** BROADHEADS ** Science & Math

[Reburn]

Here is my question. I am not a physicist although I have a firm grasp on most stuff.

When does the drag of the vanes outweight the drag of the broadhead? Is drag compounded such as broadhead drag is 3 but vane drag is 5 so 5>3 so drag =5 or is it 3+5 = drag =8?

Also if your broadhead drags more then your vanes is that when you get into planing problems?

It would appear that drag is compounded. But with that being said If I tune my broadheads to FP at 70 yards I may be a touch low at 100 and a touch high at 20 however It would seem that they both end up falling within my limits as a shooter and within the kill zone of 6"

 

[5MilesBack]

What happens when you shoot one field point and the next is a broadhead and cut fletching?

You kick yourself for shooting a BH tipped arrow at other arrows........that's what happens. But that should have happened BEFORE you decided to shoot a BH at other arrows.

 

[5MilesBack]

Very standard to get Bare Shaft, Broadhead, Field Point hitting the same at 30-40 yards, even 50-60 yards. Now, Take those same arrows, same bow, same tune, and shoot them at 100 yards. Using the same point of aim, the broadhead will hit lower. That's what we're saying. Justin is arguing otherwise.

I don't think Justin is arguing that, as I don't think he is BH tuning at short range. I think he's BH tuning at long range to start with, unless I'm mistaken.

 

[Brendan]

Yes, the drag coefficients are the same, however, there is more surface area to act on with the broadhead. Total cross sectional area is greater, no doubt. The arrow whipping back and forth and rotating as it travels downrange will have the greater affect on the BH than FP because of what many call "wind-planing". The math and science is the same for both arrows. Both follow projectile motion equations and at the least, single variable calculus.(this is where all the equations come from, a mathematical representation described over limits of integration).

Maybe you are misreading this, maybe I wasn't clear. The faster an object is traveling, the more deceleration it will have up to a certain point and then reach a point where it isn't so much as it was initially. So, the most deceleration of any arrow is at time zero right as it leaves the bow system. Initially, drag is almost negligible, but as the arrow travels downrange at time 1 second, 3 seconds, and so forth, drag will begin to take its effect on the broadheads' increased surface area. Eventually, deceleration rate will be fairly close to each arrow, the effects are more pronounced on the broadhead earlier on.

Most of the arrow's velocity where higher deceleration affects it will occur within the first 20 to 40 yards which is why POI can be stated as nearly the same. Nearly the same can be measured by tenths of a inch up to somewhere between one and two inches. Again, no big deal at those distances and FP's and BH's hit the same as you can have that variation with any group with FP's - even with a shooting machine since no two arrows are the same and nobody hunts with just one arrow.

This small variation is compounded downrange at farther distances. The thread title is the about the science and math behind broadheads. My first post on this thread stated the science and math is the same for both arrows because it is, the outcome is variable. My second portion is the realism of most every hunting situation and shot distance that it clearly does not matter because both have the same POI.

The fact about the broadhead hitting lower than the field point at 100 yds is, in general, a moot point. Unless you plan to take animals at 100 yds which opens a whole new "let me get my popcorn" thread...

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.

 

[Brendan]

I don't think Justin is arguing that, as I don't think he is BH tuning at short range. I think he's BH tuning at long range to start with, unless I'm mistaken.

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.

 

[Brendan]

Here is my question. I am not a physicist although I have a firm grasp on most stuff.

When does the drag of the vanes outweight the drag of the broadhead? Is drag compounded such as broadhead drag is 3 but vane drag is 5 so 5>3 so drag =5 or is it 3+5 = drag =8?

Also if your broadhead drags more then your vanes is that when you get into planing problems?

It would appear that drag is compounded. But with that being said If I tune my broadheads to FP at 70 yards I may be a touch low at 100 and a touch high at 20 however It would seem that they both end up falling within my limits as a shooter and within the kill zone of 6"

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.

 

[Billy Goat]

I think what @Reburn is asking is simply is it a combined effect, or a what's greater. If your broadhead has more drag than your vanes, I believe you are in trouble. You need to have more on the back to overcome the front, however minimizing the front drag, while maximizing your rear drag probably leads to less of an effect from the broadhead. So I believe it all combines, but you could shoot enough vane/feather on the back to where it won't matter, ie a flu flu. I doubt anyone could discern a difference in impact with a broadhead or a field point with uncut feathers on the back.

 

[5MilesBack]

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.

I will say that I have had BH and FP tipped arrows consistently touching at 20 yards and then shot them at 60 and the BH's were consistently 2" higher than FP's. That's not the norm though because I normally BH tune at 60 to start with. But even after tuning at 60, my BH's will still cut my horizontal line of electrical tape at 20. Any differences that I've seen aren't worth worrying about. If I BH tuned at 100, then I'd probably see bigger differences at 20, but I have no need to tune at 100.

