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Post by Cybermortis on May 2, 2014 19:11:22 GMT
Mythbusters have done a fair few myths over the years that involved rockets, from the classic JATO car to Confederate Rocket and of course the Rocket Chair myth.
Musing on this what else could MB do with rockets? Assuming that they can get a truckload for next to nothing. (In other words conventional commercial type rockets, not Saturn V sized monsters).
I recall some black and white footage of a man trying to fly using small rockets on a backpack. This didn't work well, as the rockets exploded and set fire to his backside.
Another idea was a WW2 invention, which was basically a drum containing a ton of explosives acting as an axle for two large wooden wheels that were driven by rockets set on them. This didn't turn out well either, as the blessed thing seemed determined to head off in random directions to kill its makers.
Any other ideas?
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Post by the light works on May 3, 2014 0:26:26 GMT
Mythbusters have done a fair few myths over the years that involved rockets, from the classic JATO car to Confederate Rocket and of course the Rocket Chair myth. Musing on this what else could MB do with rockets? Assuming that they can get a truckload for next to nothing. (In other words conventional commercial type rockets, not Saturn V sized monsters). I recall some black and white footage of a man trying to fly using small rockets on a backpack. This didn't work well, as the rockets exploded and set fire to his backside. Another idea was a WW2 invention, which was basically a drum containing a ton of explosives acting as an axle for two large wooden wheels that were driven by rockets set on them. This didn't turn out well either, as the blessed thing seemed determined to head off in random directions to kill its makers. Any other ideas? I recall some full color footage of buster trying to fly with bottle rockets on a sort of backpack. the results were either favorable or not depending on whether you wanted him to crash and burn or not. it would be interesting to try to make a working panjandrum. didn't they try an anniversary edition of it with similar results? I wonder if it would be workable to try to make a model gyrojet helicopter with rockets?
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Post by silverdragon on May 3, 2014 7:05:26 GMT
How about a rocket-assisted overtake.
This I hear, and doubt, about a drag race, that "Supposedly" took place on the streets of Manchester. (Although I believe it has been tried in many cities, according to urban legend, and how many pints before it is told...) Challenged to a drag race, some bright spark decided to modify the rear of his vehicle to include a number of model rocket engines... it was unspecified which ones he used?....
This is supposed to be a early 20's driver in a fully what he can afford to insure road legal but slightly modified road car. NOT a Santa-pod special.
So the question is, just how would you ignite, and when... dont they take a while to get going?... And would "Model" rockets provide enough power to make a difference to change a vehicles 0-60 from 8 seconds to 4..... "Eyeeee Donttt Thinnnkkkkk sooooooo".....
As in, I call Chins.....
Now as for Rocket Cars, we KNOW you can do that. But modify a schoolboy just-passed-his-teat road car (Possibly even actually fully road legal... )that he has modified as much as Halfrauds will allow on his pocket money?...
Limit this to about $1,000 spend on car and modifications, so about $1,500, do a 0-60 without, then a 0-60 with, to see if there is a significant gain.
I also suggest R/C the vehicle..... "Just in case"......
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Post by the light works on May 3, 2014 8:28:16 GMT
How about a rocket-assisted overtake. This I hear, and doubt, about a drag race, that "Supposedly" took place on the streets of Manchester. (Although I believe it has been tried in many cities, according to urban legend, and how many pints before it is told...) Challenged to a drag race, some bright spark decided to modify the rear of his vehicle to include a number of model rocket engines... it was unspecified which ones he used?.... This is supposed to be a early 20's driver in a fully what he can afford to insure road legal but slightly modified road car. NOT a Santa-pod special. So the question is, just how would you ignite, and when... dont they take a while to get going?... And would "Model" rockets provide enough power to make a difference to change a vehicles 0-60 from 8 seconds to 4..... "Eyeeee Donttt Thinnnkkkkk sooooooo"..... As in, I call Chins..... Now as for Rocket Cars, we KNOW you can do that. But modify a schoolboy just-passed-his-teat road car (Possibly even actually fully road legal... )that he has modified as much as Halfrauds will allow on his pocket money?... Limit this to about $1,000 spend on car and modifications, so about $1,500, do a 0-60 without, then a 0-60 with, to see if there is a significant gain. I also suggest R/C the vehicle..... "Just in case"...... sounds like fun.
