He wants to change the low pressure zone in the back - which depending upon how it's done could reduce the pressure cone produced and make it quieter. NASA proved it is possible to change the signature of the sonic boom with their modified aircraft - He just wants to take a new approach to it.
je suis charlie
It is better to live one day as a LION than a dozen days as a Sheep.
Thomas Jefferson Quotations:
"The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government."
In both cases the bullet rotates one revolution for every ten inches of advancement. How will the fins rotate faster than the bullet moves forward?Originally Posted by HollowPoint
I do understand the trig behind the high point of the fin moving faster than the point of the bullet because of the addition of the circular (angular) movement but wouldn't this create addition pressure waves?
Last edited by M-Tecs; 10-02-2013 at 12:21 AM.
Ever shoot a bullet into the ice? It stops going forward....and hops back on top of the ice and just spins.....fairly easy to spin faster than you are moving forward.
Another example is a general aviation aircraft with the brakes on....doing a run up......the prof is spinning pretty fast but not going forward....static thrust is measured that way.....with enough horsepower you cavitate....
Neither example apply to the OP statement. It’s still one revolution for every ten inches of bullet advancement. When you fire a supersonic bullet the rate of forward advancement decreases way faster than the rpms decrease. At the muzzle the bullet rotates one revolution for every ten inches of advancement but at 1,000 yards the rotation is probably closer to one revolution for every three or four inches of advancement. The reality is that the sonic boom from a bullet at 200 yard and 1,000 yards sound the same. If you doubt this spend some time in the pits at high power matches were you have bullets going a couple of feet over your head at 200, 300, 600 and 1,000 yards. I have been in the pits at 500, 800 and 900 yards and the sonic boom appears to be the same also.
Yea; I'm beginning to regret ever posting this Sonic-Crack-Theory before I made any attempts at proving or disproving it.
The image I posted served its purpose, which was to give the readers a visual idea of what I was getting at but, some folks seem to be stuck on that image as it's pictured and unable to see beyond it.
Regardless of wether it's one-in-ten revolutions or one-in-whatever revolutions, it's the angle of the fins in addition to several other factors that will determine the effectiveness of my theoretical Impeller-Setup. What appears to be happening here is that some are choosing just one of the many components of this theory and determining it to be a failure from that one component or that one perspective alone.
Please remember, this theory is brought in from outside the proverbial "Box." Up to now, most -if not all- replies to the contrary have their roots inside the proverbial "Box". That tends to make one perspective correct when viewed from inside that "Box," and frustrating when viewed from outside that same "Box." I'm on the outside looking in and you're on the inside looking out.
Close your left eye and with your right eye, fix your gaze on any object in front of you. Now close your right eye and look at the same object with your left eye. You're looking at the same thing but, you're now seeing it from a slightly different angle. That slight difference in angle can make all the difference in the world.
You'll hear no more from me on this topic until I've started this project. This thread should be dead soon soon. When I've finished my present projects I'll resurrect this thread to let you know that I've started work on this Sonic-Crack theory. Until then you are free to hash it out amongst yourselves.
HollowPoint
The laws of physics are relatively inflexible. To date every item in the atmosphere moving faster than the spend of sound has created a sonic boom. Please help us understand what the several other factors are that will allow you to change the laws of physics.
It was suggested earlier that you look at propellers. That is the closest model to what your impeller bullet model is. On the high speed prop aircraft the aircraft itself does not break the speed of sound but the prop tips in some cases do. This also happens with helicopters when the rotor tips break the speed of sound.
Larger items traveling faster than the speed of sound make a louder sonic boom than a smaller items so that would suggest that mitigating the sonic signature is possible.
Whether it’s a bullet, a prop tip, a loop on a bull whip or your impeller tip the laws of physics suggest it will create a pressure wave once the speed of sound it achieved either in a forward or a rotational velocity. What am I missing?
Last edited by M-Tecs; 10-02-2013 at 01:19 PM.
