Reverse drift

[James Park]

Has anyone experienced drift that goes against the wind?
For example, if the wind is from the right, in some circumstances the arrow can go to the right, whereas you would think it would go to the left.
This can happen when you get brief gusts of wind followed by still patches. I think the mechanism is that the gust swings the arrow around a bit sideways about its centre of mass, and then when the gust has passed the side force on the arrow as it moves through the still air then pushes it in direction from which the wind gust had come. It will not happen in a constant wind, only for gusts then still patches.
The possibility then arises that if you can get the arrow's centre of mass in the right place you might be able to cancel out the effect of gusts of wind (or at least reduce it a bit)?
What do you think?

[Kuru]

James, sounds very much like reverse swing the cricketers use when bowling that is when the flow of air runs across the seam which sits up. I know a few top bowlers did alot of reverse swing at Indian Uni's It is very interesting to watch when they pull it off right. Will keep an eye out when shooting and see if I notice anything

[Marcus]

Best way to test that would be with a shooting machine on a gusty day and see what variation you get left and right. If some arrows land into the wind then the theory should be correct.

[mike]

Can't say that I have witnessed 'reverse drift'!!


Although it sounds like a good way to put off shooters at a comp, say something to an archer struggling with the wind like, "geez mate, don't know what the problem is, I just put a bit of reverse swing on the arrows and they just find the middle!"

8)

[McDoof]

I noticed this effect too.

I think wind causes muscles to work to avoid drifting away from the target. As soon as this happens your shooting technique will change slightly (other muscles working) and it will be hard to aim at the 10. Holding against the wind may cause the bow arm to follow this direction (while releasing) - opposite direction that the wind comes from. I can not say that this is the total solution but I guess it may be a part of it.

[Marcus]

Yeah I think that could be a factor McDoof. I had a good example of that at the State short range at 50m.

10, 10, 9, 10, 5, 10.

the 5 was a break in the wind just as I released.

Reason a shooting machine would be needed. Would eliminate the muscle issue.

[2Dogs]

Sometimes when I'm fighting the wind, I tend to cant my Bow too much, and if I'm canting into the wind the arrow appears to reverse drift.

This is usually accompanied by a lot of ranting and swearing :o

Other then that I haven't seen an arrow shot by another person that appears to reverse drift. Only other thing I've seen is when you get a dud Golf ball. I've personally hit a ball with a fade then seen it get halfway down the fairway heading into the rough then turn around in mid flight and hook back into the fairway. Like an S flight path.

As it was a ball with it's internal construction stuffed and it's centre of gravity changing, maybe Jim is right about the Wind moving the centre of gravity of the arrow.

Lots of funny things happen in the wind..........Like Clint shooting a 60 59x @ 70 at the Nats....lucky bastard :lol:

[davewill2]

Hi everybody.
I'm new here, and really like a lot of the issues discussed here. I only wish that there was a bit more participation from other archers visiting or expressing their opinions, and some more up to date topics. I really want to get into exchanging ideas, but the ones that are old, might not get any responses. I figured that I would try to give my idea on the reverse drift of the arrow in wind. I've also read a few articles on it, and they make sense, I only wish I could recall those articles and put them on here for all to read.
The reason why the arrow seems to drift into the wind is that when the gust of wind hits the arrow, it acts most on the largest part of the arrow, namely the fletching, or feathers. It puts more push on the feathers, there-by changing the angle of the arrow, and giving it a new direction for a brief split second. The arrow than tries to travel into the wind, the gust than stops, and now the drag or steering force which is acting on the feathers, will try to straighten the arrow back to the original direction that the arrow was traveling before the gust. But during that brief time the gust was acting on the arrow, it had moved it over to the windy side of the target. That is why myself, I prefer spin-wings on a windy day, although I do mostly use feathers. I like their sideway stiffness
of feathers which does a better job of steering and quicker recovery time off the bow. On a gusty day, you will notice more reverse drift with larger feathers or vanes, but less drift on the arrows like the A/C/Es which have very small vanes. (less surface area for the gust to work on) I shoot the carbon express 3D select arrows with 3 inch feathers (field archery), but on a windy day, I will shoot the same kind arrows, but with the spin-wings on them. I haven't noticed any reverse drifting problems with the spin-wings yet.
Well, that is my explanation of the reverse drift problem, and it seems to make sense to me. As I mentioned, I have no drift problems with the spinwings, but they are a bit fragile, so I don't really want to shoot them all the time, specially on a calm day. I hope that my explanation helps with the reverse drift problem, and that it makes sense to everybody. Any agreements or dissagreements, lets get them out for discussion. There is a lot of knowledge out here, and we can all learn from each other.

