[Ed Ashby]

in reply to: Turbulators #22017

Bender wrote: Yes the whole purpose is of course to create turbulence. Its what you DO with that turbulence that matters. So I guess that by proper placement one could create a net INCREASE in drag as in Dr. Ashby’s explanation, OR one could create a net DECREASE in drag, such as when they are used in aircraft.

Now you’re cooking!

I’m trying to not get too technical here, but the effect a turbulator creates on a moving object can be either to increase pressure or decrease pressure. Say what? Yes, the ‘net effect’ of how the turbulator affects the moving object depends on where the turbulator is placed and the profile of the object. First, one needs to recognize that there are basically two types of ‘drag’; “skin/surface drag” and “profile/form drag”. Turbulators are used to increase the ‘surface’ drag and/or reduce the ‘form drag’.

The classic example of turbulator “net effect” is the golf ball. The dimples on the surface of a golf ball act as turbulators. They both increase the surface drag and decrease the form drag. However the net effect on a golf ball is reduced drag. Why? The ‘form drag’ results from the ‘wake’ a moving object creates. In the case of the golf ball the form drag begins just back of the widest portion of the golf ball. Thus, there is a sizable area (more accurately, volume) of form drag. Though the golf ball’s dimpled surface (the turbulators) increases surface drag on the portion of the golf ball being pushed through the air it also disrupt the air flow at the edge of the golf ball, creating a turbulence in the air which help fill in the ‘void’ just behind the ball, thus reducing the ‘vacuum effect’ behind the golf ball. This is also why long-range bullets have boat tails and is one of the (many) uses of air foils (‘spoilers’) on race cars. The reduce the form drag.

Now, think about the shape of our fletching. There’s not very much ‘area’ behind the fletching, so the form drag is minimal, and they don’t create much of a ‘wake’ immediately behind the fletching. (As an aside, the vertical trailing edge of the A&A fletching creates less turbulence – less form drag – than any other trailing edge profile on fletching – which also makes them more silent in flight.) However, our fletching has a lot of surface area. By placing our turbulator forward of the fletching we are increasing the surface drag significantly. The net effect of increasing surface drag when ‘form drag’ is minimal is going to be an increase in total drag force.

It’s hard to make a complex explanation simple but I hope that helps clear up the different effects of a turbulator.

Ed

[Ed Ashby]

in reply to: Turbulators #21703

Now this is not a precise, scientific explanation of how a turbulator works, and isn’t meant to be, but it will help give you the concept of how the turbulator works.

When air flows over the shaft and fletching there is a layer of air called the “boundary layer” between the surface of the shaft and much of the feather’s surface, where the air is relatively undisturbed. The air will flow smoothly in this thin boundary. Addition of a turbulator forward of the fletching ‘trips’ this laminar airflow, creating many small swirls of air. These swirls are now pressing on the feather’s surface laterally; from the sides of the feather. This increases pressure between the feather’s surface and the air, increasing the drag created on the feather surface. Think of pinching the sides of the feather between your thumb and index finger. The harder you squeeze the feather the more resistance it causes on the feather’s surface, increasing ‘drag’.

Hope that helps.

Ed

[Ed Ashby]

in reply to: wood v. carbon #18274

Ptaylor wrote: For some of you folks that understand the FOC concept better than I would like to hear your opinions (and correct me if I state anything wrong):

Wood shafts are stronger than carbon upon impact, and converts more energy into penetration on impact. But-

Carbon allows for higher FOC and therefore better penetration.

So which (carbon or wood shafts) allow for more consistent performance and therefore more consistent kills?

First, it is ONLY the hardwood shafts (hickory, laminated birch, purple heart, ipe, etcetera) that are more durable than carbon shafts. The more commonly shaft woods are NOT more durable than carbon, they are about the same level of durability.

