Why do arrows deviate from the target in archery?

[Deebu R]

I was wondering why arrows deviate away from the target. If the arrow aimed at an object it usually lands above the object. Also if the mass of the arrow is increased it seems to get more and more accurate. Could someone explain why this happense?

 

[Vanadium 50]

Before determining why things are true, we should determine if they are true. If this were true, how would Olympic archery work? Wouldn't they miss the target all the time?

 

[Deebu R]

Ah sorry. I was talking about the basic, less expensive tools. As your bows and arrows improve your accuracy too will improve. Also the distance of deviation is not too big. With practice you can easily lean to shoot accurately. But don't you think if it was that easy everyone would do Olympic archery ? Anyone can take a bow and aim at a target. But if you want to win you need the correct method, form, understanding of what you are doing and lots of practice.

Setting that aside I was just curious about the reason for this deviation. Even if it is because of lack of practice there still has to be a reason, right?

 

[Vanadium 50]

A reason for what, exactly? Why good archers can regulalry hit the target and bad archers can't? I'd stick with the simplest: they are good archers.

 

[Deebu R]

A reason for what, exactly? Why good archers can regulalry hit the target and bad archers can't? I'd stick with the simplest: they are good archers.

What causes the arrow to deviate? Why doesn't it just go to the aimed object?

 

[Bystander]

deviate? Why doesn't it just go to the aimed object?

Google "ballistics."

 

[A.T.]

 

[russ_watters]

What causes the arrow to deviate? Why doesn't it just go to the aimed object?

Bad aim.

 

[anorlunda]

Perhaps the OP is thinking of the archer's paradox.

https://en.wikipedia.org/wiki/Archer's_paradox

 

[ZapperZ]

Ah sorry. I was talking about the basic, less expensive tools. As your bows and arrows improve your accuracy too will improve. Also the distance of deviation is not too big. With practice you can easily lean to shoot accurately. But don't you think if it was that easy everyone would do Olympic archery ? Anyone can take a bow and aim at a target. But if you want to win you need the correct method, form, understanding of what you are doing and lots of practice.

Setting that aside I was just curious about the reason for this deviation. Even if it is because of lack of practice there still has to be a reason, right?

I am very puzzled by this, and your first question. I'm not even sure if this is a physics question.

Do you think that someone who has never ridden a bicycle before, can get onto a bicycle, and immediately learns how to ride it? No? Why do you think it requires many, MANY practices, and a few falls, before one learns how to ride a bicycle? Does it have something to do with eventually achieving a skill that one has to acquire after repeated practice?

Why isn't this the same reason for a novice not being able to hit a target?

I am with Vanadium here, because my modus operandi has always been to first establish the validity of the starting point. You made a series of statement in your first post ("...If the arrow aimed at an object it usually lands above the object. Also if the mass of the arrow is increased it seems to get more and more accurate...") all without providing any supporting document that there is clear evidence and data for this. For all I know, your claims here are not true, and so we're trying to explain why the unicorn has blue horn.

Zz.

 

[Bystander]

Perhaps the OP is thinking of the archer's paradox.

https://en.wikipedia.org/wiki/Archer's_paradox

That would explain the "heavier arrows" observation.

 

[sophiecentaur]

What causes the arrow to deviate? Why doesn't it just go to the aimed object?

It all depends on what you call the "aim" point. If you use a rifle, you can only know where the bullet is going to end up by previous observation of what happens with the sight on a particular part of the target, You can 'click' the sight left/right and up/down to compensate for error in the first try. Once it's calibrated, the 'aimed point' will be the same point that the bullet will reach. I would call the 'aimed point' the point it will hit when it's already been calibrated. Measuring the parameters involved when a good archer is aiming may not be reliable because you cannot tell what his / her aimed point actually is and when the subconscious decision was made to launch; there are no equivalent cross hairs on a bow to the sights in a (fixed) rifle scope. That guy's decision of an aim point was a predicted position, predicted a significant time before the target got there. (See the miss in the timing when aiming at the aspirin)
I am a bit skeptical of the 'explanation' of the Archer's Paradox. The 'wave theory' could well be a factor but if there really has been a lateral force, consistently in the same direction (a DC offset) during launch then how can there be any restoring force on the journey, with or without the bending of the arrow? Is it aerodynamics? Is it not more likely that the string is, in fact, not drawn back precisely in the plane of the arc of the bow? A very small torque around the vertical axis of the bow hand could achieve the necessary offset. The fact that the flexibility of the arrow is important could be much more to do with the way it interacts with the bow in the launch phase and possibly tune out this torque in some way.
Seeing an expert achieve such high accuracy doesn't necessarily mean he is using the correct physical model to explain what he is doing. The human mind is far more complex than that, He is still an awesome archer.
PS you are unlikely to find any information about this from top quality bow manufacturers. It would be commercially sensitive information .