Thanks Dave

[L-Roy]

Archers,
For a lesson in the physical properties of the motion of air to occur, I would really need a classroom and not a message board, but here goes my best effort. While some may disagree, here are the physical properties of air in motion.

Air is considered a fluid in its physical properties. Imagine, if you will a flowing stream of water travelling from left to right in front of us. We launch a long projectile by some means into the water. This projectile has stored energy from our launching source. This stored energy is great enough to enable the projectile to cross this column of water.

While crossing this moving column of water that is travelling from left to right, the projectile is travelling not only within the moving column of water in the direction of the projectile's launch away from us, but also it is moving WITH the column of water in the column's direction of travel.

While in the column of moving water, there are forces upon the projectile that for the greatest part are equal on all sides. The forces on the upstream side are NOT greater than those on the down stream side. The forces upon the projectile from its launch are only in the direction of its launch, or away from us.

Now, granted, what you see of the arrow when launched into air is a yawing motion with the fletched end travelling out of line with the direction of launch, but still maintaining a movement away from the launch site, or bow.This direction of launch is, for the most part, controlled by the point being forced in the direction of aim by the stored energy of the bow's limbs. The momentary force that caused the arrow to yaw was immediately cancelled by the pressure on the down wind side of the arrow by the launching force applied by the bow's limbs. Remember, for every action, there is an equal and opposite reaction. That is why the force causing the yaw of the arrow is immediately cancelled by the propulsion force away from us, and against the down wind side of the arrow.

The arrow is now moving in the direction of launch, but is moving away from the launching force within the moving column of air. The forces on all sides of the arrow, for the most part are equal.

In no way is the launching force applied to the arrow able to cause the arrow to fly "upwind" within the moving column of air, as the arrow only moves away from the force of launch, but within the column of air moving across in front of us, the shooters. Flying "upwind" is an optical illusion caused by the perceived attitude of the arrow seen in its direction of travel away from us.

The illusion of reverse drift is usually caused by the archer's fighting to control the bow's movement away from the wind and the archer's muscles moving the bow back in the upwind direction. If the wind should relax its pressure on the bow and equipment as well as the bow arm and the archer's body at the moment of the shot's break, the resultant shot will seem to travel upwind, when, in fact, it was sent in that direction by the over correction due to the muscle drift in the archer's controlling of equipment.

Sorry for another lengthy dissertation, but, if any are pilots among our ranks, this will be easier to understand.

Thanks for bearing with me!

[noel mac]

go and shoot at yarra bowmen on a sligthly breeze blustery day you get reverse drift and back again all the way to the target. at 90 meters you feel the wind behind you but when you shoot the arrow it will go right then left and back to the center of the target or worse. but shooting recurve maybe it wasn't the wind!

[L-Roy]

noel mac,
Without wind flags all the way to the target, you may not see that the wind, at 90m, may be swapping directions, ie; coming at the arrow from, first one side, then another. What you observe is actually the effects of the wind's changing directions and the arrow's resulting drift within the moving columns of air.

[Marcus]

To use your anology of a river, reverse drift may actually be due to shooting your arrows through 'multiple rivers' heading in different directions perhaps.

[L-Roy]

Marcus,
Agreed, with each "river" needing its own wind (river) flag to determine direction.

Without that, one guess to what is happening is as good as another's.

[Marcus]

Yeah one reason I don't care much for flags. Some shoots have them at the target, what's the use when my arrow has already stopped at that point? Also you target the flag is moving left, the next target it's moving right and the next again it's still. :roll:
Also you can have no wind at your end, none at the target and a pocket of it half way down. Plus my Dad complains about thermals, but I think that's an excuse. :)

[L-Roy]

If you mean mirage, that is the shooter's best friend. It is your "inline" wind flag. It will always tell you of the wind's direction, that is if you can see all of the different directions of different columns of air movement!

