Quote from: Rodal on 10/25/2014 03:01 pmQuote from: JohnFornaro on 10/25/2014 02:40 pmQuote from: frobnicat on 10/25/2014 02:24 pmNeeded hypothesis : air inside cavity is volumetrically heated at Pow=4W (that is, air gets around 25% of microwave power input). There are hole(s) or crevice(s) between cavity and exterior of device, in the direction of thrust (air jetting...) for a total area of A=1.6 mm². I would say that the perimeter of the big end leaks. Not sure how you'd model that leaky connection of the PCB to the copper frustrum flange.At any rate (rate? get it?) the are coming out radially at right angles to the thrust axis of the thingy.[Hint from the inappropriate humor department: Listener maximizes humor by familiarity with Brian Eno's album cover art. Linked artwork is not true color, but that's immaterial.]<< are coming out radially at right angles to the thrust axis of the thingy.>>A=1.6 mm² leaking could be axial due to the gap between the bolts and the boltholes1.6 mm² is only 0.0025 square inches or a square having 0.05 inches per sideLook deeply, look at all those bolts. I count 24 bolts, so this would be a gap of only 0.0001 square inches per boltOr the seam that appear on the side of cone (assuming it's not welded). If leaks are not perfectly axial there would still be a net thrust but with a lower efficiency (cosine of the angle relative to axis). The magnitude jet effects can get are pretty close what is to be explained, would be hard to account for less than ideal jet directions... yet it's tantalizingly close. Equations together (will try to summarize that this week-end) can give higher thrust with lower leak area but at the price of higher time constant to reach delta pressure equilibrium (more than 2s).Also a jet that would come out a seam between two planes perpendicular to axis would have a significant axial component when the flange is asymmetric (for instance the copper part ends when the PCB extends a little bit further...)In what direction (average) the jets would have to go ? I'm still all confused with the thrust directions.The big caveat : 4W volumetric heating of (presumably not perfectly dry) air out of 16W microwave power in "empty oven".
Quote from: JohnFornaro on 10/25/2014 02:40 pmQuote from: frobnicat on 10/25/2014 02:24 pmNeeded hypothesis : air inside cavity is volumetrically heated at Pow=4W (that is, air gets around 25% of microwave power input). There are hole(s) or crevice(s) between cavity and exterior of device, in the direction of thrust (air jetting...) for a total area of A=1.6 mm². I would say that the perimeter of the big end leaks. Not sure how you'd model that leaky connection of the PCB to the copper frustrum flange.At any rate (rate? get it?) the are coming out radially at right angles to the thrust axis of the thingy.[Hint from the inappropriate humor department: Listener maximizes humor by familiarity with Brian Eno's album cover art. Linked artwork is not true color, but that's immaterial.]<< are coming out radially at right angles to the thrust axis of the thingy.>>A=1.6 mm² leaking could be axial due to the gap between the bolts and the boltholes1.6 mm² is only 0.0025 square inches or a square having 0.05 inches per sideLook deeply, look at all those bolts. I count 24 bolts, so this would be a gap of only 0.0001 square inches per bolt
Quote from: frobnicat on 10/25/2014 02:24 pmNeeded hypothesis : air inside cavity is volumetrically heated at Pow=4W (that is, air gets around 25% of microwave power input). There are hole(s) or crevice(s) between cavity and exterior of device, in the direction of thrust (air jetting...) for a total area of A=1.6 mm². I would say that the perimeter of the big end leaks. Not sure how you'd model that leaky connection of the PCB to the copper frustrum flange.At any rate (rate? get it?) the are coming out radially at right angles to the thrust axis of the thingy.[Hint from the inappropriate humor department: Listener maximizes humor by familiarity with Brian Eno's album cover art. Linked artwork is not true color, but that's immaterial.]
Needed hypothesis : air inside cavity is volumetrically heated at Pow=4W (that is, air gets around 25% of microwave power input). There are hole(s) or crevice(s) between cavity and exterior of device, in the direction of thrust (air jetting...) for a total area of A=1.6 mm².
Quote from: Rodal on 10/23/2014 06:58 pmI recall that Paul March wrote that the EMDrives tested at NASA Eagleworks had a temperature that never rose more than 1 deg (F ? or C?) above room temperature.Anybody recall that statement? Is the temperature measurement in the NASA Eagleworks report? Using search I cannot find it in the text. Is it in the pictures?I also recall AcesHigh reporting on information elsewhere reporting March's statement he made on this thread regarding temperature. Was that at nextbigfuture? Does anybody still have a link for that?Yes I remember March saying the temperature didn't rise more than 1 degree F. It was F, not C.
