My club held a 3-D shoot this past weekend. I spent Saturday working the registration table, and heard lots of folks complaining about the wind on the three targets we had set in a big pasture. Well, this got me to thinking, which is always trouble.

On Sunday I shot the course, armed with my new "secret weapon" for those windy pasture shots. My standard set up is three 5" helical feathers, which really catch the wind, especially a cross wind. I figured that a lot less feather should result in a lot less deflection, so I glued one third of a full length feather to a bare shaft using contact cement. I spiralled the feather around the shaft, just like making a "porcupine" flu-flu. My group consisted of five shooters. When we got to the field, I shot last. The wind was blowing harder than the day before, and played some amazing tricks with the other shooters arrows. My crazy looking thing flew almost perfectly straight. It even made that cool flu-flu noise, but with no perceptible loss of speed. Hit 8 and 10 rings on all three wind-blown targets with the other guys happy with 5's.

I don't think I'd recommend this for broadheads on the prairie for antelope, but for foam deer it's pretty effective.

Bill

Cool,

What'd your shoot'n buddies think of it?  They didn't ask to "borry" it?  lol

Good bareshaft flight, minimum fletching and less than 10% foc works good in the wind here in NM.

Njord,

less than 10% FOC?????

Most Olympic style archers (myself included) are shooting for the highest FOC possible for windy conditions.  My ACE's are over 15.5% FOC with fully 1/3 of the total arrow weight in the point alone! 

No doubt proper tuning has a big influence on flight in the wind too.  But, the key is small diameter shafting with the highest FOC possible...

John.

if you watch people shoot in hard gusty wind it seems like the winds effect on the archer is more than it is on the arrow. a person who can maintain his body and arm position seems to be able to still hit the spot with the point even if the rest of the arrow is slanted.

IME a low foc arrow drifts parallel to the wind, where a high foc arrow tends to weathervane. The low foc allows me to hold into the wind and predict arrow drift. The weathervaning of high foc shafts can actualy make yuo miss into the wind. Not to mention the predictably poor penetration, and breaking and bending that happens when an arrow is flying sideways.

I'm not a high foc advocate for any reason, and typically shoot about 8% on a 620gr 32" arrow.

Remember objects(arrows) MUST move around their center of mass/gravity. The more FOC you have the longer the lever arm on the fletch end becomes(distance from the nock to the balance point). The wind is pushing on the feathers, and you have a longer leverarm so it has more advantge over the point than an arrow with a lower foc

I'm with Limbwalker and the Olympic Team, High FOC for the Wind (also minimal fletching for non-broadhead apps).

Njord, keep in mind that when an arrow "weathervanes" it points into the wind, reducing the drift. Now, you say, "high foc shafts can actualy make you miss into the wind" Ok, this can occur if the arrow flies into a slower moving patch of air. BUT in either case, the high FOC arrow will miss by less than a low FOC shaft because the high FOC shaft drifts less, period.

The amount of yaw is minimal (can't imagine why you'd refer to it as "flying sideways"). You can calculate the theoretic maximum yaw quite easily, Yaw Angle = Inverse Tangent(wind speed/arrow speed). Any arrow will adopt this Yaw, regardless of FOC. Why? Simple, the pile end has far less cross-wind drag than the fletched end. Has nothing to do with FOC. An arrow will Yaw, period.

Perhaps what you are experiencing is reduced arrow velocity due to the added weight in a High FOC shaft resulting in slightly greater Yaw.

So, you might ask, "Why does a High FOC arrow drift less if both arrows attain this Yaw?" Fair question. The arrow with the concentrated mass at the tip spends more time cutting through the cross-wind before it reaches full Yaw. It's a simple angular momentum problem: and the secret is... High FOC shafts require less fletching surface area! Less fletch means less cross-wind drag which means less rotational force on the arrow. So it's harder to get that mass to rotate about the center of gravity - and a High FOC arrow generally has more mass.

A high FOC arrow has penetration to spare, IMHO. High FOC slam sticks rule!

Now, if you disagree, why not write the Olympic Team Coaches and educate them?

Oooopps!  The first part should have read:

...when an arrow "weathervanes" it points into the wind, reducing the drag.

My distance arrows all have higher FOC and yes, in the wind you can watch them "weathervane" just before they hit the gold. Looks pretty cool. ;)

You are both right, it is just that you are talking about two different things.

The olympic team shoots high front of center for wind because the have almost no arrow weight to speek of. So for them a hight foc(heavy point)can dictate where the arrow will go. Drive the arrow if you will.

For a heavy arrow, this is the exact opposite. A 620 grain arrow that NJORD shoots is not much going to be dictated in flight by raising his tip weight by 25 grains. So for him, his lever theory is not only good it is quite accurate in fact.

Deerdander, I protest, for a heavy arrow it is exactly the same - not opposite.  The laws of physics simply do not take a vacation because of a little shaft weight.  No arrow drifts parallel to the wind.  Sorry, not while I've got time to kill.

FOC works in percentages.  A heavy arrow needs a lot more tip weight to increase it's FOC.  Adding a mere 25 grains to the point of a 620 arrow has an insignificant impact on FOC.  High FOC means High FOC, regardless of arrow weight.

If he were to shoot lighter, longer, stiffer shafts with heavier points and smaller fletching (tuning out at the same 620 grain total weight, but with substantialy higher FOC) he would have a pleasurable experience.

