Matt Jackson: I’m here with Bill Vanderheyden, Co-Founder and Lead Engineer of Iron Will Outfitters and in this interview we will be discussing arrow construction. In this article you will quickly learn some of the top considerations and methodology you may use to build your “perfect arrow”.
Bill Vanderheyden: In past years, a lot of the arrow setups had been geared more towards target archery and maybe 3d shoots. Arrow weights that are light and fast.
More recently there's been a push for arrow weight to be really heavy, as heavy as 650 grains. I think it's left a lot of people, especially new archers, confused about what's right for them.
What applies to somebody shooting 15 or 20 yards, isn't the same as somebody that's going to shoot 50 to 60 yards. I don’t believe, for out West Big Game hunting, either extreme is right. It's more somewhere in between.
You need to look at the science and the physics and understand which factors are important and how it can help you be a more effective hunter. I've spent many years working on it for myself. And that's really what I want to share here.
Matt: That’s awesome. Let's just jump right in.
Bill: Let’s start with mass first. Your bow's gonna have a certain amount of energy because of your draw force curve. Whatever poundage you're shooting, whatever draw length, that's really going to determine how much energy you have.
Hang with me here, I'm gonna jump around a little bit from energy to momentum.
- Momentum (P) equals mass (M) times (V) velocity(V). (P=MV)
That's the most direct way to quantify how much penetration you're gonna get and how much momentum you have left down range. In that straight line, momentum is a vector quantity.
So that direction matters here, but really it’s maximizing that mass times velocity (M x V) at the target that will give you the best indicator of how much force you're going to get. (F=MA)
And so, this is Newton's second law of motion here, force (F) equals mass (M) times acceleration (A). (F=MA)
Acceleration is change of velocity over time. So you rearrange that little bit and momentum (P) is going to equal force (F) times time (T). (P=FT)
So having the most momentum you can have down range is gonna give you the most force times time on that arrow, penetrating through the animal. So what can you do to maximize your momentum? You can also reduce the force it takes to penetrate and that's by broadhead design.
Let's just talk about maximizing momentum. As you increase mass, you will increase your retained momentum down range and there's really not a threshold. It's a continuous improvement.
The negative though is, with increasing mass, the trajectory drops off. To me there's a balance there. What I recommend is go as heavy as you can for the trajectory that you want. For most people, that's about 450 to 550 grains of total arrow weight. That's a good balance between mass and speed really.
For me, I'm shooting around 500 grains or a little more. I'm shooting around a 72 pound bow with a 30 inch draw. I do have the advantage of a little more draw length.
Matt: What's the feet per second (ft/s), please?
Bill: I just set up an arrow to test our 100 gr single bevels. It was a 504 grain arrow going 288 ft/s. Thank you.
I can dial my site down and shoot 130 yards. So to me, there's no reason to go a higher speed than 288 ft/s. If you are higher than that, add some mass. It's gonna be better for you.
In fact, I'm gonna set up a hunting arrow. That's just a little heavier than that for me personally, more like 525, 530 gr. I might drop my speed down to 285 ft/s, but I'll gain a little advantage in mass.
Matt: Will you share with us why 280 ft/s is the magic number for you? Because there are some successful archers out there that say speed never hurt me. Let's address that.
Bill: Yeah. Like I said, there's a trade off when you get more speed, you can shoot further. Your trajectory is a little flatter. Here’s the advantage. If you range an animal and it moves a few yards. Let’s say the animal is at 60 yards, that flat trajectory is helpful.
It's kind of a personal preference there on what trade off you want to make between mass and speed. What I would tell you is that increasing mass will help everybody penetrate better. It's gonna slow everybody's arrow down too.
280 ft/s is a great range for a nominal speed. And I really just would say like 265 ft/s to 285 ft/s is great. You go up over 290 ft/s and the problem with that is drag (FD) is proportional to velocity squared.
FD∝v2 F D ∝ v 2
A fast light object slows down a lot more than a slower heavier object. So that's the retained momentum issue here. Which is why increasing mass, choosing mass over velocity, will give you more retain momentum down range. Think, if you are really going faster and lighter, you're hurting yourself on penetration.
