#### Rodal

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##### Re: EM Drive Developments
« Reply #2580 on: 10/25/2014 03:37 PM »
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.

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 boltholes

1.6 mm² is only 0.0025 square inches or a square having 0.05 inches per side

Look deeply, look at all those bolts.  I count 24 bolts, so this would be a gap of only 0.0001 square inches per bolt

Or 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".

The problem: dependence on Q

As 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.

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2581 on: 10/25/2014 03:38 PM »
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?

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.

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2582 on: 10/25/2014 03:40 PM »
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

Well March said the temperature of the device didn't increase more than 1 degree F. Seems that those lower power tests <30 watts didn't lend themselves to much heat production. I've commented previously about the value of conducting low power tests, as they allow the experimenter to separate artifact (heat et al) effects from dominant mode effects.) I really think the Chinese tests are flawed because they are dumping large amounts of power into their test device and are claiming eureka off a flawed test protocol. Too much power was used.

Edit:
send became lend
« Last Edit: 10/25/2014 05:28 PM by Mulletron »
Challenge your preconceptions, or they will challenge you. - Velik

#### Rodal

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##### Re: EM Drive Developments
« Reply #2583 on: 10/25/2014 03:42 PM »
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?

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.

Yes, frobnicat, you are correct.  It is the temperature of the copper walls that Paul March was alluding to.
And I also agree, the air being <5 deg C higher than the copper would not translate into any appreciable increase in temperature of the copper wall in the seconds response measured in the experiments (due to the fact that conduction through air is negligible and convection would rely on very low coefficients of natural air convection).  This is straightforward to show from q/A = h deltaT
« Last Edit: 10/25/2014 03:46 PM by Rodal »

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2584 on: 10/25/2014 03:46 PM »
.....
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.

Just to be clear, there is air in that partial vacuum. The Crookes Radiometer is not working by radiation pressure. It is working by heat flow. Black surfaces are hotter than white surfaces when exposed to light. I couldn't get my Crooke's Radiometer to move under a 1W green laser. In a complete vacuum, no workie.
Challenge your preconceptions, or they will challenge you. - Velik

#### frobnicat

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##### Re: EM Drive Developments
« Reply #2585 on: 10/25/2014 03:52 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 Q

As 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.

Well, I guess none of the experiments gone to the trouble of drying the air inside cavity, and that doesn't prevented them to reach Qs of 45000 (Shawyer b). So if humidity did get to a point where there was enough to catch a big ratio of MW power then yes, more humidity -> less Q. But below that point, say 25% power gets into heating water vapor, that's still 75 losses on the walls, there is room for improvement of walls quality, increasing Q, increasing stored energy levels, making available more power for water vapor heating. Better Q would make stronger jets (higher effective air heating power, higher Tdot)

To asses the matter we would need a model of MW coupling with water vapor diluted at typical atmospheric levels.

#### aero

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##### Re: EM Drive Developments
« Reply #2586 on: 10/25/2014 03:54 PM »
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.

Retired, working interesting problems

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2587 on: 10/25/2014 03:58 PM »
...I hope your records are better than mine because I don't have lengths recorded, (or the other dimensions, for that matter.)

Here's what I do:

Go to google, type in your word or phrase in quotes, include the word emdrive, and type site:nasaspaceflight.com

example:
copy and paste this into google

"dielectric thrust" emdrive site:nasaspaceflight.com

google is a better crawler than the website itself is

Challenge your preconceptions, or they will challenge you. - Velik

#### Rodal

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##### Re: EM Drive Developments
« Reply #2588 on: 10/25/2014 04:00 PM »
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.
Need some more help from you in interpreting the information from the image.  Is the point that the bolts in this picture are oriented towards the small end, and presuming that there are no holes exposed on the (unseen) big flat end, and therefore that for this particular device there could not be axial air escaping from the boltholes in the direction of the big end, and that all the air from the big end would have had to escape either radially through the circumferential gap between the flat end and the cone or backwards oriented through the backwards oriented bolts?

==> It would be nice if we could find a front image of the big end on this device, to settle this issue

« Last Edit: 10/25/2014 04:18 PM by Rodal »

#### zen-in

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##### Re: EM Drive Developments
« Reply #2589 on: 10/25/2014 04:18 PM »
Where was this device tested?  It is very different from the Eagleworks and Shawyer's device.   Is there a picture of it in a test stand and a test report?

#### aero

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##### Re: EM Drive Developments
« Reply #2590 on: 10/25/2014 04:28 PM »
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.

« Last Edit: 10/25/2014 04:32 PM by aero »
Retired, working interesting problems

#### Rodal

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##### Re: EM Drive Developments
« Reply #2591 on: 10/25/2014 04:51 PM »
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.

By << no holes exposed on the (unseen) big flat end>> I meant the holes through which the visible bolts where threaded through.  Of course it goes without saying that I also agree that << conspiracy theories between Shawyer, the Chinese, Cannae, and Brady to make hot air thrusters and pawn them off as thrusting from RF wave energy>>.

