Wind effect on bullet

[Guthwine]

Ok so I am starting to get more into the theory of long range shooting or ballistics in general and after a bit of reading and I learned something new today:

Wind deflection, or drift as we usually refer to it, does not occur from wind blowing on the side of the bullet. It is caused by the bullet aligning itself to the relative wind vector. Basically, like a wind vane on a roof or windmill, the bullet will align itself with the prevalent wind.

Along with this picture:

https://www.gunwerks.com/uploads/images/original/longrangeballistics_4.jpg

From this pic the resulting force of the wind path and the flight path should in my understanding point to the left.

All other sites just mention that the bullet turns into the wind, but I have not found the "why" yet. Is this something that just happens - no questiosn asked - or am I missing the crucial detail so this makes sense? Is it precession acting against the wind that causes the momentum? Or is because the center of gravity of the projectile is further in the front and the wind forces have more leverage on the back that cause the projectile to turn? Any help?

 

[Lowlight]

there are other images, but yes the CG is a factor

 

[Guthwine]

Yeah but shouldn't a resulting force look like this?

https://www.phyley.com/images/page/find-resultant-force/1200x1200.png

 

[Lowlight]

Think of a boat on the water, it will turn the boat into the wave, not completely push it sideways

Part of this realization is why, quietly, David Tubb believes a wind that is off 90 degrees, more like in this circle, at 30 degrees actually has more influence on the bullet vs a 90-degree wind. It's a bit controversial and makes sense if you figure the bullet has less turn to make into the wind.

Wind is subjective and while we can see more of it using Doppler it's still an artform in a lot of ways.

If you watch it in a spotter you can see it turn. Not push

 

[_Windrider_]

Velocity is a factor as well. A faster bullet wont have as much correction or crabbing into the wind as a slower bullet in the same conditions. as velocity slows the crab angle increases since the wind has more time to affect the bullets path.

 

[308pirate]

Even though I'm an engineer, I literally give zero fucks about why a bullet drifts away from a cross wind.

All my interest and effort is directed to understanding how to determine how much that drift will be with respect to the observable wind. THAT is something that I can take action on to affect the outcome of my shot. And there's really only one way to learn it: shooting in the wind. Obviously some analytical ability and decent shooting skill are required, but you have to drop the books and go shoot.

 

[brianf]

im a math nerd

but as said above, there is a moment in time where field test are required

go out and learn how to read Natural Wind Indicators (grass, leaves, branches, mirage)

every piece of equipment works well in the lab...its on the shop floor that the real R&D happens

 

[seansmd]

But understanding why this happens, and why spinning objects respond to wind or resistance is interesting and illuminating in how to predict winds effects. The magnus effect I believe it is called.

 

[Guthwine]

Yeah I agree that nothing goes over practice, but as an engineer myself, I also want to know why things happen.

Also long range shooting is difficult to practice here in Austria, so that's why sadly I have more book- than range time. (maximum at civilian ranges is 300m) At least I can practice wind reading, everywhere I go. Thanks for the replys!

 

[MountainRogue]

When you get to a range with distance, remember to factor in spin drift as well. Some forget and think it’s wind deflection.

 

[Dthomas3523]

When you get to a range with distance, remember to factor in spin drift as well. Some forget and think it’s wind deflection.

Define “distance” in which you need to factor in spin drift.

I.E. what distance does spin drift become larger than the error capability of the shooter and/or gun.

 

[MountainRogue]

I usually don’t worry about spin drift when hunting till I’m at 300+yds. But, Spin drift effect is different for every different round and barrel twist. You gotta know your round and rifle before shooting long range at any animal.

 

[squishee]

Tagged in for the fun ( education/ humiliation)thats about to be unleashed

 

[Dthomas3523]

I usually don’t worry about spin drift when hunting till I’m at 300+yds. But, Spin drift effect is different for every different round and barrel twist. You gotta know your round and rifle before shooting long range at any animal.

Oh boy........nevermind.

 

[_Windrider_]

Oh boy........nevermind.

??

 

[Deleted member 113831]

Oh boy........nevermind.

???

 

[ShadowBear]

And I thought spin drift was the distance the washing machine lurches across the basement with an unbalanced load.......