Sometimes it seems best to shoot and allow the arrow's path to be determined by the "arrow gods". Just hope your "god" treats you better than your competition's!

[mike]

Allowing for the rules of physics there really aren't any circumstances where an arrows could fly 'upwind' as described, however, it would be possible to get a kind of 'arrow refraction'.

Assuming this arrow is fletched, once in flight it will be pointing into the wind (fletches down wind of the point). The amount of this pointing effect is determined by the wind strength and the drag properties of the arrow, but generally for a given arrow, the higher the wind strength, the greater the angle of the arrow.

If this arrow were to go from a high strength wind (wind A) suddenly in to a lower strength wind (wind B) in the same direction as the high strength wind, then the arrow will enter wind B with an arrow angle the same as that was in equilibrium for wind A. This would cause a sudden, but momentary, imbalance in the forces acting on the arrow, with a relatively higher force acting (as a direct result of drag) on the down wind side of the arrow, resulting in accelaration towards wind B. Due to the shape of an arrow this would tend to appear to "push" the arrow upwind. Until the arrow reaches its equilibrium angle for wind B, it will to some extent be counteracting the force of wind B, resulting in an apparent temporary "upwind travel" effect.

This is a refraction type effect, similar to the situation of looking at an object that is in a swimming pool.

Of course the arrow will still infact be moving to one side or the other relative to the direction in which it was shot, but, in the lighter wind will do it at a lower rate.

It appears to 'drift back' to the target because, in effect, you have over corrected for the average wind between yourself and the target. Ie, you shot it too far to one side.

Difficult to explain without a diagram... :x

Viewed from behind, if this effect were great enough (ie if there was an almost still pocket of air towards the target) it could well appear to be drifting back towards the target.

If the effect seems to be great enough that you don't need to adjust for the wind then it probably means that the "Wind A" in the example was never strong enough to have a substantial enough effect on the arrow anyway.

[James Park]

I agree with Michael - he has the physics correct.
What I think it means is that if for the first part of the arrow's flight there is a wind from say the left, the arrow will take up an angle with the fletches to the right. Then, if the wind stops, or gets significantly less, until the arrow once more orients itself in accord with the change of wind there will be a side force on it pushing it to the left. This is where the "reverse drift" comes from. That is, can only happen where the wind is gusty, and you shoot at the monent of a strong gust.

[L-Roy]

Mike,
In your example, there will be no acceleration of the arrow "upwind" regardless of the relative orientation of the arrow. It will weathervane only until the forces on each side become the same, though it will, in fact, loose a very small amount of forward momentum due to momentary increase in drag. Regardless of the wind's strength, downwind drift will continue.

The arrow may assume the angled orientation in flight because of the drag of the fletch at the moment of original encounter with the crosswind, though if the cross wind is not very brisk, the arrow may fly virtually un-angled to the target, but still will be travelling in the direction of the flow of the wind.

If, as in your example of flight into wind of the same direction, but of lesser momentum, the arrow will, momentarily angle, relative to the new wind. It will, however, travel along with the new wind's direction.

If your example were possible, at some point the arrow, if it encountered wind at right angles to flight path with force equal to the arrow's forward momentum, would turn directly in the wind and loose flight, or fall downward from gravity. This will not happen due to the initial launch direction of the arrow and the fact that nothing is forcing it from its intended flight direction. The arrow is only "going with the flow" of the wind's path while flying in its original flight direction toward the target.

[mike]

As I said

Of course the arrow will still infact be moving to one side or the other relative to the direction in which it was shot, but, in the lighter wind will do it at a lower rate.

If that rate changes significantly enough it would be possible to see that (as the archer standing back at the shooting line) as a "reverse drift".

This is because, as I said:

It appears to 'drift back' to the target because, in effect, you have over corrected for the average wind between yourself and the target. Ie, you shot it too far to one side.

