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    Fletchless bolts (for repeating bows)

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    jake-owa

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    • Post n°1

    Fletchless bolts (for repeating bows)

    Post by jake-owa on Tue Nov 09, 2010 11:14 pm

    Are there any specs for fletchless type bolts for use in a hopper? I have a couple of small x-bows that I have been working on this problem with. I had a NASA buddy of mine direct me toward the flachette. This seems workable but after messing with grooves and weighting for a day I really didn't find any designs that jumped out as being better. At this point I have had best results with a few shallow grooves and a substantial forward weighting.

    Any thoughts or ideas on this subject would be much appreciated. Here's a shot of two flachette designs, I was modelling after the bolt looking one.
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    Basilisk120

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    • Post n°2

    Re: Fletchless bolts (for repeating bows)

    Post by Basilisk120 on Wed Nov 10, 2010 5:23 am

    everything old is new again. the top fletchet looks like one of the fletchless bolts from payne-gallways book. So yeah that would work. Sounds like you have the basic idea down. Weight out front and something to cause drag in back.



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    jake-owa

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    • Post n°3

    Re: Fletchless bolts (for repeating bows)

    Post by jake-owa on Wed Nov 10, 2010 2:30 pm

    Are there any design specs or standards that people use? Are there and fletchless bolts available for sale anywhere that anyone knows about?
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    Basilisk120

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    • Post n°4

    Re: Fletchless bolts (for repeating bows)

    Post by Basilisk120 on Wed Nov 10, 2010 3:57 pm

    I don't think there are any fletchless bolts for sale, at least none that I have seen.
    Here is the Dresden bolt from "The Crossbow" by Sir Payne-Gallwey. Another take on fletchless bolts.
    The basic premise is that the Center of Gravity has to be in front of the Center of Pressure for stable flight. I believe that holds true for everything that flys. The distance between the two is the control arm (or moment arm) on which the control surfaces can act. Basically the greater the distance the smaller the control imputs need to be.
    I believe that standard 10-12% FOC still works for good flight from Fletchless bolts. If some one wants a run down on what FOC (Forward of Center) is just let me know.



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    Basilisk120

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    • Post n°5

    Re: Fletchless bolts (for repeating bows)

    Post by Basilisk120 on Wed Nov 10, 2010 4:16 pm

    Had a simple idea for a basically fletchless bolt. Either use a little tape or some twine tied around the bolt were the fletching should be. Either should add a little drag (the twine will obvioulsy add more) to the end of the bolt and move the CP back.

    If you want to test stablity with out shooting the bolt. Tie a 3 to 6 foot string around the bolt at the Center of Gravity. The bolt should hang parrell to the ground. then Spin the bolt through the air, if it is stable it will fly straight. This idea comes from testing small model rockets.

    For those really interested how to calculate CP can be found at the NASA website



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    jake-owa

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    • Post n°6

    Re: Fletchless bolts (for repeating bows)

    Post by jake-owa on Wed Nov 10, 2010 7:14 pm

    basilisk120 wrote:Had a simple idea for a basically fletchless bolt. Either use a little tape or some twine tied around the bolt were the fletching should be. Either should add a little drag (the twine will obvioulsy add more) to the end of the bolt and move the CP back.

    If you want to test stablity with out shooting the bolt. Tie a 3 to 6 foot string around the bolt at the Center of Gravity. The bolt should hang parrell to the ground. then Spin the bolt through the air, if it is stable it will fly straight. This idea comes from testing small model rockets.

    For those really interested how to calculate CP can be found at the NASA website
    Aha, I remember testing my own rockets that way! Thanks for the reminder! My NASA buddy was just giving me the refresher in CP VS CG and it all makes perfect sense but the devil is in the details. A tiny aberration in weight or balance equals a tumbling bolt.

