Arrow FOC

[sclancy27]

From what I can tell, one of the more difficult things about high FOC arrows is good flight in the wind. I’m not sure whether or not it’s possible to get an arrow with really high FOC to fly straight in high winds, especially at low arrow velocity.

You could adjust the amount of fletching area at the end of the shaft. Less SA catches less wind. You then run into the problem of being able to control the broadhead with the fletchings....

Im sure a missile guy could answer that question with very little thought required. Even if it’s possible to get a really high FOC arrow to fly properly in high wind, I’m almost 100% certain that it’s easier to get a more balanced arrow to fly properly in the wind.

Yes

Remember, there is a difference between wind drift and an arrow shaft that is aligned with the direction of flight. I feel like higher FOC should result in reduced wind drift, but worse shaft alignment to flight path. I may be totally wrong. I don’t remember anything from fluids. That said, I’ve heard a podcast or two involving complaints about high FOC and high wind. An arrow shaft that is misaligned with the arrow’s flight path is going to rob a lot of penetration.

That is the single most important aspect of penetration, having a well flying arrow that is able to take advantage of all the KE in the arrow.

 

[ImBillT]

Given a properly spined arrow, dynamic spine (and there for deformation) at the shot is the same. You get more deformation at the shot with a weak arrow spine. A weak arrow spine is not accurate with fixed broadheads.

Dynamic spine is the same for proper arrow flight. More weight in the front requires higher static spine for equal dynamic spine. You get less deformation on impact. You got that one backward.

Force per unit area the nock has it, total force is same

I’m not even sure what you’re talking about.

Only in highly elastic systems, or very large, rigid systems (like a bridge, where material deformation is calculated). An arrow is not a highly elastic system or a large rigid system. It is a small, semi-rigid system.

This proves you don’t know what you’re talking about. Someone tried to explain to you when you could ignore deformation and when you couldn’t. In an arrow you can’t. If you could, spine wouldn’t matter.

Improper arrow flight is what breaks inserts

Lots of things break inserts. I was addressing people I’ve heard on podcasts, or encountered here, who complain that too much broad head weight is hard on components. A heavy broad head is hard on a component during launch, but not during impact. Broad heads aren’t breaking inserts at launch, and during impact it is the mass of things behind the broad that is applying the force that is breaking inserts.

It’s not just arrow flight that misaligns the forces and places stress on inserts. You don’t perfectly hit a target that is orthogonal to the direction of flight very often, and an animal isn’t planar. Perfect arrow flight will not spare the insert from stress on impact, nor will it prevent the shaft from flexing. The shaft flex and the stress at the insert are a result of the shafts own mass, the mass of the fletching and the mass of the knock. A heavier broad head, as long as it cuts equally compared to a lighter one, is not contributing to any increased forces on parts of the arrow to the rear of it.

I don’t have time to cover ever part of what you posted. I have better things to do, but I disagree with almost all of it.

 

[TheTone]

Improper arrow flight is what breaks inserts

I’d also say bad designs and cheap materials contribute a lot to arrow failure.

One of the things that people tend to do when they’re chasing FOC is go to a light, thin walled arrow. They’re losing durability in the arrow just so they can put a bunch of weight up front and still maintain the total arrow weight they want.

 

[ImBillT]

Dude, you this is a vast oversimplification. Arrow deformation at impact pales in comparison to putting half a pound of weight at the end of a 30" arrow shaft. Deformation at impact is easy to show with low-speed video. Hint, there ain't much, even when hitting a very, very hard target.

This is like picking fly shit out of the ocean.

It’s a vast oversimplification to help people acknowledge that the arrow deformed at impact, and that a longer arrow shaft flexes more, and a heavier knock and heavier fletching flexes more.

You think it’s nit picking, but it is one of the reasons that higher FOC leads to increased penetration.


People say “high FOC shouldn’t increase penetration because physics says it doesn’t”. Now I explain an effect that does result in increased penetration and you basically say, that’s not a big enough effect, so we must ignore it.

 

[ImBillT]

I’d also say bad designs and cheap materials contribute a lot to arrow failure.

One of the things that people tend to do when they’re chasing FOC is go to a light, thin walled arrow. They’re losing durability in the arrow just so they can put a bunch of weight up front and still maintain the total arrow weight they want.

I was only addressing the people out in the ether who complain that heavy broad heads break components. I’ve read it and heard it. Those people may not be everywhere , but they tend to crop up when discussing FOC.

 

[ImBillT]

You could adjust the amount of fletching area at the end of the shaft. Less SA catches less wind. You then run into the problem of being able to control the broadhead with the fletchings....

Decreasing fletching would decrease the surface for the wind to push, but it also decreases the ability to steer using the forward velocity of the arrow. In a balanced arrow the wind deflects the front and rear of the arrow equally. In a front heavy arrow the tail is deflected more by the wind. Decreasing fletching would reduce wind drift, BUT it would not eliminate the the yaw(maybe the correct term) caused by the front of the arrow resisting wind deflection more than the rear of the arrow. For still conditions, where fletching only has to overcome direction changes caused by the broad head flying through the air, you can absolutely reduce fletching with higher FOC because the fletching is working with a longer lever than with low FOC. In wind however, you actually need more steering from the fletching because of the imbalance between wind deflection of the front of the arrow compared to the back. Increasing the size of the fletching would increase wind drift, reduce FOC etc., but it should cause the arrow to fly with the nock more closely in line with the tip as long as forward velocity is greater than the wind velocity.