I see bolts that are used to fix the base plate to the cone, those bolts may be threaded into threaded holes on the base plate.

My question was whether the threaded holes on the base plate were blind drilled or whether they were drilled all the way through.  If they were drilled all the way through, it is possible that pressurized air would escape between the holes and the bolts without the researchers being aware of it.  No conspiracy theories or evil intentions are needed and of course they were never intended. I was just objectively giving fair review to frobnicat's theory and analysis

==> As I wrote, It would be nice if we could find a front image of the big end on this device, to settle this issue, as it would reveal whether the threaded holes were blind drilled (hence not visible from the front and hence no air jets) or whether they were drilled all the way through (hence visible and hence able to have air jets escape through them like axial nozzles)
« Last Edit: 10/25/2014 05:07 PM by Rodal »

#### aero

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##### Re: EM Drive Developments
« Reply #2592 on: 10/25/2014 05:06 PM »
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
Retired, working interesting problems

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2593 on: 10/25/2014 05:07 PM »
...could this be the culprit behind the EM Drive?...

I'm not a Scot, so I cannae work on that druve,

Thank you sir.
Challenge your preconceptions, or they will challenge you. - Velik

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2594 on: 10/25/2014 05:13 PM »
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 = 293K
Cavity volume V = 0.027 m^3
Initial 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/s
Speed of ejection is volume flow divided by hole section : v = 7.1 m/s
Clearly not sonic or supersonic.

The reaction force imparted (thrust) = mdot * v = 9.65 10^-5
Thrust = 96 µN

Reported by Brady a : 91.2 µN

After 30 seconds of this "steady state" of constant rate of heating and expelling air :
T would be 3.7 ° above initial conditions
Mass 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/s
From required thrust during 30s : 96e-6 N * 30 s = 2.9e-3 kg m/s

When 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.

I have nothing but the utmost respect for you for providing that analysis. I really wish I could give the same treatment for the non-radiative inductive effects I'm chasing after. I really feel like a Faraday without Maxwell.
« Last Edit: 10/25/2014 05:17 PM by Mulletron »
Challenge your preconceptions, or they will challenge you. - Velik

#### Rodal

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##### Re: EM Drive Developments
« Reply #2595 on: 10/25/2014 05:17 PM »
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) 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, B) holes drilled all the way through, and  C) very rough surfaces on the bolt and hole threads, and  the gaps would be extremely small.
« Last Edit: 10/25/2014 05:19 PM by Rodal »

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2596 on: 10/25/2014 05:18 PM »
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).

RTV.........to seal bolt holes, no biggie. But as soon as you introduce a gasket, the resonant cavity is no more. A resonant cavity isn't just mechanically enclosed; it is electrically enclosed. A short in all directions. As we say, a short is a short....loosely related to another saying frequently used, ground is ground.
« Last Edit: 10/25/2014 05:23 PM by Mulletron »
Challenge your preconceptions, or they will challenge you. - Velik

#### Rodal

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##### Re: EM Drive Developments
« Reply #2597 on: 10/25/2014 05:30 PM »
Can the polymer gasket between the base plate and the cone act as a dielectric barrier discharge (DBD) actuator?
« Last Edit: 10/25/2014 05:31 PM by Rodal »

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2598 on: 10/25/2014 05:38 PM »
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

Yeah I know. I'm hearing you loud and clear too!; but I have questions too. The first one is why wouldn't Guido Fetta have given Nasa his better performing superconducting cannae device (same for Shawyer)? I don't think it actually exists outside of paper. The dates on the photos in the Nasa conference paper are Jan 2014.

Also the latest paper by Shawyer contains no actual data, it is just another quick and dirty powerpoint type of presentation designed to stir hearts and minds. I smell a rat in all this. This all ties into why I give much more credence to the Nasa conference paper than other sources. The Nasa papers have no conflict of interest. Shawyer is trying to sell me a cow, but where's the beef!??!
« Last Edit: 10/25/2014 05:50 PM by Mulletron »
Challenge your preconceptions, or they will challenge you. - Velik

#### Mulletron

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##### Re: EM Drive Developments
« Reply #2599 on: 10/25/2014 05:47 PM »
Can the polymer gasket between the base plate and the cone act as a dielectric barrier discharge (DBD) actuator?

I investigated these too. They are a neat way to get rid of flaps and ailerons. I like where you're going with this, but I can't see how this technology applies to emdrive's anomalous thrust because of the penetrating bolt through the whole assembly of the test device, which are conductive. I dismissed them because of this. Another possible interaction in my search for ways rf on the inside, influences the world on the outside.

Electrical and magnetic evanescent fields finally won out in my view.
« Last Edit: 10/25/2014 06:00 PM by Mulletron »
Challenge your preconceptions, or they will challenge you. - Velik

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