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Post by the light works on May 12, 2014 2:46:37 GMT
interesting thought. rocket assisted aerodynamics. I'd agree with lightworks, in that the basic idea seems interesting - that the exhaust gasses from a rocket could potentially reduce drag and increase performance beyond what could be expected from the amount of thrust the rocket itself could or is producing. and it is something that may be completely unheard of (besides us, obviously)
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Post by chriso on May 13, 2014 0:46:37 GMT
I have been putting some thought in. *snip* If we just had a tame rocket scientist..... Not a rocket scientist, but a physicist in training. Maybe I can provide some insight? I have not yet taken any classes in fluid dynamics, but I can tell you anything you want about the non-aerodynamic parts of a rocket. And some information about the fluid dynamics part. Don't know if you guys are still interested? As for neutralizing the drag: sounds like an interesting idea, though not sure you would gain that much. It would seem to me like if you had enough rocket exhaust to fill in the bubble you are leaving behind, you probably have enough to just use the thrust directly.
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Post by silverdragon on May 13, 2014 6:05:16 GMT
If there is no atmosphere, there is nothing to push against... but... keep reading... as luck would have it, the rocket engine has the answer, it creates its own atmosphere in the very nature its creating its own gas cloud to push against.
I have been beyond basics and got into the very nature of how this works...... its beyond interesting, its a whole afternoon of discovery.
I think we are actually arguing the same two different sharp points on one end of the same stick?....
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Post by silverdragon on May 13, 2014 6:10:30 GMT
I have been putting some thought in. *snip* If we just had a tame rocket scientist..... Not a rocket scientist, but a physicist in training. Maybe I can provide some insight? I have not yet taken any classes in fluid dynamics, but I can tell you anything you want about the non-aerodynamic parts of a rocket. And some information about the fluid dynamics part. Don't know if you guys are still interested? As for neutralizing the drag: sounds like an interesting idea, though not sure you would gain that much. It would seem to me like if you had enough rocket exhaust to fill in the bubble you are leaving behind, you probably have enough to just use the thrust directly. Which is what I was alluding to. But in that, how much of the extra thrust is now from the main car engine which, minus the drag caused by the hole, is now able to work more efficiently?... In the case of the Bugatti Veyron, much of the 1,000 horses that are not used to turn the engine are used to counter aerodynamics?... (Above, the veyron has Turbo, and a LOT of the original engine power is used to turn the actual turbo's... as in more than an average family car's horsepower just to spin up the turbo.)
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Post by Cybermortis on May 13, 2014 12:34:43 GMT
Maybe instead of thinking 'rockets' what about just thinking in terms of 'artificial' airflow. (The principle is basically the same).
If you were to set blowers to 'fill' the dead area at the back of a moving object could this act as a form of aerodynamics?
This might be a more practical design than rockets (which have limited burn times anyway), and in regards testing on MB is also something that could be reset and retested several times without costing them money for each run.
Would be interesting to know if the physics supports this idea, even if only in theory, because as has been noted it is a rather intriguing one.
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Post by the light works on May 13, 2014 14:44:07 GMT
If there is no atmosphere, there is nothing to push against... but... keep reading... as luck would have it, the rocket engine has the answer, it creates its own atmosphere in the very nature its creating its own gas cloud to push against. I have been beyond basics and got into the very nature of how this works...... its beyond interesting, its a whole afternoon of discovery. I think we are actually arguing the same two different sharp points on one end of the same stick?.... only a very tiny fraction of the rocket's thrust comes from pushing "against" something - except the mass that it is pushing out of the nozzle. much like much of a gun's recoil does not come from pushing against the air in front of it - it comes from pushing against the projectile it is throwing out of the muzzle.