I'll eyeball judge things too. If they're under 50, I'm gonna get a shot off quickly. If it's 50 or over, I'm gonna range and get that pretty dialed. Just know, 10 feet per second doesn't matter that much on how much you're gonna miss by. A lot of guys like that speed for that reason, it's a little flatter trajectory and that's why there's a balance there.
The other bad thing about having too high speed is drag is proportional to velocity squared. It makes it harder to get your arrow to fly really well and tune your bow because of that higher velocity and higher forces on your arrow. If everything's not perfect, it makes it more difficult to get good arrow flight.
Good arrow flight is really number one in this whole thing.
If you wanna go up a little bit in mass, don't just add a bunch of point weight and not be properly spined, because arrow flight is number one. You need that momentum going in a straight line. So if you're underspined, your arrow will have excessive flexing and you're losing a bunch of energy and momentum that you could have had there.
If you didn't and your bow's not tuned, your arrow could come fishtailing off of your bow. There's a couple problems here. One is, you have a bunch of wasted momentum there.
If your arrow is not traveling in a straight line, it's gonna slow your arrow down and you're gonna have less retained momentum. So if you have to shoot a mechanical to hit the target, you should really fix the root cause there. It’s possible your arrow is underspined or your bow isn't tuned.The point is you're getting a lot less momentum than you could have had if your bow was tuned and your arrow was spine properly.
Also, it takes a tremendous amount more force to get a pass through. It's kind of a double whammy there. You have less momentum out there and it takes a lot more force to get that through the animal. This means you're not going to penetrate nearly as far.
Front Of Center Weight (FOC)
Matt: Now that we have a good understanding of the importance of considering your arrow’s mass, let’s talk about the optimal percentage range of an arrow’s mass placed nearer to the point in relation to the center of the arrow. We all know this as an arrow’s front of center (FOC) weight.
Will you take us through how to calculate an arrow’s FOC weight percentage and your recommendations to achieve optimal arrow flight?
Bill: To calculate your arrows FOC weight follow these steps. First, find the balance point of your arrow. This is your arrow’s center of mass. From that point, measure the distance to the center of your arrow front to back on length. Divide that number by the total arrow length, that's your front of center percentage.
10% to 12% has been recommended for target archers for years. A lot of the arrow manufacturers recommend 12% to 14% for broadheads. I've done a lot of testing at 12% to 16%. That's what I recommended.
You'll hear out there you need to have 20% FOC or that going from 19% to 23% can increase penetration by 30%. Well, that doesn't agree with physics. It really doesn't.
It's what I see happening a lot right now. People will hear extreme FOC will give you more penetration. However, they are compromising arrow flight, by just adding a bunch of mass out front and now they're underspined.
We could get you to high FOC that way, but you'll be underspined. The excessive arrow flexing is going to hurt your arrow’s penetration. What it does help you with is stability. It gives you a longer lever arm to your vanes. It'll help fixed blades fly better. It may help you with traditional archery as well.
The one thing I want to touch on is don't try to hit a certain FOC number.
The amount that it’s going to penetrate is really your retained momentum, mass times velocity, and it's a vector quantity. It's in that straight line, there's no FOC in that calculation. It's Newton’s Second Law of Motion. You can't argue that. That's what it comes down to. The most mass times velocity (M x V) in a straight line at impact.
Now increasing FOC 5% might only change that center of mass a half inch forward. The physics wouldn't say that that's gonna have a 30% increase in penetration. It just wouldn't.
What do I recommend for FOC? I think 12% to 16% is a great range for good stability. You can go higher than that, but your trajectory really starts dropping off typically. There's kind of diminishing returns there.
Going lower than that, you might be okay, you'd have to go test it, but I think nobody recommends going really below 10%.
I believe, for the western big game hunter, where you're also trying to get 50 to 60 yard shots, assuming you've practiced and are effective at that distance, extreme FOC is very hard to do without dropping your trajectory way off. It's more difficult to get your bow to tune and everything else when you've got a lot of mass out front that you're trying to launch off your bow.
DO VANES ADD STABILITY?
