G
Greg Culpepper
Guest
Morning Boyd,
With acknowledgment that there is nothing new under the sun, I may have coined the phrase on this board "backing down the wind".as a descriptive paradigm to illustrate a somewhat counter-intuitive phenomena of bullet behavior. If I didn't, apologies to he who did. If I did, I'll continue to own the phase happily and extend its use with or without demand of attribution to any and all who might choose its shorthand to some lengthier and more exhausting description of "what exactly the wind does to a bullet".
Depending on one's perspective, bullets can be said to back up. For example, suppose you were piloting an airplane vertically, either up or down to eliminate non-axial gravity effects. Suppose you shot a bullet straight out the front of the plane. Now wait a moment or two. As the plane continues on at a constant air speed with thrust and drag exactly equal you will catch up to and pass (or run into) the bullet you just fired. Air creates drag on the bullet but the bullet has no thrust so it slows as drag absorbs its inertial energy is changed into heat. Without a reference to the ground but only the airplane you're in the bullet would appear to fly away, slow to a stop, reverse and then accelerate back at you. Is the bullet backing up? If your frame of reference is your location in the moving plane then you might say the bullet has "backed up".
Now I'll ask that you imagine that you are in space. In space what is motion? Can you tell if you are moving? If an object that you see is changing position relative to you is it moving or are you? Maybe you're both in motion relative to some third object. Is the third object moving? Is it backing up? It's relative, isn't it.
Now lets come back to shooters, targets and bullets. Shooters and targets are typically earthbound. (An exception would two airplanes whose pilots are attempting to shoot one another.) Bullets, by contrast, are not earthbound. They are in flight in air and are unaffected by the earth (other than by gravity). Bullets in flight behave separately from the earth, just influenced by air. Once fired, the air is their whole world. Understanding and accepting this fact is necessary to understand wind drift of bullets.
Were this true rifling round ball guns might not produce any effect different from smooth bore musket.
Your incorrect statement concerning round ball flight might fall into this category.
There is a situation where there would be no lag and it applies directly to understanding wind drift of bullets and the utility of the phrase "backing down the wind" as an aid to that understanding. That would be for a rocket or airplane flying at a constant speed through the air when thrust and drag are exactly equal. I'll use the example of the rocket only as it, as fin stabilized projectile, more closely resembles a spin stabilized bullet than does an airplane with its movable flight control surfaces.
A rocket in steady state flight does not exhibit wind drift. It will fly on a straight line, point-on into the air. If the air is moving relative to the earth (wind) the rocket will turn relative to the earth (but not in the air) and will proceed on vector. To an observer on earth the rocket will appear to fly slightly sideways but on an absolutely straight path. Now if that rocket has more thrust than drag and is accelerating, it will still point straight into the air but if the air is moving across the earth the rocket will travel upwind relative to the earth. If the rocket has less thrust than drag it will decelerate and travel downwind.
Why am I talking about rockets? I'm talking about rockets to provide a frame of reference that is not earthbound. To more easily understand bullet wind drift it helps to get one's frame of reference up in the air with the bullet. Keeping you feet and frame of reference firmly planted on the ground does "more to obscure than illuminate".
Climb on the rocket with me Boyd and look over your shoulder at where we have been. Let go of some object, maybe one that resembles a spin stabilized bullet. Would you expect it to slow as drag overcomes its inertia? Sure. Would you expect it to curve left or right as it "backs up" accelerating away from and behind us? Why would it? OK. We're on the rocket and the bullet we dropped is slowing down from drag and trailing straight behind us (and down from gravity of course).
What is someone on the ground going to observe? We're in the air going straight in the wind and the bullet is dropping away from us straight behind and down. But the person on the ground sees us flying slightly sideways to the ground (although straight in the air whose motion as not directly observable as air is transparent). The dropped bullet remains exactly on the horizontal vector of our travel, but increasingly behind us from the moment of its release from our rocket. But the earthbound observer sees the bullet from his earthbound reference. For him the bullet isn't traveling straight at all but arcing downwind and the faster it slows due to drag, the more it arcs. When we on the rocket look back it is still straight behind us, increasing farther away and below as drag and gravity exert their influence. Wind doesn't blow bullets over. Drag pulls them back along their own axis from where they would be without drag. This difference between a no drag bullet and a real bullet is time lag. Time lag (time delay produced by drag) is the only mechanism that causes air movement to alter bullet travel in flight relative to the earth.
Think expansively. Let your mind soar. Don't be bound to the earth. Maybe some day "backing up", relatively speaking, will mean something to you. I can hope. And you can hope that I buy wind flags for LR Benchrest and LR Prone.
