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Old 9th June 2019, 05:43 PM   #3241
JayUtah
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Originally Posted by bknight View Post
Now I see where your problem lies. Back up and take the course again.
No, his reticence has some basis in fact. Bernoulli's theories assume a lot of things that don't necessarily hold in real world situations. They're good for first-order approximations, and often those are good enough to design by. It's only when your design needs to optimize into second or third order effects that you reach for more sophisticated models.
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Old 9th June 2019, 06:49 PM   #3242
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Originally Posted by JayUtah View Post
No, his reticence has some basis in fact. Bernoulli's theories assume a lot of things that don't necessarily hold in real world situations. They're good for first-order approximations, and often those are good enough to design by. It's only when your design needs to optimize into second or third order effects that you reach for more sophisticated models.
True. The Bernoulli's principle in its raw form applies only to ideal flow where namely (not only) (1) Fluid is in-compressible or below 0.3 Mach (2) Does not offer any friction or has zero viscosity (3) The flow is steady and laminar.
But it doesn't mean it is "flawed". So, my advice "if you see any flaw, look for what you are missing (like the above) first." is right.
Also, most of the "flaw spotting" stems from mere misinterpretation, that is in case of Bernoulli very easy and common.
https://user.uni-frankfurt.de/~weltn...20internet.pdf

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Old 9th June 2019, 07:07 PM   #3243
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Originally Posted by curious cat View Post
True. The Bernoulli's principle in its raw form applies only to ideal flow where namely (not only) (1) Fluid is in-compressible or below 0.3 Mach (2) Does not offer any friction or has zero viscosity (3) The flow is steady and laminar.
But it doesn't mean it is "flawed". So, my advice "if you see any flaw, look for what you are missing (like the above) first." is right.

Tbf, Caveman1917 didn't say Bernoulli's principle is flawed. He said "the Bernoulli explanation" (as applied to wing lift) is flawed. Which I took to mean incomplete or doesn't tell the whole story. YMMV.
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Old 9th June 2019, 07:21 PM   #3244
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Originally Posted by Elagabalus View Post
Tbf, Caveman1917 didn't say Bernoulli's principle is flawed. He said "the Bernoulli explanation" (as applied to wing lift) is flawed. Which I took to mean incomplete or doesn't tell the whole story. YMMV.
Sounds right. My apology, I inadvertently took that statement out of context.
Anyway, I think we are really getting in this deeper than is needed in this thread .
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Old 9th June 2019, 07:34 PM   #3245
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Originally Posted by curious cat View Post
Sounds right. My apology, I inadvertently took that statement out of context.
Anyway, I think we are really getting in this deeper than is needed in this thread .
And a bit off-topic as well. I think we can agree that wings don't work in a vacuum. Star Wars excepted, of course.
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Old 10th June 2019, 12:58 AM   #3246
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Originally Posted by Elagabalus View Post
Tbf, Caveman1917 didn't say Bernoulli's principle is flawed. He said "the Bernoulli explanation" (as applied to wing lift) is flawed. Which I took to mean incomplete or doesn't tell the whole story. YMMV.
Yes, I didn't say that Bernoulli's principle is flawed but that the Bernoulli explanation for wing lift is. To define these terms:

The Bernoulli explanation: The flow along the top increases in speed, therefor decreases in pressure, and the resulting pressure difference creates a lift force.

The Newtonian explanation: Air is accelerated downwards so by conservation of momentum the wing is accelerated upwards. (Note here again that this is not (solely) the downwards deflection of the air by the bottom surface at a non-zero angle of attack but the downwards deflection of the air by the top surface at a zero angle of attack).

Why the Bernoulli explanation is flawed: The devil is in the details, Bernoulli's principle relates to static pressure (ie the isotropic pressure in the rest frame of the flow). The flow along the top increases in speed therefor its static pressure decreases. The implicit assumption being made in the Bernoulli explanation is that the static pressure is the only relevant pressure, an assumption which holds for normal wings but which can be broken by designing a wing to explicitly break it (see my earlier diagram of the "extended wing" which was explicitly designed to bring out and break this implicit assumption).