I think the only way to get a partial solution is to make a fluted ogive. Kind of like the phillips boolit. Stay with me here. You will get a pressure ridge off the nose and off the flutes. Imagine umbrella spines as the pressure ridge, doubled and rotating. To the listener, it pulsates and would be longer - time-wise. Same principle a muffler or suppressor uses, but you can't get the ridge to point forward on a boolit. May turn a crack or boom into a thud. 'Super-sonic' prop blades have to be short to keep the tip speed down and sub/super modes down to prevent the blade from coming apart. Light flies on my fly rod will give that 'crack' and usually break the leader.
Last edited by popper; 10-02-2013 at 02:02 PM.
Whatever!
Something of an explanation about supersonic propellers: The only thing going supersonic are the tips of the propeller blades. The plane itself never went supersonic. Which brings me to what I wanted to point out. I too am a bit skeptical that you are trying to push something through the air without disturbing it. While it's an admirable goal, and you could be quite famous and wealthy if you succeed, I'm afraid you've bitten off more than is chewable. But anyway, since your bullet is going supersonic, it seems to me a closer analogy in the aircraft world would be a jet engine in a plane traveling faster than the speed of sound. Not a perfect analogy because the actual power comes from the jet and, most importantly, the air going in to the compressor must be slowed down to subsonic speeds before it hits the blades, but at least a jet engine is successful in moving air through the middle of an object going faster than sound.
That little bit is all I had to offer, good luck and please report your results.
Oh great, now I am going to have to go on vacation somewhere to see this. I think it might have been cold enough in Texas once in my life time for the ponds around here to freeze up enough to stop even a .22.Ever shoot a bullet into the ice? It stops going forward....and hops back on top of the ice and just spins.....fairly easy to spin faster than you are moving forward.
No vacation needed when you have youtube
http://www.youtube.com/watch?v=zHrBm8C3WEE
http://www.youtube.com/watch?v=foZlciP6gUQ
Say everyone if Hollowpoint wanted to design say a bullet that shot the same at 500ft/sec as it does at say 4000 ft/sec how many would help him in that endevour instead of telling him that the mathamatics say you can't do it. Look at how the bullet lube has come along cause some of you just didn't listen to the nay sayers and pushed ahead. I think he needs some good support cause even if at first he doesn't succeed, he may just do it in the future. Lets face it a man jumped from atmos. limits and broke the barrier and there was not a sonic boom to be heard.
Go for it hollowpoint and good luck. I've been there and proved 10 engineers wrong about producing .001 dia. carbide drills with flutes and releifs also pointed with releifs.
CD
I think the impeller design would destabalize the bullet and actually increase the sonic boom. There would be no way to get rid of yaw which would lead to a greater high pressure cavity on one side of the bullet or the other. The surface area on the leading edge of the bullet would have no choice but to get larger.
Think of a powerful electric motor in your hand. When juice is put to the motor, it wants to twist out of your hands until the armature gets up to near neutral acceleration. The bullet would never reach a static state and would always be forced to overcome gravity, atmospheric pressure, and declining potential energy. There would be a torque curve due to the bullets rotation and increased suface area of the flutes (fins). The bullet would yaw and surface area would increase no matter how the fins were designed.
Hey let me know when you fellas get it figured out!
This will be a while down the road. I still have about four other projects ahead of this one; and with me, there's no telling if an even more interesting project might appear on top of the four projects I'm working now.
I will get to it in the future though. When that happens I'll resurrect this thread to give you all an update.
"I think the impeller design would destabilize the bullet and actually increase the sonic boom. There would be no way to get rid of yaw which would lead to a greater high pressure cavity on one side of the bullet or the other. The surface area on the leading edge of the bullet would have no choice but to get larger. "
You make a valid point but, your point is based on the known dynamics of conventional bullets. Remember, we're working outside the box here. Your "Electric Motor" analogy is a good one. With conventional bullets this is an accurate analogy.