The next thing you need is good stability. Add a fixed blade broadhead on the front and the arrow's different in flight. I don't think this is talked about enough out there. When you have a fixed blade on the front, you need more vane on the back for stability. This is critical to get great arrow flight.
If you think about the center of mass, that's the pivot point on the arrow. Say the arrow is a little bit off course. It's not flying perfectly straight. but let's say the tip is tipped up a little bit, now as you get that airflow across the fixed blades those blades have some surface area that's going to drive it off course. Right?
At the back end of the arrow, you have the vanes that are also getting that airflow across them. That's putting it back on course, having stability means that the vanes win. If something goes off course, it'll steer back.
Being unstable means if it starts off course, it just keeps going off course because you don't have enough force at the rear to help.
The height, or the surface area, of the vanes gives you that restoring force, but it's also that lever arm between your center mass and the vanes. So increasing your FOC is basically moving your center mass forward. That gives you a longer steering arm for your vanes to correct, and a shorter steering arm for your broadheads to steer you off.
People ask how much vane are we talking about there? What I find is most efficient, and by efficient, I mean, the job of a vane to me is you don't want to add any more drag or weight than you need to at the back, but you want to have good stability if it starts tipping off.
You want to have a lot of restoring force that puts it back on track. So the most efficient to me is like three higher profile vanes. Two inches or a little bit longer and about 0.5 inches high. I find they seem to kind of work similarly.
I think three vanes at 2.5 to 3 degrees of helical work well. It’s probably the most efficient for restoring trajectory. Some people like to go with four vanes and I don't think that's a bad setup either. It's just adding a little more mass and drag and it does give good stability.
I find that height is a bit more effective than length. The reason for that is that there's kind of this boundary layer effect over the arrow shaft. The velocity of the air right near the shaft isn't at full velocity. It isn't at 280 ft/s. It's much lower than that.
A long but low profile vane isn't as effective as a taller, shorter vane.
Once you're up over a quarter inch, closer to half inch, now you've got the full velocity there. That's giving you more restoring force, more stabilizing force.
That's my experience. More length does give you some benefit, but not as much as height. I believe height's more effective than length. I don't like going below a 1/2 inch high vane for a fixed blade head on the front.
Vanes and Rotation
Matt: What has your engineering background and testing experience taught you about vanes and rotation?
Bill: I like two and a half to three degrees of helical or offset. It’s kind of a sweet spot. I feel it helps to get the right amount of rotation and averages out any asymmetry. It can help make fixed blade heads fly better.
The thing you don't want is straight vanes. And I think that's really all you can get for a factory fletched arrow, a zero or one degree. And to me, that's not really enough to get the rotation you want.
The reason you want rotation is not actually for stability. It's to average out any asymmetries. Say your arrow's not straight, it has a little curvature to it. Your insert isn't straight and your broadhead isn’t perfect. If the point is off a little bit to one side of your trajectory that's just going to cause your arrow to kind of drift off that direction.
If you're not rotating, it's just going to keep going further off that direction. As you get down range, if it's rotating, it's gonna open up your groups, but it's gonna stay on the average. The shot is going to be, at least, on center or on that center line.
So if you can picture rotating around that force kind of pushing the arrow, as it's rotating, that force is also rotating with it. So it's kind of pushing it around in a circle as it goes down range, but it's not just going straight off in one direction.
Components & Maximizing Momentum Downrange
Matt: What’s the next thing an arrow builder should be considering?
Bill: Next is durability of components. I think a lot of people are finding out aluminum components, especially aluminum halfouts or outserts, can't take that impact force and they bend very easily.
For example, If you're just touching the leg bone. you're just kind of hitting the edge of that leg bone. If you've got weak components, it can bend right over and stop penetration right there. Stay away from aluminum. Hardened steel is really the best, or grade five titanium for ferrules or components.
Having very strong material is critical. So, to me, the ideal front end setup is a durable fixed blade. It’s got to be very sharp and have the ability to retain that edge through the animal, to keep the force low.
If you have a hard impact or side impact, it keeps that force driving straight through and doesn't bend over and take out all your energy and stop you right there. You want something that has good alignment to the arrow because it’s important that that broadhead spin true.
