Bullet revolutions per 100 yards

When you see something with bullets, it is very important to make sure that you understand what you are seeing - other wise, new "wives tales" are created

Me start a wives tale, never!!
 
Originally Posted By: KlrDrvrI "think" it's more like the interaction of a spinning baseball with the air it goes through. Backspin imparts an upward force, topspin a downward force and sidespin a lateral force (the direction depends on the direction of the spin). Combine front or back with side and you can make a baseball or soccerball do wondrous things.

It's called "Bernoulli's Principle". As the velocity of a fluid increases on one side of an object, the surrounding pressure of that side of the object decreases. It's what provides lift in avionics and what makes batters knees buckle.


Chupa
 
Son of a B.......irch tree !!!

You guys are giving me a headache ....
laugh.gif
 
Originally Posted By: CatShooterOriginally Posted By: Ridgeline17The wobble would translate from the direction of the lands. And if you go to the Redfield site there is a video in slow motion of them testing the Accurange reticle, firing from 100-500 yds. In the video you can actually see some of this wobble in the vapor trail.


The vapor trail does not show wobble - it is showing the turbulence of air once the bullet has passed. Think of the smoke trails of rockets a few seconds after the rocket has passed - the trail is not straight, it is wobbley. When you see something with bullets, it is very important to make sure that you understand what you are seeing - other wise, new "wives tales" are created.

The mass of a bullet cannot wobble while it travels - the gyroscopic momentum will not allow that kind of motion.

IF, a crown is bad (very very rare) and it launches a bullet off the axis, then THAT is the direction of the bullet, and there is nothing that can be done, nor is there any difference in it's path. It will behave like any other bullet shot in any other direction.


.

The wobble in a vapor trail, agreeably, is NOT bullet wobble.

What you're seeing is known as "alternating boundary layer separation", or "vortex shedding" (also known as "oscillating Karman Vortex Wake" in certain textbooks). It's the same reason a flag whips back and forth in the wind, and why you sometimes feel a side to side "buffering" if you follow a semi-trailer too closely on the highway (incredibly dangerous for those of us that ride motorcycles). Check out case C below, the vortices are alternating off of the object's tail edge...

boundary_layer__turbulent_wake__418_399.gif


Basically, the boundary layer of air long the surface of the rocket in this case is separating at the rear, in an alternating pattern. It builds on one side then sloughs when it gets to large, and builds on the other side, and back and forth and back and forth...

Wikipedia: Karman Vortex shedding

In certain cases, it's thought that Karman vortex shedding can cause destabilizing forces on the leading object, but to what extent, that's debatable. Some people believe it's a contributor to high speed wobble in racecars and motorcycles as well. Either way, it's a real thing, and that's what's happening in rocket vapor trails...
 
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Originally Posted By: Tim NeitzkeSon of a B.......irch tree !!!

You guys are giving me a headache ....
laugh.gif


I'm learning and having fun. Seriously, I enjoy this topic.
 
Originally Posted By: VarminterrorOriginally Posted By: CatShooterOriginally Posted By: Ridgeline17The wobble would translate from the direction of the lands. And if you go to the Redfield site there is a video in slow motion of them testing the Accurange reticle, firing from 100-500 yds. In the video you can actually see some of this wobble in the vapor trail.


The vapor trail does not show wobble - it is showing the turbulence of air once the bullet has passed. Think of the smoke trails of rockets a few seconds after the rocket has passed - the trail is not straight, it is wobbley. When you see something with bullets, it is very important to make sure that you understand what you are seeing - other wise, new "wives tales" are created.

The mass of a bullet cannot wobble while it travels - the gyroscopic momentum will not allow that kind of motion.

IF, a crown is bad (very very rare) and it launches a bullet off the axis, then THAT is the direction of the bullet, and there is nothing that can be done, nor is there any difference in it's path. It will behave like any other bullet shot in any other direction.


.

The wobble in a vapor trail, agreeably, is NOT bullet wobble.

What you're seeing is known as "alternating boundary layer separation", or "vortex shedding" (also known as "oscillating Karman Vortex Wake" in certain textbooks). It's the same reason a flag whips back and forth in the wind, and why you sometimes feel a side to side "buffering" if you follow a semi-trailer too closely on the highway (incredibly dangerous for those of us that ride motorcycles). Check out case C below, the vortices are alternating off of the object's tail edge...

boundary_layer__turbulent_wake__418_399.gif


Basically, the boundary layer of air long the surface of the rocket in this case is separating at the rear, in an alternating pattern. It builds on one side then sloughs when it gets to large, and builds on the other side, and back and forth and back and forth...

Wikipedia: Karman Vortex shedding

In certain cases, it's thought that Karman vortex shedding can cause destabilizing forces on the leading object, but to what extent, that's debatable. Some people believe it's a contributor to high speed wobble in racecars and motorcycles as well. Either way, it's a real thing, and that's what's happening in rocket vapor trails...

And why some suspension bridges and tall smokestacks fail in pretty spectacular fashion?
scared.gif
 
Originally Posted By: Ridgeline17Originally Posted By: Tim NeitzkeSon of a B.......irch tree !!!

You guys are giving me a headache ....
laugh.gif


I'm learning and having fun. Seriously, I enjoy this topic.

Yes I've learned some myself, but to learn I must forget ....
Wonder what I don't remember anymore !
laugh.gif
 
Originally Posted By: KlrDrvrAnd why some suspension bridges and tall smokestacks fail in pretty spectacular fashion?
scared.gif


Youtube-Tacoma Narrows Bridge

The Vortex Shedding frequency on the backside of the Tacoma Narrows Bridge lined up perfectly with a natural harmonic of the bridge structure, causing the wave to propogate, ultimately destroying the bridge...
 