I recall that Paul March wrote that the EMDrives tested at NASA Eagleworks had a temperature that never rose more than 1 deg (F ? or C?) above room temperature.Anybody recall that statement? Is the temperature measurement in the NASA Eagleworks report? Using search I cannot find it in the text. Is it in the pictures?I also recall AcesHigh reporting on information elsewhere reporting March's statement he made on this thread regarding temperature. Was that at nextbigfuture? Does anybody still have a link for that?
Ok. That's well thought out. Now can you explain the lack of thrust from the Brady device without dielectric? Remove the dielectric and there is no thrust. What happened to the heat dissipation?The other problem that continues to arise is the total momentum .vs. the power dissipated
Quote from: Mulletron on 10/25/2014 03:31 pmQuote from: Rodal on 10/23/2014 06:58 pmI recall that Paul March wrote that the EMDrives tested at NASA Eagleworks had a temperature that never rose more than 1 deg (F ? or C?) above room temperature.Anybody recall that statement? Is the temperature measurement in the NASA Eagleworks report? Using search I cannot find it in the text. Is it in the pictures?I also recall AcesHigh reporting on information elsewhere reporting March's statement he made on this thread regarding temperature. Was that at nextbigfuture? Does anybody still have a link for that?Yes I remember March saying the temperature didn't rise more than 1 degree F. It was F, not C.Presumably it was the temperature of copper walls ? My guess (pursuing ideas of warm jets) is that <5°C rise in cavity's air would have remained unnoticed. Mass of air<<mass of copper.
Quote from: zen-in on 10/24/2014 12:10 am.....I used the Crooke's radiometer as an example. The rotation of the paddles is not from convection. Considering Crookes radiometer, eliminates both conduction and convection. Crooke's radiometer is contained in a partial vacuum. None of the tested devices (NASA Eagleworks, Shawyer of Chinese) to my knowledge were tested in a partial vacuum. To my knowledge Crooke's radiometer does not move under ambient pressure conditions.
.....I used the Crooke's radiometer as an example. The rotation of the paddles is not from convection.
Quote from: frobnicat on 10/25/2014 03:21 pm.../...The big caveat : 4W volumetric heating of (presumably not perfectly dry) air out of 16W microwave power in "empty oven".The problem: dependence on QAs I understand it, to heat the air inside the cavity by microwave heating the air needs to have water molecules (it needs to be humid) because the gases in air are non-polar (nitrogen, oxygen, etc.) and hence do not get heated by the microwaves.But, the more humid the air, the lower the Q. Hence one would expect an inverse relation between measured force and Q: the higher the Q the smaller the force.However, statistical examination of all the data (Shawyer and NASA Eagleworks) points in the other direction: the higher the Q the greater the measured force.
.../...The big caveat : 4W volumetric heating of (presumably not perfectly dry) air out of 16W microwave power in "empty oven".
Quote from: aero on 10/24/2014 10:38 pm...I hope your records are better than mine because I don't have lengths recorded, (or the other dimensions, for that matter.)The "search" function of this thread is really awful. Too bad that this thread does not use Google as a search engine
...I hope your records are better than mine because I don't have lengths recorded, (or the other dimensions, for that matter.)
I looked at thrust due to air leaks early on. I discount it just because of the repeatability of the tests across a range of laboratory and thrusters. The inadvertent air leaks are just to consistent across the spectrum of devices for me to consider that as a cause. And we have Brady's example of "no dielectric, no thrust." Of course removing the dielectric could have uncovered air leaks at the small end to precisely counter the leaks in the large end, I guess. But look at the attached device and test data while considering air leaks.
Really, the point is that it is a thruster intended to be flight qualified. It appears to be solidly constructed with gaskets sealing both end plates. Such gaskets would also seal the bolt holes. A flight qualified device (Nowhere that I can find does it say "space qualified.) would be sealed due to the range of ambient air pressure over the flight regime.Yes, of course there could be a deliberate hole drilled in the base plate but I can't imagine an accidental hole. And I am not into conspiracy theories between Shawyer, the Chinese, Cannae, and Brady to make hot air thrusters and pawn them off as thrusting from RF wave energy.We all await the IV&V testing of the new Eagleworks vacuum qualified device. That will either prove or disprove the ion wind and air leak theories.Add: There is not much more information available about this device. It is one of Shawyer's EM thrusters. Go to emdrive.com and look at the very bottom of the text. There is a link there.
Quote from: ThinkerX on 10/25/2014 04:56 am...could this be the culprit behind the EM Drive?...I'm not a Scot, so I cannae work on that druve,
...could this be the culprit behind the EM Drive?...
