** BROADHEADS ** Science & Math

[jmez]

Isn't life defined on a stationary object traveling through a media, airplane wing. Shape of the wing gives the air more distance to travel over the top of the wing. Therefore the air is moving faster over the top of the wing than the bottom of the wing as it has a farther distance to travel. Velocity difference leads to high pressure under the wing and low pressure above the wing causing lift. That is going to be different on a rotating object vs a stationary object.

 

[roadrunner]

Not sure what you're trying to say at all, and whether you're agreeing with the premise of the thread, or not. So, no, not clear. Seems to me like you're just making general statements about physics without talking about the impact as it relates to why this thread was started.

This thread was started as: Broadheads and Field Points will not hit the same at long range if they are tuned to do so at short range (because a broadhead has more drag, and thus will drop more). Doug provided data as such in the first post. Some people are still disagreeing. That's the thread.

Not making general statements at all. The impact you see downrange is a function of what happens initially "up-range". Both arrows will initially decelerate at the same rate (negligible) until the surface area of the broadhead begins to have an impact. Cross-sectional area of the broadhead will have more of an impact initially as the arrow stabilizes in flight through rotation and flexing back and forth with air contacting the blades at some resultant vector relative to perpendicular lines of action than linear flow of air parallel to the cross-sectional area (air flow in the same direction the blades run). The purpose of the thread seems to be trying to have an "ah-ha!" moment when there is really nothing special about it.

The title of the thread is "BROADHEADS Science and Math". But nobody wants to really talk the science and math. Doug's data is based on his own anecdotal evidence, and not someone else's. It is improper to discredit someone else's anecdotal findings while expecting them to accept yours...

There's no formula for it. You need to test. The more vane you have, the more offset, the more helical, the more stabilization you have. How much you "need" depends on the broadhead, and how far out of tune your bow is, as well as your form and how much you torque (or don't torque) the bow. This is why most people recommend more vane - like a 3 or 4 fletch max stealth with offset or helical, so when you torque the bow under a hunting situation, the arrow is still going to hit pretty close to your point of aim, if not dead on...

You're correct in that you can tune BH to FP at 70 and be a little low at 100 and not worry about it (You'd be a little high at shorter ranges too) You just have to test and know where they hit.

Yes, there is a formula for it. It's complex and doesn't mean much when there are too many variables at play.

Justin is arguing that his broadheads will hit with his field points both at short range (20-30 yards) and at long range (100 yards) with the same point of aim. Pretty much everyone else all along has said you can tune them to hit together at short, or long, but not both.

As a side note, the magnitude of difference between BH and FP at long range is dependent on a lot of things: Initial speed, total arrow weight, fletching, etc. Haven't tested this myself recently, but a heavier arrow with more momentum and more fletching/offset/helical should show less of a discrepancy between BH and FP.

Initial speed is equal. Total arrow weight is equal. Fletching is equal. Without these three parameters being the same, your results are skewed and invalid.

The heavier arrow will have slower initial speed(s) which will decelerate at a lower rate giving "more speed" available downrange comparative to a lighter and faster arrow.

As far as POI being the same close and at distance, it matters what you define the POI as being acceptable is. 3 inches at 30 yds and 12" at 100 yds due to compounded error, or some other metric as in bullet holes?



This is the science and math behind broadheads and still very lacking to say the least...

 

[RosinBag]

Acceptable is a personal thing. 3” at 30 or 12” at 100, not the same to me. At 30 yards filed points being 3” from broad head, center to center is about a 3 or 4 yards difference between them for a bow shooting in the 290 ish range. 12” center to center for the same bow is also about 3-4 yards. That isn’t acceptable for my personal standard.

 

[4rcgoat]

Been following along the best i can.....

 

[Brendan]

Isn't life defined on a stationary object traveling through a media, airplane wing. Shape of the wing gives the air more distance to travel over the top of the wing. Therefore the air is moving faster over the top of the wing than the bottom of the wing as it has a farther distance to travel. Velocity difference leads to high pressure under the wing and low pressure above the wing causing lift. That is going to be different on a rotating object vs a stationary object.

Yes, that is part of it. I am not 100% on this, but angle of attack can create a pressure difference too which generates lift.

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Could be wrong, but easy to imagine a high pressure area on bottom front of a broadhead and low pressure area on top back of a broadhead that is nose up.

 

[Billy Goat]

The arrow is rotating, so I don't see the high low pressure making it rise, also you would need to have your broadheads turned exactly the same.


This might be why a broadhead at 300+ fps is that much harder to tune tho.

 

[Brendan]

Not making general statements at all. The impact you see downrange is a function of what happens initially "up-range". Both arrows will initially decelerate at the same rate (negligible) until the surface area of the broadhead begins to have an impact. Cross-sectional area of the broadhead will have more of an impact initially as the arrow stabilizes in flight through rotation and flexing back and forth with air contacting the blades at some resultant vector relative to perpendicular lines of action than linear flow of air parallel to the cross-sectional area (air flow in the same direction the blades run). The purpose of the thread seems to be trying to have an "ah-ha!" moment when there is really nothing special about it.