A missile guy would know readily. A missile guy however, lives in a world of computer controlled adjustable fletching, so he can have his high FOC and steer it too. I’m not sure if we can properly steer it under all conditions with fixed fletching.

 

[TheTone]

A missile guy would know readily. A missile guy however, lives in a world of computer controlled adjustable fletching, so he can have his high FOC and steer it too. I’m not sure if we can properly steer it under all conditions with fixed fletching.

being as how they’re being propelled by a rocket engine I’m not sure missiles and arrows are super compatible

 

[ImBillT]

being as how they’re being propelled by a rocket engine I’m not sure missiles and arrows are super compatible

The only differences are that the missile has adjustable fletching and never leaves the string(it’s string is permanently attached). Believe it or not, a glider follows the basic principles of flight exactly the way a jet does.

Someone designing missiles for the military has all our answers and/or knows how to get them, but has likely never thought about our problems.

 

[Mighty Mouse]

Someone designing missiles for the military has all our answers and/or knows how to get them, but has likely never thought about our problems.

I often disagree with the Ashby crowd, but they do have some good info on the aerodynamics of arrow flight as explained by a former DoD ballistics engineer. It doesn't have all the answers, but it's a good start.

https://www.ashbybowhunting.org/s/Barnette_Arrow-FLight-101.pdf

 

[Redman]

It’s a vast oversimplification to help people acknowledge that the arrow deformed at impact, and that a longer arrow shaft flexes more, and a heavier knock and heavier fletching flexes more.

You think it’s nit picking, but it is one of the reasons that higher FOC leads to increased penetration.


People say “high FOC shouldn’t increase penetration because physics says it doesn’t”. Now I explain an effect that does result in increased penetration and you basically say, that’s not a big enough effect, so we must ignore it.

Thinking this guy is a "Troll" just wanting to argue on facts that have disproven his opinions.

 

[Mighty Mouse]

Thinking this guy is a "Troll" just wanting to argue on facts that have disproven his opinions.

I don't think he's a troll, just an engineer...we're not known for our charm or interpersonal skills

 

[ImBillT]

Thinking this guy is a "Troll" just wanting to argue on facts that have disproven his opinions.

He admitted that I was right about a few things a troll would not usually have acknowledged.

 

[Redman]

I don't think he's a troll, just an engineer...we're not known for our charm or interpersonal skills

Well then you should test building a heavy arrow then test building a FOC arrow that equals the same weight. If properly done you will see where the FOC arrow out performs the "standard heavy" arrow.

 

[Ought Six]

The target I was shooting.. lol I had a half dozen without the inserts at the time, and shot them side by side

Foam targets have actually shown speed to have the same or deeper penetration as weight/FOC

 

[Ought Six]

I’m going to go ahead and say that people on Hunttalk are much smarter than all other platforms that I frequent. Thank you for all the discussion

 

[Mighty Mouse]

Well then you should test building a heavy arrow then test building a FOC arrow that equals the same weight. If properly done you will see where the FOC arrow out performs the "standard heavy" arrow.

In what way(s) will a higher FOC arrow outperform a lower FOC arrow of equal weight?

 

[Irrelevant]

In what way(s) will a higher FOC arrow outperform a lower FOC arrow of equal weight?

Here is my understanding: with the same exact physical specs except a change in the location of the weight, you get two improvements
1. Friction is being applied to the broadhead causing it to slow, while the center of mass has inertia that want to continue, the shorter that gap the less deformation in the shaft.
2. IF we assume a constant density of the material and therefore constant frictional forces along the arrow for the entire duration it's is traveling through the animal, you simply have a shorter duration of time and thus less frictional resistance, when the broadhead is being subjected to critter induced friction before the center of mass completes it's pass through the animal.

I know I didn't explain #2 well enough, I need a white board.

 

[ImBillT]

In what way(s) will a higher FOC arrow outperform a lower FOC arrow of equal weight?

They will penetrate more deeply. Ashby couldn’t show it experimentally until he reached 19% or more FOC, and that was in animals. It may require more to show up on an archery target. My guess is that drag against the target by a vibrating arrow shaft is the primary factor reducing penetration when comparing normal FOC arrows to high FOC arrows. If that is the case, then in order for the effect to appear, you will have to be impacting a target which allows a meaningful amount of the arrow shaft to enter the target.

I don’t think that’s the only factor reducing penetration in low or normal FOC arrows. If more shaft can flex and vibrate, then the peak force applied to the target will be lower. I’m a soft medium, a lower peak force for a longer time could result in similar penetration, but if the arrow impacted a something harder, which required a higher peak force to penetrate, then the arrow shaft’s flexing could absolutely reduce penetration aside from the friction alone.

Lower FOC arrows of the same weight at as higher FOC arrows will have more shaft flex upon impact than the higher FOC arrows.

 

[Flatbrimmer]

Foam targets have actually shown speed to have the same or deeper penetration as weight/FOC

What’s that mean? Lol it was commercial grade core bond I had the insulators at work fill for me in a box. Stops a broadhead almost instantly, field points make it a little further. These are with broadheads and you can see it was easily 6-8” deeper when I added an additional 50 gn to the front, W/O adjusting anything else.

 

[golfer]

What’s that mean? Lol it was commercial grade core bond I had the insulators at work fill for me in a box. Stops a broadhead almost instantly, field points make it a little further. These are with broadheads and you can see it was easily 6-8” deeper when I added an additional 50 gn to the front, W/O adjusting anything else.

Musta hit a soft spot…