It's not that Bernoulli's principle is flawed but that the Bernoulli explanation leaves out sources of pressure on the wing which are not caused by the static pressure of the flow, in particular pressure caused by deflection of the flow by the surface. See post 3234 by Myriad and my response in post 3235.
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Old 10th June 2019, 07:26 AM   #3247
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Originally Posted by JayUtah View Post
No, his reticence has some basis in fact. Bernoulli's theories assume a lot of things that don't necessarily hold in real world situations. They're good for first-order approximations, and often those are good enough to design by. It's only when your design needs to optimize into second or third order effects that you reach for more sophisticated models.
This is what he posted
Quote:
So I think the Bernoulli explanation is flawed, or at least misleadingly incomplete.
Do you understand it to be flawed?
Do you understand it to be misleadingly incomplete? What parts of the equation should be added to make it complete for your second or third order solution?
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Old 10th June 2019, 08:15 AM   #3248
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Originally Posted by bknight View Post
Do you understand it to be flawed?
I said his reticence has some basis in fact. Any other words are not mine.

Quote:
What parts of the equation should be added to make it complete for your second or third order solution?
Straw man. I said we reach for other models, notably those based on the work of Euler, Navier, and Stokes.
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Old 10th June 2019, 08:30 AM   #3249
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Originally Posted by Gingervytes View Post
Thatís exactly what Iíve been saying when I said back pressure pushes the rocket. Just like an area of high pressure is built up underneath the wing, an area of high pressure is built under the rocket where the exhaust flows out and pushes the rocket as the gas expands towards lower pressure.
Do you agree that whatever ultimately pushes the rocket must be something in physical contact with a part of the rocket?

Do you think that the recoil of a gun is caused by air pressure building up in front of the barrel, or would a gun still recoil if fired in space?
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Old 10th June 2019, 08:32 AM   #3250
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Originally Posted by Gingervytes View Post
Thatís exactly what Iíve been saying when I said back pressure pushes the rocket. Just like an area of high pressure is built up underneath the wing, an area of high pressure is built under the rocket where the exhaust flows out and pushes the rocket as the gas expands towards lower pressure.
So close to getting it. The area of high pressure is inside the combustion chamber and the nozzle. It pushes on the walls of the combustion chamber and nozzle.
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Old 10th June 2019, 09:19 AM   #3251
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Old 10th June 2019, 10:23 AM   #3252
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Originally Posted by bknight View Post
This is what he posted


Do you understand it to be flawed?
Do you understand it to be misleadingly incomplete? What parts of the equation should be added to make it complete for your second or third order solution?
Originally Posted by JayUtah View Post
I said his reticence has some basis in fact. Any other words are not mine.



Straw man. I said we reach for other models, notably those based on the work of Euler, Navier, and Stokes.
Just to be clear, again, I did not express any reticence about Bernoulli's principle nor about any of his theories. As far as I know Bernoulli never said anything about airplane wings. My reticence was about the "Bernoulli explanation" for wing lift, a colloquial name for a particular explanation for wing lift which invokes Bernoulli's principle. And I'm aware that Bernoulli's principle is an approximation to the underlying Navier-Stokes equations[*] but that's not what I meant nor what I said, you're both arguing about a strawman which I never expressed.

* Indeed, as I posted a couple of pages back, I am myself using a numerical integration of the Navier-Stokes equations by Euler methods for a different problem (water simulation models for game worlds). Well, to be precise I'm not actually using it but I researched it before rejecting it for being too time-consuming (given the requirements that it has to run in real-time on an average consumer GPU) and switching to a simpler model.
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Old 10th June 2019, 10:31 AM   #3253
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This thread has been an unexpected boon.

First details on rockets in space, how space flight works.

Then, airfoil dynamics.

Wow!