Certainly, total arrow weight is a concern: too much weight yields too little speed resulting in too much time in flight and thus, too much wind drift.  The only wood arrow I know of that can yield exceptional High FOC without weighing in for an elephant hunt, is ForgeWood.  Carbon is the best choice, obviously.  This is all primarily a target gunner's concern...

I may have been buttering it a little to show the fact that the breeze is not going to have as much effect on a heavy arrow as a light one.

And remember were not talking about flight characteristics, where talking about wind drift.

I think the biggest part of minimizing wind drift is minimizing cross-wind drag.

That means tiny fletches and a skinny little shaft.

The arrow must also have enough mass to resist being too easily wind blown.  That mass is best located at the tip - in others words, High FOC.

Tapered shafts like the Arrow Dynamics or Grizzly Stiks might add some degree of yaw stability - the back side of the shaft itself having less cross-wind drag than the front (neglecting fletching).

I know just enough physics to be dangerous. I also know that general physics is always taught "in a vacuum with no air resistnance", to teach the concepts. And in the real world where vacuums are unnatural, and the winds blows. Empirical evidence is useful and may be required along with the physics modeling.

"Parrallel to the wind", sounds a bit ambiguous, perhaps I should have said "MORE parrallel to the wind". I'm guessing you really knew what I was trying to describe. What i was trying to describe was the arrow flying straighter, less yaw, more perpendicular to the target face. This allows ME to better adjust for wind drift, as the arrow is flying in a more natural attitude, or at least one I'm used to seeing

So Mozark since you are assuming the role as the expert and you have the time. Perhaps you could explain how a heavier point which has less wind resistance when compared to a lighter point of the same surface area, does not yaw much faster. I'm sure ther must also be some time interval that needs to be accounted for. Yet I don't have the background to caculate it.

It is my suspicion that at very long ranges (+50yds) that both lite and heavy foc arrows will have the same attitude of flight due to the fact that there is a FOC ballance and, I assume, both have feathers on the back. This is probably the time factor calculation.

I have no reason to doubt your position yet I'm intuitively sure that center of mass(FOC) helps determine how rapidly the arrow yaws. And that, over reasonable ranges for windy conditions, may explain the results I have observed.

I never claimed that a low foc arrow drifts less, only that it's flight was more predictable to my eye.

I have little desire to convince the Olympic team of anything. And, I'm sure they care little if I can kill an elk at 20 yds in a gusty NM canyon. Physics is fun and helps to predict behavior, engineering as well. I'm sure the Tacoma narrows bridge(good film of it's destruction by harmonic superposition caused by wind) was engineered, and physics still has a hard time making a bumblebee fly.

I'm sure my analysis is not the final answer, as I'm sure there are many factors I haven't considered. As well, I'm sure that your analysis is not the whole picture either

"Perhaps you could explain how a heavier point which has less wind resistance when compared to a lighter point of the same surface area, does not yaw much faster."

A heavier point won't have less wind resistance.  Think in terms of the whole shaft and a cross-wind (not just a point cutting through the air).  Again...  So, you might ask, "Why does a High FOC arrow drift less if both arrows attain this Yaw?" Fair question. The arrow with the concentrated mass at the tip spends more time cutting through the cross-wind before it reaches full Yaw. It's a simple angular momentum problem: and the secret is... High FOC shafts require less fletching surface area! Less fletch means less cross-wind drag which means less rotational force on the arrow. So it's harder to get that mass to rotate about the center of gravity - and a High FOC arrow generally has more mass.

"I'm intuitively sure that center of mass(FOC) helps determine how rapidly the arrow yaws."

Say it this way, "I'm intuitively sure that mass helps determine how rapidly the arrow yaws, rotating around the center of mass."   There is more to it than the arrow's mass.  The big player is drag (in the cross-wind world the big drag element is the fletching).  Again, it's a simple angular momentum problem: and the secret is... High FOC shafts require less fletching surface area! Less fletch means less cross-wind drag which means less rotational force on the arrow. So it's harder to get that mass to rotate about the center of gravity - and a High FOC arrow generally has more mass.

"I'm sure there must also be some time interval that needs to be accounted for."

Exactly!  It's a matter of how long it takes that external force (cross-wind drag) to rotate the arrow to full yaw or to push it about.

"It is my suspicion that at very long ranges (+50yds) that both lite and heavy foc arrows will have the same attitude of flight..."

I think you are correct, given that they are flying at the same speed.  Another difference comes into play at longer yardages.  That is, changes in cross-wind speed during flight.

"...it's flight was more predictable to my eye."

That's important, "Become the arrow" and all.  Would not an arrow with less driftability be easier to visualize?  ... ?

Mayby not...?  We see the effect of the wind and have lots of input as to it's speed - we see the gust waves in the grass, the leaves blowing, etc.  Perhaps it's easier to visualize the arrows flight if the arrow moves with the wind when shooting instinctively.  Perhaps you have a nack for it.

I'm not claiming to be an expert, just doing my best to shed some light on this topic.  Hope this helps.

 

You dont have to know anything about physics to try this. (this will validate what I said earlier)

Take a fletched arrow outside and hold it with 2 fingers in a verticle position. (obviously you have to have wind for this to work)

first hold it about four or 5 inches above the tip. (notice how hard you have to squeeze to keep the arrow from falling over in your hand)

Now, pinch the arrow in the center. See how it resists the crosswind much better than when the balance point was lower.