    That Dresden bolt design seems do-able, though with a regular target tip.
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    • Post n°7

    Re: Fletchless bolts (for repeating bows)

    Post by Geezer on Thu Nov 11, 2010 3:55 am

    Fletchless bolts for Chinese repeater: You might try glueing a pice of stout twine in a spiral around the back half of the bolt. I've seen something similar done with a very low (1/8 inch?) rib of feather, but I'll wager a bit of string would give you just a bit of spin without hanging up on the next bolt in the stack. Couldn't hurt to try it. Geezer
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    • Post n°8

    Re: Fletchless bolts (for repeating bows)

    Post by Ivo on Fri Nov 12, 2010 6:26 am

    There is a topic "Levers, cranks, and other spanning devices" that has a video of a magazine fed repeating crossbow called "Strelets" which uses really low profile helical vanes for stabilization of flight.

    PS: I don't have a computer right now other wise I would post the link, If you don't find it, perhaps one of the guys will post the video here.



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    • Post n°9

    Re: Fletchless bolts (for repeating bows)

    Post by GR-13 on Mon Nov 29, 2010 6:44 pm

    another fletchless design I have seen somewhere is fence airfoil, basically cone at the back end of a bolt. Though it does not cut but only adds drag when considering possible wound channel. Stiff metal fletch with razor sharp front edge that works as a broadhead - that is where gains are, in terms of stability, airdrag and game getting efectiveness.
    Yet another fletched design, suitable for repeat crossbows, involves soft bird feathers for fletching.
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    • Post n°10

    Re: Fletchless bolts (for repeating bows)

    Post by jake-owa on Mon Nov 29, 2010 11:27 pm

    Thanks for the thoughts guys!

    I have added metal tips with a long...what do you call it, tang? Anyway, I have the weighting down to where they shoot pretty straight with no fletching. I have done some grooving but it doesn't really seem to make a noticable difference to the ones that are properly front heavy.
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    Basilisk120

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    • Post n°11

    Re: Fletchless bolts (for repeating bows)

    Post by Basilisk120 on Tue Nov 30, 2010 3:21 pm

    Glad to here the bolts are shooting well for you. What are the specs on your bolts? and what is the weight of the points?



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    • Post n°12

    Re: Fletchless bolts (for repeating bows)

    Post by jake-owa on Tue Nov 30, 2010 4:58 pm

    They are 5" oak bolts with about 1 3/4" steel made from 1/4" stock. Not sure on the exact weight but I removed about half the material so...1.75X.24" divided by .5 whatever that weighs...

    I will put the next batch of tips on the scale and make a note.
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    • Post n°13

    Re: Fletchless bolts (for repeating bows)

    Post by Ivo on Fri Dec 03, 2010 2:22 am

    GR-13 wrote:another fletchless design I have seen somewhere is fence airfoil, basically cone at the back end of a bolt. Though it does not cut but only adds drag when considering possible wound channel. Stiff metal fletch with razor sharp front edge that works as a broadhead - that is where gains are, in terms of stability, airdrag and game getting efectiveness.
    Yet another fletched design, suitable for repeat crossbows, involves soft bird feathers for fletching.


    I believe the cone stabilizer is used on solid aluminum bolts for match target crossbows...air drag...no doubt there.



    The older version of the match dart/bolt looks to have had stabilizing grooves that faded into a cone at the butt of the barreled shaft...so it's technically a combo...cool.. cool, but does the cone really have to be the same diameter as the shaft? Dumb I know, but perhaps we can make it work?

    PS: Razor fletching...you know the good stuff! Very Happy Very Happy Very Happy



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    • Post n°14

    Re: Fletchless bolts (for repeating bows)

    Post by testhero on Mon Dec 06, 2010 8:24 pm

    Some of the Scandinavian bolts are carved as a single piece. Death bolts for whale hunting are in the Nordsmuseum collection carved from oak with a heavy tanged head being bound to the front. Target shoots for the poppinjay are identical to the Dresden bolt. Piston bolts for small birds have a simple cylindrical enlargment for the head and some illustrations, woodcarvings show fletched and unfletched piston bolts
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