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Post by OziRiS on May 5, 2014 0:17:08 GMT
How about a rocket-assisted overtake. This I hear, and doubt, about a drag race, that "Supposedly" took place on the streets of Manchester. (Although I believe it has been tried in many cities, according to urban legend, and how many pints before it is told...) Challenged to a drag race, some bright spark decided to modify the rear of his vehicle to include a number of model rocket engines... it was unspecified which ones he used?.... This is supposed to be a early 20's driver in a fully what he can afford to insure road legal but slightly modified road car. NOT a Santa-pod special. So the question is, just how would you ignite, and when... dont they take a while to get going?... And would "Model" rockets provide enough power to make a difference to change a vehicles 0-60 from 8 seconds to 4..... "Eyeeee Donttt Thinnnkkkkk sooooooo"..... As in, I call Chins..... Now as for Rocket Cars, we KNOW you can do that. But modify a schoolboy just-passed-his-teat road car (Possibly even actually fully road legal... )that he has modified as much as Halfrauds will allow on his pocket money?... Limit this to about $1,000 spend on car and modifications, so about $1,500, do a 0-60 without, then a 0-60 with, to see if there is a significant gain. I also suggest R/C the vehicle..... "Just in case"...... I'm voting this one up! First time in months we've had an actual urban legend and not just something we've come up with or seen on BoobTube/read in some online paper, so I'm all for it!
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Post by silverdragon on May 5, 2014 10:32:36 GMT
Go ahead. May I ask, how many people have heard this one before, and what variants are there out there to your knowledge?... Anyone?.... Do VWEngineer/Oldguy/other mechanics have "Older" versions?.... I just would like to know the history. I would also like to know an first-hand experience.... Has anyone reliable tried this before?... If so, how?...
I have handled small scale solid rockets for small rocket models. However, I am thunking that if I just went ahead and glued a line of them on my back bumper, I would end up with bits of back bumper down the road.
Aside... We all know that a car drags a huge hole of dead air behind it that contributes to drag. Just how efficient would filling this hold with a rocket motor be?... would it cut drag?... Can you see where I am going here?.. as in, it may not produce much thrust, but if it fills the hole that creates drag, it may improve performance...?...
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Post by the light works on May 5, 2014 13:54:36 GMT
Go ahead. May I ask, how many people have heard this one before, and what variants are there out there to your knowledge?... Anyone?.... Do VWEngineer/Oldguy/other mechanics have "Older" versions?.... I just would like to know the history. I would also like to know an first-hand experience.... Has anyone reliable tried this before?... If so, how?... I have handled small scale solid rockets for small rocket models. However, I am thunking that if I just went ahead and glued a line of them on my back bumper, I would end up with bits of back bumper down the road. Aside... We all know that a car drags a huge hole of dead air behind it that contributes to drag. Just how efficient would filling this hold with a rocket motor be?... would it cut drag?... Can you see where I am going here?.. as in, it may not produce much thrust, but if it fills the hole that creates drag, it may improve performance...?... interesting thought. rocket assisted aerodynamics.
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Post by silverdragon on May 8, 2014 6:36:56 GMT
I have been putting some thought in. The idea of rocket propulsion is that for every action there is an equal and opposite reaction. The rocket pushes backwards creating high pressure behind the vehicle and in turn the vehicle is pushed forwards.
I cant quite work it out, but, its not exactly rocket assisted aerodynamics, its rocket low level propulsion with the added bonus that having that low level propulsion negates the drag caused by aerodynamics of the rear of the vehicle.
If the rocket engine had a "Diffuser" on it that it did not push backwards but up down and sideways exhaust flow filled that gap in the air, then it would be a gas assisted aerodynamics?..... Or would creating a high pressure zone behind the vehicle push the vehicle forwards, which is the same as rocket power anyway.
If the exhaust flow was bent to push forwards on the rear of the vehicle?... Think blow your own sail there a moment.
I have too much to think about here... If we just had a tame rocket scientist.....
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Post by the light works on May 8, 2014 14:14:33 GMT
I have been putting some thought in. The idea of rocket propulsion is that for every action there is an equal and opposite reaction. The rocket pushes backwards creating high pressure behind the vehicle and in turn the vehicle is pushed forwards. I cant quite work it out, but, its not exactly rocket assisted aerodynamics, its rocket low level propulsion with the added bonus that having that low level propulsion negates the drag caused by aerodynamics of the rear of the vehicle. If the rocket engine had a "Diffuser" on it that it did not push backwards but up down and sideways exhaust flow filled that gap in the air, then it would be a gas assisted aerodynamics?..... Or would creating a high pressure zone behind the vehicle push the vehicle forwards, which is the same as rocket power anyway. If the exhaust flow was bent to push forwards on the rear of the vehicle?... Think blow your own sail there a moment. I have too much to think about here... If we just had a tame rocket scientist..... but in RIA, the rocket's thrust is mainly offsetting aerodynamic drag. I would expect doing blow your own sail would be the same with a rocket as with a fan - it would only work so well as the surface acted as a thrust reverser.