As James said, it will happen in gusty conditions, because those are the conditions that can cause the kind of wind velocity contrast necessary to produce the 'refraction' effect.

Any way, if a force acts at right angles (or effectively at a right angle) to the motion of an object such as an arrow, it will not change the speed of the object at all, it will merely change its direction.

Drag and gravity slow an arrow down if they have a component that acts in the opposite direction to the movement of the arrow, whereas the component of wind force that acts perpendicular to the arrow will only ever change its direction.

Don't worry, my theoretical arrow is not going to fall out of the sky... :wink:

[mike]

Returning to the original post for this topic...

The choice of center of mass of an arrow is an interesting one.

If the physics above is correct, then factors to consider to reduce the effect of a variable wind strength would be:

Where on the arrow the force acts as an arrow moves into a different wind strength 'zone'.

How easily that force can cause the arrow to rotate around its center of mass, rather than move the entire arrow (we would rather the arrow just rotated a little rather than moved completely)

If this is the case, then we want the center of mass to be close or at the part of the arrow experiencing the least drag force. That way, when the drag acts on the arrow (at the part with greatest crossectional area -- generally the part where the fletches are) it will have a greater rotational effect.

It would seem to suggest that this means that its best to have the center of mass as close to the arrowhead as possible, hence the high % FOC people often try to acheive by putting heavy tips on their arrows.

So, does this mean we should all aim not only to have the narrowest arrow possible, but also the highest % FOC that will still tune well enough?

It seems that an X10, with at least 110 grains at the front, and very light and small fletches (say for example small spin wings) and a lightweight nock system (not the pin nock then) would produce a high % FOC in an already low drag arrow. This would make the arrow less vulnarable to wind changes. Instead of the arrow getting blown around, you would see very dramatic "weather-vane effect" as the arrow went towards the target.

This also suggests that FOC has no effect of the stability of flight in dead still conditions (of course you want to have a small % FOC to get the arrow to arc down, point first)

I have noticed with my target arrows, that only have 82 grains at the front, that they are susceptable to wind changes whereas other peoples' with heavier points are less so.


:-?

[L-Roy]

Mike,
And, of course it can't "fly into the wind", even though it may appear to do so! It will only drift with the movement of the wind while continuing onward with its propelled direction.
:D

[L-Roy]

Mike,
I can think of one instance when an arrow may fall from the sky unnaturally.

If you shoot an arrow missing its point weight system, what may happen?

[L-Roy]

Mike,
It is amazing that even considering our great distance apart, we must have been thinking along similar lines!

I have shot as little as 4-5%FOC indoors in relatively still air, with very good results. Outdoors, I usually shoot 18-20% FOC, with equally good results. "Wind bucking" ability seems to favor the heavier FOC.

Yes, while the arrow with the heavy FOC looks very strange while cocked in flight, they fly very well.

I have experimented with much heavier FOC with ACE's. I've bare shafted to 80yds by using 30+% FOC! I've always wanted to go to the NFAA Indoor Nationals with nothing more than fur tracers on my arrows as fletching. If I were of the ability of Mike Anderson, or Terry Ragsdale, I'd do it in a heartbeat!

[Joe]

First vist to this forum. Nice layout and good content.

James

I think your explanation of reverse drift is exactly right. It is in principle possible to reduce/eliminate reverse drift. The gust blows the arrow a certain amount downwind. The amount the arrow is rotated by the gust and how fast the arrow then straightens up determine how much drag moves the arrow in the opposite direction to the gust. If you get the right combination of arrow mass, FOC and fletching size/position then the two movements can cancel each other out.

[James Park]

Joe,
The thing that interests me here is:
I understand how reverse drift can work, but can it be arranged such that it always cancells the correct amount? I suspect not, because the amount of reverse drift will depend on the wind profile as the arrow travels to the target (that is, how the "gustiness" of the wind changes).
So: given that (if I am correct) it is not possible to get the perfect cancellation for all wind conditions, what is the optimum to aim at?

