longbow

[ozzy]

g'day all

i have just bought a longbow from the states it is a handmade bow its specs are 58"55#@26" it is not centre cut it is just shot off the hand my question is because the bow is not centre cut i have to use a weak spine arrow than i would if it was centre cut is this correct

cheers mick

[g_r]

yes sir, the further out from center, the stiffer the arrow acts, the weaker spine you need.

Try Stu Millers calculator, itll get you in the right region, if you want.

[greybeard]

Hi Mick,

The following link should explain it to you.

http://en.wikipedia.org/wiki/Archer's_paradox

The following AMO charts will give you a starting point.

AMO Spine Selection Charts..doc

(123.5 KiB) Downloaded 157 times

Daryl.

[GrahameA]

Morning G_R

the further out from center, the stiffer the arrow acts, the weaker spine you need.

I would dispute that.

read Jim's notes http://www.ozbow.net/phpBB3/viewtopic.php?f=2&t=4836

[perry]

COOL a disagreement
The further a bow is cut from centre the more an arrow needs to paradox to clear the bow - you will need a lighter spined arrow.

Sorry Grahame being mischievous

Where Grahame's point comes in is that this is easily achieved if your arrow spine is in the ballpark to start with by manipulating mass of points or less so nocks.

By increasing or decreasing the forward or rear mass of the arrow you are effectively altering the Forward of Centre. More weight up front the arrow spine behaves weaker , less weight up front the arrow spine behaves stiffer. I have strong veiws based on years of experimenting that 15% FOC is a minimum for superior arrow flight and that FOC in excess of 20% is desirable.

regards Jacko

[ozzy]

thanks guys

daryl i have been after a wood amo spine chart like that for ages thanks

cheers mick

[dmm]

Morning G_R

the further out from center, the stiffer the arrow acts, the weaker spine you need.

I would dispute that.

read Jim's notes http://www.ozbow.net/phpBB3/viewtopic.php?f=2&t=4836

I get a database error when trying to follow the link to archerytalk.

My simple understanding of the archers paradox, is that the back of the arrow closest to the string (power) tries to accelerate faster than the front of the arrow. This causes the arrow to try to bend to accommodate this rush from the back.

If the arrow was shot true center, then this effect would matter the least, as the back of the arrow is pushing directly into the front.
If the arrow is more off set, such as shooting off your hand, then this affect will be more noticeable, and therefore it will be more important to have a arrow that can bend initially, and fly straight, rather one that cannot, and will shoot off to whatever side it is pointing.

+1 on Stu Millers spreadsheet. Much better than the Hoyt's charts I used to use.

[ozzy]

Morning G_R

the further out from center, the stiffer the arrow acts, the weaker spine you need.

I would dispute that.

read Jim's notes http://www.ozbow.net/phpBB3/viewtopic.php?f=2&t=4836

I get a database error when trying to follow the link to archerytalk.

My simple understanding of the archers paradox, is that the back of the arrow closest to the string (power) tries to accelerate faster than the front of the arrow. This causes the arrow to try to bend to accommodate this rush from the back.

If the arrow was shot true center, then this effect would matter the least, as the back of the arrow is pushing directly into the front.
If the arrow is more off set, such as shooting off your hand, then this affect will be more noticeable, and therefore it will be more important to have a arrow that can bend initially, and fly straight, rather one that cannot, and will shoot off to whatever side it is pointing.

+1 on Stu Millers spreadsheet. Much better than the Hoyt's charts I used to use.

picking up what you putting down there

[GrahameA]

Morning All

I get a database error when trying to follow the link to archerytalk.

That is probably because it is an old post, etc. A direct link http://www.archery-forum.com/showthread ... ight=spine

My simple understanding of the archers paradox, is that the back of the arrow closest to the string (power) tries to accelerate faster than the front of the arrow. This causes the arrow to try to bend to accommodate this rush from the back.

Yes - columnar loading - same effect as why columns bend when you placed a lot of weight on them.

If the arrow was shot true center, then this effect would matter the least, as the back of the arrow is pushing directly into the front.

No. The arrow will bend and if the amount is towards the bow (riser) then the arrow will hit. I have shot high speed videos of extremely stiff arrows being shot from compounds with drop away rests and the arrow whilst flexing only a small amount will take up a nose attitude during the launch due to, probably, nock travel. The same will happen conventional bows as the string does not follow a straight path.

If the arrow is more off set, such as shooting off your hand, then this affect will be more noticeable, and therefore it will be more important to have a arrow that can bend initially, and fly straight, rather one that cannot, and will shoot off to whatever side it is pointing.

"it will be more important to have a arrow that can bend initially" yes - but how do get that to happen?

With an arrow you want it strong enough so that it does not break under the launch loads - and spine is an indication of that. You want it to flex enough, amplitude, so that everything clears the bow. And then, because the arrow is vibrating, you want the rate of vibration, frequency, to be such that section of the arrow that is next to the bow is flexed away from the bow as the arrow goes past the bow. Spine is a good indicator of the natural frequency of a shaft as it is an indicator of the "spring constant" for the beam.