This doesnt prove that the arrow can not be blown off course by wind. It just proves that even though the arrow gets blown off course, it flies straighter with a lower FOC and therefore penitrates on game better.

Try to get Penitration when a breeze has your arrow all Jack-Legged out to one side.

In an attempt to say the main points of my last post more succintly.

When the arrow encounters a cross wind , a torque is induced due to the different length leverarms, determined by the center of mass(foc), and by the surface areas exposed to the force(wind). This is the angle I'm coming from to interpret the results I have observed. An arrow with a higher foc yaws faster, than an arrow with a lower foc, yet they will eventually achieve the same yaw, because in any reasonable arrow the fletch end has more leverage. If the equilibrium isn't yet reached inside of a 20-30yd bowshot the lower FOC has the advantage, at a longer range (after equilibrium) the higher foc has the advantage has the advantage because it has drifted less.

I won't have time to digest your last post until tommarrow, and will reply then.

There's an easy way you can see how an arrow behaves in a cross-wind.

Get yourself up off the ground about 12 feet or more.  Hold the arrow horizontal, hold it only at it's balance point (center of mass).  Let it drop.  The arrow will pitch forward and then fly forward. 

This is pretty much how it behaves in a cross-wind, except you're seeing it in a vertical plane.

The pitch is equivalent to the cross-wind yaw.

The forward motion of the arrow occurs because gravity is accelerating the arrow, pushing it against the air.  Now turn your world 90 degrees and think cross-wind.  This forward motion happens in a cross-wind to a much smaller degree - only the momentum of the arrow can push against the cross-wind, gravity will have no affect (horizontally).

Smaller dia., heavier shaft weight and lower profile shield cut works good.

I should mention that you can compare how long it takes different arrow designs pitch by dropping them that way.

Deerdander, you are misinterpretting your example.  What it shows you is how important small fletching is - that's what catches that air.

An arrow does not fly straighter with lower FOC.  Yaw Angle = Inverse Tangent(wind speed/arrow speed). Any arrow will adopt this Yaw, regardless of FOC.

Ok Im not arguing that the two arrows you speek of will not achieve equil Yaw and be thrown off course equily. I dont know that to be true, but I will take your word for it.

What I am saying is the arrow with a more centered balance point will shift in the direction that the wind is blowing at less of an angle than one with a high foc.

Let me better explain.

I speek only for the higher weighted hunting shafts(500 grain give or take 50 grain.) When I shoot my 2413(compound bow) arrows with 85 grain heads (which I use for target) in approx. a 5 MPH cross wind, they will probably blow off course just about the same as my hunting arrows that have the same setup only with a 125 grain head.

The difference is that in flight the heavier heads move the FOC forward giving the fletchings more leverage (Same concept as a cheater bar for lugnuts) to kick out than if the FOC is farther back.

The arrows travel approx. the same distance off coarse, but the lower foc arrow flies straighter, (less porposeing) therefore it would penitrate into game better because it is straighter upon impact.

One thing we know:  Tiny fletch, skinny light shaft, heavy tungsten point is what works for the 90M Olympic guys out in the wind.  This is a High FOC setup.

Question is, why does it work?  and, obviously, how can we adopt some of this to hunting or 3D shooting, if any.

I think part of my arguement might be wrong.  Gotta think on it some.

Actually everyone is missing the obvious here... Under NFAA rules Ashville should have been disqualified for using that arrow. "All arrows shall be identical in length, weight, diameter, and fletching with allowance for wear and tear." So if you're gonna use a cheater arrow, you have to use it all day on all targets.

I hate to speek for everyone, but most trad guys are just out to enjoy themselves. Advancements in the sport like that are welcomed because it gives people new ideas. If I was shooting beside him, I would just go home and make me some.

I agree with deerdander. Do you have any pictures of them?

I saw a picture of something similar a little while back. Search the forum for Flu-Flu's or something like that.

The open shoot I was in at the time had no arrow restrictions in the trad classes at all (I checked beforehand!) so there was no rules violation. I shoot in lots of different types of competitions and am keenly aware of possible rules violations. The arrow was exactly like all the others in my quiver except for the fletching. I was really just curious to see if the thing was advantageous or not. I was playing with it in the yard today and discovered that it worked even better after I trimmed off about half the length of the vanes. Still makes that cool noise, though.

I'd post a pic, but my computer is not at all friendly with the wall, I guess. In advanced edit, I get an error message when I hit the pic icon (404, page not found), and when I try to submit text, a blank post appears (see above!). I tried to email the bowsite tech support, and the mail was returned as undeliverable. I'm not feelin the love here, I can tell you! Any suggestions? (other than refletching my monster?)

Bill

High FOC and skinny shafts win in the wind, period.  If you doubt that, ask Vittorio Frangilli, father and coach of Michele Frangilli, #1 ranked olympic recurve archer in the world.  Even though Easton came out with their ridiculously priced X10 shafts ($290/doz.) and ballistic tungsten points ($190/doz.), Michele still uses ACE's with 125 grain points due to the higher FOC they offer.

When I'm #1 in the world at shooting recurve bows in a crosswind at 90 meters, I might have my own opinions.  Until then, I'll just trust his judgement ;0)

John.