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Post by memeengine on May 13, 2014 16:56:18 GMT
If there is no atmosphere, there is nothing to push against... but... keep reading... as luck would have it, the rocket engine has the answer, it creates its own atmosphere in the very nature its creating its own gas cloud to push against. As I've already stated, there's no need for any external atmosphere for a rocket to "push against". That simply isn't the way that Newton's third law of motion works. The action and reaction forces are between two 'bodies' that are in direct contact. These forces are equal in magnitude and opposite in direction and act at the same time. In the case of a rocket, the two bodies in contact are the rocket and what NASA refers to as the "working fluid" (and what everyone else would call the exhaust gases). Action (the gases moving) and Reaction (the rocket moving the other way). No atmosphere is required. but... keep reading... as luck would have it, the rocket engine has the answer, it creates its own atmosphere in the very nature its creating its own gas cloud to push against. The rocket is NOT creating its own atmosphere in space - as I already pointed out, the gases leaving the rocket are moving away from the rocket. Since there's no atmosphere in space, there's nothing to slow the gases down therefore they keep moving away from the rocket at the same velocity as they exited. There's no way that a gas cloud can form and there's no way that the rocket can push against that non-existant gas cloud. You could power a spacecraft by accelerating any other mass out the back. For example, you could use an ion engine. Instead of a stream of gas, you have a stream of high-speed charged particles. The thrust mechanism is different but the result is the same. Just like a chemical rocket, forward motion of the spacecraft is purely a reaction to the backwards movement of the exhaust stream. And, just like a chemical rocket, there's absolutely no need for an external atmosphere to "push against".
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Post by Cybermortis on May 13, 2014 17:09:18 GMT
You could also use a rail gun, heck in theory you could move a spacecraft by strapping yourself to the hull and throwing baseballs. Neither of which requires an atmosphere. (Well, OK you would need one for the latter example so the pitcher didn't suffocate).
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Post by the light works on May 13, 2014 17:15:58 GMT
You could also use a rail gun, heck in theory you could move a spacecraft by strapping yourself to the hull and throwing baseballs. Neither of which requires an atmosphere. (Well, OK you would need one for the latter example so the pitcher didn't suffocate). funny, I was going to use baseballs as an example, too.
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Post by memeengine on May 13, 2014 17:20:40 GMT
You could also use a rail gun, heck in theory you could move a spacecraft by strapping yourself to the hull and throwing baseballs. Neither of which requires an atmosphere. (Well, OK you would need one for the latter example so the pitcher didn't suffocate). funny, I was going to use baseballs as an example, too. I actually typed one using cricket balls before I replaced it with the ion engine example instead.
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Post by Cybermortis on May 13, 2014 18:21:57 GMT
funny, I was going to use baseballs as an example, too. I actually typed one using cricket balls before I replaced it with the ion engine example instead. Interesting question/thought here. If you were to 'throw' a baseball inside a vacuum chamber that was in zero gee (say in the 'vomit comet' they used for the Moon Myths special). Would that move the chamber - and hence show the principle? *Edit* And idiot that I am, it occurs to me that you wouldn't have to do that. All you'd need a a vacuum chamber and a small throwing device on wheels. The 'recoil' from throwing the projectile should move the device backwards.
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Post by chriso on May 13, 2014 18:54:17 GMT
Okay, most rockets do have pressure of a sort involved their operation. Its just not where you think it is. Remember, all you need to get a rocket moving is a force imbalance.. On the pressure side of things: There is pressure in a rocket in the combustion chamber. Assume for a second that at the center of the combustion chamber, the pressure is approximately equal. On all sides of the chamber then there is an equal force applied per square meter. However, there is one part of the chamber, the exit, where there is no force. Since the exit side has no force applied, but the far side does, there is a force imbalance in the rocket engine, which is applied to the rest of the rocket. In other words, one part is being pushed harder then the other. But wait, what does the nozzle do? How does making the gas go faster speed up the rocket? Well, if you plug up part of the exit what will happen inside the combustion chamber? The pressure in the chamber will rise. And the pressure in the exhaust will fall. This will, obviously, mean that the gas involved will exit the nozzle at a faster rate, and it also mean you are getting far more force imbalance per unit of propellent then you would otherwise. However, make that nozzle too small, or the wrong shape, and the force on the exit side of the combustion chamber increases. That's not the whole story, though. Once a fluid is moving above its speed of sound, pressure no longer works in one direction. This is because the molecules in a gas are moving away from you faster then the pressure wave can approach. In this case at some point in the nozzle the exhaust moves faster then its speed of sound. No further pressure can be gained in the combustion chamber from here. At this point, you start to widen your nozzle. Instead