Second, there is nothing inherent in wood shafts that allow it to ‘convert more energy into penetration’. The ability to convert arrow force into penetration is dependent on the arrow’s transfer efficiency, and there are several penetration enhancing factors that affect transfer efficiency. That’s what the penetration factors are all about, and the degree of FOC the arrow carries ranks at number three in overall importance, right after total arrow integrity and quality of arrow flight.

If the choice is between the commonly used shaft woods and carbon shafts then carbon offers the potential for much higher FOC; ergo, carbon would offer the potential for greater penetration.

Not certain if that was what you’re asking but I hope it helps a bit.

Ed

[Ed Ashby]

in reply to: Turbulators #17265

jpcarlson wrote: Gentlemen, If memory serves, the goal when adjusting/testing the size of the fletching on tuned FOC arrows was to get the size down to as small as possible. This added significant FOC up front as a little off the back compounds to the front. The feather size one would end up shooting was the very shortest you could get away with that would still control a broadhead in a stiff cross wind, and account for a sloppy release. The arrow flight was supposed to be a little squirrely but be corrected by addition of the turbulator which in effect causes turbulence along the arrow shaft starting 1/4″ in front of your fletching. This made your small as possible fletching more effective as the feathers were able to “bite” into more of the turbulent air.

I have found with my own set up at around 32-34% UEFOC that I do not need them until my feathers get REALLY small:) I have one set fletched with 1 3/4 x .5″ feathers in a 4 fletch. The FOC on those are at 34%. I found I need the turbulator to stabilize the small fetching for hunting. Boy are they quiet with the small feathers!

Jans

I can’t add ANYTHING to that!

Ed

[Ed Ashby]

in reply to: Man Eaters of Kumaon #11529

My all-time favorite. I have two copies. No telling how many times I’ve re-read it. I think Gentleman Jim understood more about what was going on around him in the wilds than any writer I know of.

Ed

[Ed Ashby]

in reply to: Bench Grinder vs Broadhead #9459

J.Wesbrock wrote: When I shot Zwickey Deltas I used a bench top belt sander to put a straight edge on them before sharpening. Go slow so you don’t overheat the edge and ruin the temper and you should be fine.

Sound advice. In the testing I had an enormous number of arrows to sharpen, and many were the ‘old style’ Grizzly heads, which need a huge amount of work. I routinely did the initial sharpening on a belt grinder (one made for shaping/edging knife blades). I kept a large bucket of water right beside the grinder and cooled the head frequently during sharpening. Having water on the blade while sharpening also gave me an idea of how hot the blade was becoming. When the water evaporated off the blade it was time to re-dip the broadhead in the water. Be sure to use a LARGE bucket of water or the water becomes pretty warm after doing several broadheads.

Ed

[Ed Ashby]

in reply to: Plains Indian arrows #9447

I’ve had the opportunity to measure the FOC on a few original arrows of some American Indian tribes (museum pieces), both from the plains region and the southeastern costal areas. Most of their arrows exhibit EFOC, and some have Ultra-EFOC. I’m convinced that we are just relearning what more primitive cultures learned eons ago. So much for EFOC/Ultra-EFOC not being ‘traditional’. Notice too how the primitive tribes readually changes from stone points to steel points, when the steel points became available. Switching from what has been ‘historically used’ to things that improved arrow terminal effectiveness seems ‘traditional’ too.

Ed

[Ed Ashby]

in reply to: Happy BD Dr. Ed! #45166

Thanks to all for the birthday wishes. I’ve had a grand day here, with just me and the critters (but sure would have would have welcomed THAT company, Dave.). Started the day off at first light around the campfire with coffee (with just a touch … or two … of Amarula added in) while listening to the soundtrack from Out of Africa playing in the background. It brought a lot of wonderful memories forward. I started lots of days in the African bush just that way; campfire, coffee with Amarula and Out of Africa music playing. Finished the day off with a wild Texas turkey cooked on the grill and a Wild Turkey 101 in hand (okay, it was a FEW Wild Turkey 101’s)!