Gasp...   $290 + $190 + Beiter Nocks + Fletching + Shipping = excess of $550...   For a dozen arrows!?  That's an archer's divorce if I ever saw one.

So, where do you put the little rocket booster?

Mozarkid, I'm sure they're working on that...

Like I said, ridiculously priced.  But the throngs of wannabees (and many top shooters too) are flocking to them at breakneck speed.  You can hear the bank accounts bursting as we speak.  Easton (and their lead technical guru who shoots the O.R., but not very well) has everyone convinced that you must shoot the X10 to be competitive.  Funny thing is that the scores today in the U.S. aren't any higher than what Darell and Rick were shooting 10 years ago with the ACE.

John. 

Interesting discussion guys... I gota go with Limbwalker and Mozarkid on this one. What you "see" standing with both feet on the ground is far different from what is really happening. The arrow is going to stabilize reletive to the wind period. If as you shot you moved with the wind at the same velocity you'd see nothing but nock the whole way just like you do with zero wind. The arrow is part of the air mass once it stabilizes and will drift down wind at the same velocity the wind is blowing. They can never hit "up wind" from where they are pointed. The best factor to reduce it's effect is velocity, the faster the better. Part of why skinny with small vanes are going to help....O.L.

Yes, EVENTUALLY both arrows will adopt the same attitude. The "EVENTUALLY" is the question IMO. An arrow with a greater FOC will react to the wind sooner(almost sure that this is fact), if it takes an arrow with a lower FOC 1/2 sec (??) longer to adopt the eventual maximum yaw then the arrow with a lower FOC will exhibit less yaw on the way to a 20-30yd target. Because 1/2 sec is about the flight time for an arrow to travel 30yds.

I think vector diagrams are somewhat misleading in this case, as they represent the eventuality, and don't show how or when it is reached. I'm sure an experienced pilot could shed some practicle light on this issue. Or maybe a barge or tanker Captain

I don't have the background to calculate the time before maximum yaw in either case

Anymore thought Mozark?

I have a thought, but I have to compare another sport.

I think much of the drag created by the fletch is not directly comparable to the size of the fletch, but the count and shape, as each one creates its own vortex (disturbance) as it passes through the air, which equates to drag.  Windsurfing sails are designed to minimize additional drag from varying loads (gusts) by "twisting off" at the top portion of the sail.  They open up as load or lift increases, looking as if they are spilling air, and allow the top of the sail to change its angle of acceptance to the wind, thus maximizing lift and minimizing drag created by the tip vortex.

I would think the best cross wind fletch would be a soft and pliable one, but not necessarily the smallest, with a clean trailing edge (parabollic?) that allows it to self adjust at the outside edge.

Also, I was shooting long shots on the beach last week (250 yds) in some crosswind and it seemed like my 5" helical vanes drifted less than 4" straight vanes, what's with that?

For the sake of arguement we should standardize everthing and only vary foc so as to study the effects of foc indepedant of other variables

ttt

Felipe, you said, "I was shooting long shots on the beach last week (250 yds) in some crosswind and it seemed like my 5" helical vanes drifted less than 4" straight vanes, what's with that?"

That fits with what I've been thinking about.  Here are my current thoughts, I think I've got it nailed:

The Steady State Yaw Angle = Inverse Tangent(Wind Speed/Arrow Speed).  Any arrow will eventually adopt this Yaw, regardless of FOC or weight.  This is because the pile end has far less cross-wind drag than the fletched end.  Has nothing to do with FOC, etc.  An arrow will Yaw, period.

When an arrow yaws, it points into the wind, reducing the drag.  Drag is a key issue.  You must maintain high velocity to reduce the drift.

Now, "Why does a High FOC arrow drift less if both arrows attain the same yaw?"  Well, I have to point out that a Low FOC arrow will not attain the same yaw as an otherwise identical High FOC arrow.  This is because the down range velocity of the High FOC arrow is higher.  Increase the arrow speed relative to cross-wind air speed and the yaw angle decreases.

So, "Why does a High FOC arrow have higher down range velocity?"  Well, it starts with what Deerdander pointed out.  The lever arm length that the cross-wind drag force acts on is the distance from the fletching to the center of mass.  On a High FOC arrow, more mass is concentrated closer to the center of mass.  This plus the longer lever arm makes the arrow easier to rotate - not harder.  The High FOC arrow yaws faster.  Since it yaws faster, it suffers cross-wind drag for a shorter time.  Less drag, less lost velocity, less time in flight, less wind drift.

That leaves the fletching question.  Big or small?  Could it depend on how long the flight time is?  A large fletch will cause the arrow to rotate (yaw) faster, minimizing cross-wind drag.  But, it will have greater head-wind drag.  Darn the luck, we'll have to go shoot some arrows...   ;o}

I'd have to think there's a good reason the Olympic guys/gals use those little fletch jobbies.  Sure makes those flop-eared things look interesting...

yeah Kid, those were my thoughts also, that the faster the arrow reaches a stable yaw attitude the more efficient it encounters crosswind drift.  What we need are fletch that are high for the launch but will slowly recede into the arrow leaving a low profile once the arrow is stable (smart arrows?(may not be ethical though)).