The title of the thread is "BROADHEADS Science and Math". But nobody wants to really talk the science and math. Doug's data is based on his own anecdotal evidence, and not someone else's. It is improper to discredit someone else's anecdotal findings while expecting them to accept yours...

I agree with what you're saying, and I don't see anyone disagreeing with you, but all of the science and math in the world doesn't mean a damn thing if it's just mental masturbation. What I'm getting at is I still have no idea what your point is and what you're getting at. I understand the science, and math, and I'm trying not to parade around saying random stuff while not getting to an actual point.

Initial speed is equal. Total arrow weight is equal. Fletching is equal. Without these three parameters being the same, your results are skewed and invalid.

The heavier arrow will have slower initial speed(s) which will decelerate at a lower rate giving "more speed" available downrange comparative to a lighter and faster arrow.

You're not paying attention to what's being said, Two different points in that statement above.

Yes, swap just field point to broadhead and everything else is equal. That's the main discussion at play here when talking about a broadhead tipped and field point tipped arrow and point of impact down range.

But, Perform the exact same test with a heavier arrow (traveling the same speed) as compared to a lighter arrow and you see a different magnitude of drop because of the different momentum between the two arrows. Making up some numbers, let's say a 300 grain arrow traveling 280 fps, and the broadhead hits 10" lower than the field point at 100 yards when sighted in to hit together at short range. If you do the same test with the same broadhead with a 500 grain arrow going 280 fps, it's not going to be 10" lower, it'll be less than that.

Look, I'm happy to have a discussion, I just don't know what you're getting at, or if you're agreeing or disagreeing with the main premise of the thread, or you really don't care...

 

[Brendan]

The arrow is rotating, so I don't see the high low pressure making it rise, also you would need to have your broadheads turned exactly the same.


This might be why a broadhead at 300+ fps is that much harder to tune tho.

Yes, as it rotates the low/high pressure areas change to different parts of the broadhead, high pressure staying on the front / downside of the arrow. And, once the arrow stabilizes through rotation and is traveling "true" then the pressure difference and thus lift is gone...

Again, aerodynamics isn't my wheelhouse, but that's my read on it.

Regarding a 300 FPS + arrow: Drag goes up exponentially I think, not in a linear fashion. So you get to a point where the increase in speed is causing much, much more drag, where if the arrow isn't flying true, can throw it off much easier. Same reason an arrow loses a lot more speed initially when it's traveling faster.

 

[Billy Goat]

Yes, as it rotates the low/high pressure areas change to different parts of the broadhead, high pressure staying on the front / downside of the arrow. And, once the arrow stabilizes through rotation and is traveling "true" then the pressure difference and thus lift is gone...

Again, aerodynamics isn't my wheelhouse, but that's my read on it.

Regarding a 300 FPS + arrow: Drag goes up exponentially I think, not in a linear fashion. So you get to a point where the increase in speed is causing much, much more drag, where if the arrow isn't flying true, can throw it off much easier. Same reason an arrow loses a lot more speed initially when it's traveling faster.

Either way we are agreeing that the broadhead arrow is going down range X amount higher from shortly after the bow, until the point where the broadhead path intersects the field point path, and then the broadhead is lower after that.

X changing depending on the factor of the arrow, namely the amount of drag created from the broadhead, and the distance that they intersect.

 

[jmez]

I think it has to do with the direction of rotation depending on lift or drop.

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[5MilesBack]

As far as POI being the same close and at distance, it matters what you define the POI as being acceptable is. 3 inches at 30 yds and 12" at 100 yds due to compounded error,

For me it's very easy to "hold" on a single plane.......i.e. vertical or horizontal lines. So when I tune (and also set my pins), that's what I shoot at.....lines. I know when I've executed a good shot with the "line" splitting my pin. So a "good" BH arrow release, and a "good" FP arrow release will give me instant feedback as to what the FP's and BH's are doing in relation to each other. The further out this is done, the easier it is to make tuning adjustments and immediately see the effects of those adjustments. So just a few adjustments usually gets them on the same elevation at that distance (60 yards for me). For me, both arrows need to be touching that horizontal line consistently (i.e. same elevation POI) to have an acceptable BH "tune". The same applies to horizontal tuning on a vertical line as well. So when all the tuning is done I'm confident where my BH's are going to hit, then it's just up to me to ensure I make good shots.

