February 19th, 2010, 05:49 AM
ARROW DYNAMICS.....OR.....Blazers, Feathers, BiDeltas, FOBs or Regular Vanes?
OR... How Do Arrows Fly Straight?
I've been reading a lot about people's preferences for one style of fletching vs. the other and thought I might post some general info that might be of interest.
Note- I am not declaring a knowldege of all things aero, but I have a pretty thorough knowledge base in the field. If I forgot something or have overly simplified something, please let me know. This is a short and sweet version of a bigger paper I wrote a while back that cuts the really boring stuff out.
Many people know that fletching or "fins" make an arrow or rocket fly straight, but here is a little more background knowledge that might be found interesting-
Bernoulli's Principle is often described as how an airplane's wing creates lift. It's the idea that a vacuum is created above the wing since air traveling over the curved surface of the wing must travel faster than the air on the bottom or flat side ofthe wing. (easily proven with a straw and a piece of paper and someone to blow through the straw)
Bernoulli's is only part of what allows airplanes to fly. Another part (of many) of the equation are the simple effects of Angle of Attack or AoA.
The word "PLANE" in Airplane has been found to originate with the definition of "level". This can be interpreted as "angle".
Ever heard the boating phrase "up on plane"? The angle of the hull at a certain speed will force the boat up onto the top of the water. Boat hulls are designed to "plane" at certain speeds when loaded within certain weight tolerances. The exact same thing happens with an aircraft's wings. At a certain speed, the angle of attack of the oncoming air to the wings will force the plane upwards, overcoming gravity. AoA lifting forces are aided by Bernoulli's findings. Thats why airplanes land and take off with the nose up higher than the tail. At slower speeds, the AoA needs to be much higher than during faster flight.
Kites use the same idea- they "plane" in the wind. The weight of the kite's tail helps keeps the AoA angle up. Your hand out of your car window on the highway makes a good example (fun until a bee hits it). If your a boat or river fisherman, think of a "side planer" by Luhr Jensen.
By the way... Airplanes fly with the help of the TAILPLANE, or "TAILFEATHERS", or simply as the TAIL. The tail is what forces the wings to hold a certain AoA using a reference angle called "Decalage". The tail stays in back of the plane during flight because it causes drag further away from the center of gravity on the aircraft. The tail usually has a longer moment or lever arm action than the nose.
Center of gravity is the point where we take the measure to find out FOC on our arrows or the "balance point". These points can be called a fulcrum. The want is to have a long moment so you can use small tailfeathers, therefore keeping the tail light. But to be effective, you need to have strength (read as arrow spine) in the fuselage (shaft) and stronger usually means more material and an overall gain in weight. Increasing FOC makes a longer tail moment and decreases the need for larger fletching.
(Sorry to you flying wing lovers out there, I wont get into tail-less aircraft stability in this post since an arrow is actually a wingless airplane with a tail)
How does all of this make it's way into archery? The "tail" of an arrow is the fletching. An arrow just has non existant wings. Vane or feather offset angle (AoA) causes spin. Spin is a side effect of drag. The higher the AoA, the higher the drag, the more stability. But, the more stability, the faster the arrow decelerates after launch.
Spinning forms stability in its own. Since most fletching force the arrow to spin, the arrow will tend to ignore small attempts to change it's path. (Think of a football or a bullet. )
A much more fun experiment would be to take a wheel off of a bicycle and have someone spin the wheel while you hold the axle. Try to rotate the wheel. It will resist small attempts to turn it, but allow some heavier attempts to turn it. (These same forces help you stay upright on a moving bicycle so you can enjoy the scenery.)
So the trick is, to have a strong, light tail that is the most effective for the task at hand. If an airplane needs more stability, it will get a bigger vertical fin or horizontal stab, but will have to add more noseweight to compensate for the increase in tail weight in order to hold the same FOC. An airplane designer can also change the rake angle or thickness of the fin or stab to play with drag properties and therefore stability. Stability in Arrows can be simplified to meaning drag at the rear of the shaft.
More drag = more noise. Sucks, but it's the truth. Noise is caused by vibration or flutter. The faster something travels, the stronger it needs to be to keep from fluttering.
"High speed, low drag" is a common phrase associated with modern sleek aircraft. Problem is, higher speed and lower drag can mean less stability. Our arrows dont have computers onboard (yet) to make minute changes to AOA or airfoil thickness in flight to compensate for different speeds like modern jet fighters, so they are stuck working great at only one speed- launch. To get vanes or any fletching for that matter, to work great at many different speeds, we will need offset (AoA), airfoil and camber changing capabilities in flight. What works at one speed might not work well at another. It's a fact of life that an arrow is going to change speed constantly during it's flight.