of increasing the pressure in the combustion chamber further, the molecules will hit the wall of the nozzle, impart more momentum, then fly off into space, never to return. Because the exhaust is leaving at faster then the speed of sound and pressure requires air moving slower then the speed of sound, there will NEVER be any atmospheric pressure on the rear end of a spaceborn rocket. Now, whats this talk about a rocket working off newtons third law? Well, what it comes down to is you cannot recycle that exhaust. If you were to try to catch and reuse your exhaust, you would end up applying the same force that was used to accelerate it in the first place, only in the opposite direction. Meaning, the rocket would go nowhere. And whats more, you don't actually need to use pressure to accelerate that exhaust. You can use electric fields, magnetic fields, heck some designs even just use fission directly. All that matters is you push one piece of matter in one direction, and it in turn pushes you in the other. Does this clarify things? Here is a bit more reading and a nice picture of the inside of a rocket engine if anyone is interested: www.braeunig.us/space/propuls.htm
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Post by memeengine on May 13, 2014 19:16:25 GMT
I actually typed one using cricket balls before I replaced it with the ion engine example instead. All you'd need a a vacuum chamber and a small throwing device on wheels. The 'recoil' from throwing the projectile should move the device backwards. That set up would prove that you didn't need an atmosphere to push against to produce motion, however, I suspect that someone would argue that the device was pushing against the friction with the ground. An alternative would be to hang the device from wires in the vacuum chamber. The device would be free to move but there would be nothing solid for the device to push against.
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Post by the light works on May 13, 2014 19:27:49 GMT
of course, the other way that restricting your nozzle too much may be counterproductive is if you restrict it too much, the pressure will be redirected through a new orifice.
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Post by chriso on May 13, 2014 19:49:27 GMT
Ha. Yep, that is always an option.
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Post by the light works on May 13, 2014 20:04:26 GMT
Ha. Yep, that is always an option. "failure is always an option" Adam Savage
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Post by Cybermortis on May 13, 2014 21:25:36 GMT
All you'd need a a vacuum chamber and a small throwing device on wheels. The 'recoil' from throwing the projectile should move the device backwards. That set up would prove that you didn't need an atmosphere to push against to produce motion, however, I suspect that someone would argue that the device was pushing against the friction with the ground. An alternative would be to hang the device from wires in the vacuum chamber. The device would be free to move but there would be nothing solid for the device to push against. I guess wheels would also provide a degree of friction that *might* make it hard to notice any backwards movement. Maybe a better solution, and one just as viable as any, would be to levitate the firing device using magnets. That way there is no friction at all, and any backwards movement would be very easy to notice. This rig is, come to think of it, something that MB could set up fairly quickly. They already have the vacuum chamber and Jamie has a ton of magnets in the shop. The only thing they might have to build is the mini-catapult, which shouldn't be hard.
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Post by the light works on May 14, 2014 0:42:15 GMT
That set up would prove that you didn't need an atmosphere to push against to produce motion, however, I suspect that someone would argue that the device was pushing against the friction with the ground. An alternative would be to hang the device from wires in the vacuum chamber. The device would be free to move but there would be nothing solid for the device to push against. I guess wheels would also provide a degree of friction that *might* make it hard to notice any backwards movement. Maybe a better solution, and one just as viable as any, would be to levitate the firing device using magnets. That way there is no friction at all, and any backwards movement would be very easy to notice. This rig is, come to think of it, something that MB could set up fairly quickly. They already have the vacuum chamber and Jamie has a ton of magnets in the shop. The only thing they might have to build is the mini-catapult, which shouldn't be hard. MIGHT.
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Post by the light works on May 14, 2014 0:44:10 GMT
It occurred to me today that blower assisted aerodynamics would be different from rocket assisted aerodynamics, because the blower pulls airflow from somewhere else, whereas the rocket manufactures its own volume of gas. they might be able to do a smaller scale test with a pressure tank (and I would expect them to start with water tunnel tests with a supply tube for water)
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Post by chriso on May 14, 2014 1:20:17 GMT
It occurred to me today that blower assisted aerodynamics would be different from rocket assisted aerodynamics, because the blower pulls airflow from somewhere else, whereas the rocket manufactures its own volume of gas. they might be able to do a smaller scale test with a pressure tank (and I would expect them to start with water tunnel tests with a supply tube for water) The effect should be negligible. But if you think it might have a significant effect, you could have two intakes arranged so that any force due to suction cancels itself out.
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