 

[traviswdalton]

For me it's very easy to "hold" on a single plane.......i.e. vertical or horizontal lines. So when I tune (and also set my pins), that's what I shoot at.....lines. I know when I've executed a good shot with the "line" splitting my pin. So a "good" BH arrow release, and a "good" FP arrow release will give me instant feedback as to what the FP's and BH's are doing in relation to each other. The further out this is done, the easier it is to make tuning adjustments and immediately see the effects of those adjustments. So just a few adjustments usually gets them on the same elevation at that distance (60 yards for me). For me, both arrows need to be touching that horizontal line consistently (i.e. same elevation POI) to have an acceptable BH "tune". The same applies to horizontal tuning on a vertical line as well. So when all the tuning is done I'm confident where my BH's are going to hit, then it's just up to me to ensure I make good shots.

Have you ever shot a bare shaft after your broadhead tune just to see what it does?


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[5MilesBack]

Have you ever shot a bare shaft after your broadhead tune just to see what it does?

Yes. After BH tuning they seem to follow what the BH's are doing (but I've never shot one at 60 yards before.....50 max.) I've also BS tuned at 20 first and still had BH's way off at 60 yards. So I just jump to the BH tuning first these days, and then BS's are also decent.

But here's a weird one.......last year I was BS tuning at 20. BS's were left of fletched 2" with a nock right. I kept twisting my right yoke and untwisting my left and it wouldn't correct.......at all. So I eventually got tired of that, set my yokes back to where they were to start with, and shot BH's at 60. BH's were 4" right of FP's at 60. Those are two totally conflicting results with opposite corrections. So I shot BS's at 40 and they were consistently 3" right of fletched with a nock left........again, opposite of the BS's at 20.

So I figured my grip was somehow different at 20 than at 40 and 60. So I put my portable target halfway between my stationary target and my 40 yard shooting mark. I'd draw back first and then decide while I was holding which target to shoot......20 or 40. At 20 the BS's were still left of fletched with a nock right, and at 40 they were right of fletched with a nock left. So probably not the grip. So these days I ignore BS's at 20 altogether, and if I'm going to shoot them I shoot them at 40. That seems more reliable with what my BH's are going to show as well.

 

[traviswdalton]

Yes. After BH tuning they seem to follow what the BH's are doing (but I've never shot one at 60 yards before.....50 max.) I've also BS tuned at 20 first and still had BH's way off at 60 yards. So I just jump to the BH tuning first these days, and then BS's are also decent.

But here's a weird one.......last year I was BS tuning at 20. BS's were left of fletched 2" with a nock right. I kept twisting my right yoke and untwisting my left and it wouldn't correct.......at all. So I eventually got tired of that, set my yokes back to where they were to start with, and shot BH's at 60. BH's were 4" right of FP's at 60. Those are two totally conflicting results with opposite corrections. So I shot BS's at 40 and they were consistently 3" right of fletched with a nock left........again, opposite of the BS's at 20.

So I figured my grip was somehow different at 20 than at 40 and 60. So I put my portable target halfway between my stationary target and my 40 yard shooting mark. I'd draw back first and then decide while I was holding which target to shoot......20 or 40. At 20 the BS's were still left of fletched with a nock right, and at 40 they were right of fletched with a nock left. So probably not the grip. So these days I ignore BS's at 20 altogether, and if I'm going to shoot them I shoot them at 40. That seems more reliable with what my BH's are going to show as well.

I would spend hours tuning then I figured out it’s easier to tune the arrow to the bow. I use OT2 to build my arrows and they always shoot BS BH and field points same POI at 20 yards. Being a tree stand whitetail hunter my average shot is 20 yards. However I recently moved to CA and I’ll probably need to increase my max so it’ll be interesting to see if it’ll work out to 60.


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[Coveyleader]

Get 30 yds or in on your animals, and it's all a moot point.

 

[Billy Goat]

I have seen broadheads way off at 30 yards.

 

[Coveyleader]

I have seen broadheads way off at 30 yards.

No doubt, but going back to The original post, no real loss in speed between FP and Broadhead so drag shouldn’t be an issue at short yardages.

 

[Billy Goat]

No doubt, but going back to The original post, no real loss in speed between FP and Broadhead so drag shouldn’t be an issue at short yardages.

True, just seemed the way your post read it was that none of this matters under 30 yards don't worry about it.

That's what my response was aimed at.

 

[worx53]

I participated in this post earlier but have not read through all of the latest comments so this may be redundant but there is a great video on YouTube from Eastmans bowhunting journal regarding broadhead and field tip tuning and it’s titled “easiest way to tune your Matthews bow for broadheads “and obviously it applies to almost all bows..
It reiterates my post way back about fine rest adjustments to tune the Broadhead back to the field point impact.


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[Bill V]

I've only read the initial post, not the 14 pages that followed, so maybe this has been covered already, but this will vary by arrow setup, speed, bow tune, and broadhead design. You shouldn't lump all fixed heads together or all mechanical heads together. Labradar showed the following for Iron Will S125 broadheads vs field points:

Initial speed = 270 fps
Field Point at 80 yards = 230 fps (85.2%)
S125 Broadhead at 80 yards - 228 fps (84.4%)

The difference in drop is negligible out to 100 yards in my testing between Iron Will V Series, S Series, SB Series and field points.