Originally Posted By: Tim NeitzkeOriginally Posted By: Ridgeline17Originally Posted By: Tim NeitzkeSon of a B.......irch tree !!!

You guys are giving me a headache ....
laugh.gif


I'm learning and having fun. Seriously, I enjoy this topic.

Yes I've learned some myself, but to learn I must forget ....
Wonder what I don't remember anymore !
laugh.gif



If I could remember half of the facts that I have forgotten and forget half of the "FACTS" that I knew to be "TRUE"........well

Think about that for a second
grin.gif



Chupa
 
Originally Posted By: VarminterrorOriginally Posted By: CatShooterOriginally Posted By: Ridgeline17The wobble would translate from the direction of the lands. And if you go to the Redfield site there is a video in slow motion of them testing the Accurange reticle, firing from 100-500 yds. In the video you can actually see some of this wobble in the vapor trail.


The vapor trail does not show wobble - it is showing the turbulence of air once the bullet has passed. Think of the smoke trails of rockets a few seconds after the rocket has passed - the trail is not straight, it is wobbley. When you see something with bullets, it is very important to make sure that you understand what you are seeing - other wise, new "wives tales" are created.

The mass of a bullet cannot wobble while it travels - the gyroscopic momentum will not allow that kind of motion.

IF, a crown is bad (very very rare) and it launches a bullet off the axis, then THAT is the direction of the bullet, and there is nothing that can be done, nor is there any difference in it's path. It will behave like any other bullet shot in any other direction.


.

The wobble in a vapor trail, agreeably, is NOT bullet wobble.

What you're seeing is known as "alternating boundary layer separation", or "vortex shedding" (also known as "oscillating Karman Vortex Wake" in certain textbooks). It's the same reason a flag whips back and forth in the wind, and why you sometimes feel a side to side "buffering" if you follow a semi-trailer too closely on the highway (incredibly dangerous for those of us that ride motorcycles). Check out case C below, the vortices are alternating off of the object's tail edge...

boundary_layer__turbulent_wake__418_399.gif


Basically, the boundary layer of air long the surface of the rocket in this case is separating at the rear, in an alternating pattern. It builds on one side then sloughs when it gets to large, and builds on the other side, and back and forth and back and forth...

Wikipedia: Karman Vortex shedding

In certain cases, it's thought that Karman vortex shedding can cause destabilizing forces on the leading object, but to what extent, that's debatable. Some people believe it's a contributor to high speed wobble in racecars and motorcycles as well. Either way, it's a real thing, and that's what's happening in rocket vapor trails...

VT... Good post!!
 
Originally Posted By: KlrDrvrSo Cat, what I'm hearing is the "corkscrew" effect Litz and others discuss doesn't happen?

Yup... it doesn't happen.

From what I have read, Brian comes from military work with small guided rockets. (Under wing aircraft weapons).

It is an entirely different field from spinning projectiles. The biggest differences are:

1 -Nothing spins, no gyroscopes, so he has little understanding of the forces involved.

2 - The presumption that your "bullet" is eventually going to go where you want it to - he believes that a bullet fired, and going off course, will find it's way back to the "true path" like a guided missle will.

3 - That pointed projectiles fly and fall point first. They don't, and Brian does not understand that or except that. Failure to except that bullets travel at the angle they are fired, is the biggest error that people make, when trying to understand the vagaries of bullet flight.

So a fair amount of his writings are skewed, or broken.

I read his book some time back and sent him a note about some errors, and notes regarding the science of gyroscopes, and never got an answer.


.

 
Holy cow. I guess this thread proves that there are no simple questions when dealing with ballistics. Some very very intelligent folks on here for sure. Thanks for all the good info.
 
Originally Posted By: CatShooterOriginally Posted By: KlrDrvrSo Cat, what I'm hearing is the "corkscrew" effect Litz and others discuss doesn't happen?

Yup... it doesn't happen.



Hmmm. Thanks. Food for thought.

At the terminal ballistics end, for those that haven't seen it, this is an interesting video.



If this is possible, someone ought to be able to empirically confirm what we're talking about.
 
Originally Posted By: VarminterrorOriginally Posted By: KlrDrvrAnd why some suspension bridges and tall smokestacks fail in pretty spectacular fashion?
scared.gif


Youtube-Tacoma Narrows Bridge

The Vortex Shedding frequency on the backside of the Tacoma Narrows Bridge lined up perfectly with a natural harmonic of the bridge structure, causing the wave to propogate, ultimately destroying the bridge...

Vortex shedding definitely can be and is a factor in bullet flight as described.

However, even though vortex shedding was one of the early proposed causes for the failure of the original Tacoma Narrows Bridge in 1940, it was later rejected as the cause because the frequency of the vortex shedding did not match that of the bridge. The bridge actually failed by aeroelastic flutter.

This link is from Wiki, but its a pretty good description of aeroelasticity and aeroelastic flutter.

http://en.wikipedia.org/wiki/Aeroelasticity#Flutter
 
You learn something new every day.
I did not know artillery shells landed on their asses.
w00t.gif


1 -Nothing spins, no gyroscopes, so he has little understanding of the forces involved.


You would be amazed at what these little boogers will do to a projectile...and sometimes the quad contrail(one per stabilizer for those of you who do not know anything about 6534) are awesome to see...

rolleron.jpg


 
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