Learned something new today

[Mighty Mouse]

mighty, I see what you're saying but COG isn't determined by the fact there are fins on the front. as far as archery is concerned, I agree with you simply because an arrow never actually leaves straight so it becomes easier for rear steer to have an effect on trajectory by way of leverage. but if both are launched straight then aerodynamically the broadhead is more stable. this is why there are front fins on alot of things that fly. we see it as less stable but really its the opposite because it simply maintains its course resisting the counter effects of the fletching. again, I agree this is not ideal in archery but its because arrows never truly leave straight so its all a balancing act between components and enviro. variables. even through all of that, some of us still manage to send broadheads and FP's out to 100 yds with no problem so I honestly don't believe any one is more accurate than the other, I think its more that we don't want to spend the time perfecting our setup and that's OK.

Center of gravity (COG) isn't affected by the broadhead's surface area, but center of pressure (COP) absolutely is. Any drag-inducing component "draws" the COP of the arrow toward that component. For any given arrow, COP will lie further forward with a larger surface area/higher drag fixed head on the front than with a smaller surface area/lower drag mechanical head (COG will be the same in both cases as long as both heads weigh the same). Positive aerodynamic stability (defined as the arrow's tendency to return to its original flight path after a disturbance) decreases as COP moves forward; thus, an arrow with a fixed blade head will tend to be less stable and more susceptible to drifting off course than the same arrow with a mechanical head. If/how much this difference matters in practice is debatable, but the aerodynamic principles at work are not.

 

[stanginthe11s]

I think the positive aerodynamic stability you refer to comes from FOC and not from front or rear steering. I cannot argue COP because pressure makes a change anywhere its applied but whether something is front or rear steering makes no difference as the arrow will fly wherever it is pointed or steered. I think we may be on the same page but not realizing it or leaving out details. when equal pressure is applied to both front and back the arrow will go straight as they do not fight each other and therefor have no need to correct and when working together the arrow should be at maximum stability. now this again assumes perfect launch which can't happen in archery due to arrow flex. as such, the fins with the higher amount of pressure become the main force in steering which is why some broadheads require bigger vanes. maybe I will shoot some BH tomorrow without any fletching and see if I can get them to group. I suspect they will go wherever they are pointed, just like bare shaft tuning.

 

[Billy Goat]

Y'all arguing over stuff, put spin on it...


What about the pressure differential on either side of the blades? And the front fighting the back...

Which is why most heads are vented.

 

[stanginthe11s]

damit billy, now you messed us all up lol. now we have to talk about high and low pressure across a plane and we might as well throw eddies and flow disturbances in the mix.
not arguing, just comparing theories. I think it helps to learn the science behind things, I know it helps me. If mighty knows things I don't know then I want to learn it.

 

[MattB]

I'd say fixed heads are actually more accurate. if they weren't then why would we fine tune our bows with fixed heads aka broadhead tuning.

Quite the contrary, many use fixed blades to tune because they are most critical because of the surface area of the blades and magnify any issues with tune or form. Field points are the most accurate but as a result they mask tuning and form errors and show us very little.

 

[ddd-shooter]

I think the positive aerodynamic stability you refer to comes from FOC and not from front or rear steering. I cannot argue COP because pressure makes a change anywhere its applied but whether something is front or rear steering makes no difference as the arrow will fly wherever it is pointed or steered. I think we may be on the same page but not realizing it or leaving out details. when equal pressure is applied to both front and back the arrow will go straight as they do not fight each other and therefor have no need to correct and when working together the arrow should be at maximum stability. now this again assumes perfect launch which can't happen in archery due to arrow flex. as such, the fins with the higher amount of pressure become the main force in steering which is why some broadheads require bigger vanes. maybe I will shoot some BH tomorrow without any fletching and see if I can get them to group. I suspect they will go wherever they are pointed, just like bare shaft tuning.

I'm just trying to think of a projectile that is launched with fins on the front?

 

[stanginthe11s]

missiles

 

[nphunter]

I can't believe this is even a debate, a quality mechanical is more forgiving than a quality fixed head period. Smaller surface area heads recover faster, an arrow can recover from poor form much easier with a small mechanical than a fixed head. I've tested all kinds of heads, not as many as bohntr obviously but I could care less about penetration, I test for accuracy and actually results on the animals I kill.