Everybody should get one of those little arrow spinners. Put your broadheads on your arrows, spin them and make sure the points are staying on center and not wobbling around.
The problem with wobbling is it could be caused by arrow straightness, the components or the broadhead. Any of those things can add to the wobble. It's one of the reasons I don't really like halfouts or outserts.
You’re mounting the broadhead an inch out in front of the arrow and you're adding some tolerances to it. It’s harder to get the arrow to spin true. My favorite system there is the HIT system. The broadhead and shank align directly to the head of the arrow.
We make a reinforced HIT system where we put an impact collar over that to reinforce the arrow. It helps well for those side impacts. Having good alignment, your broadhead to your arrow, so it spins true, is really important.
Matt: Share with the reader a little bit of the problem with engineering tolerances. I think there's a lot of folks out there that believe if they buy a package of 125 grain broadheads, every broadhead will weigh exactly the same. The reality is, depending on the manufacturer, you might get 125 gr, 129 gr or 121 gr broadheads. More importantly, let's talk about the extras on the front of the arrow, you know, collars and inserts and things like that.
Take the reader through why they should minimize what's on the front of their arrow because of tolerances. Does it really make a difference on arrow performance?
Bill: A simple system on the front of the arrow may help to minimize engineering tolerance variations. Does that make sense?
There's mass tolerances and then there's dimensional tolerances. If all your arrows are within a few grains of each other, I think you're good there. A lot of pros have said they don't see a difference with less than 10 grains variation.
I'm fine if there's a couple grain tolerance. You just don't want big tolerance variations. So it's good to weigh your arrows when you're done building.
Dimensional tolerance is a bigger concern. So if you have bigger tolerances, things are cheaper to make, right? They're easier to make, they're cheaper to make.
A lot of the components you get free with arrows can be worth what you paid for them. They're produced as low cost as possible. They're often low grade aluminum. Manufacturers don't want to add any cost that not everybody needs.
A lot of these components are just for target archery and you're not gonna have any hard impacts. You're shooting into a bag or foam or whatever. Why add a bunch of costs? Why have to increase the price for everybody just to take care of the 5% of hunters that really care about having the best possible setup?
I've heard that exactly from arrow manufacturers. And I don't blame them for it. I understand. People need to know that. It's the reason why on most half outs there are multiple significant tolerances that will affect the run-out of your broadhead. They're only holding things to maybe three thousandths of an inch on many of the dimensions.
You should consider arrow diameter size, shank diameter going into the shaft, shank concentricity to the bore that the broadhead goes into. Then you have a clearance between your broadhead shaft and that diameter. The diameters on the insert have a tolerance. Add these up and it's pretty easy for that point to be off 10 thousandths to the side.
You’ll see it if you spin your arrow and it's 10 thousandths off. It might not sound like a lot, but that looks like a lot. That's quite a bit and that will affect your down range flight. That's why I say tolerances matter.
The other negative is that it adds a lever arm if you get a side impact. You have force on the side of your broadhead. It's like a breaker bar. It's much easier to bend or break when the broadhead is mounted an inch out in front, compared to if it's mounted right into the arrow. If you want to have just the most robust set up to pass through scapulas, you have to know how to avoid the problem.
Matt: The thing that I'm worried about is people falling victim to the thinking “my target set up is gonna do me well in the field. What's good for the average archer is also good for me.” No, because of all the things that you just reviewed.
Bill: I think a lot of people, especially new archers, assume that the arrow and components they get for free are going to work best in the field. Why wouldn't it? They also might buy some broadheads at a big box store and think these are gonna be sharp. Why wouldn’t wouldn't they be sharp? Right. I thought the same thing.
Bill: I've studied a lot of broadheads. I had a broadhead fail to penetrate an elk shoulder blade in 2004. It was pretty devastating. I had moved to Colorado in ‘99 and hunted elk for four years. Finally, I got a shot on a nice bull and it hit the back edge of the shoulder blade and just stopped.