Blazers work well because they were designed to create more drag than standard vanes due to the rake angle mixed with the plastic thickness. For their weight, they create more drag than standard vanes. They are also stiffer, which makes them work great in a Whisker Biscuit style rest. Stiffness also allows them to vibrate and flutter less at high speeds like the older vane styles do. Vibration causes more drag and noise and is very hard to design a stability formula for, since there are so many variables.
At today's speeds Blazers work great. At slower speeds, and as the arrow decelerates, they might not work so great. Because of this, I have never told anyone with a slow bow to use Blazers (until I do some lower speed tests). With the increase in drag, and smaller size and weight, they allow for higher FOC on arrows than regular shaped vanes but...many shooters end up using lighter arrow points for greater speed. (Lighter points equals lower FOC, so its a vicious cycle. )
Bi-Delta vanes are a neat item as well. These vanes utilize several drag creating features while keeping the stiffness up. I think these vanes deserve more credit than they get. I describe them as a 6 fletch arrow using only 3 fletchings. They even sell a synthetic feather version that might be pretty cool.
I shot Bi-Delta's in the early 90s. I have not tried their fake feathers yet. Not sure they would work better than real feathers or regular vanes though. Bi-Delta makes vanes in several sizes and shapes. They might do even better now that average arrow speeds are higher than the early 90s. My plan is to test them on the new headhunter style turkey broadheads this summer.
FOBs are a neat breed on their own. I like their modern spin on aerodynamics, but am not impressed with their weight and the overall drag that they create. The outer circle does some amazing things for stability, but I'm not sold yet on the weight so far out from the arrow. My mind says it will create more stability, but I need to do a few tests. In aeronautics, weight further out from the axis is good for some things and bad for others.
Having a larger frontal area than most regular fletched arrows, and around the same wetted area will make for some neat drag numbers. I have not played with them yet. Hopefully I will this summer. I'm really looking forward to testing them.
If you are interested- one of the neat things about encircling the fins is that it usually makes using a smaller vertical fin and sometimes save weight. (engineering nightmare though- involves stiffness and weight comparisons)
So far, to my testing, feathers work well because they work good at many different speeds. This is better than plastic vanes and their 1 speed. At launch, with the higher speeds, they compress, dropping overall wing chord a little and create less drag. Once launched and in flight, they spring outwards and expand a little, and loosen up, causing more overall drag and therefore more stability at the slower speeds. That is from my theories and testing so far. They are light weight, yet have good surface area and thickness. They seem to work good, and are fairly durable.
I have a set of aluminums that I fletched back in 92 that I still use today. A buddy of mine is using feathers on his aluminums right now during winter league that are so badly beaten and fluffed out that they look like a dead crow on the side of the highway. He's getting groups that are just as good as the rest of us.
I've seen people get good results with cutting bad parts out of their plastic vanes, but I've heard them scream like a banshee as they fly. Feathers just seem to get more of a SHHHH! sound as they age. By the way- I've seen crappy feathers in use and can tell you- there are some feathers that should not be used as fletching.
Watch out for moths! That seems to be the number one durablity issue of feather fletched arrows around my house.
Shooting in wet weather with feathers does kinda suck. To their credit, I've shot wet feathers with good results. Dry them a little by waving the arrow in the air, and fluff them up a bit. They still work OK. I've seen people Saran Wrap their fletchings before heading out in the rain.
I like feathers. I use feathers on my hunting compound and recurves. I'm shooting vanes on my target compound. Not sure why. Indoors might be the place they work best!
BTW- One of the coolest things you can do with feathers is to kill a turkey with an arrow fletched with turkey feathers from a previous kill.
I need to rewrite my paper when I get some good info on FOBs.
Note- I know I left some things out, simplified others and just plain forgot about even more things, but this is a simplified version of a long drawn out paper.
Hopefully someone enjoys all this besides me!
Your mileage may vary, void where prohibited. You have the right to disagree to anything. You have the right to enjoy green popsicles and Wednesday afternoon newspapers. These notes may contain thoughts and opinions by poster. They do not have to be your thoughts and opinions, but you may consider them for yourself. Dont try the experiments at home unless you take full responsibility for yourself and the death of the Bee, and the possible loss of your arm or sight or life.
