** BROADHEADS ** Science & Math

[RosinBag]

To hell with the broadbeads, I'm interested in hearing more about this Hooter Hooter...

That’s a special shooting machine with a stripper!

 

[307]

Yea Maybe so. I’m aiming for the same spot not
Higher. I usually bareshaft tune and when my bareshafts are hitting with fletched then that usually means a fixed blades hits with fletched for
Me.

Here is a pic of a field point and an Iron will fixed blade at 105 yards. Fixed blade is on the bottom. Aiming for the green dot which I’m off a little but both arrows are pretty darn close for 105.

Next pic is the next groups I shot. Again it’s at 105 yards. 1 BH shot 1st and then 2 field points. The BH is the middle arrow. Aiming for the green dot but that’s close enough lol

Wouldn’t you agree they are hitting together ?


I obviously can’t shoot like this all the time. But what I’m trying to convey is that it’s possible to have them Broadheads Hit with Field points at 100 yards. Because it happens.

The giant variable in this "experiment" is the human operating the bow.

Another critical statement Doug so eloquently stated/understated, was something to the effect of, "across all ranges". It's a critical part of the experimental design. I have no doubt that a bow could be tuned to impact the same at 100 yards due to planning effects offsetting drag, but that same biw will not then shoot together at 30 yards, bh will necessarily be a higher POI.

There is simply no arguing that a fixed blade will produce more drag than a field point unless shooting in a vacuum.

There is simply no arguing that increased drag will cause the bh to hit below the fp, unless shooting in a vacuum.

This assumes that all other variables are neutralized of course.

If the facts above are not what you are experiencing then:

A. You may be shooting in a vacuum
B. Some other variable in the mechanical system is changing.

 

[307]

That’s a special shooting machine with a stripper!

Move over John Dudley, there's a new guru in town!

 

[RosinBag]

I think Dudley has forgotten more about archery than I know.

@307, you are spot on the human is the problem. No knock on Justin, but at 100 yards aiming at no defined spot area and hitting three arrows in the size of something his pin would obviously cover completely is more likely the human error getting involved.

 

[307]

I think Dudley has forgotten more about archery than I know.

@307, you are spot on the human is the problem. No knock on Justin, but at 100 yards aiming at no defined spot area and hitting three arrows in the size of something his pin would obviously cover completely is more likely the human error getting involved.

You may have been unaware of the fact that it's 2019, and Dudley's actual expertise and knowledge can be easily overcome with well presented Hooter Hooter(s).

Just try to stay out of the pictures and we'll be on the "influencer" gravy train before you know it.

 

[hobbes]

I've not ran these kind of numbers in a long time, but the discussion got me interested in the calculations involved. I could have easily made an error at this hour, but here is my reasoning and a few numbers to look at:


First, gravity doesn't care how heavy an object is. Second, the distance an arrow drops is based on the time it's in the air between leaving the bow and the target. Since gravity is an acceleration (ft/sec squared), the rate if drop increases the longer it's in the air (the graph is not linear).

The time it's in the air is directly related to velocity. There are relatively simple formulas for calculating the time it takes an arrow traveling at some velocity to go from the bow to a target at X yards Then calculating the distance an arrow drops is simple matter of using that time and the acceleration of gravity.


However, as already shown, the velocity of the arrow isn't constant. It's decelerating during it's flight. Also, the deceleration isn't linear. If it's 300fps at 0 yards and 275fps at 50 yds, you can't assume it's 250fps at 100. I think if you plotted the original examples you'd see that it starts to decelerate at a steeper rate the farther it travels.


Since the two setups are decelerating, it's not as simple as just looking at the difference in velocity at a given point. The easiest thing to do would be assume an average velocity over the 100 yards. If the difference was 20 fps at 100, the difference between average velocities would be 10 fps (if linear deceleration). But….we aren't decelerating linearly, so the "average" would require more complicated calculations.


If you graph the fixed head and field point head example from the original post as velocity vs distance, you see a difference of 6fps at 60 and 24 fps at 100. That means 25 % of total velocity difference at 60% of the distance traveled. The average velocities would be higher for both than the average between the two points, zero and 100. The difference between average velocities from 0 to 60 yards in this case would be less than 3. I'm eyeballing a crude hand drawn graph, but believe you'd be looking at around 271fps vs 269fps. Meaning, .664 vs .669 seconds to cover 60 yards. The difference in distance dropped in .664 and .669 seconds is 1.28 inches. I'd call that grouping together at 60 yards, at least for my abilities.