Thanks from a fan.
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Old 10th June 2019, 10:31 AM   #3254
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Originally Posted by caveman1917 View Post
My reticence was about the "Bernoulli explanation" for wing lift, a colloquial name for a particular explanation for wing lift which invokes Bernoulli's principle.
That's what I understood your meaning to be. Bernoulli's principle does not completely explain how you get lift from an airfoil. But that doesn't mean it's an incorrect principle, nor that it isn't operative in developing lift. I'm not trying to prove anyone necessarily right or wrong on these points. I mean to say that the mechanics of lift can be thought of simplistically or with greater rigor. You just have to match the model to the degree of discussion you wish to have.
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Old 10th June 2019, 10:43 AM   #3255
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Originally Posted by caveman1917 View Post
I researched it before rejecting it for being too time-consuming (given the requirements that it has to run in real-time on an average consumer GPU) and switching to a simpler model.
And this is exactly the sort of trade-off that means simpler models retain their utility. Economy of effort is itself a valuable commodity. If a less refined model gives you results within your tolerance for error, then there is nothing wrong -- practically or theoretically -- with that model. And there may be practical advantage in less time, money, and risk of error. In many cases, Bernoulli's formulations give us useful and reliable results within our tolerances. It would be foolhardy to insist on more complicated models. But then once we start talking about cases that the simpler models can't handle, it's proper to say the simpler models aren't complete. In fairness, we should say that they are incomplete only with respect to circumstances we've now decided are relevant, that weren't relevant before. In lots of cases we can ignore viscosity because the other elements of the problem dominate. We may later run into a problem where viscosity matters, either because a different fluid has a non-negligible viscosity, or because the problem now requires greater precision in its solution than can be obtained if we ignore tiny effects like viscosity.
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Old 10th June 2019, 11:08 AM   #3256
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Originally Posted by JayUtah View Post
I said his reticence has some basis in fact. Any other words are not mine.

Straw man. I said we reach for other models, notably those based on the work of Euler, Navier, and Stokes.
Fair enough.
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Old 10th June 2019, 11:50 AM   #3257
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Originally Posted by JayUtah View Post
And this is exactly the sort of trade-off that means simpler models retain their utility. Economy of effort is itself a valuable commodity. If a less refined model gives you results within your tolerance for error, then there is nothing wrong -- practically or theoretically -- with that model. And there may be practical advantage in less time, money, and risk of error. In many cases, Bernoulli's formulations give us useful and reliable results within our tolerances. It would be foolhardy to insist on more complicated models. But then once we start talking about cases that the simpler models can't handle, it's proper to say the simpler models aren't complete. In fairness, we should say that they are incomplete only with respect to circumstances we've now decided are relevant, that weren't relevant before. In lots of cases we can ignore viscosity because the other elements of the problem dominate. We may later run into a problem where viscosity matters, either because a different fluid has a non-negligible viscosity, or because the problem now requires greater precision in its solution than can be obtained if we ignore tiny effects like viscosity.
In my case the real-time requirement put a stringent limit on how much time the simulation can use. Every frame the simulation is advanced by 20 ms and GPU time is at a premium, the water simulation has to share the GPU with other parts of the program, in particular rendering and particle systems. The water simulation itself only has about 4 ms of GPU time available per frame, so in effect it actually has to run at 5x real-time. A game world is about 5km2 and the grid cell size can not be larger than 1m2 to still appear realistic so that's 5 million grid cells that need to be simulated in 4 ms, and it has to do this on an average consumer GPU so there's no specialized hardware or anything. Euler integration of the Navier-Stokes equations just wasn't fast enough, even removing viscosity (which I tried) didn't cut it. And that's just using a 2d simulation, a full 3d simulation was hopelessly too slow. In the end I settled on an extremely simple model which still gave surprisingly good results, each grid cell is considered a column of water with a certain depth (above terrain height) which is connected to its four neighbours by virtual pipes. Basically a huge grid of communicating vessels.
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Old 10th June 2019, 01:42 PM   #3258
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Yes, they can. I have seen them do it.
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Old 10th June 2019, 02:08 PM   #3259
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While we're on the subject, for those of you living in the eastern US, if you're planning a vacation in July, you might want to take the launch of SpaceX CRS-18 Mission.