[Joe]

James

If an arrow could rotate instantaneously then the only sideways movement from gusts would be more or less only from pile drag. Most (target) arrows carry a lot of fletching so their rotation response is fast - as a result the downwind movement from shaft drag during a gust is pretty much compensated for by the upwind movement from shaft drag after the gust has passed. The main factor on how much sideways shift there is on the target results from when the gust hits. If the gust hits early in the flight then the arrow has time to move upwind after the gust has passed. If the gust hits late in the flight then the arrow doesn't have time to move upwind and it hits with a larger downwind displacement.

Reverse drift results from a specific set of (unpredictable) condtions. The gust has to hit early in the flight, the gust wind speed as to be relatively high and the gust duration has to be short. As a consequence when the wind speed drops back to normal the arrow has not yet stabilised and the nock is still rotating down wind. The extra time required for the rotation to brake to a halt and start to swing back results in the upwind shaft drag acting for longer (and stonger) so the overall upwind arrow movement exceeds the initial downwind movement. You can't plan for this. The rotational characteristics of the arrow are selected to give good groups for 'general' shooring conditions.

[James Park]

Joe,
I agree with all that.

[L-Roy]

Joe, James,
Hey guys, try your "theories" with a high school or college physics class.

Unless the arrow contains onboard propulsion, it cannot and will not fly "upwind". The arrow only moves within a moving column of air in a direction only away from its initial launch toward the target. If it exits a laterally moving column of air, forces become equal on the sides of the arrow post haste with the arrow continuing along its merry way toward the target.

[Joe]

L-Roy

Maybe a good example is a para-glider. A para-glider can go upwind, downwind any direction he likes even when there is a crosswind. The "onboard propulsion unit' is the drag force on the chute resulting from the vertical descent speed. The guy can point this any direction he likes and hence go in that direction.

An arrow works in similar way only in this case it's the drag force on the arrow shaft resulting from the arrow's velocity that provides the onboard propulsio unit.

[GaryH]

James,

An arrow works in similar way only in this case it's the drag force on the arrow shaft resulting from the arrow's velocity that provides the onboard propulsio unit.

Is there anything to indicate that the arrow's velocity provides lift??
Is the shaft capable of creating lift??

At which points in the travel of the arrow does it cease acceleration, reach maximum velocity, begin to fall under gravity (I know it's dependant on trajectory). (Given ideal (still) :lol: conditions)

Joe,
A chute (ram air) gains it's propulsion as a result of gravity. Given infinite vertical space (and perfect conditions) it will continue to go forward.
An arrow gains it's propulsion as a result of an expendable force. Given the same infinite vertical space the arrow will be overcome by gravity and will no longer be capable of forward movement.

[L-Roy]

Joe,
Not quite right. Physics 101




The arrow will not do this.

[mike]

Gary:

Maximum velocity (under normal shooting circustances, on flat ground) will be at the moment the arrow leaves the string.

From that point on the arrow's speed is decelerating as a result of drag (drag is the primary displacement force acting on the arrow apart from gravity)

Gravity always acts on the arrow (even when it is nocked at full draw).

That is to say that all the forces mentioned are acting on the arrow during flight and it is the balance of those forces that affects where the arrow will go. If there is a component of a force that is acting "unopposed" on the arrow it will cause an acceleration (acceleration can be positive, negative or, this is the important one, have no effect on speed, but simply move the object in a different direction). If the forces reach equilibrium, or balance eachother out, the arrow moves in a straight line. This rarely happens to an arrow as gravity is usually providing an imbalanced force, but if drag forces cancel out gravity as well, then you reach "terminal velocity". This is where the "floating effect" takes place that helps flight archers -- the drag on the arrow is counteracting the gravity effect and so the arrow appears to 'defy' gravity and just sails through the air. Since drag on an arrow is dependant on its speed, when the arrow slows down, the drag deacreases and then gravity starts pulling it down again...



Interesting...

[Joe]

Gary

Re your question about lift, defining lift and drag in the conventional sense, typically about 70% of the "total drag" is drag and 30% of the "total drag" is lift. These figures represent a qualitative overall ball park average as the lift to drag ratio is very sensitive to the arrow pitch and yaw angles.


L-Roy

Curious - what is 101?

[L-Roy]

Your first university level class in any subject, sorry for the confusion!