For the 100 yard numbers comparing fixed to field point, we see a difference of 24 fps at 100. However, we still need the difference between the average. Considering the graph is non linear, the averages will be more than half. In other words, the difference between average velocity will be considerably less than 12 fps. Someone that can recall how to be more precise than me could be exact using a little calculus, but a rough graph has me guessing averages of 260 and 253 for a difference of 7fps. The times to travel 100 yards are 1.154 and 1.186 seconds. The difference dropped between those times is 14.4". That is significant.


Remember, this is really rough and based only on the velocities shown and some eyeballing. Different set ups will have more or less wind drag and more or less weight that could increase or decrease velocity loss. However, I think it's pretty safe to say "grouping with field points" in at least the 60 yard example.

I'd guess that someone that isn't as far removed from these type calcs as myself will shred my numbers at some point, but it's still something to consider.

 

[RosinBag]

@hobbes, you a scientist? You have me convinced. Your calculations are nearly spot on. At 60, I figured roughly two inches I could see and 15” at 100 yards. That is with a human holding and shooting the bow. So a machine may get numbers closer to yours.

 

[wildbill34]

I don't think we will get a more complete and accurate estimation, thanks @hobbes

 

[Brendan]

I think if you plotted the original examples you'd see that it starts to decelerate at a steeper rate the farther it travels.

One small point here, I think it's the other way around. With Turbulent flows, drag goes up with the square of velocity. That would mean, higher drag for an arrow driven faster than slower, so the further it travels, the slower it decelerates. Balancing that out, slower arrow in the air longer with acceleration due to gravity acting on it longer.

 

[Billy Goat]

Am I thinking about this right or wrong?

If a bh is going to hit low by 1.5" at 60 yards because of the loss of velocity, if your setup is tuned so that it actually shoots a bh with a very slight amount of increased elevation (think nock low and arrow recovers slightly higher) wouldn't the difference in impact be half the amount at half the yardage? Not to mention the drag factor is coming in at longer distance. So I'm wondering if it might be that when a bow is tuned to the same impact at 60 yards it might actually be 1/2 or maybe 3/4 high at 30. Might actually be less than that.

 

[hobbes]

One small point here, I think it's the other way around. With Turbulent flows, drag goes up with the square of velocity. That would mean, higher drag for an arrow driven faster than slower, so the further it travels, the slower it decelerates. Balancing that out, slower arrow in the air longer with acceleration due to gravity acting on it longer.

I've not done this stuff in ages so I can't argue it one way or the other. I was just observing the points provided. I'm guessing that anything further would start getting into components of velocity in x and y directions. I had to do a couple Google searches to recall the formulas I used. I'm too far removed from it to be terribly confident in getting much deeper without dragging out a dusty text book.

 

[5MilesBack]

@5MikesBack I have a feeling as much as you shoot, we probably do many of the same thing in either a different order or a different technique to get to the same ending.

I didn’t mention much about tuning, just the shooting portion.

And this is the confusion. Everything I posted in the BH Tuning thread with the picture of 2 arrows (one BH, one FP) was all about Broadhead TUNING........and nothing more than that. Like I said, with only those two arrows the only thing I care about when BH tuning is the relationship between those two......that's it. Then when I make an adjustment to the bow, I'll shoot them again to see how that relationship (i.e. gap) changes.......until they are hitting together.

Does that put the BH 1/4" higher at 20 yards? I don't know.........20 is about my worst shooting distance, so they may very well be. But they're still very very close to the center of the bullseye. I've never BH tuned beyond 60. But I did shoot a bull at 71 several years ago with a fixed blade head, and that arrow may have very well hit the hair I was aiming at. No additional drop noticed. I shoot BH's in base camp at 90 yards with my Rinehart Rinoblock sitting on a camp chair and the BH's and FP's aren't that much different.

 

[hobbes]

@hobbes, you a scientist? You have me convinced. Your calculations are nearly spot on. At 60, I figured roughly two inches I could see and 15” at 100 yards. That is with a human holding and shooting the bow. So a machine may get numbers closer to yours.

No scientist but I do have a few documents that say I'm an engineer. However, if you don't use it you lose it, and I never do these calcs anymore and rarely think about them. This was stuff I survived back in the 90s. I don't think I'm off on my numbers based on velocity, but some of my reasoning may be off. A good student in college would eat my lunch on these calcs.

 

[Brendan]

Am I thinking about this right or wrong?

If a bh is going to hit low by 1.5" at 60 yards because of the loss of velocity, if your setup is tuned so that it actually shoots a bh with a very slight amount of increased elevation (think nock low and arrow recovers slightly higher) wouldn't the difference in impact be half the amount at half the yardage? Not to mention the drag factor is coming in at longer distance. So I'm wondering if it might be that when a bow is tuned to the same impact at 60 yards it might actually be 1/2 or maybe 3/4 high at 30. Might actually be less than that.