Thanks to all,

Ed

[Ed Ashby]

in reply to: Arrow length as substitute for more FOC #43979

My pleasure.

Ed

[Ed Ashby]

in reply to: Arrow length as substitute for more FOC #43473

In ‘flight stability’ it’s not the length of the arrow that matters, it’s the relative relationship between the forward and rear leaver arms, and the degree of force exerted on each. Lengthening your arrow, without adding additional point weight, is going to lower the FOC, because you are adding additional weight to the rear leaver arm.

With a given shaft material, when length is added without adding point weight, it does lengthen the rear leaver arm but, because it shifts the gravitational center to the rear (lowering the FOC) it also lengthens the forward lever arm. As long as there is still some positive FOC there will be some degree of flight stability.

The degree of dynamic stability demonstrated in flight will depend of the balance of forces exerted on each of the lever arms. For example, a field point exerts very little wind sheer pressure on the forward lever arm, and would require less pressure on the rear lever arm to achieve a given degree of stability, but a broadhead will exert far more wind sheer on the forward lever arm, requiring more pressure on the rear lever arm to achieve the same degree of flight stability.

It must be recognized that it is not only the broadhead and fletching that exerts pressure on the leaver arms. As an arrow deviates from the flight direction the surface area of the shaft also exerts pressure on the rear leaver arm, providing some additional steering effect; but that’s also true for the forward lever arm, except that the force is a destabilizing one. As long as there is positive FOC the differential in ‘shaft pressure’ will be in favor of the rear lever arm. The degree of this ‘shaft pressure’ differential is also reflected by the relative position of the gravitational center; ergo, it, too, is reflected by the FOC of the projectile in flight.

I always found that longer arrows shot better for me when using field points, but not with broadheads, and the flight got worse as the degree of broadhead wind sheer increased. Now, I tune my EFOC/UEFOC arrows by altering the shaft length, and many of these are longer than my minimum arrow length but the added length is not what is creating the great stability, it is the FOC. Ideally I would want the shaft as short as usable because it would give greater FOC, at any given point weight. However, the benefits of EFOC/UEFOC is squandered without quality arrow flight so arrow length will be wherever it tunes best, even if I have to sacrifice a bit of FOC.

In a nut shell, it’s the relationship between the forward and rear leaver arms that you need to be looking at when seeking flight stability, and it’s the degree of FOC that reflects this relationship. Hope that’s the info you were looking for.

Ed

[Ed Ashby]

in reply to: how good is good enough? #33985

Don’t be put off just because your shooting accuracy isn’t the best. Mine aren’t. Just know your effective distance and then learn how to get game within that distance.

I’ve probably put more time into honing my stalking skills than into my shooting skills. I’ve known a great many folks who shoot more accurately than I, but the average shot distance across my last 627 big game animals was just under 16 yards. It’s not about long range accuracy.

If one wants to be a consistently successful bowhunter developing shooting skills is very important but developing hunting skills is essential.

Ed

[Ed Ashby]

in reply to: 300 Tuffhead testimony #27092

“In bowhunting there’s no such thing as overkill”. – Ed

[Ed Ashby]

in reply to: 300 Tuffhead testimony #25936

jpcarlson wrote: … She ran back down the way she came and stood looking back and trying to figure out what had stung her …

One of the many reasons to use a setup that gives a high percentage of pass-through hits.

Sounds like a great day afield!

Ed

[Ed Ashby]

in reply to: Tuffhead testing #9163

Yes, and that’s what I call the ultimate “stocking stuffer’!

Ed

[Ed Ashby]

in reply to: Tuffhead testing #9020

vintage archer wrote: I am in the process of having a adapter/insert for a 5/16 arrow made from grade 5 titanium tentative that will weigh 200 grains but will hopefully be 3 inches long so it would be an adapter/insert/internal footing. i am excited about that hopefully it will test well……

That’s great news because … what’s up front does make a difference! (Merry Christmas y’all.)

Ed

[Author]

Posts