 

[Greg Langelius *]

I imagine a pool table. When it's level, the ball rolls straight. When it's tilted, the ball's path curves downward. When it's unsteady, the ball seeks the lower side, adding complexity to the path.

How, why? These are all interesting from an academic point of view.

I try to reframe the academic into visual terms and rules of thumb; simpler being better to manipulate outside the classroom.

It's easier in the long run.

Greg

 

[6-5_swede]

Ok so I am starting to get more into the theory of long range shooting or ballistics in general and after a bit of reading and I learned something new today:



Along with this picture:

https://www.gunwerks.com/uploads/images/original/longrangeballistics_4.jpg

From this pic the resulting force of the wind path and the flight path should in my understanding point to the left.

All other sites just mention that the bullet turns into the wind, but I have not found the "why" yet. Is this something that just happens - no questiosn asked - or am I missing the crucial detail so this makes sense? Is it precession acting against the wind that causes the momentum? Or is because the center of gravity of the projectile is further in the front and the wind forces have more leverage on the back that cause the projectile to turn? Any help?

Guthwine, the answer you seek is to be found in the drag equation. There are at least one variable in it that is of interest to you: the fluids (the air) velocity toward the projectile. When the projectile flies through crosswind the air hits the bullet with slightly higher velocity on the wind side. This causes an increase in drag on that side. Have you ever been i a row boat? What happens when you put down the oar on one side only? The boat turns that way because of the increase in drag on that side. The exact same thing happens to the projectile in flight: the increase in drag on the wind side causes the bullet to turn ever so slightly into the wind. The gyroscopic stabilization of the projectile fights this tendency, and the angle of the center line is typically no more than 1 degree. This is enough to make the general air resistance push the bullet off course.

If you have any more Qs about ext ballistics feel free to tag me in them. I enjoy the subject. Btw I love Austria. Great country, rich culture.

Best regards
//

 

[XTCBoltAction]

Just to clarify. Turning into the wind is not what pushes the bullet in the direction of the wind - it will affect it, but the force that pushes the bullet to the side comes from the air molecules pushing against the side of the bullet.

 

[Deleted member 113831]

Just to clarify. Turning into the wind is not what pushes the bullet in the direction of the wind - it will affect it, but the force that pushes the bullet to the side comes from the air molecules pushing against the side of the bullet.

Nope.

Drag is what causes a bullet to drift. When a bullet turns into the wind, the drag coming off the bullet is on a different angle than the direction of travel of the center of gravity.

Just like an airplane wing, the high pressure is below the wing while the low pressure is above the wing. The plane flys because lift is created and the wing moves in the direction of the low pressure.

The bullet does the same thing. As the bullet noses into the wind, the drag coming off the back of the bullet is at a different angle than the trajectory of the center of gravity. This creates drag (low pressure) and the bullet moves in the direction of that low pressure.

 

[SanPatHogger]

If I am shooting pointed north and the wind is blowing from the east my bullets will land left on the target, the west side of the target. Correct? If the bullet turned INTO the wind it should be now headed up wind? Pointing more east? That goes against everything I ever thought. Wouldn't you see the bullets key holing on the target? Sorry if I sound ignorant, as I'm just pushing into shooting longer ranges myself.


But now I just re read what Skookum said, if the butt of the bullet is kicked left because the front is heavier then the left side slows down because of the air coming from the bullets velocity forward. So more drag on the left moves left, makes sense.

I like simpler better, If I throw a paper ball and the wind takes it it moves, a tennis ball would move less, and a steel ball less then that.

But thank you all for lernin me something new.

Now how bout that spin drift?

 

[Deleted member 113831]

If I am shooting pointed north and the wind is blowing from the east my bullets will land left on the target, the west side of the target. Correct? If the bullet turned INTO the wind it should be now headed up wind? Pointing more east? That goes against everything I ever thought. Wouldn't you see the bullets key holing on the target? Sorry if I sound ignorant, as I'm just pushing into shooting longer ranges myself.


But now I just re read what Skookum said, if the butt of the bullet is kicked left because the front is heavier then the left side slows down because of the air coming from the bullets velocity forward. So more drag on the left moves left, makes sense.