For 50 yard and under shots a properly tuned bow will shot most heads well, that is of course if were talking shooting 280fps or less. You back up to 80 yards or a 315fps bow and the difference is noticeable to a blind person. I've owned and shot most of the high-end fixed heads over the years, Solid, IW, Kudu, an array of G5 heads, Exodus, TT, the list goes on, for years in OR you could only use fixed heads. The best flying fixed head I have ever shot was a Solid Legend 100 with 1/4" bleeders. Even then at 80 yards unless you execute a perfect shot they are hard to get to group, even harder with 300fps+ bows. I ended up over the years adding arrow weight until I was around 280fps which seems to be the sweet spot for speed and forgivingness.

Fast forward to when mechanicals were legalized, 80 yard shots became less stressful, no more feeling like if I bock my release that I will be ruining a 30+ dollar head. They don't fly like field points but out of a well-tuned bow a mechanical head flys extremely well out well past 100 yards. Even at 80 they have more drag than a field tip and will his a couple of inches low. I always tune my bows with a bare shaft, I get what I feel is perfect arrow flight and then switch to tuning with a good fixed head to magnify any imperfections in my tune. (yes, fixed heads magnify imperfections in tune and/or form) After that I switch to mechnicals and use them for hunting, I have zero interest in ever switching back to fixed heads, mechanicals not only fly better and are more forgiving, they also make larger holes in animals which kills them faster and makes it easier to track. I am color blind and struggle with finding blood, since switching to mechnicals tracking jobs have also been much less stressful, normally I watch them fall. I still get two holes most of the time in elk and some of the heads you could literally clean and put back in the quiver afterward, all broadheads have come a long ways in the last several years, when most think of mechanicals they think of a cheap aluminum head with thin blades that break off, that just isn't the case nowadays.

Far more animals are lost due to poor shot placement than penetration, with today's fast bows penetration with a compound bow is a non-issue. I really feel like the mass majority of bows are poorly tuned and most people have no clue of how to properly execute a shot, even a poorly tuned bow with shoot a mechanical well but won't shoot a fixed head for crap, that is because they aren't as forgiving.

 

[stanginthe11s]

not really a debate, I was just getting down to the science on the component. and what the OP was basically saying is that neither a broadhead or mechanical is more accurate than the other. is one less forgiving to a bad tune or bad shooter? sure, but that is of no fault to the broadhead as a component. I regularly shoot my broadheads to 100 yds, and they are accurate. now are they precise? well depends on the day I'm having lol but with every shot that broadhead goes exactly where it points. and, at the end of the day, the actual science behind it is irrelevant. whatever works for your shooting style or ability is what you should use.

 

[Billy Goat]

missiles

Don't think a missile is actually a projectile. It has its own propulsion.

Projectile gets its energy from something else.

But I don't know if that's the actual definition.

 

[*zap*]

A spear has noting on the back and may have a broad head on the front...atlatl also.

 

[Billy Goat]

Well dern, learned something new.

https://www.jstor.org/stable/23486489

According to this single bevel edge is more accurate because it causes rotation.


Who would have thought that an arrow in rotation is more stable?


I remember years ago a broadhead that you could chose 3 different blade angles. I'm thinking it was Golden Key/Futura, had slots for left offset, straight, and right offset blades.
Seems like that's the kinda thing you could sell the piss out of now.
I'm not big on the single bevels, but if you could get a head that was a fixed 3 blade with a 2 or 3 degree offset, I think I'd actually try them.

 

[*zap*]

After the little discussion about bh vs mech the guy said he needed better blood trails also and that was another advantage of mechs....

 

[Dos Perros]

I kinda realized no one has even defined accuracy.

Is accuracy hitting with your field points?

Is accuracy tight groupings of the same headed arrow, regardless or correlation to field points?

Is accuracy tight groupings of a group of headed arrows?

 

[Mighty Mouse]

I think the positive aerodynamic stability you refer to comes from FOC and not from front or rear steering. I cannot argue COP because pressure makes a change anywhere its applied but whether something is front or rear steering makes no difference as the arrow will fly wherever it is pointed or steered. I think we may be on the same page but not realizing it or leaving out details. when equal pressure is applied to both front and back the arrow will go straight as they do not fight each other and therefor have no need to correct and when working together the arrow should be at maximum stability. now this again assumes perfect launch which can't happen in archery due to arrow flex. as such, the fins with the higher amount of pressure become the main force in steering which is why some broadheads require bigger vanes. maybe I will shoot some BH tomorrow without any fletching and see if I can get them to group. I suspect they will go wherever they are pointed, just like bare shaft tuning.