In fact, here's a link to all the NASA launches this year:

https://www.nasa.gov/launchschedule/

For something that's impossible we're putting lots of rockets into space...and bringing a few back.

Flat Earth twits are not invited.
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Old 10th June 2019, 02:20 PM   #3260
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Question for the experts. If due to 'magic' rockets don't work in space (they do of course) how would the Germans have detected this anomaly? What would have been the indications that the V-2 wasn't performing per design as it went higher?
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Old 10th June 2019, 02:58 PM   #3261
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Originally Posted by caveman1917 View Post
Just to be clear, again, I did not express any reticence about Bernoulli's principle nor about any of his theories. As far as I know Bernoulli never said anything about airplane wings. My reticence was about the "Bernoulli explanation" for wing lift, a colloquial name for a particular explanation for wing lift which invokes Bernoulli's principle. And I'm aware that Bernoulli's principle is an approximation to the underlying Navier-Stokes equations[*] but that's not what I meant nor what I said, you're both arguing about a strawman which I never expressed.

* Indeed, as I posted a couple of pages back, I am myself using a numerical integration of the Navier-Stokes equations by Euler methods for a different problem (water simulation models for game worlds). Well, to be precise I'm not actually using it but I researched it before rejecting it for being too time-consuming (given the requirements that it has to run in real-time on an average consumer GPU) and switching to a simpler model.
I didn't take your post in that way, my appologieso.
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Old 10th June 2019, 05:10 PM   #3262
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My simplistic understanding of the Bernoulli velocity/pressure relationship is that if I were to throw a tennis ball directly at a wall at a certain speed then it will hit the wall with a certain force but the velocity, parallel to the wall, will be zero. If I throw it at the same speed 45 degrees it will hit the wall with a lesser force but the velocity parallel to the wall will be greater and if I were to throw it at an even smaller angle to the wall the force would be more reduced and the velocity parallel to the wall would be increased. If I throw it parallel to the wall there will be no force on the wall at all.

So if there were a lot of tennis balls being thrown around in various directions close to the wall then we would find if the component of the average velocity of the tennis balls parallel to the walls increased then the force of tennis balls hitting the wall would decrease.

And for something like a gas flowing through a pipe, velocity through the pipe will be related to pressure on the walls of the pipe in much the same way for more or less the same reasons.

This is obviously a gross over simplification of the behaviour of a gas but I think that it basically gets at the main reason for the relationship.

Do I have that more or less right (as a simple layman's explanation)?

(And, yes, if people were throwing tennis balls to each other parallel to the wall then the average velocity parallel to the wall would be zero and the force of tennis balls hitting the wall would also be zero so the analogy is not perfect).
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Old 10th June 2019, 05:19 PM   #3263
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Originally Posted by Gingervytes View Post
Thatís exactly what Iíve been saying when I said back pressure pushes the rocket. Just like an area of high pressure is built up underneath the wing, an area of high pressure is built under the rocket where the exhaust flows out and pushes the rocket as the gas expands towards lower pressure.
What you've actually been saying is "the only reason people pay attention to me is because I tell them I have these ideas that are demonstrably untrue".

You just need to find your "tribe" or people who share your other, non-crackpot interests. You'll probably enjoy the attention of people who share your interests more than the people who only want to talk to you to tell you that you're wrong.
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Old 10th June 2019, 05:42 PM   #3264
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Originally Posted by Robin View Post
My simplistic understanding of the Bernoulli velocity/pressure relationship is that if I were to throw a tennis ball directly at a wall at a certain speed then it will hit the wall with a certain force but the velocity, parallel to the wall, will be zero. If I throw it at the same speed 45 degrees it will hit the wall with a lesser force but the velocity parallel to the wall will be greater and if I were to throw it at an even smaller angle to the wall the force would be more reduced and the velocity parallel to the wall would be increased. If I throw it parallel to the wall there will be no force on the wall at all.

So if there were a lot of tennis balls being thrown around in various directions close to the wall then we would find if the component of the average velocity of the tennis balls parallel to the walls increased then the force of tennis balls hitting the wall would decrease.