I like simpler better, If I throw a paper ball and the wind takes it it moves, a tennis ball would move less, and a steel ball less then that.

But thank you all for lernin me something new.

Now how bout that spin drift?

In easy terms, the bullet weathervanes into a side wind.

Say you have a head wind of however many thousand FPS, and a side wind of say 14 fps (10mph). The bullet turns ever so slightly into the wind creating drag on the down wind side. The more the wind, the more it turns and the greater the drag.

 

[CoryT]

The amount the bullet turns is very, very small. Now, the drag is an angle to the line of departure, so part of the drag is now pointed downwind of the path, and now the bullet drifts downwind.

Shoot an arrow with a good crosswind and you can see it happen. An RPG is powered in flight, it drifts upwind as a result of being turned

 

[XTCBoltAction]

At speeds our bullets fly, the drag force is much less than the force of molecules hitting the bullet. The drag force does cause the bullet to, slightly, point into the wind, but, at the speed our bullets fly, the vast majority of the force comes from 'things' [i.e., molecules] hitting the surface of the bullet.
Check it out.

http://www.physics.utah.edu/~mishch/wind_drift.pdf

 

[Dthomas3523]

At speeds our bullets fly, the drag force is much less than the force of molecules hitting the bullet. The drag force does cause the bullet to, slightly, point into the wind, but, at the speed our bullets fly, the vast majority of the force comes from 'things' [i.e., molecules] hitting the surface of the bullet.
Check it out.

http://www.physics.utah.edu/~mishch/wind_drift.pdf

You better reread and reinterpret that link.

It’s telling you how drag forces work. Not just the “molecules pushing” the bullet.

I’m going to recommend you read more and post less. Your posts are starting to show a pattern of misunderstandings.

 

[XTCBoltAction]

Hmmm. Directly from the pdf
"With increasing velocity u the Stokes law fails as viscosity becomes progressively less important compared with the force of the air directly “crashing” into the object ."
Stokes Law describes the drag force.
The article then goes on to develop the force resulting from air molecules hitting the surface of an object and derives the equation that shows the cross over point between the strength of the two forces.
It is noted that the strength of the force from molecules impacting the bullet is lessen by a factor that can be expressed in terms of the drag coefficient.

Most of my understanding is based on what I learned in engineering school. What am I missing?

Ah. So, here's an article from Wikipedia that does say drag causes the bullet to drift in a cross wind "From a scientific perspective, the "wind pushing on the side of the projectile" is not what causes horizontal wind drift. What causes wind drift is drag. Drag makes the projectile turn into the wind, much like a weather vane, keeping the centre of air pressure on its nose. This causes the nose to be cocked (from your perspective) into the wind, the base is cocked (from your perspective) "downwind."

From a physics standpoint, an object cannot change momentum without an external force. That force must come from something pushing or pulling on the object. The force that is moving the bullet is air molecules hitting from one side. I'm guessing that this force is being referred to as 'drag' since it comes from the air flowing over the bullet. The force being the same as if the bullet were moving into no crosswind at the same speed.

In any case, the force comes from particles [in this case molecules] hitting the bullet.

 

[_Windrider_]

is it yaw force or drag that causes the tip to point into the wind. This yaw causes induced drag which speeds up the decay in velocity. Drag doesn’t cause the tip to move it’s a side effect of yaw

 

[THEIS]

I’m going to recommend you read more and post less. Your posts are starting to show a pattern of misunderstandings.

Hi,

You mean the small side of an allen wrench is not designed to hurt your hand once you reach the optimized torque values???

Sincerely,
Theis

 

[Dthomas3523]

 

[Dthomas3523]

Hi,

You mean the small side of an allen wrench is not designed to hurt your hand once you reach the optimized torque values???

Sincerely,
Theis

I’m sure he learnt that in engineering school too.

 

[Dthomas3523]

 

[Dthomas3523]

exterior ballistics

 

[Deleted member 113831]

At speeds our bullets fly, the drag force is much less than the force of molecules hitting the bullet. The drag force does cause the bullet to, slightly, point into the wind, but, at the speed our bullets fly, the vast majority of the force comes from 'things' [i.e., molecules] hitting the surface of the bullet.
Check it out.

http://www.physics.utah.edu/~mishch/wind_drift.pdf

That whole paper is dealing with sub-sonic flight.

