Author Topic: Question on fletching theory  (Read 773 times)

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Offline Badger

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Question on fletching theory
« on: October 14, 2017, 05:45:58 pm »
    Suppose you had a stiff fletching .01 thick and 3/8" high X 2" long, it seems it would cause little drag as long as the arrow was going straight but have good influence anytime it wandered off straight and bring it back to straight quickly assuming good point weight. I think I have been making my fletching to short in height and length and too thick. It would seem we only need drag when things aren't going well otherwise. 

Offline willie

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Re: Question on fletching theory
« Reply #1 on: October 16, 2017, 01:55:26 pm »
Quote
It would seem we only need drag when things aren't going well otherwise.

from working with boats and rudders quite a bit, I would say you need enough steerage to keep thing going well at the lowest speed of the trajectory.

Offline avcase

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Re: Question on fletching theory
« Reply #2 on: October 17, 2017, 09:54:40 am »
According to the rocket builders, the most efficient vane is rather tall and short. The most efficient cross-section is an airfoil because the job of the vane is to provide a counteracting lift. An airfoil does this very efficiently as long as it isnít misaligned so far that it stalls.

But, with natural materials, this isnít so easy to do, especially using feathers. I think the Turkish Flight arrow fletch profile is a pretty good compromise where feathers are concerned. It would require a very stiff feather to go much taller and shorter without fluttering.

Alan

Offline Badger

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Re: Question on fletching theory
« Reply #3 on: October 17, 2017, 03:38:45 pm »
   I am really not sure when I started the post exactly what I was trying to say but basically I have always thought of the fletches as something I wanted as little of as possible. I am now starting to think studying them might put them to better use. I don't believe the short low fletches can get the arrow to respond as quickly as needed. Light arrows will slow extremely rapidly when they are not in line.

Offline DC

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Re: Question on fletching theory
« Reply #4 on: October 18, 2017, 09:22:58 am »
Has anyone ever tried a different method instead of fletching? I don't know, maybe dragging a ball of fluff or something. Also once the arrow flight has stabilised, what can happen to disturb the flight?
Vancouver Island

Offline avcase

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Re: Question on fletching theory
« Reply #5 on: October 19, 2017, 09:52:46 am »
One year, one of the Flight archers shot these very short arrows with a long overdraw device called a majra that resembles a tube that was split in half lengthwise. The arrow is nocked to the string and the majra is drawn back with the arrow. He was using a modern bow and very short graphite arrows with no fletching and a heavy point. They seemed to fly pretty well and I believe landed over 300 yards away. His regular length feathered arrows didnít go quite as far, although they were also heavier so it wasnít a completely fair comparison.

Once an arrow is stabilized, it is continuously being forced to change its direction due to the curved arc of its trajectory. There are also atmospheric disturbances that occur. The wind a couple hundred yards above the ground is usually different than on the ground where the arrow is launched. Iíve seen Flight arrows do a little dance after they initially stabilize as they encounter turbulence or layers of changing wind direction.  We often find arrows pointing in unexpected directions where they land. Sometimes even pointing the opposite direction that they should have been travelling.

Alan

Offline sleek

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Re: Question on fletching theory
« Reply #6 on: October 19, 2017, 01:11:09 pm »
Longer is always better. Things move faster through a fluid the longer they are.
Tread softly and carry a bent stick.

Dont seek your happiness through the approval of others

Offline willie

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Re: Question on fletching theory
« Reply #7 on: October 19, 2017, 01:47:56 pm »
I was looking for info on laminar flow, (which could be a good thing when designing an arrow for flight), and found this report that has some interesting observations about fletching choices. Are the gas-pro vanes  being used in the non-primitive classes?

 http://www.sciencedirect.com/science/article/pii/S1877705813010680#

Offline Del the cat

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Re: Question on fletching theory
« Reply #8 on: October 20, 2017, 11:35:52 pm »
I was looking for info on laminar flow, (which could be a good thing when designing an arrow for flight), and found this report that has some interesting observations about fletching choices. Are the gas-pro vanes  being used in the non-primitive classes?

 http://www.sciencedirect.com/science/article/pii/S1877705813010680#
Another "scientific" article written by someone who doesn't understand what the Archer's Paradox is....  >:(
Del
Health warning, these posts may contain traces of nut.

