Let's talk broadhead physics

[LeanMachine]

Broadheads have great appeal to me and I am always looking for a better mouse trap. I have read ashby's reports and drew great pleasure from his obsession.

Lately something has been on my mind and I'm curious if I am correct in my thinking. There are many varying broadhead designs on the market but I am focused on fixed 2 blade designs. Furthermore we can break them into 3 categories; straigt blade, convex blade, and concave blade.

My theory is that anything other than a straight blade is hindering penetration. It has been some time since i have read ashby's reports and I'm sure he mentioned this, but i can not remember. The way I see it is that whether curving the blade out or in, you are increasing the cutting diameter more rapidly than if it were a straight edge. In addition you are also increasing the surface area of the blade which in theory would cause greater friction.

Do you see what i am saying? I understand the rib catching mechanics behind a concave blade design such as the simmons but what advantage does a convex design give? I possibly prefer the appearance of convex blades, such as silver flames, but am unwilling to sacrifice performance for appearance.

I know they all work. Period. But I've begun building my own broadheads and was thinking of making a convex design until I had this thought.

Anybody agree with my thought process?

[Bisch]

I'm not sure it all makes a hill of beans. i have shot many Bh's over the years and currently shoot Silverflames. I shoot a fairly liht draw weight (50#@my DL) and have come to the conclusion that 2 blades are the best for penetration for lower draw weights.

I really think that have well tuned arrows is the most important thing of all. Even the best designed BH will not penetrate as well if the arrow is not well matched to the bow and archer.

JMHO

Bisch

[LeanMachine]

I agree. I also agree that any amount of difference is probably negligible. However, when i do not get to hunt, my mind must be occupied with hunting related thoughts...however trivial they might be

[jreyna920]

I agree with a lot of your outlook on the designs, you mention the factors and how they relate to penetration but I believe the benefit to other blade designs is the cutting surface factor or the balance of the cutting factor and penetration, I agree the strait edge would probably penetrate the best, the concave is the worst design in my thoughts because of the blade angle on the trailing edges. I think they would produce the biggest thump but not necessarily the most penetration or cut. I think the convex design is the closest to the optimum balance between penetration and cutting surface. So depending on what poundage you shoot the most lethal head might be the straiter edge on the lower end to the convex if you have the thump to push it threw and the con caved if you have the horsepower and want the extra knockdown factor.

[LeanMachine]

The convex has more cutting surface but I do not see it being utilized. If you push a convex and a staight edge head, of equal cutting diameter, thru a potato, the holes will match. The only way I can see the increased surface benefiting is if the head remains in the animal as they run off.

Though this is a frequent outcome, I do not believe it is the goal of anyone.

As a side note, I have shot animals with multiple styles and sizes of cuts. I have yet to not a difference in the end result. This is all for the sake of discussion.

[4feathers]

You will need to find that magic ratio as well, short heads with wide cut do not seem to penatrate as well as a point with a longer cutting surface and the same cutting

[Draco]

Do you believe that aerodynamics count on going through a body the same as air or any other substance?

[wassaw]

I'm not sure it all makes a hill of beans. i have shot many Bh's over the years and currently shoot Silverflames. I shoot a fairly liht draw weight (50#@my DL) and have come to the conclusion that 2 blades are the best for penetration for lower draw weights.

I really think that have well tuned arrows is the most important thing of all. Even the best designed BH will not penetrate as well if the arrow is not well matched to the bow and archer.

JMHO

Bisch

totally agree!

i think the balance and spin (no wobble) of a properly spined arrow, help the energy transfer better to the tip and push the arrow through.

[LeanMachine]

Do you believe that aerodynamics count on going through a body the same as air or any other substance?

Yes I would think so

[txfireguy2003]

Here's my take on it. A (totally) straight edge is going to have the most penetration, as you said, however, that sharp tip with a 3:1 ratio of length to width (I think Ashby said this is best) is a narrow tip with a propensity to curl when hitting hard stuff like bone etc. This is why a lot of designs have the tanto tip, it's stronger. So, a convex design will give you that wider tip as well, which is stronger. The problem, IMO, with convex heads, is the surface area of the blade (surface, not cutting edge) can cause an arrow that's not perfectly tuned to plane more, decreasing accuracy. This is the main benefit of the concave blade, less blade surface area to inferfere with accurate flight, but again, it suffers from a weak tip like the totally straight edge (even more so in a lot of cases actually), and it's going to have penetration issues due to the lack of the 3:1 ratio on the trailing edges. Another (supposed) benefit of the concave design is the wound could potentially be wider than the actual cutting diameter of the head, since the tip pushes in and causes the hide to be pushed in with it before the trailing edge catches hide. There is actually a new design for compound shooters that hit the market in the last year that has notches cut on the leading edge to "pull" the hide before the trailing edge cuts it, of course, this is all theory. So, here is my conclusion:

The perfect head is a "straight edge" with tanto tip and 3:1 ratio. The convext design gives a stronger tip, and if your arrows are perfectly tuned and you have enough KE/momentum, might be beneficial due to a stronger head, but penetration won't be as good as the straight edge. If you're having flight problems due to a less than perfect tune, a concave head MIGHT help some, but you're going to suffer tip weakness and again, lack of penetration when compared to a straight 3:1 design, but again, if you have enough umph behind the arrow, you can overcome the decreased penetration.

So, basically, I'm agreeing with you, but giving a couple of reasons why the other designs might actually be beneficial.

Then again, what do I know, I'm a compound shooter.

[Draco]

The reason I ask is because of a couple articles I've read through the years with broad head penetration tests. I really don't buy the 3:1 thing. Dr. Ashby is working with a head of one inch or less in width which is cutting a lot less meat than almost any other head ever made. The narrow width coupled with the single bevel allows him to get more bone breakage which is what he really needs on the game he hunts. Why not 4:1 or 5:1? Of course the heads would then weigh too much. If you go any wider than 1" and have 3:1 the head is too heavy as well.

In the late sixties, Bow and Arrow magazine had a broadhead penetration test. They tested all the broad heads currently available and shot them with a shooting machine. The Howard Hill 3:1 broadhead really didn't perform all that well and is one reason I have never bought any. The head that won was a head that was pretty short in length and 1 1/4" wide. It was called an Apollo or Sonic or some other space age name.

In the late seventies another magazine did a broadhead penetration test. There were a lot of new heads on the market to try. The same broadhead won again. The only difference in design, from any other broadhead, was it had rounded back corners. The cutting edges were straight except for the last 1/4" and it was rounded. It just had better aerodynamics than any other head in the test.

I've talked to Dr. Ashby about this and he tends to think it would be right but wanted to test it first. He said he would test it some time in the future and let me know.

[Ron]

Let me first say that I am fairly new at hunting big game with trad equipment.
I have killed hogs and deer both, but my experience has been better flight and penetration with a three blade head vs. a two blade. I did have a complete pass through with a two blade on a hog, but flight is never as good for me, than with the three blade heads.
Just my thoughts and they are not as experienced as you folks.

Ron

[meangene1969]

I agree with Bisch so I hope the world doesn't stop turning. haha. I believe most broadheads will do the job if you have a properly tuned arrow. It is amazing how much energy an arrow loses when not tuned.

[LeanMachine]

Draco, I would like to see a picture of the head you mentioned if you can find one.

I personally also feel that the 3 to 1 is unnecessary unless you are very likely to encounter heavy bone.

[bm22]

I belive you will never see the difference in penetration between 3 blade and 2 blade heads if you are just shooting deer. Thats why so many people still shoot snuffers, woodsman and other 3 blade heads, the critters they shoot and 150-200 lbs. and if you have every looked at how much meat you have to cut to het across a rib cage of a deer it is not very much, 3-4 in of tissue at most on a perfectly broadside shot.

Where a 2 blade shines is when you make that bad shot or the deers spins and you hit it in the hams angling foward or shoot one in the shoulder from a tree stand and the arrow just stops. Thats when every inch of penetration is needed.

The howard hill broadhead is an ok design but with one major flaw, it has that rivot in the front, common sense says anything sticking up on a broadhead like a nut and bolt is Going to kill penetration especially if you hit something hard like bone.

At some point have a 4 to 1 or a 5 to 1 has a dimishing rate of return when you start to figure the weight the broadhead would have to be and the added chance of bending, i think 3 to 1 was just a good middle ground.

I shoot wide abowyer broadheads when i am hunting on the ground because i feel they penetrate better than small three blade and it is a good comprimise of good penetration and a wider cut in case it goes through gut. From a tree i shoot the smaller 3 to 1 abowyer, the chances of hitting a shoulder are higher and i want to go through it.

Also my arrows are at 40% foc slightly more than 600 grain.