Not sure that is the same.

 

[Nowhere_001]

View attachment 7337192

Rephrasing for my own brain, and tell me if I'm massively missing the point:
Target at 0
Wind from 90
Bullet nose turns toward 90 - "crabbing" into the wind and creating a pressure differential
Resulting lift pulls the projectile toward 270 (generally speaking. given lift direction would be a function of crab angle)

 

[SanPatHogger]

Rephrasing for my own brain, and tell me if I'm massively missing the point:
Target at 0
Wind from 90
Bullet nose turns toward 90 - "crabbing" into the wind and creating a pressure differential
Resulting lift pulls the projectile toward 270 (generally speaking. given lift direction would be a function of crab angle)

That almost makes it seem backwards. If the butt of the bullet was toward 270 then there would be higher pressure at 270, and the "lift" would push toward 90. But the bullet is not the shape of a wing, so it doesn't create lift, it creates drag.

 

[SanPatHogger]

I think someone should set up an experiment. We should find a really big overgrown field, find a day with with a light steady wind. Light the field on fire and when it slows down and is very smokey someone shoots across it. High speed video cameras and Doppler radar should clear things up. I suggest a .22LR a round ball from a Colt Navy pistol, a .243 (because that's what I shoot) a .50 BMG and maybe a 30mm or so should all be tested.


And while typing that I thought....
Will a round ball move the same in the wind?

 

[THEIS]

Hi,

@Dthomas3523

Translation please, lol..

Sincerely,
Theis

 

[Deleted member 113831]

That almost makes it seem backwards. If the butt of the bullet was toward 270 then there would be higher pressure at 270, and the "lift" would push toward 90. But the bullet is not the shape of a wing, so it doesn't create lift, it creates drag.

Lift and drag are opposite sides of the same coin. One cannot exist without the other.

Drag comes off the back of the bullet (mostly). That is why the boat tail bullet was invented...to decrease drag. That is why a commercial airliner fuselage is pointy on the back end...drag, that is why some of the 18 wheelers you see going down the road have fold out panels that close off the back of the trailor...drag.

High pressure is at the nose, low pressure at the back (aka drag).

All this shit was figured out before most of us were born. It has not only has been theorized, it has been observed and filmed with extreme high speed photography.

 

[Nowhere_001]

That almost makes it seem backwards. If the butt of the bullet was toward 270 then there would be higher pressure at 270, and the "lift" would push toward 90. But the bullet is not the shape of a wing, so it doesn't create lift, it creates drag.

Yes, you would be correct. I was visualizing it incorrectly, and drag would greatly exceed any generated lift.

@Skookum looks like you saw where I was headed. You can have zero-lift drag, though. Parasitic drag is an example. Or an airfoil at zero effective angle of attack.

 

[Deleted member 113831]

View attachment 7337673


Yes, you would be correct. I was visualizing it incorrectly, and drag would greatly exceed any generated lift.

@Skookum looks like you saw where I was headed. You can have zero-lift drag, though. Parasitic drag is an example. Or an airfoil at zero effective angle of attack.

I stand corrected.

 

[_Windrider_]

so much to say not enough energy to type it all. I suggest you all read Litz book AB for Long Range Shooting, specifically Chapter 5. i also recommend you read and reread the section at the bottom of page 76 titled The Mechanism of Wind Deflection. In addition, i recommend reading Aerodynamics For Naval Aviators. It is an Ancient Text written long ago but is still considered the foremost authority for aspiring naval aviators and is the go to reference for all disciplines of aviation when it comes to Aerodynamics. whil;e we are talking ballistics, there is a lot of crossover from a wing to a bullet, both technically airfoils but with many different characteristics.

Velocity and Drag are opposites, not Lift.

Lift and Gravity are opposites.

There are 2 primary types of drag, Induced and parasitic.

a bullet never has a zero angle of attack.