 

[sophiecentaur]

over 4 million references to ballistics on Google...can you help me and the OP narrow our search.
Google was very dissapointing

If google is "disappointing" then you are not driving it right. You have to try all the possible combinations of key words that you can think of. You have to read some hits and get a clue from what they are about and the key words in them. Searching for information is a skill that needs to be developed with practice and it may even involve spending some money on the more useful information sources.
Quite frankly, you have it very very cushy in a world where Google is there to help you get results. In the old days, all that was available was lists of abstracts in the library and you had to order printed copies of papers. Then, of course, there were textbooks. No one spoon fed you in those days.
Caveat: Even if you do get a load of hits on Google, you cannot rely on getting the one that's most suitable. You must try other search engines and read the reference lists in links that you initially try. The last thing you can do is to go on to PF or another forum and expect all the ground work to be done for you.

 

[sophiecentaur]

Now, has anyone any comments on my problem with the lack of a restoring force to compensate for the offset due to the lateral force from the bow?

 

[sophiecentaur]

This paper (ref in the Wiki article) seems to discuss the matter but not exactly in the terms I would like. He does mention the lateral forces from the archer's fingers during release, which would displace the string to the left. This would provide a restoring force to counter the force from the side of the bow. Would this be enough?

 

[Bystander]

lateral forces from the archer's fingers during release, which would displace the string to the left.

Plus the dearth of discussion to this point regarding fletching and, for lack of a better word, "spin" rate; averages out the curvatures in flight characteristics.

 

[doggonemess]

I was wondering why arrows deviate away from the target. If the arrow aimed at an object it usually lands above the object. Also if the mass of the arrow is increased it seems to get more and more accurate. Could someone explain why this happense?

There seem to be a lot of overly complex responses here that are more questions than answers. I make wood bows and arrows, so I'm very familiar with the way the arrow behaves after leaving the bow.

In simplest terms, the arrow tends to get more accurate as it gets heavier because the mass prevents the air from affecting the trajectory of the arrow as much. I've made very light arrows from phragmites with tiny points. When loosed from a heavy bow, they go very fast, but over longer ranges, usually will deviate wildly due to the wind. I've also made English warbow arrows, which are basically short javelins. These will go slower, but are very stable over long range.

As for the fall of the arrow, this all depends on how you're aiming, how the bow was built, what kind of arrows and fletching, and more. I've never heard of arrows that rise after leaving the bow, but some types of bows could 'kick' the arrow when it passes and cause deviations in flight. This is especially true if the arrow doesn't have the correct stiffness ("spine" in archery terminology) for the bow being used. If the arrow has too much spine, it won't bend around the bow properly and usually will go off to the side opposite the bow. If the spine is too little, the arrow tends to go towards the bow, but it can be unpredictable. As a heavy bow will greatly distort the shape of the arrow at launch (with too little spine) it can go practically any direction, and if there is way too much power, the arrow can break in the middle. I've had this happen, it's not pleasant.

I hope this provides some of the info you were looking for!

 

[doggonemess]

Another thought - when we talk about arrows, are we talking about modern carbon fiber arrows with fletching attached perfectly by machines, or are we talking about the kind of arrows I make? If you use natural materials (wood, reed, bamboo, etc.) there are always going to be differences from one arrow to another, even ones taken from the same plant. On top of that, when I straighten, balance, and fletch an arrow, all these things are done by hand, meaning not one of the arrows will behave exactly the same way. They all will go where I aim (I hope) but may be off by a small amount, even if launched by a special rig that could release each arrow identically to the last. With hand made, natural materials, you will never get perfection, just a close facsimile.

I always say "If you wanted perfection, you would have made it with a machine." :)