And for something like a gas flowing through a pipe, velocity through the pipe will be related to pressure on the walls of the pipe in much the same way for more or less the same reasons.

This is obviously a gross over simplification of the behaviour of a gas but I think that it basically gets at the main reason for the relationship.

Do I have that more or less right (as a simple layman's explanation)?

(And, yes, if people were throwing tennis balls to each other parallel to the wall then the average velocity parallel to the wall would be zero and the force of tennis balls hitting the wall would also be zero so the analogy is not perfect).
You can easily get it from conservation of energy. Let v = vf + vr be the velocity of some particle in the fluid, where vf is the local average velocity of the particles around it (|vf| is the flow speed) and vr is the remainder (|vr| is the static pressure). If |vf| increases then by conservation of energy |vr| decreases.
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Old 10th June 2019, 06:25 PM   #3265
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Originally Posted by Hans View Post
Question for the experts. If due to 'magic' rockets don't work in space (they do of course) how would the Germans have detected this anomaly? What would have been the indications that the V-2 wasn't performing per design as it went higher?
Acceleration due to thrust would have decreased with altitude, due to the lessening of back pressure. In the real world thrust increased due to the decrease in atmospheric pressure.

Specifically, they would have seen the rocket falling below the predicted track.

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Old 10th June 2019, 10:59 PM   #3266
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Rockets cannot propel in the vacuum of space.

Originally Posted by Axxman300 View Post
In fact, here's a link to all the NASA launches this year:

https://www.nasa.gov/launchschedule/

For something that's impossible we're putting lots of rockets into space...and bringing a few back.

Flat Earth twits are not invited.
Does that mean that we get paid for being part of the conspiracy if we turn up?
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Old 11th June 2019, 02:16 AM   #3267
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Originally Posted by Gingervytes View Post
Thatís exactly what Iíve been saying when I said back pressure pushes the rocket. Just like an area of high pressure is built up underneath the wing, an area of high pressure is built under the rocket where the exhaust flows out and pushes the rocket as the gas expands towards lower pressure.
No, both are wrong.

1) An area of high pressure does not build up under the wing. The flow of air under the wing exerts a higher pressure because it slows down. Also the main lift comes from the fast airflow over the wing which has a reduced pressure. None of it is "built up", it is all a result of a continuous air flow.

2) There is, of course, some increased pressure right under a rocket, but nothing that can lift hundreds of tons. Such a pressure would immediately disperse into the surrounding air.

Exactly how can you claim that there is no pressure to speak of acting inside the rocket chamber AND at the same time claim that once the gas escapes into FREE AIR, it can build enough pressure to lift the rocket?

Please try to think through your claims before you post them.

Hans
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Old 11th June 2019, 02:22 AM   #3268
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Originally Posted by Hans View Post
Question for the experts. If due to 'magic' rockets don't work in space (they do of course) how would the Germans have detected this anomaly? What would have been the indications that the V-2 wasn't performing per design as it went higher?
Uhm, ehr:

[MODE=FlatEarther]The Germans knew they would get less thrust as the rocket rose and factored it into their ballistic calculations. In secret, of course. After the war, NAZI rocket engineers were hired by NASA and Soviet and continued the deception. [/MODE]

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Old 11th June 2019, 03:54 AM   #3269
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Originally Posted by Craig4 View Post
You just need to find your "tribe" or people who share your other, non-crackpot interests. You'll probably enjoy the attention of people who share your interests more than the people who only want to talk to you to tell you that you're wrong.

Iíve known a number of people over the years who sought out negative attention for a variety of reasons. The most common ones I noticed were crippling self-esteem issues or they were repeating abuse pattens from their childhoods.
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Old 11th June 2019, 03:56 AM   #3270
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Originally Posted by MRC_Hans View Post
[MODE=FlatEarther]The Germans knew they would get less thrust as the rocket rose and factored it into their ballistic calculations. In secret, of course. After the war, NAZI rocket engineers were hired by NASA and Soviet and continued the deception. [/MODE]
[MODE=FlatEarther] German scientists were very important after the war because they were the only ones to have experience with avoiding hitting the firmament with their rockets! [/MODE]
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Old 11th June 2019, 04:15 AM   #3271
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Originally Posted by steenkh View Post
Does that mean that we get paid for being part of the conspiracy if we turn up?
Only if you have your official up to date shill card.
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Old 11th June 2019, 07:09 AM   #3272
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Originally Posted by bknight View Post
Only if you have your official up to date shill card.