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Post by memeengine on May 9, 2014 6:10:34 GMT
The idea of rocket propulsion is that for every action there is an equal and opposite reaction. The rocket pushes backwards creating high pressure behind the vehicle and in turn the vehicle is pushed forwards. While the first statement is correct, I don't think the second statement is what's happening in a rocket. For a rocket, the equal and opposite reaction that produces the motive force occurs at the nozzle of the rocket motor. The hot gases exiting the engine have a force equal to the mass of the gas times the acceleration of that gas. This force is balanced by an equal and opposite reaction that acts on the rocket engine (and, consequently, on the rest of the vehicle to which the rocket is attached). The velocity of the gases exiting the rocket is many times that of the vehicle itself, therefore it's very unlikely that those gases would fill the area immediately behind the body of the vehicle. If you did slow the gases down, so that they could expand to fill this area, you would be reducing the acceleration of the gas and therefore reducing the thrust of the rocket.
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Post by silverdragon on May 10, 2014 6:38:15 GMT
I think the second statement is correct. If you had no high pressure behind the vehicle, what would the gasses push against?... In space, or a vacuum, the presence of the rocket exhaust creates its own "Atmosphere" to push against, you are creating your own gas cloud, which is trying to expand to fill the vacuum, therefore creating thrust.
The nozzle is there to regulate the thrust rate. Too small, you dont get enough. Too big, its an explosion that creates too much thrust that the body of the vehicle cannot withstand... The forces of thrust do not occur ONLY at the nozzle of the rocket. The gasses passing through interact with the gasses (already) behind the rocket, if you had a high power vacuum cleaner on a toy rocket engine that could remove the gasses faster than they were produced, you would have negative thrust.
In fact, I propose an experiment to prove just that....
take a small model rocket engine and place it in a steel pipe on a grating that prevents it going backwards. Put a high power vacuum on the back end of that pipe, and switch it on. Ignite, and see if the rocket engine has enough thrust to escape the pipe.
I think I have seen this experiment done somewhere... cant remember where though. I remember the discussion on the length of pipe being it had to be long enough to cool the exhaust otherwise it would cook the vacuum cleaner engine?....
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Post by memeengine on May 10, 2014 9:57:37 GMT
If you had no high pressure behind the vehicle, what would the gasses push against?... Wrong, it doesn't need to 'push' against anything to create thrust. force = mass * acceleration Therefore if you have a mass (the exhaust gas) that is accelerating, you have a force. The reactive force to this, is what pushes the rocket forward. Those forces can only act on the rocket at the nozzle because once the gases exit the rocket they stop accelerating. Once it stops accelerating, it no longer exerts any force. Nasa's page on rocket thrustIn space, or a vacuum, the presence of the rocket exhaust creates its own "Atmosphere" to push against No, it doesn't. In space, the gases that exit the rocket would not be slowed by any atmospheric interaction. They would, therefore, keep moving away from the rocket at the same velocity that they left the rocket engine. Since all of the exhaust gases are in motion at the same velocity, there's no way they could push against each other.
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Post by the light works on May 10, 2014 11:53:30 GMT
correct. a rocket is a reaction engine. for the best illustration of the basic principle of rocketry, stand on a skateboard and try to jump either forwards or backwards off of it. for the illustration, the skateboard is the vehicle and you are the exhaust. what the rocket exhaust is pushing off of is inertia.
if you did your pipe experiment, with the air coming the length of the pipe to make up what the vacuum was drawing, the rocket could only reach its maximum airspeed, which would stop it if you drew air rapidly enough - but if you drew the air from vents at the tail of the rocket, and only enough to maintain atmospheric pressure despite the rocket exhaust, then the rocket would theoretically not be impeded.
the idea behind rocket assisted aerodynamics is producing enough exhaust to eliminate the low pressure zone behind the vehicle, but not provide appreciable reaction thrust.
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Post by silverdragon on May 11, 2014 10:17:51 GMT
I think you may find that it does. Think of a propeller in space.... Right. Your getting there. The propeller has nothing to pull or push on, so its effectively useless?... A Rocket short cuts that by eliminating the air in front of the propeller but pushing gasses out at high speed, and for every action, there is an equal and opposite reaction.