All the best to you Boyd,
Greg
With acknowledgment that there is nothing new under the sun, I may have coined the phrase on this board "backing down the wind".as a descriptive paradigm to illustrate a somewhat counter-intuitive phenomena of bullet behavior. If I didn't, apologies to he who did. If I did, I'll continue to own the phase happily and extend its use with or without demand of attribution to any and all who might choose its shorthand to some lengthier and more exhausting description of "what exactly the wind does to a bullet".
Depending on one's perspective, bullets can be said to back up. For example, suppose you were piloting an airplane vertically, either up or down to eliminate non-axial gravity effects. Suppose you shot a bullet straight out the front of the plane. Now wait a moment or two. As the plane continues on at a constant air speed with thrust and drag exactly equal you will catch up to and pass (or run into) the bullet you just fired. Air creates drag on the bullet but the bullet has no thrust so it slows as drag absorbs its inertial energy is changed into heat. Without a reference to the ground but only the airplane you're in the bullet would appear to fly away, slow to a stop, reverse and then accelerate back at you. Is the bullet backing up? If your frame of reference is your location in the moving plane then you might say the bullet has "backed up".
Now I'll ask that you imagine that you are in space. In space what is motion? Can you tell if you are moving? If an object that you see is changing position relative to you is it moving or are you? Maybe you're both in motion relative to some third object. Is the third object moving? Is it backing up? It's relative, isn't it.
Now lets come back to shooters, targets and bullets. Shooters and targets are typically earthbound. (An exception would two airplanes whose pilots are attempting to shoot one another.) Bullets, by contrast, are not earthbound. They are in flight in air and are unaffected by the earth (other than by gravity). Bullets in flight behave separately from the earth, just influenced by air. Once fired, the air is their whole world. Understanding and accepting this fact is necessary to understand wind drift of bullets.
Were this true rifling round ball guns might not produce any effect different from smooth bore musket.
Your incorrect statement concerning round ball flight might fall into this category.
There is a situation where there would be no lag and it applies directly to understanding wind drift of bullets and the utility of the phrase "backing down the wind" as an aid to that understanding. That would be for a rocket or airplane flying at a constant speed through the air when thrust and drag are exactly equal. I'll use the example of the rocket only as it, as fin stabilized projectile, more closely resembles a spin stabilized bullet than does an airplane with its movable flight control surfaces.
A rocket in steady state flight does not exhibit wind drift. It will fly on a straight line, point-on into the air. If the air is moving relative to the earth (wind) the rocket will turn relative to the earth (but not in the air) and will proceed on vector. To an observer on earth the rocket will appear to fly slightly sideways but on an absolutely straight path. Now if that rocket has more thrust than drag and is accelerating, it will still point straight into the air but if the air is moving across the earth the rocket will travel upwind relative to the earth. If the rocket has less thrust than drag it will decelerate and travel downwind.
Why am I talking about rockets? I'm talking about rockets to provide a frame of reference that is not earthbound. To more easily understand bullet wind drift it helps to get one's frame of reference up in the air with the bullet. Keeping you feet and frame of reference firmly planted on the ground does "more to obscure than illuminate".
Climb on the rocket with me Boyd and look over your shoulder at where we have been. Let go of some object, maybe one that resembles a spin stabilized bullet. Would you expect it to slow as drag overcomes its inertia? Sure. Would you expect it to curve left or right as it "backs up" accelerating away from and behind us? Why would it? OK. We're on the rocket and the bullet we dropped is slowing down from drag and trailing straight behind us (and down from gravity of course).
What is someone on the ground going to observe? We're in the air going straight in the wind and the bullet is dropping away from us straight behind and down. But the person on the ground sees us flying slightly sideways to the ground (although straight in the air whose motion as not directly observable as air is transparent). The dropped bullet remains exactly on the horizontal vector of our travel, but increasingly behind us from the moment of its release from our rocket. But the earthbound observer sees the bullet from his earthbound reference. For him the bullet isn't traveling straight at all but arcing downwind and the faster it slows due to drag, the more it arcs. When we on the rocket look back it is still straight behind us, increasing farther away and below as drag and gravity exert their influence. Wind doesn't blow bullets over. Drag pulls them back along their own axis from where they would be without drag. This difference between a no drag bullet and a real bullet is time lag. Time lag (time delay produced by drag) is the only mechanism that causes air movement to alter bullet travel in flight relative to the earth.
Well, it allows science to model and predict the path of projectiles.
Think expansively. Let your mind soar. Don't be bound to the earth. Maybe some day "backing up", relatively speaking, will mean something to you. I can hope. And you can hope that I buy wind flags for LR Benchrest and LR Prone.
All the best to you Boyd,
Greg
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