I would think all arrows will eventually reach the same drift speed during flight, which will be near the speed of the crosswind, so after a stable yaw is obtained fletch size/shape comparisons would be the same as in still air, and the fastest arrow will drift less because of less time spent in the crosswind drift.

Yup.  Ya know, this appears to be yet another slightly good arguement for front heavy, tapered shafts like Grizzly Sticks or tapered & footed woodies.  I keep telling myself I gotta get me some Grizzly's...  but, dawg...  $$$.$$.

Nope, none of this really matters.  Seems like the average long shot around here is 17 yards.  Could make that shot in a hurricane.

For me, it isn't just about hunting.

Mozark isn't that exactly what I have been saying?.

Another thing that adds to the faster yaw of the high FOC arrow is that since the point is heavier and the same surface area as the identicle arrow except with a lower FOC, the heavier foc arrow point resists being accelerated to the lee when compared to the lower FOC.

Now, factor in the difference of the lengths of the leverarms foward of the center of mass of the high and low FOC arrows, and I think you see why the high FOC arrow achieves the yaw considerably faster. Which is why a lower foc arrow flys straighter to a short range target. And, a lower foc arrow may in fact be better in this particular instance.

Here's another thing to think on, and I think it supports hi FOC. Which arrow penetrates better if the arrow IS NOT flying perfectly perpendicular to the target at impact?. Think about the two axis' of center of mass, as they apply to an arrow

Dang, all this nonsense over a cool production of a creative mind.  I could see how it would be important, pertaining to all the physics debating, if you were talking about the flight of a multimillion supersonic aircraft.  But, this is an arrow that Ash built up just to have some fun and see if it would work.

This ol' backwoods boy needs a tylenol.

Well, not exactly...  but we're quickly converging.

"the heavier foc arrow point resists being accelerated to the lee when compared to the lower FOC"  No, High FOC will rotate faster as a result of changing cross-wind pressure, reacts faster no matter what.

A lower FOC arrow would be straighter at short range, but inside 15 or so yards there would be no real difference no matter what arrow you shot.  Wind on the bow arm and body would be much worse, I think.  Wear slippery tights and shave the head, LOL.

After reading Byron Feguson's reasons for liking concave broadheads, how they turn in on impact, I'd have to believe a high FOC arrow would be better, faster to rotate.

Think about the force of the wind on the individual shafts forward of the center of mass as well.

O.L., et.al.

I'm having trouble with the "arrow becomes part of the air mass" idea.  Maybe I need it explained in layman's terms.

I regularly shoot at 90 meters (you know that).  At that distance, with my arrows traveling 212 fps., it takes my arrow approx. 1.4 seconds to reach the target.  In a 10 mph crosswind, I will have to compensate approximately 3 feet in the direction the wind is coming from. 

So, if you do the math, the arrow is only moving at a rate of 1/3-1/4 the wind speed.

I think I have that correct. 

Is the shaft causing the arrow to plane upwind and reduce the affect of drift?

John.

Mozark, I'm not trying to be a smarta$$, but read Carefully. "Lee" more properly leeward or downwind.

The wind acts forward of the center of mass as well as behind, the rear ward portion has a much greater effect due to surface area and leverage. But I don't think you can ignore the forces acting forward of center of mass. The forces forward of center, also cause the hi foc arrow to achieve maximum yaw faster, due to leverage surface area and weight.

I think we can agree that high foc makes an arrow more susceptable to yaw, and that might not always be a good thing(gusty conditions??)

Limbwalker, I think that the arrow's momentum initially carries it through some of the cross-wind, along with some wind planing - and who knows what else goes on with the paradox waggle, yaw overshoot, etc.

The arrow certainly takes some time to reach equilibrium with the air - it doesn't happen instantaneously.  Sounds like it takes longer than I thought it might.

I calculate 20.5 feet of drift in a 10 MPH cross-wind with 1.4 sec of hang time.  So, you only have to compensate for a mere 15% of the total possible drift!  Isn't that something!    The other 85% is taken care of by the arrow's design and flight characteristics.

If that doesn't make a person think about this, nothing will...

yea, I always screw up the fps to mph conversion...

Anyway, I think the air mass has more of an influence downrange where the arrow has less kinetic energy (traveling more like 180 fps., I'm sure).

Does make you wonder...

John.

Njord, I agree with what you're saying about the forward mass cross-wind drag, it's not ignored, but why is it an issue?  The importand thing is that High FOC is more susceptable (reaching full yaw faster), and drag is reduced.  That is always a good thing.  Always.  Unless you're shooting Flu-Flu's, I guess.

Are you concerned about getting too much yaw?  Run some numbers, we're not talking about very much yaw.  180 FPS is about 123 MPH (not exactly NASCAR are we?).  In a 30 MPH cross-wind, the yaw can only reach 13.7 degrees.  If you have a good persentage of the arrows weight forward in the tip, penetration won't suffer much.  You still sure as heck don't want to be on the receiving end of that arrow!

Limbwalker, has anyone been looney enough to try big fletching in windy conditions on the 90M?  Felipe's 250 yard beach experiment has me wondering...

Mozark, I see it as another reason, a contributing factor for the reactions of the differents arrows, helps the arrow yaw faster

Not trying to be right just trying to understand.