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Post by memeengine on May 11, 2014 11:03:48 GMT
I think you may find that it does. Think of a propeller in space.... Right. Your getting there. The propeller has nothing to pull or push on, so its effectively useless?... A Rocket short cuts that by eliminating the air in front of the propeller but pushing gasses out at high speed, and for every action, there is an equal and opposite reaction. Your analogy is wrong, because your understanding of the physics is flawed. The action/reaction forces act at the same point, at the same time. The thrust from a propeller comes from the air at the front of the blades being accelerated (by the rotation of the propeller) backwards. The force produced is determined by the mass of air being moved and the acceleration that the air undergoes (F=ma). This backward motion of the air produces an equal and opposite reaction force on the propeller pushing the propeller forwards. There is no requirement for there to be anything behind the propeller for the accelerated air to push against. In space, a propeller won't generate thrust simply because there is no air in front of the blades which it can accelerate backwards. However, as you state yourself. a rocket doesn't need any atmospheric air to generate thrust. It does so simply by generating expanding gases and channeling those gases out of the back. As I stated before, the force exerted on the rocket is equal in magnitude to the product of the mass of gas being moved and the acceleration that the gas undergoes and opposite in terms of direction. The action and reaction both act at the same place and at the same time, at the nozzle of the rocket engine. Again, these forces do not need any external atmosphere to push against in order to function. If you don't believe me, read the NASA page I linked to - there's no mention of any requirement for there to be an atmosphere to push against.
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Post by silverdragon on May 11, 2014 11:11:16 GMT
The action of creating gass does not create thrust. Directing those gasses in one direction creates thrust. The reaction of those gasses against an object creates thrust... As the gasses push one way, the object goes the other.
Simple experiment, put a small piece of C4 on a solid bit of ground under a plank and a brick on top of that plank, ignite, what throws the brick?.... there is nothing attached to the brick, where does it get that thrutch from?... The brick is thrown because the expansion of gasses have nowhere else to go so create a bubble between the ground and the plank. The expansion of that bubble pushes on the plank, and therefore the brick. The brick therefore receives thrust. (Or Thrutch)
A Rocket engine is no more than a controlled explosion.
The rocket nozzle does not create thrust, as you are trying to force me to believe, it only controls the explosion, the expansion of gasses in a controlled direction create thrust, and that is final, I cant get it any simpler than that.
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Post by memeengine on May 11, 2014 13:44:32 GMT
T The rocket nozzle does not create thrust, as you are trying to force me to believe, it only controls the explosion, the expansion of gasses in a controlled direction create thrust, and that is final, I cant get it any simpler than that. I never claimed at any point that the nozzle created the thrust. In fact I was very clear in saying that the force was created by the acceleration of the gases. The nozzle is simply the point at which the action/reaction forces act, since it's the point at which the gases leave the body of the rocket. If you actually read my posts, you'd see that my problem with your statement was your assertion that the rocket required an external high pressure area or atmosphere on which to act, i.e. you stated "the presence of the rocket exhaust creates its own "Atmosphere" to push against, you are creating your own gas cloud". That statement isn't true. As you stated in the post above "As the gasses push one way, the object goes the other.", there is no requirement for an external atmosphere to push against. The gases and rocket are pushing against each other and that's all there is to it.
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Post by the light works on May 11, 2014 15:01:45 GMT
The action of creating gass does not create thrust. Directing those gasses in one direction creates thrust. The reaction of those gasses against an object creates thrust... As the gasses push one way, the object goes the other. Simple experiment, put a small piece of C4 on a solid bit of ground under a plank and a brick on top of that plank, ignite, what throws the brick?.... there is nothing attached to the brick, where does it get that thrutch from?... The brick is thrown because the expansion of gasses have nowhere else to go so create a bubble between the ground and the plank. The expansion of that bubble pushes on the plank, and therefore the brick. The brick therefore receives thrust. (Or Thrutch) A Rocket engine is no more than a controlled explosion. The rocket nozzle does not create thrust, as you are trying to force me to believe, it only controls the explosion, the expansion of gasses in a controlled direction create thrust, and that is final, I cant get it any simpler than that. follow up experiment - duct tape your assembly together and hang it from a light string 10 feet off the ground and repeat the explosion. or for a more controlled test, take three identical rockets. set one off in a vacuum chamber, one in atmosphere, and one in a pressure chamber at two atmospheres. if your allegation that rockets act against the atmosphere is correct, then the 2 atmosphere rocket should have about twice the thrust as the atmosphere rocket which should have about twice the thrust of the vacuum rocket. what you are describing is ground effect, which also happens with aerodynamic and jet propulsion.
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Post by the light works on May 11, 2014 15:02:55 GMT
now, if you are saying that a rocket carries its own reaction mass in its backpack, instead of harvesting it from the air around it as a propeller does - than that is a different meaning from what we thought you said.
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Post by Cybermortis on May 11, 2014 19:08:22 GMT
Aside... We all know that a car drags a huge hole of dead air behind it that contributes to drag. Just how efficient would filling this hold with a rocket motor be?... would it cut drag?... Can you see where I am going here?.. as in, it may not produce much thrust, but if it fills the hole that creates drag, it may improve performance...?... 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.
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