I spent many years really applying my mechanical engineering knowledge to become a better bowhunter. It involved studying the physics behind all parts of bowhunting.Then I studied a bunch of different broadheads, did a bunch of testing and really found that getting that force to penetrate low is important.
The lowest force to penetrate is with a durable, very sharp, cut on contact type head like a two blade or two blade with bleeder. That will reduce the force the most and get you the most penetration. The next level from that would be a durable, sharp, 3-blade fixed head.
If your broadhead is not able to shave hair or cut through paper without tearing it, fix that first. A dull broadhead will increase the force to cut
through that hide and that animal tremendously. That's really important.
Like we said, whatever momentum you have down range is equal to force times time. If the force to penetrate is two or three times more, you're gonna get a third of the penetration you would have compared to a broadhead that's sharp and has lower force to penetrate.
Part of it is sharpness. For others it's geometry. Three blades versus a two blade just takes more force to get through. Especially if you hit scapula and you're trying to split even a thin bone. You're trying to maybe split out three directions with a bit more of a wedging effect than a two blade or two blade with bleeders.
I'm not saying you can't be effective with a three blade. I'm just saying it's gonna take more force to penetrate. If you want more margin, you can get that with a really sharp cut on contact, say two blade or two blade with bleeders. Then you jump up to mechanical and that's like 10 X the force to go through compared to a sharp fixed blade.
Key Components to Focus On
Matt: What are the key components a target archer, who really wants to be a western big game hunter, should stay focused on?
Bill: Arrow flight's number one
. Don't do anything that compromises it. Don't try to add too much mass at the front if you're going to be underspined.
For instance, have a properly spined arrow for your bow, with the appropriate mass up front and enough vane at the back to stabilize the broadhead up front. Be sure to have some rotation.
Next, I would say durability is really important
. If you're trying to maximize your momentum and maximize your penetration, grade five titanium and steel (hardened steel) are the best options. I like to build the strength into the arrow instead of building it out front. Personally, I choose mass over speed. It will give you continuous improvement in down range momentum.
The trade off there is trajectory. So you’ve gotta balance that out. I think that 450 to 550 grain weight range is great for most people. If you're shooting an 80 pound bow and 32 inch draw, it's probably more like 600 grains. If you're going over 290 ft/s, add some mass. It's going to help you. You are still plenty fast at 285 ft/s, really 265 ft/s to 285 ft/s is great.
Choose mass over speed to improve penetration
. Keep the force to penetrate low. Very sharp broadheads are important. A two blade or two blade with bleeders is probably the lowest force to penetrate and will get you the most distance through. Three blades, make sure they're sharp, can be very effective as well.
Penetration really depends on your setup, how much energy you have and what you hit, really. Weight up front is good as long as you're properly spined for it. It gives you a little more front of center (FOC) weight, helping with stability. Stability is not a bad thing to have. There's no need to go extreme on it.
Arrow Shot / Penetration
Matt: The most important factor in penetration is shot placement. Let's talk about the importance of shop placement real quickly.
Bill: Really the goal of every bowhunter should be a very quick kill. Make it as humane as possible. If you're not hitting vitals, it is not going to die. If you're not hitting in the heart/lung area, it's not gonna die quickly.
That's why I like shooting up kind of in that vital V area, the crease, or even a little bit in front where you're shooting for the top of the heart & lung area. If you hit there the animal's gonna be dead in seconds. That really should be the goal. If you aim back to avoid the shoulder, you are more likely to hit the liver or guts.
Shot placement is the most important. Practice. Know your setup and have good arrow flight with your broadheads. Be able to have good shot placement. That’s #1!
About Bill Vanderheyden:
Bill is a mechanical engineer and an adjunct instructor of mechanical engineering. He grew up bowhunting whitetails in Wisconsin before moving to Colorado in 1999 and then became obsessed with bowhunting elk. In 2004 he had a broadhead fail on an elk shoulder blade and that started a 10 year process of testing other broadheads and then developing one to be as reliable as science allows.
Bill co-founded Iron Will Outfitters
in 2016 and is currently the owner and lead engineer. He hunts throughout the year to test and continuously improve his products to help bowhunters be more successful.