Picture this in your mind's-eye; a sheet of paper laying on a flat surface. Now wave your hand over the top of it and that sheet of paper wants to rise up off the flat surface. What you've basically done by waving your hand over the top of it is wipe away the gravity that held in place where it lay. (for lack of a better description) Your Electric Motor analogy only shows spin drift of a static spinning object. It doesn't take into consideration the super-sonic forward momentum of that same static spinning object for the majority of it's time of flight.
In my mind, the combination of the super-sonic forward momentum of my bullet through the air in front of it and the impeller-fins on the bullet spinning at many times the FPS of the bullet, boring a hole through the air in front of it will combine to negate the effects you've eluded to.
That forward momentum is the equivalent of the "Hand Wave" over the sheet of paper laying on a flat surface. It serves as the catalyst that wipes away or mitigates yaw or spin drift, as well as the sonic-crack that this thread centers on.
I guess I'll just have to wait to find out if it will work as I picture it in my mind.
HollowPoint
Last edited by HollowPoint; 11-01-2013 at 10:56 AM.
Actually, what you've done is created a lesser air pressure area above the paper, the same way air moving faster over the curved (and thus longer) upper surface of a wing creates lift.
Faster moving air creates lesser air pressure, and things move from greater air pressure to lesser.
That's why on the highway, when you fart in the car, it's sucked out easily by just cracking the window... whereas at a red light, you and your passengers stew in it even with the windows down.
Bren R.
Ah; the old "Farting In A Car" scenario huh?
Less pressure is a good thing as more pressure will cause deviation of trajectory. I'm sorry I don't really know alot of the engineering jargon that would help to make my "Theory" make more sense to you more technically minded guys out there. I work off of pictures in my mind.
HollowPoint
In my mind that's know as a Freeze FrameAh;
the old "Farting In A Car" scenario huh?
...
I work off of pictures in my mind.
HollowPoint
je suis charlie
It is better to live one day as a LION than a dozen days as a Sheep.
Thomas Jefferson Quotations:
"The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government."
Figured everyone could wrap their heads around that a little easier than the Bernouilli Principle and Continuum Mechanics.
Bren R.
shooting with out the sonic boom, humm "fire the laser". i like how you think out side the box but your theory wont work, here's a few reason why. no matter what design the fins are they are creating resistance, which will slow it down and create more of an airdisturbance cone on the nose as it goes through the air. you could never get it to spin fast enough to "pull" its way through the air to suck in enough air and displace it with out creating that pressure wave it's creating more. the same fins that are causing it in theory to spin are also slowing it down which is the opposite of what it needs to do for this theory to work, it needs to speed up not slow down rotation. its like trying to create a blackhole just infront of the nose of the bullet. the fins dont have an energy source to keep it spinning fast enough to pull it, the gunpowder will get it up to a specific speed which up to this point the fins would be resistance trying to slow it down, after max velocity of the round is reached it will slow down and the spin will also slow also. sonic crack can be minimized but not eliminated, and wouldn't be obtainable in shooting ever due to the nature of our fire arms. If you have a .223 going at 2500fps i'm willing to bet you would get more of a crack than something that is real thin (a few mm dia.) long and tapered on both ends at the same speed, so in modern guns we wont be shooting long thin tapered darts. you might be able to play with that pressure cone a little to form "sound cancellation". long thin tappered would obviously be best but for a gun application a projectile shaped more like a hollow tube could be played with (like a hollow slug) min thickness of the tube walls would be minimal resistance cutting through the air, length can be extended for more weight and minimal drag out the back, since air is passing through it not around it which would help with "cancellation" of the drag current out the back caused by the thin walls of the tube. but the problem with a tube would be keeping it stable to fly straight. now your design as a self defence round I like, I just wouldn't want to sit infront of a jury after popping some one with one of those things and try to convince them it was self defence! just a thought..
Last edited by giericd; 01-09-2014 at 04:56 AM.
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