First attempt to model thrust from cavity's air volumetric heating and jet effect through small aperture. Case studied : Brady a. Model needs refining (please be patient) but first rough estimates put in the ballpark of 100µN effect during 30s with fast rise of 2s. For now I will give numerical values and derive feasibility from them, in reverse from the set of general equations from which those values derive because I'm still struggling to put some order with all parameters and dependences. Also I want a clean differential equation, takes some time.Needed hypothesis : air inside cavity is volumetrically heated at Pow=4W (that is, air gets around 25% of microwave power input). There are hole(s) or crevice(s) between cavity and exterior of device, in the direction of thrust (air jetting...) for a total area of A=1.6 mm². Mind you, volumetric air heating Pow=4W and hole area A=1.6mm² are unknowns, so these values were carefully chosen to get to some magnitude to explain... not the other way around.Temperatures around 20°C T = 293KCavity volume V = 0.027 m^3Initial mass of air m = rho*V = 1.2 * .027 = .0324 kg (32 grams of air)Assuming some air will be leaving but only a small part of that, so not significantly alter the heat capacity of the whole. Heat capacity supposed constant.We put 4W of power into that, with a specific heat of C=1000J/kg/K Tdot = Pow / ( C * m ) = 0.123 K/s Consider first a short transient period with pressure buildup (like the hole is closed), m constant, p*V=m*Rs*T (Rs around 287 J/kg/K for air)pdot = m*Rs/V *Tdot = 42 Pa/s (Pascals per second, please remember there is 10^5 Pa in one atm. pressure). So in 2s we would reach 84 Pa more pressure inside vessel than outside. Note that Tdot uses an isobar value of C (1000) while strictly in this phase we would be in isochore conditions (C=720) : that would only lower the time. So in less than 2 seconds 84 Pa differential. Pd = 84 Pa.This is the transient. At this level of pressure differential the rate of air escaping through the hole becomes important enough that this pressure will be kept constant while the temperature continues to rise (why I choose isobar heat capacity overall) : The mass flow through aperture mdot = Cf A sqrt(2 rho Pd) where Cf is a flow coefficient depending on geometry and I understand is around 0.6 for rough holes.This is from orifice plate article on wikipedia (repress any second thought here), I took the most simplified forms assuming incompressible flow (pressure differential / absolute pressure < 1/1000 so I guess this is a good first approximation). On this chapter, equation (2).=> mdot = 1.36 10^-5 kg/s of air expelled through the 1.6 mm² hole(s).This is a volume flow of mdot/rho = 1.13 10^-5 m^3/sSpeed of ejection is volume flow divided by hole section : v = 7.1 m/sClearly not sonic or supersonic.The reaction force imparted (thrust) = mdot * v = 9.65 10^-5Thrust = 96 µNReported by Brady a : 91.2 µNAfter 30 seconds of this "steady state" of constant rate of heating and expelling air :T would be 3.7 ° above initial conditionsMass of air expelled 0.41 g (a bit more than 1% of initial air mass of 32g)Sanity check on total momentum : From momentum expelled by jet : 0.41e-3 kg * 7.1 m/s = 2.9e-3 kg m/sFrom required thrust during 30s : 96e-6 N * 30 s = 2.9e-3 kg m/sWhen power off, Tdot falls to 0, sharp fall to 0 thrust ( differential pressure is quickly released, pressure equilibrium restored with same time constant as rise time < 2s). Conduction slowly release the heat of gas through the (colder) copper walls with a long time constant. No visible effect of contracting gas sucking air through the hole(s) when restoring T equilibrium.Thank you for your patience.
Having said that, aero makes very good points concerning <<A flight qualified device (Nowhere that I can find does it say "space qualified.) would be sealed due to the range of ambient air pressure over the flight regime.>>and that <<the point is that it is a thruster intended to be flight qualified. It appears to be solidly constructed with gaskets sealing both end plates. Such gaskets would also seal the bolt holes. >>yes, if the gasket is compliant enough under stress produced by the torqued bolts, it should seal the whole perimeter. The only other escape would be between the threaded bolts and the threaded holes (if threads were used) which are of course not gasketed. Then frobnicat would need to posit a means for air to make it to the boltholes and to have air still be able to escape between the threaded holes and the bolts (this would require very rough surfaces on the bolt and hole threads, and the gaps would be extremely small).
Something we've been overlooking is the age of the devices we have been considering from Shawyer. His demonstrator EM thruster program leading to the device that we are looking at was started in 2003, 11 years ago. He has national government money and private investor money to forward his research. I don't know the date that the flight thruster test program was completed, but I do know that in 2010 he published a photo of his follow-on device, a superconducting EM thruster, photo attached. That was 4 years ago. There is just to much money being spent on these devices for the test results to be bogus or caused by some bogus effect and not be detected. And if such bogus effect was detected then 4 years is just to long to keep it a secret, it would leak to the news and make a big splash in the headlines. JMO
Can the polymer gasket between the base plate and the cone act as a dielectric barrier discharge (DBD) actuator?