February 19th, 2010, 03:07 PM
I forgot to note-
A target arrow basically has no wings, but a broadhead tipped arrow does have wings. Short, stubby wings way at the front with an "aft of wing" balance point. This is one of the reasons why it can be harder to tune and stabilize a Broadhead tipped arrow. The closer to the tip that you can get the balance point, the more effective the fletching will be and the smaller they can be. It takes much more force to move a shorter lever arm than a longer one. The bigger the wings, the more drag that is needed at the tail to stabilize.
Target point tipped arrows can get away with hardly any fletching at all. One friend of mine uses three 1 inch vanes on his target arrows. He does have a perfect release though....
With the want for higher FOC and higher speeds, many have chosen to go with mechanical heads over standard broadheads. This is because broadhead blades create a pressure differential (lift and drag) as they spin in the wind, progressively altering the AoA of the "wings" and forcing the arrow to "plane" off in a different direction than usually wanted by the shooter.
We are forced to work with 27 to 30 inch arrows because of our draw length. Some of the figures change drastically if you shorten the overall arrow. Some amazing work was done in the 70's and 80s with crossbow bolts, and even on regular sized bows using very short arrows (around 6 inches) launched like regular length arrows, but not using a rest. These were actually nocked by the point onto a 2 string bow and the trigger release snapped onto the rear of the shaft. Some of them even had fletching that was more like today's FOBs than fletching.
One argument I also forgot to note-
Target arrows have been likened to a tailless aircraft. For most of my work, it was easier to use the wingless idea, and then use broadheads as a wing when needed. Both ways work- to balance a tailless aircraft, you place the FOC far forward of the wing to get the most stabilizing arm that you can. One even more interesting point is to think of a broadhead tipped arrow as a Canard- small tail in front, large wing in rear. The math still agrees most any way you put it though.
There is a whole argument about the shape of an arrow point as well, but I'll save that info for another time.
This stuff can get complicated!
February 19th, 2010, 03:11 PM
February 19th, 2010, 04:43 PM
pretty technical but good stuff....I think i understand most of it
Question for you. I am in the process of changing arrows and I'm begining to experiment with vanes to see which will work best. I shoot heavy arrows, 2315 aluminum with a 125 grain original muzzy 4 blade broadheads. I also use a WB rest. I used to use blazer vanes or Fusion vanes on carbon arrows but I was thinking I would want to go to a longer vane,,,maybe 3 inch or 4 inch. You noted that the larger the broad head the more drag you need on the back end of the arrow to get good arrow flight...that makes perfect sense to me. Will the weight of the arrow shaft make a difference; that is does it stand to reason techincally that a larger vane is needed for heavier arrows?
February 19th, 2010, 05:24 PM
As with all things, there are more things at work than what is on the surface, but here's my thoughts-
Originally Posted by goathollow
My Answer- No. A heavy arrow shaft will not require more fletching area than a lighter weight shaft.
Why- Unless you are using the tapered or extra forward weighted arrows (they make those) most any bare shaft will still balance in the middle of the length.
Deeper Yet- Some of the demons at work can be the speed difference of a lighter vs. heavier shaft from your bow. Heavier shaft flies slower, needs different stabilizing properties than a lighter, faster shaft.
Also, the larger your fletching, the heavier you need to make your tip to compensate for fletching weight if you want a good FOC....so you can use smaller, lighter fletching..... (DO YOU SEE A TREND HERE?)
Even Deeper- If you really want to complicate things, blades with vents in them can be even more of a nightmare for drag and stability issues. But they are effective for creating lighter heads with large cutting diameter. (That gets us back to the accuracy vs speed debate)
Really, the only reason to go with larger fletching is if the broadhead is large. There is an old saying that you "Never use fletching smaller than the blades of your broadhead." Pretty good guideline.
There was also one that said "Use the same number of fletchings as you have blades on the tip." This one has some deeper things at work, and might not be as true as the other guideline. Good guideline though.
To a certain point, the heavier the broadhead is, the less you really need large fletching. This is a product of the FOC being higher.
By the way- the more I look at the science of arrow flight, the more I want to go with small but heavy 4 blade heads and 4 fletch arrows.
Now I'm looking for 4 blade 200 grain broadheads with 1.25 inch cutting diameter and really stiff, but light arrows.......
Now do I put feathers or vanes on those arrows?
May 16th, 2010, 12:31 PM
I have and still do try varying the point weights between 100 and 125 grains to see if it makes a difference. It seemed to make no difference on my compound out to 30 yards, and not really noticeable out to 40 yards. Big difference after 45 yards and incredible difference after 50 yards.