Njord, back to, "Why is it an issue?"   It dawned on me as I was out working on the orchard this morning, "What if you're shooting a broadhead?"  I'd think that what you're talking about becomes a player with broadheads.  But, the cross-wind drag elements ahead of the center of mass, slow the rotation.  The drag force is pushing on the tip, trying to make the arrow rotate in the opposite direction.  Yes?

High FOC would be better for that case, too.  But the point end works against rotation and slows the time to full yaw.

Oh, and I'm trying to be right!  Not to be right, but to better understand what I'm having so much fun with.  So, it doesn't bother me one darned bit to be wrong now and then.  Stuff Occurs.

Just food for more thought (seems like maybe time for a mental snack).

Once the arrow is weathervaned, it is directly facing the apparent wind flow, what aeronautical engineers call the angle of incidence.

Once an arrow yaws, the air flow along its length is exactly the same as if there were no side wind. The forces on the arrow are also exactly the same as if there were no side wind. In this position, there is NO WINDPLANING either into the crosswind or with it.

Now the drag on the arrow is entirely acting in the direction opposite the pile end.

So, the drift for this portion of the flight could be calculated directly from the arrow speed, wind speed, and angle of the wind in relation to the angle of initial flight.

However, drag would be induced in bringing about the rotation to the yawed position and changes in wind velocity and decreasing arrow speed would have their effects.

An annoying complication is that the loss of velocity due to air drag is not a constant, but is proportional to the cube of the speed.

Yet another thing to remember is that a round rod placed at an angle to an air flow produces no lift (wind planing), only drag.

There are enough factors at work to make an empirical approach to the question at least equally efficient. I like the story of Thomas Edison who saw one of his engineers with a light bulb at hand working feverishly with a pencil and paper. The story goes that Edison asked what he was doing, and was told the engineer was trying to calclulate the volume of the lightbulb. To which Edison said, "Why don;t you fill it with water, pour the water into a graduated cylinder and read the volume.

Lets go shoot some arrows in the wind. There seems to be no scarcity! :-) lol

Jim in Maine.

Mozarkid,

I doubt it.  The loss in velocity would be more of a concern at 90M than anything else.

John.

I don't think you can generalize from FITA. We were told a few years ago by the PSE coaches that FOC hardly matered on compounds, and that it was mainly a FITA concern due to the distance and arc effects.

Of course that isn't the wind part of FOC whatever that may be, but it does go to show that once you change many things, many other thing change too. For instance in this case perhaps all that happened was the arrangement stabilized the arrow better.

If one is actualy trying to answer the question that started this thread, rather than working on one's FITA chops (fine by me), there are a number of options:

-The wind was lower at certain times

-The wind blew some archer's cool

-Some got to watch targets shot an did better shooting later

-I did once have arrows that defied gravity, they sorta ski jumped to the target. You could I guess have such arrows for shooting into a crosswind, but they would only work in one wind direction.

What seems least likely is that the wind was totaly unpredicatble, the effect of gusts alone was sufficient to move arrows from the 10 to 5, and that yet the change of fletching alone was sufficient to counter that effect. The only basis sufficient to account for that would be a massive difference in arrow stability. In other words the arrow isn't beating the wind, it's just not getting nocked into instability.

My position(to sum up all my posts, and what I was thinking in my original post) is that a low foc arrow takes more time to adopt maximum yaw. And that this is probably the reason that a low foc arrow appears to fly straighter to a 20-30yd target.

The reason it(low foc arrow) yaws less quickly is the leverages based on center of mass and how the force of the wind works both forward and rearward of center of mass. What happens forward of center of mass also contributes to the the time it takes to achieve maximum yaw. And in this case at bowhunter or 3-d ranges a low foc arrow probably has penetration advantages, especially when the angle of the arrow at the moment of impack is considered.

Man there are a LOT of FERTILE minds in this place! LOL I'll add more of my own fertilizer!.. John, you made me go dig up my old books from my flying days. With a 90 degree cross wind, the drift will be the summed vector of the winds velocity to the arrows velocity. If the wind is doing 10fps and an arrow 100fps (to keep the numbers round), the drift will be about 1 foot at 100 feet. Double the arrow to 200fps and the drift would be .5ft.

As for FOC....A stable arrow is going to "weather vane" into the relative wind. As long as it has a forward FOC, it's going to be stable and weather vane. Njord, you are correct in that a low FOC would probably weather vane sooner. The closer the FOC is to the center of pressure, the less force it would take to make it weather vane. But, it's closer to being unstable so it's likely to over correct and "hunt" for the zero yaw attitude. More FOC is more stable in that it takes more force to disturb it from stable flight. A high FOC being more stable, the less fletching would be needed, lower drag, higher down range velocity. That "yaw" you are seeing happens in the first few feet until the arrow stabilizes. At that point you see a "yaw" but the arrow is not yawing at all, it has simply stabilized into the relative wind. If you took that 10fps wind and the 100fps arrow and drew a vector triangle with two sides of 10, and 100, you could measure the degrees of preceived yaw....Well, got to go reload the fertilzer!....O.L.

 

"With a 90 degree cross wind, the drift will be the summed vector of the winds velocity to the arrows velocity"

O.L.,

That sounds more like it...  I can certainly believe that.  Joe Tapley (physicist/FITA archer guru) made up some wind drift coefficient graphs based on arrow diameter, FOC and weight.  He cautioned folks to use those with a grain of salt, since arrow speed wasn't factored in, and that makes a big difference.  Not only for time in the air, but also kinetic energy downrange.  In theory, the X10 drift coefficient is better than the ACE because it is heavier with a smaller outside diameter.  Only trouble is, it travels slower.  Some of that might be made up by downrange energy/speed though.