If you want to delve deeper into the topic of center of pressure and how it relates to flight stability, here's a good (albeit lengthy) resource in the context of airplanes: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/07_phak_ch5.pdf Obviously there are major differences between an airplane and an arrow so not everything translates exactly, but the basic principles of stability do apply. Pages 12-20 of the linked document are the most relevant to this conversation. We want positive (not neutral or negative) stability so the arrow tends to stay on the path initially imparted by the bow string. Some aircraft (and actively steered projectiles) are intentionally designed with negatively stabilizing features (such as forward-mounted wings/fins known as canards) to improve maneuverability under certain conditions. We don't need/want maneuverability with an arrow—we just want it to stay on its original course—hence the desire for maximium positive stability. Positive stability increases as the center of pressure (the point through which the resultant force of all pressures exerted on the arrow acts) is shifted further behind the center of gravity. Drag-inducing elements located rearward of the center of gravity (e.g., fletching) enhance positive stability; drag-inducing elements forward of the center of gravity (e.g., broadhead blades) reduce positive stability.

In The Physical Laws of Archery, Tom Liston notes that "broadheads act like fletching at the wrong end of the arrow" (page 10-4, emphasis mine):


If you truly believe that it makes no difference whether an arrow is steered from the front or from the rear, fletch up some arrows with vanes on the front instead of the rear and see if they group as well as rear-fletched arrows. If you're correct, you might be able to start a front-fletching trend and obviate the need for expensive, complicated drop away rests since there would be no rear-mounted vanes to avoid

 

[Billy Goat]

Is accuracy tight groupings of a group of headed arrows?

To me this is it. An assortment of arrows, not the same arrow, hitting in the same small group. My fixed blade accuracy seems the best when they are also hitting with my field points, tho I know some who group tune with target shafts and that will frequently not have bareshafts impacting with fletched....


Ultimately accuracy should be the smallest group that falls behind your pin.

 

[Mighty Mouse]

Y'all arguing over stuff, put spin on it...


What about the pressure differential on either side of the blades? And the front fighting the back...

Which is why most heads are vented.

I'm not a broadhead designer, but I suspect that the primary reason for venting is to increase cutting diameter while keeping weight down (not to reduce drag/pressure differential across the blades).

 

[Dos Perros]

To me this is it. An assortment of arrows, not the same arrow, hitting in the same small group. My fixed blade accuracy seems the best when they are also hitting with my field points, tho I know some who group tune with target shafts and that will frequently not have bareshafts impacting with fletched....


Ultimately accuracy should be the smallest group that falls behind your pin.

That's what l believe, too.

I haven't been an archer very long, 8 years or so, but I've tried three different models of fixed blade broadheads on 5 different models of shafts over the years, and my group sizes are noticeably larger than with field points. Sure, it could be form, but if it is, that's a legitimate limiting factor for me. I have managed to tune individual broadheads to individual shafts by swapping them around, but that is time consuming and expensive. I am more lethal with a quality mechanical, and that includes longer shots on elk.

 

[Billy Goat]

I'm not a broadhead designer, but I suspect that the primary reason for venting is to increase cutting diameter while keeping weight down (not to reduce drag/pressure differential across the blades).

After playing with similar broadheads of both vented and solid, I think it weighs a lot more on the forgiveness than on the strength.

Try shooting some vpa vented and solids. I find a big difference in the forgiveness of the vented heads.

 

[Billy Goat]

That's what l believe, too.

I haven't been an archer very long, 8 years or so, but I've tried three different models of fixed blade broadheads on 5 different models of shafts over the years, and my group sizes are noticeably larger than with field points. Sure, it could be form, but if it is, that's a legitimate limiting factor for me. I have managed to tune individual broadheads to individual shafts by swapping them around, but that is time consuming and expensive. I am more lethal with a quality mechanical, and that includes longer shots on elk.

Not to go out into the weeds too far but....

Have you tried nock tuning?
Also, I find if I go plenty stiff on hunting arrows, it makes broadhead tuning a good bit easier. Eliminates the variables in the dynamic spine reaction, or that's my thoughts anyways.

But yes, I think you are experiencing exactly why a mech head will be more accurate for a majority of shooters, because they are generally more forgiving. That's to form, differences in arrow reaction at the shot, wind, face pressure....