With my recurve I am shooting 100 and 125 grain points, field and broadhead, with 30" 1816's and 30" and 31" 1916's XX75's. I have like 20 plus arrows in my quiver and I just pull one out and shoot. I havn't noticed any difference, and I think it's because I don't shoot that well, "yet". I don't group arrows much at 10 yards, and I try not to group broadheads at all, (although I did cut one 1816 in two last time I shot). I'm trying to keep myself from shooting farther than 25 yards when I practise because after 10 yards I suck. I want to know which spine will work best for me. I'm thinking I would like a heavier point than 100 grains to get more momemtum on a slower arrow than one from a compound to aid in penetration. And I don't even have the shafts yet for my flu flus. They should arrive tomorrow, 2016's full length.
Now part of this quest coincides with yours. Save gallon milk cartons. You can fill them with a little sand, attach a short rope, and have someone throw them into the air while you fling flu flus their direction. That's practise for duck hunting on the wing. Where I hunt white tail deer, I have very good duck and goose hunting. Hopefully I will increase my accuracy/skill with my recurve with practise, practise, and practise this summer. Being able to shoot at the birds when I am deer hunting would make it oh so much more fun.
Now for the important question, feathers, secondary feathers to be exact, a little less stiff than primary feathers, will they work for flu flus. I only shoot so many turkeys and have a limited amount of feathers. Just bought a left wing clamp and that will double my supply. And come fall I'll save the goose wings as well. But until then I am going to be using secondary turkey feathers. Is stiffness, or the lack thereof an issue? I need a killing range of 30 to 40 yards maximum, and then I want my arrow to stop in its tracks and safely return to the pickup zone.
May 20th, 2010, 01:07 PM
Trying different point weights is a good way to change spine a little, but most people notice more change comes from having longer arrows or shorter arrows than 25 grains on the tip. Keep testing, its the only real way to match your release and bow with arrows.
At this stage in the game, dont worry about having to have heavier tips for increased penetration at distance. As a beginning bowhunter, try to limit yourself to 30 yards or less. Even a 25 pound bow at 30 yards has killing power with 1916s.
From your numbers you posted, Im guessing you are shooting a 25- 30 pound bow?
1916's are stiffer than 1816's but not by much.
At this point, it would be best to just continue shooting until you are grouping at 20 yards.
At that point, you can bareshaft test for spine, or test several different arrow/point combos.
I was just shooting a 25 pound recurve last night and had a strange thing happen. The stiffer spined arrows were grouping better than the correctly spined arrows.. I need to solve this mystery.... Proves there is no 100% correct way of matching spines with bows.
The gallon jug thing- I've used them before with some sand and "GREAT STUFF" expanding foam. Tie a string onthe handle and you can really whip the jugs into the air!
Use secondary feathers. They work just fine on FLU FLUS. They lay down longer after the launch than regular wing feathers, but create more than enough drag. If your using 2016's on a 25 pound bow, you need them to be at least 31 inches long to approach correct spine weight.
Circular fletching works best with secondaries, but standard helical wokds fine.
You can also use pieces of leftover primaries to make flu flus. Just splice them together and fletch helical.
A hint on grouping arrows. Shoot at 20 yards distance, aiming at a sheet of cardboard with a single 1 to 2 inch dot in the center. Pick one set of matched arrows to shoot until you start grouping. By shooting different spined arrows, you are creating confusion in the aiming center of your brain. Without thinking about it, you are trying to calibrate your aimer. If the variables are different each time you shoot, there is no control to base your aimpoint on for the next shot. This can mean a zillion more required shots to get better.
The matt color of a large piece of cardboard with a single aimpoint in the middle will help you concentrate on the bull with less distractions.
May 20th, 2010, 05:07 PM
A very simple thing to increase the leverage of the fletching is to move them back closer to the nock. The standard distance between the nock and fletching is about 1 inch, that came from the clearance needed for finger shooters. Most modern shooters are using a release aid, with a release you can move your fletchings back 1 inch. That's a significant improvement in leverage.
May 20th, 2010, 05:11 PM
What are your thoughts on arrow straightness? There are significant price differences between .006 and .002 arrows?
May 20th, 2010, 07:40 PM
Good (interesting) thread. Thanks.
May 21st, 2010, 02:30 PM
Greg- I just found a paper I wrote on my findings of arrow straightness and accuracy relationships. I will try and post part of it here soon.
SPOILER ALERT- I did find differences
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