone is based on spherical Bessel functions and associated Legendre functions. To find out what modes are cut-off at what frequency for a truncated cone, you have to solve two eigenvalue problems, you cannot just get it from a table of values (like you do when you solve for a cylinder).The only way you have to improve this would be for you to find out the equation for the cut-off frequency for a truncated cone: which I don't think you are going to find, because there is no closed-form equation for the cut-off frequency for a truncated cone.Anyone using that cut-off frequency equation (based on a cylinder) is going to make an error when modeling a cone. COMSOL FEA, MEEP and the exact solution do not make that error because they don't model the truncated cone as a cylinder.Therefore, I think that the evidence points towards the fact that NASA Eagleworks conducted the TE012 test probably at the correct frequency:1) Your equation is based on the cut-off frequency for a cylinder, instead of the cut-off frequency for a truncated cone. Your equation is off by only 6% (it is really not that bad, when considering you are modeling a different geometry). Your formula fits on a postage stamp, the exact solution takes several lines of Mathematica code. The FEA solution comprises millions of computer instructions and inverting a huge matrix.2) NASA would not be "flying blind". NASA Eagleworks probably had a S21 plot available and was able to see the resonance peak and calculated the loaded Q at the frequency they tested, so they knew they were at resonance.

Therefore, I think that the evidence points towards the fact that NASA Eagleworks conducted the TE012 test probably at the correct frequency