 

[Brendan]

I think what @Reburn is asking is simply is it a combined effect, or a what's greater. If your broadhead has more drag than your vanes, I believe you are in trouble. You need to have more on the back to overcome the front, however minimizing the front drag, while maximizing your rear drag probably leads to less of an effect from the broadhead. So I believe it all combines, but you could shoot enough vane/feather on the back to where it won't matter, ie a flu flu. I doubt anyone could discern a difference in impact with a broadhead or a field point with uncut feathers on the back.

I don't think of it as a more or less thing, I think it's more of a sliding scale. With not enough vane and a bow out of tune, you see a big difference between BH and FP. As you increase number of vanes, offset, helical, vane height and length (or probably use a flu flu like you said) - you start to see the difference shrink but I'm not sure it ever totally disappears because the arrow doesn't recover and stabilize instantaneously, just faster.

 

[Dos Perros]

Drag coefficient is irrelevant; it’s total drag that matters. (Although certainly drag coefficients between BH and FP arrows are different).

 

[Thomas Hermann]

Someone mentioned having arrows with more steering on the back to overcome the steering from the broadhead. The problem with too much fletching is it tends to lead to major parachuting groups at long range. So, in terms of accuracy I don't think that will work when dealing with distance.

In my opinion you need just enough fletching to steer the arrow and any wings (blades) on the front point. Too much will open up your groups at long range. Look at most long distance target shooters they are shooting just enough vane, most are running 1.75-2" low profile vanes for skinny shafts at long distance. 3d's (and most eastern hunters) you only shoot to 50 yards you can get away with a lot of vane and helical because the shots are close. ( I know about redding and opa, but those are dot shoots IMO)

 

[Reburn]

I think what @Reburn is asking is simply is it a combined effect, or a what's greater. If your broadhead has more drag than your vanes, I believe you are in trouble. You need to have more on the back to overcome the front, however minimizing the front drag, while maximizing your rear drag probably leads to less of an effect from the broadhead. So I believe it all combines, but you could shoot enough vane/feather on the back to where it won't matter, ie a flu flu. I doubt anyone could discern a difference in impact with a broadhead or a field point with uncut feathers on the back.

Yep thats exactly what Im asking.

 

[Billy Goat]

I don't think of it as a more or less thing, I think it's more of a sliding scale. With not enough vane and a bow out of tune, you see a big difference between BH and FP. As you increase number of vanes, offset, helical, vane height and length (or probably use a flu flu like you said) - you start to see the difference shrink but I'm not sure it ever totally disappears because the arrow doesn't recover and stabilize instantaneously, just faster.

I'd agree that the difference doesn't ever disappear, but I think it can be at a point that it's so trivial that it doesn't matter. Say you have a setup that tuned at 65 yards broadheads are impacting with fieldpoints, when your broadhead is 1/2" or 3/4" high at 27.5 yards or wherever the most difference would be doesn't matter, probably same setup would be same difference at 85 or 90 yards again.

I'm not into statistics, so I don't know the numbers, maybe this isn't at all how it works. However, if we agree that 1" every 10 yards is sufficient, then let's talk about a 3" group at 30 yards with field points. Say that you hold a 4" group with broadheads at the same distance, that's a group that has opened by 33% correct? Probably a lot but for sake of argument take that 4" group and put the center of it 3/4" high from the center of your field point group. How much area do they share? Probably 90% of the same area. So they aren't exactly the same poi, but for practical situations where you are using broadheads (I don't know anyone who shoots Vegas or NFAA 300's with broadheads) I'd call 3/4" at 30 close enough. Not to mention if the difference is actually 1/2". I know I can't see a difference in impact from my broadheads to field points from 0-75 yards. Not saying their isn't actually a difference, but it's close enough that I'll say they shoot together, besides the cutting area of my broadheads are big enough to catch the line if I needed them to.

Lots of setups I don't think you could get that to work, but smaller coc heads certainly minimize the difference.

 

[307]

Hmmm...

Maybe the lift created by broadhead planing offsets the increase in drag. The lift would increase as launch angle increases, which is the same conditions in which there would be more difference between bh/fp due to drag.

If the lift offsets the drag, then bh should hit with fp... Lift would increase with increasing launch angle, up to some point. If functional launch angles were equal, say exactly perpendicular to gravity, then bh will hit low by some amount due to the increase in overall drag, this is fact

I think we can all agree that a bh will have more drag than fp by some amount, but what I wasn't thinking of is that lift would change with launch angle, might it be plausible that just the right bh could offset drag to within the margin of error? I guess it's plausible.