 

[_Windrider_]

Guthwine, the answer you seek is to be found in the drag equation. There are at least one variable in it that is of interest to you: the fluids (the air) velocity toward the projectile. When the projectile flies through crosswind the air hits the bullet with slightly higher velocity on the wind side. This causes an increase in drag on that side. Have you ever been i a row boat? What happens when you put down the oar on one side only? The boat turns that way because of the increase in drag on that side. The exact same thing happens to the projectile in flight: the increase in drag on the wind side causes the bullet to turn ever so slightly into the wind. The gyroscopic stabilization of the projectile fights this tendency, and the angle of the center line is typically no more than 1 degree. This is enough to make the general air resistance push the bullet off course.

If you have any more Qs about ext ballistics feel free to tag me in them. I enjoy the subject. Btw I love Austria. Great country, rich culture.

Best regards
//

no, the stabilization fights to keep the center of pressure behind the center of gravity. What causes the “push” is the decay in velocity and the bullets inability to create velocity once its fired. so that yaw angle gets larger when compared to the direction of flight (or line of sight throgh the scope) which does increase the aerodynamic drag forces on the projectile. Drag is a sideffect not a cause.

 

[_Windrider_]

Lift and drag are opposite sides of the same coin. One cannot exist without the other.

Drag comes off the back of the bullet (mostly). That is why the boat tail bullet was invented...to decrease drag. That is why a commercial airliner fuselage is pointy on the back end...drag, that is why some of the 18 wheelers you see going down the road have fold out panels that close off the back of the trailor...drag.

High pressure is at the nose, low pressure at the back (aka drag).

All this shit was figured out before most of us were born. It has not only has been theorized, it has been observed and filmed with extreme high speed photography.

then why is a fighter jet super pointy on the front and fat on the back? hard to compare a jet that was designed for subsonic flight to a projectile designed for supersonic flight.

 

[_Windrider_]

View attachment 7337673


Yes, you would be correct. I was visualizing it incorrectly, and drag would greatly exceed any generated lift.

@Skookum looks like you saw where I was headed. You can have zero-lift drag, though. Parasitic drag is an example. Or an airfoil at zero effective angle of attack.

that diagram is so wrong it makes me sad.

 

[MCHOG]

So let me see if I understand. If the wind blows to the left, the bullet will be pulled, pushed, and/or dragged left??? LOL

Seriously though, for what it's worth, I two ran scenarios through TRASOL, 4DOF, and Applied Ballistics. In the first scenario, I had wind coming at 10 mph from 45 degrees. In the other scenario, I had the same wind but from 135 degrees. At 800 yards with a 6.5 CM, each ballistic engine calculated the hold to be the same from both angles (although the programs obviously differed from each other somewhat). I got the same result going out to 1,200 yards. It seems to me that if the bullet angle theory is correct and has any practical significance whatsoever, the holds would be different. Even if the ballisticians or programmers got it wrong, I would think that all of the shooters relying on that software and applying it in the real world would have collectively figured out and noted the problem by now.

I'm not saying I'm right. I'm just saying that the explanations above (from those I follow and respect) don't make sense to me.

 

[Dthomas3523]

Rephrasing for my own brain, and tell me if I'm massively missing the point:
Target at 0
Wind from 90
Bullet nose turns toward 90 - "crabbing" into the wind and creating a pressure differential
Resulting lift pulls the projectile toward 270 (generally speaking. given lift direction would be a function of crab angle)

 

[Deleted member 113831]

then why is a fighter jet super pointy on the front and fat on the back? hard to compare a jet that was designed for subsonic flight to a projectile designed for supersonic flight.

Fighters are designed for more than fuel efficiency. I would assume that has many more implications for the design than I am able to fathom.

Thank you for setting me straight on this:

Velocity and Drag are opposites, not Lift.
Lift and Gravity are opposites.
There are 2 primary types of drag, Induced and parasitic.

 

[Nowhere_001]

that diagram is so wrong it makes me sad.

Care to correct, then?

 

[_Windrider_]

Care to correct, then?

Post 47 above is perfect. Straight out of the book and chapter I recommended. Angle of attack is the relation of the nose of the bullet to the relative wind not direction of travel. Angle of attack in that diagram is yaw. AoA happens in the vertical plane not the horizontal. Furthermore, the relative wind is rarely straight down the axis except for a direct headwind or direct tailwind.