I try not to worry too much about it.  I just use the heaviest points I can in my target arrows (120 grains) and go practice.  Shot 309 at 90 meters today, so I think the new Easton Navigators are going to be keepers ;0)

O.L., I ran them through the chrono the other day.  396 grain arrow, 32.5" draw, 8.5" brace ht., 49# at click.  Result? 205 fps. 

Something tells me you can do better than that.  ;o)

John.

OL,You read it wrong or wrote it wrong. I'm saying a HIGH foc will yaw sooner.

I admit my physics is stronger in the kinetics area than in arrow dynamics ;' )

Despite the fact that I teach science and I have found this discussion quite fascinating, I'm pretty sure that I'll keep my experimentation to myself from now on.

OL, if an object travels 100 fps,  then it takes 1 second to go 100 feet.  The cross-wind traveling at 10 fps travels 10 feet in that time.  How then can wind drift be 1 foot?  I am no navigator, but I did study it briefly at McDonnel-D.

I love your stability aproach.  But I don't agree with your conclusion that Lower FOC reacts faster.  The center of pressure (COP) on an arrow is in front of the fletching (ignoring broadheads for now).  The Lower FOC arrow will certainly have a center of gravity (COG) that is closer to the COP.  Control theory dictates that this will be less stable, more susceptable to "ringing."  Yes, it takes less energy to upset a less stable condition - BUT that's relative to comparable systems.  It absolutely does NOT mean that System A (low stability) requires less energy to upset than System B (high stability).  A High FOC arrow and a Low FOC arrow of equal mass are not identical systems.

Here goes:

Given two tuned arrows of equal mass (come out of the bow at the same speed), but having different FOCs.

A High FOC arrow has greater distance between the COP and the COG.

A High FOC arrow has less mass in the rearward area (because more of the arrow's mass is concentrated at the tip - and closer to the COG).  Angular momentum is therefore, low.

So, the force acts on a longer lever arm with a High FOC arrow.  The High & Low FOC arrow masses are the same, BUT the High FOC arrow has more of its mass closer to the COG, meaning more of it's mass has less distance to travel.  A High FOC shaft has less angular momentum to overcome.  So, overall it takes less force to move a High FOC arrow.

The Low FOC shaft has higher angular monmentum, takes more force to move it.  Different system, different relative energy required to upset.

OL, for what you said to hold true, the two compared arrows would have to have the same angular momentum.  So, it would be impossible for them to have the same mass or same bow speed or the same yaw.  (I see we're using two different definitions of yaw).

OK, now I'll shut-down my manure spreader...

That's OK Mozar, I'll hold my nose if you will! LOL OK, if you played around at MD, Take an airplane and load it more forward...It becomes more stable and it will take more effort on the controls to cause a direction change the further forward the CG is moved....Now move the CG aft (shift cargo so the AC still weights the same) The controls get light, takes little effort to disturb it's flight path, move the CG back a bit more and it becomes unstable at some point. Same AC just different CG's, how is that not the "same system".

Same with an arrow, high FOC, more stable and will resist change, opposite for low FOC.  High FOC is more stable due to the fletching moment arm length being longer. Drag will over ride mass....O.L.

Asheville,

I can't say I blame you...LOL!  That's the trouble with asking other Leatherwaller's thier opinion.

You tend to get lots of opinions... ha,ha,ha... ;o)

John.

OL, the aircraft analogy is a totally different animal - thrust is involved - not applicable.  The aircrafts controls always have the same leverage relative to the COP.  The leverage does not change as it does with an arrow.  An aircraft in flight is an "Active" system.  An arrow is a "Passive" system.  The two are simply not comparable.

Think about angular momentum and the arrow.

Asharrow, "a round rod placed at an angle to an air flow produces no lift (wind planing), only drag."

That is false.  It may have no "lift" but it will plane.  Easy to observe too.  Take a plain carbon shaft, no inserts, nocks, fletches, etc., just a bare shaft.  The COG and the COP will be the same spot.  Hold the shaft at that spot, tilt it 45 degrees so that the lower end is to your right.  Let it drop about 15 or more feet.  The shaft will accelerate to the right.  Every time.  It planes.  And that is without feathers!

Too much fertilizer kills the crop  ;o)

I utterly failed to make two FOC dissimilar arrows of the same weight that would even remotely tune to the same bow...  and the winds have died out today...  [-|

However I think the following test is more repeatable, observable and measurable anyway:

I made two arrows of the same weight.

Very Low FOC:  Nock end has 12 gr fletch, 15 gr insert, 5 gr weight, 145 gr point = 177 gr.  Point end has 15 gr insert, 50 gr weight, 125 gr point = 190 gr.  Total arrow weight 630 gr.

Very High FOC:  Nock end has 12 gr fletch = 12 gr.  Point end has 15 gr insert, 50 gr weight, 289 gr point = 354 gr.  Total arrow weight 630 gr.

Test is conducted in still air, indoors.  Each arrow is supported only at the center of gravity (COG) and dropped from a horizontal position.  Height above floor is 12 feet.

Results:

The Low FOC arrow strikes the floor at an angle of roughly 5 degrees.  It avhieved very little rotation.