Offline avcase

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Re: Question on fletching theory
« Reply #9 on: October 21, 2017, 11:08:31 am »
I was looking for info on laminar flow, (which could be a good thing when designing an arrow for flight), and found this report that has some interesting observations about fletching choices. Are the gas-pro vanes  being used in the non-primitive classes?

 http://www.sciencedirect.com/science/article/pii/S1877705813010680#

I feel the research these guys are doing in the wind tunnel is pretty well done. It gives some indication of the effect of arrow vibration on drag, which can be pretty significant. One thing I donít understand in this report is why one type of vanes has such a dramatic effect compared to the other. I guess it may have to do with vibration from fluttering, but it is just a guess. I am not aware of anyone who tried Gaspro vanes in flight shooting. The king of vanes used for Flight archery is another type of very stiff Mylar vane that does not have a curled shape.

Alan

Offline Badger

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Re: Question on fletching theory
« Reply #10 on: October 21, 2017, 01:08:01 pm »
   Allen, has anyone ever dried wood vanes. I made a couple the other day and I liked the way I was able to work it. and shape it. Not so sure how well it would come out of the bow though. I am thinking an offset string might remedy that.

Offline willie

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Re: Question on fletching theory
« Reply #11 on: October 22, 2017, 01:13:00 pm »
Quote
One thing I donít understand in this report is why one type of vanes has such a dramatic effect compared to the other. I guess it may have to do with vibration from fluttering, but it is just a guess.
Seems like a reasonable guess, Alan. The spinwing rotation rates are along the order of 4800 RPM @ 150 FPS, as reported in an associated study    https://www.researchgate.net/publication/235908721_Aerodynamic_properties_of_an_archery_arrow
while the gas pros were reported to not have any rotation in the wind tunnel.  Hope it doesn't take near that much rpm to add stability to a well balanced flight arrow.


Offline avcase

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Re: Question on fletching theory
« Reply #12 on: October 23, 2017, 09:08:02 am »
Less than 1000 rpm should be more than sufficient. 400-500 rpm should be enough to keep the arrow from bobbing up and down as it realigns itself to a constantly changing direction of travel.  I am not sure how much of an effect this will have on laminar Vs. turbulent flow around the arrow. The model I was playing with always assumes turbulent flow. My real arrows seem to do about 20% better than the simulation and I figure that this might be due to the assumption that the arrow is always 100% turbulent.

It seems one is probably better off always insuring turbulent flow for a target arrow.

Alan

Offline JNystrom

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Re: Question on fletching theory
« Reply #13 on: October 23, 2017, 01:39:43 pm »
Interesting tech talk about fletchings! Just popped in to my mind that we haven't talked about two fletch arrows. So the arrow would be fletched only with 2 feathers. Not on opposite side, but on their "original" place, only the third missing. A fletching at say, 10 o'clock, the second at 2 o'clock. I heard that Monus uses this method of fletching and well, has succes. Next time you hit your arrow and break a fletching, just rip the rest off and shoot a perfect flight arrow! Lol...
In case this is proved to be complete nonsense, i blame Mikke (m.reinikainen atleast in paleoplanet) :D.

Offline avcase

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Re: Question on fletching theory
« Reply #14 on: October 23, 2017, 02:33:14 pm »
   Allen, has anyone ever dried wood vanes. I made a couple the other day and I liked the way I was able to work it. and shape it. Not so sure how well it would come out of the bow though. I am thinking an offset string might remedy that.

Steve,
Iíve never tried wood vanes. I believe they used to be used on crossbow and ballista arrows. I think I would try bamboo. Tonkin cane would probably be able to take some impact if made thin. I think it would be a lot like the vanes made from horn.

Alan