Mine has the three tongued reptoid with a third eye. Are those still valid or do I need the card with the Gray dissecting the real Alex Jones while Q and the Alex Jones clone watch?
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Old 11th June 2019, 07:37 AM   #3273
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Originally Posted by halleyscomet View Post
Mine has the three tongued reptoid with a third eye. Are those still valid or do I need the card with the Gray dissecting the real Alex Jones while Q and the Alex Jones clone watch?
Well, they're both valid. Which one you need to use depends on whether or not you've been chipped.
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Old 11th June 2019, 08:37 AM   #3274
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Originally Posted by Hellbound View Post
Well, they're both valid. Which one you need to use depends on whether or not you've been chipped.
Which chip?

The forehead chip for access to Illuminati managed venues?

The thumb webbing chip for payments and bribes?

Does the robotic baculum for "those" parties count as a chip? I've used it for access to a variety of locations, like the Denver Intergalactic "Traveler Comfort" room.

To keep this post on-topic:

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I AGREE
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Old 11th June 2019, 08:42 AM   #3275
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Originally Posted by halleyscomet View Post
Which chip?

The forehead chip for access to Illuminati managed venues?

The thumb webbing chip for payments and bribes?

Does the robotic baculum for "those" parties count as a chip? I've used it for access to a variety of locations, like the Denver Intergalactic "Traveler Comfort" room.

To keep this post on-topic:

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE
Too many questions. The Overlords are becoming suspicious.
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Old 11th June 2019, 08:53 AM   #3276
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Originally Posted by Steve View Post
Too many questions. The Overlords are becoming suspicious.
I'm not looking for NEW information. I'm seeking procedural clarification on things I already know about.

Besides, I just got clarification through my G6 cranial implant. The robotic baculum provides all the same access as the forehead implant so I can skip getting the forehead chip. Unfortunately, I'll have to get the thumb webbing implant as not all venues have the hardware to discretely verify a robotic baculum.

On the bright side, I've also learned that the thumb webbing implant can be used to activate some extra, er, features of the robotic baculum. My wife will be very pleased.

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE
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Old 11th June 2019, 09:47 AM   #3277
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Originally Posted by The Greater Fool View Post
This thread has been an unexpected boon.

First details on rockets in space, how space flight works.
I learnt that the X-15 had reaction control thrusters.
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Old 11th June 2019, 10:01 AM   #3278
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Originally Posted by halleyscomet View Post
Which chip?

The forehead chip for access to Illuminati managed venues?

The thumb webbing chip for payments and bribes?

Does the robotic baculum for "those" parties count as a chip? I've used it for access to a variety of locations, like the Denver Intergalactic "Traveler Comfort" room.

To keep this post on-topic:

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE
The chip on your shoulder ..

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Old 11th June 2019, 10:08 AM   #3279
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Originally Posted by Pope130 View Post
Acceleration due to thrust would have decreased with altitude, due to the lessening of back pressure. In the real world thrust increased due to the decrease in atmospheric pressure.

Specifically, they would have seen the rocket falling below the predicted track.
Thanks!
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Old 11th June 2019, 10:09 AM   #3280
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Originally Posted by MRC_Hans View Post
Uhm, ehr:

[MODE=FlatEarther]The Germans knew they would get less thrust as the rocket rose and factored it into their ballistic calculations. In secret, of course. After the war, NAZI rocket engineers were hired by NASA and Soviet and continued the deception. [/MODE]

Hans
Thanks but I was interested in how the Germans would have detected such an odd occurrence - had it occurred.

Follow up question how far up would the engine have stopped firing - would it have stopped prior to entering 'space'?

If so what was the first rocket engine to function in space? (yeah I know its trivia but it interests me)

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