The High FOC arrow strikes the floor at an angle of roughly 85 degrees.  It achieved nearly complete rotation.

The difference in yaw rotation of these two arrows is obscene.

When dropped together at that height I could not make any definate calls as to which arrow hit first, wind planed most or was most stable.  Stability in a passive system can be observed by noting the damping.  The more stable system will have less overshoot and ringing.

I would expect that a High FOC arrow is significantly more stable.

Mozarkid, Think so?? OK, how bout a sailplane?? No power involved there, As passive as it gets, and it works the same. There is NO doubt a high FOC is more stable...O.L.

Yes, I think so, (Lord help me, I'm disagreeing with a Nationally renowned sailplane expert...)  The sailplanes controls also always have the same leverage relative to the COP.  A sailplane also generates thrust, it's control surfaces and wings generate lift.  These lifts generate various fixed moments about the COP.  What you're observing is how these interact.  Gotta compare apples with apples.

There is no way to make a case against the results posted above nor with the learned observations of 90M target gunners.  I took me less than 10 minutes to snap those arrows together, why not try it and see what happens?

I found a place where I can test outdoors at 28 feet, I'll give it a try this evening when the air settles down.  I expect that the High FOC arrow has more damping and will reach the ground faster with less planing.  We'll see...

Stability and reaction time are two different things, different systems do have different qualities of each.  I have absolutely no doubt that your understanding of aircraftis right on.  Though I think your calculation of drift yielded the added flight distance, not the drift component.  100 fps in a 10 fps cross wind for 1 sec yields a flight path 100.5 feet long - the drift is 10 feet.  At 200 FPS it's 200.25 feet long.

 

So...  cross-wind simulation drop test at 28 feet:

High FOC arrow beats Low FOC arrow to ground by about 4 feet.  That is quite significant.

High FOC arrow is far more stable, about critically damped, slight overshoot with no ringing.  Again, rotates way faster than the Low FOC arrow.  Very slight wind plane, less than six inches.

Low FOC arrow is seriously underdamped, huge overshoot and strikes ground almost horizontally.  Windplanes a bit less than a foot & a half - and that is after flopping over and planing back the other way.  very ugly stuff...

There we have it.  High FOC arrows are more stable and rotate faster (takes less force to rotate them).  What's not to like? (unless you're a flight shooter)

I'm not saying, "Avoid Low FOC like the plague.,"  Keep in mind that the Low FOC arrow I made was an end-weighted nightmare a bit beyond the extremes of what we'd actually shoot.

Fabulous work Mozark, I'm glad you have the time, inclination, and background to conduct and iterpret such an experiment. Rminds me of my own foc drop tests years ago.

Now subjectively, what is the potential accuracy advantage to say a 15%foc arrow to one of say 8%.

I have found one instance where low foc is a distinct disadvantage, and thats with a strong tailwind. But, as a bowhunter I don't expect many shot opportunities under those circumstances, so I don't really worry about it

"But, as a bowhunter I don't expect many shot opportunities under those circumstances, so I don't really worry about it "

Njord, that's kinda how I feel about the 90 meter shooting...LOL!

Although you wouldn't believe how many folks have stopped to ask me ( my 70 meter mark is next to the road in front of my house) "you killed anything with that bow?" or "Do you hunt with that thing?", or some other stupid question.  Most are surprised to find out that I would never shoot at a deer from 70 meters away!  And this is bowhunter country too!

It always gives me a good chuckle as they drive off.

John.

Mozark, what were the focs of the arrow in the experiments? Guess if you have to.

I see Gold Tip's FOC calculator is gone...

I'll measure them tonight.  In the mean time, the Low FOC was below 5% and the High FOC was above 20%.  The shafts are 32" Gold Tip XT 5575 weighing 264 gr.  Here's a pic of what I used:

Went to Joe T's FOC calculator:

Low FOC:  1.7%

High FOC:  27.8%

I just realized that in trying to clarify and boil down all my leverage thoughts that my bow arrow combo is significantly faster than alot of my shooting companions(due in large part to a 70lb draw weight and a 31.5" draw length). And that many of my mental pictures are of my arrows from my bow compared to others most of which are higher focs around 15% or so. Which isn't to say that I haven't done my own foc experiments. Just that I'm sure some of my own experience Is influenced by dissimilar empirical testing.

I still stand by my leverage theories, and believe they contribute significantly to the overall effect.

The benefits of high FOC as I understand them are: #1 Potentially better accuracy(which I would guess is due to the short forward lever arm). How much better has never been quantified, but I would s.w.a.g. it to be on the order of 1 inch at 20yds due to point oscillation.#2. Potentially better penetration, which I can concur with especially if the arrow is not flying perfectly point on at the moment of impact, as the center of mass of the arrow would be more in line with the axis of the arrow, and have less leverage over the point of the arrow when compared to an arrow with less FOC.

Mo, those sure are short arrows, what's your draw, about 1" (hee hee)

I went back to the beach to shoot long flight arrows again, this time the wind was about 18 / 20 knots (shoulda been windsurfing).  Over shot my target and lost 3 arrows right off, then the rain came and the wind quit, what's with that.

I did notice the lack of penetration when there is much of a yaw angle.  I think heavier bows and faster arrows is the correct tackle in high wind situations.

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