You can tune the BH to hit dead on at 60 or 100, but then it'd actually be higher than FP at shorter ranges. Some people do do that

I've not done this stuff in ages so I can't argue it one way or the other. I was just observing the points provided. I'm guessing that anything further would start getting into components of velocity in x and y directions. I had to do a couple Google searches to recall the formulas I used. I'm too far removed from it to be terribly confident in getting much deeper without dragging out a dusty text book.

No scientist but I do have a few documents that say I'm an engineer. However, if you don't use it you lose it, and I never do these calcs anymore and rarely think about them. This was stuff I survived back in the 90s. I don't think I'm off on my numbers based on velocity, but some of my reasoning may be off. A good student in college would eat my lunch on these calcs.

I'm in the same boat you are. BS and an MS in engineering, but that's 20 years ago...

 

[Dos Perros]

We know there's a difference. We know the BH's are going to hit lower at distance. We believe we can calculate, or at least demonstrate, by how much.

Now what are you going to do about it?

 

[5MilesBack]

Lots of potential answers to that question, but physics is physics, drag is drag, and gravity never sleeps. What you are stating is mathematically impossible if we agree that a fixed blade broadhead will have more drag than a field point, and I think we all agree on that, right?

Perhaps you subconsciously aim higher with broadhead? Perhaps your tune is a bit knock low and that gives the arrow a slight bit of lift that offsets the effects of drag...?

This is why we broadhead tune.........so that those aerodynamically challenged BH's WILL hit with FP's. It's like the guys that ask the question all the time........."If I move my rest, won't both FP's and BH's move that direction"? Yes, but the BH's move more.

It's the same with cable adjustments........the BH's move more than the FP's. So when BH's are shooting lower than FP's a cable adjustment will move the BH closer to the FP.........until they're hitting the same spot. These adjustments have a much more profound effect at distance than up close. So if you move a BH up 2" at 60 yards with tuning, it may only move it up 1/4" at 20. 1/4" at 20 won't make a hill of beans difference on a big game animal. But that 2" gap you closed at 60 could make a difference.

 

[Brendan]

Does that put the BH 1/4" higher at 20 yards? I don't know.........

Yes, it absolutely does. That's the point. If you BH tune at 60 such that they hit dead on together at that range, broadheads will be higher at shorter ranges, lower at longer ranges. That's physics.

But, based on your level of shooting, and your setup, you may not see the difference, especially at shorter ranges.

So, can you get broadheads and field points to hit together at your shooting ranges from a "practical" perspective? Yes, of course.

Can you get them to hit together exactly at all ranges? Not unless you're shooting in a vacuum.

 

[hobbes]

We know there's a difference. We know the BH's are going to hit lower at distance. We believe we can calculate, or at least demonstrate, by how much.

Now what are you going to do about it?

I don't shoot super long distance, so nothing on my part. The farthest that I actually practice at is 60 besides occasionally winging an arrow out farther and holding over. I think the numbers demonstrate why a bow is still a close range weapon, but I'll stay out of that argument.

I should add that I didn't think it was going to be a significant difference even at 100. I thought I'd demonstrate that the difference between bh and fp was within what most folks consider a good group, but I was wrong out at 100. I think each set up would differ and knowing the difference would require shooting through a Chrono with your set up.

 

[5MilesBack]

No knock on Justin, but at 100 yards aiming at no defined spot area and hitting three arrows in the size of something his pin would obviously cover completely is more likely the human error getting involved.

People mention their pin covering the target at distance, but depending on what you're shooting at you use the correlation between the outside of your pin to possibly larger rings on the target, or even the anatomy of the animal you're shooting at. If your arrows are actually set up to impact "behind your pin" (i.e. the center of your pin) then even if your pin covers the entire 15" target, the arrow should still hit behind the middle of the pin. So as long as you have your pin centered on target, the arrows should still hit the middle. Otherwise the bow isn't setup for arrows to hit behind the pin. Some of the best long range groups I've ever shot, like all arrows touching, was with a sight with .029" pins. Those larger pins dance around a lot less too.

 

[hobbes]

You can tune the BH to hit dead on at 60 or 100, but then it'd actually be higher than FP at shorter ranges. Some people do do that





I'm in the same boat you are. BS and an MS in engineering, but that's 20 years ago...

No MS here, but BS about 25 years ago. I considered it about 10 years after the BS because I'd gotten off track in another field, but doing that with a family would have been hell. I worked my way back then nocked out the PE 13 or 14 years after graduation. Now I avoid design.

Sorry, I'm getting off track here.