Hmmm...

Perhaps a crossbow, a simple excalibur with the string running on the rail, could be used to test the 2 arrows. It's a much simpler and more repeatable system than even a compound in a hooter shooter.

 

[Billy Goat]

How does a broadhead produce lift?

Only way I can see it is if you are using a 2 blade clocked horizontal and are nock low, assuming that makes the arrow bend downward on launch. Thing is arrow rotation would change that, I have some arrows that will rotate 180 in the first 6'.

I'm kinda of the idea that a 60 yard broadhead tune is just slightly out of tune, where once the broadhead arrow is recovered it is just slightly over the line, or cone, that a field point would be flying.

 

[Billy Goat]

Hmmm...

Maybe the lift created by broadhead planing offsets the increase in drag. The lift would increase as launch angle increases, which is the same conditions in which there would be more difference between bh/fp due to drag.

If the lift offsets the drag, then bh should hit with fp... Lift would increase with increasing launch angle, up to some point. If functional launch angles were equal, say exactly perpendicular to gravity, then bh will hit low by some amount due to the increase in overall drag, this is fact

I think we can all agree that a bh will have more drag than fp by some amount, but what I wasn't thinking of is that lift would change with launch angle, might it be plausible that just the right bh could offset drag to within the margin of error? I guess it's plausible.

Hmmm...

Perhaps a crossbow, a simple excalibur with the string running on the rail, could be used to test the 2 arrows. It's a much simpler and more repeatable system than even a compound in a hooter shooter.

Compound in a HS is an amazingly repeatable device. It holds it exactly the same, no difference in sight picture or anything like that. Just crank it back to where it was and let it rip.

Only problem is it's more difficult to aim.

My understanding is crossbows need to be tuned as well, I don't know, don't mess with them.

 

[307]

A recurve crossbow is an incredibly simple and repeatable machine, especially if shot from a vice.

Throw a paper airplaine perpendicular to gravity, then throw the same airplane at 15* higher launch angle. See which one achieves a higher peak height. That's the same thing that would happen with a broadhead as far as launch angle producing more lift at longer distances.

 

[Brendan]

I'd agree that the difference doesn't ever disappear, but I think it can be at a point that it's so trivial that it doesn't matter.

Agree - we're on the same page here.

Hmmm...

Maybe the lift created by broadhead planing offsets the increase in drag. The lift would increase as launch angle increases, which is the same conditions in which there would be more difference between bh/fp due to drag.

I don't think a broadhead creates lift, it planes due to launch angle as you said (although, I think we're splitting hairs here, I could be wrong on the exact definition). Raise the rest too high, broadhead planes up, will be high at shorter ranges, dead on at some longer range as compared to your field points. Put the rest down too low, it'll plane down and hit below your field points.

Basically, you have to pick the range that you want it to hit dead on with your field points and you tune that with rest position (and cable timing). If you have the arrow flying dead straight, not planing up or down, it will be dead on with your field points at shorter range, until drag slows it down more and it starts to hit lower as distance increases. If you want it to be dead on at longer range, you want it planing slightly up as it leaves the bow, so it hits high at shorter range, and then as it slows down hits dead on at longer.

The other thing to keep in mind, at certain shorter ranges the differences are so small you're not going to see them unless using a Hooter Shooter. So that "slightly high" at shorter range, might not even show up for a lot of shooters, which allows the arrow to be dead on further out.

 

[307]

I'm referring to planing upwards, against the direction of gravity, as lift. I'm not sure that's accurate in absolute terms.

 

[Brendan]

I'm referring to planing upwards, against the direction of gravity, as lift. I'm not sure that's accurate in absolute terms.

You know what, I'm taking it back. I think we are dealing with lift.

Let's say direction of travel of the power stroke of the bow (The nock and your D-loop), and direction of travel of the arrow is 90 degrees parallel to the ground, with the arrow completely parallel to the ground and the power stroke. (No planing)

Now, raise your rest slightly so tip of the arrow is pointing up. Powestroke of the bow, and direction of travel of the arrow are still parallel to the ground. But with the tip of the arrow slightly higher (which results in the upward planing) this angle of attack should result in higher pressure on the bottom of the broadhead, lower pressure on the top of the broadhead, which I think is the definition of lift. (If the arrow, powerstroke, etc are all parallel and just pointed up roman archer style - no lift there as the arrow is flying "true" to the power stroke)

What should happen then is that the more vane you have, the more quickly the arrow stabilizes (eliminating the initial lift and planing), but it doesn't do so instantaneously. What you see is the arrow stabiliizing on a slightly higher track.