To finish off. Here is a case where the arrow spine is a tad wrong, soft. The arrow flexes enough so that that it clears the bow but the frequency is wrong and the end of the arrow collides with bow. http://www.youtube.com/watch?v=eoDNYLJcvrU

Sorry Grahame being mischievous

All good. You and I are reasonably aware of all stuff and it is good to talk about it - or at least it adds some spice to the day.

For those who want simple predictive values:
http://en.wikipedia.org/wiki/Roark%27s_ ... and_Strain
For those who want something a bit more complicated
http://mech.vub.ac.be/teaching/info/Ont ... oblems.pdf
For those who enjoy reading about such:
http://www.fpl.fs.fed.us/documnts/pdf1997/murph97a.pdf

[dmm]

This video is an interesting explanation.
http://www.youtube.com/watch?v=DgZWV3op ... re=related

Although he says a stiff arrow from a compound with a release aid doesn't need to bend.

I just hope
a) Stu Millers spreadsheet takes all this into account
b) If my arrows aren't flying optimally that I can tell without a high speed camera

[GrahameA]

Morning.

a) Stu Millers spreadsheet takes all this into accountThey are good enough for all intents and purposes.
b) If my arrows aren't flying optimally that I can tell without a high speed cameraYou can. This is an example of a mismatched arrow. http://www.youtube.com/watch?v=t8Obmz8b7jE Excuse it being a bit wobbly but it was shot handheld.

People have made thousands of arrow for thousands of years without truly understanding what was actually happening snd they hit the target.

Although he says a stiff arrow from a compound with a release aid doesn't need to bend..

Sounds good in theory and with a dropaway you do not need the arrow to bend however, I have two questions. a) How do you stop the arrow bending and still have something that is shootable, b) with an extremely stiff arrow how do you stop the longitudinal rotation (pitch) of the arrow due to nock travel, etc. In my opinion I would rather have the arrow flex compared to rotate.

[ozzy]

yes sir, the further out from center, the stiffer the arrow acts, the weaker spine you need.

Try Stu Millers calculator, itll get you in the right region, if you want.

g_r hmm dont really know about stu millers calculator i have doubts about it,it really hasnt worked for me in the past with my recurve...i dont know i might be using it wrong....in which more than likely i am... but coming back to the another question in stu's calculator in the centre cut measurement i take it that its taken from the centre of the string and limbs (as in the string lines up with the centre of the limbs and the measurement is taken from the centre of, to the outside (to the left cause im righthanded opposite if lefthanded)of the handle so i have googled for some spine charts and some say to use 10#below the recommended for bows that are shot off the hand with no centre cut some up to 20# less all these are for 125gr heads

cheers mick

[g_r]

ok, i dont really know about shooting of the hand. With longbows that had a small shelf my experience was that the further out the stiffer it acts.

Stus calc was three out of three times correct for me. I think relaese and personal form are e big point why some people get differing results. I have a very static relaese, dont know about you e.g. this might be the cause. On the other hand, its just another virtual gimmick, if in doubt always trust youreself more than anything like this.IMO

[dmm]

Stus calc was three out of three times correct for me. I think relaese and personal form are e big point why some people get differing results. I have a very static relaese, dont know about you e.g. this might be the cause.

I downloaded the Stu Miller latest calc the other day. You might be interested to know he has now added a variable for personal form.
It's a little unclear to me exactly how this works, but the instructions basically say use the calc, then if you test it in practice and it work, adjust the personal form number so that dynamic spine matches dynamic draw. This number should then stay constant for you unless your form changes/improves.

I just left it on 0 and it reads ike it always did

http://heilakka.com/stumiller/

[g_r]

ive used this feature too, for me its a -5 dont know if thats good or bad

[ozzy]

got an email today the bow is on its way and sorry gents i was wrong it has a shelf not much of one but it has a shelf

http://cgi.ebay.com.au/Handcrafted-long ... 3a573fb553
i know they are cheap but im trying them out to see if i like them
cheers mick

[Stickbow Hunter]

That bow looks alright Mick. If it was me with that poundage and draw I would buy a few 50 - 55# spine wood shafts (or arras) in either 5/16" or 11/32" and see how they go. You could also try one spine range above and below that and see which arras fly the best.

Jeff

[ozzy]

they are jeff

will see how they go might even grab a couple more in different poundage if they go alright

he seems to have sold alot to so they might go alright

cheers mick

[Dennis La Varenne]

Why do so many people on Ozbow have so much trouble getting their arrows to fly straight to the target??

I have never paid much attention to spinning other than to match a set of arrows. So long as they were within a 15 lb spine range they shot where I looked. Mostly mine were nominally overspined from 10 - 15 lbs, but sometimes underpined by 5 lbs.

I just don't understand all the grief.

[alaninoz]

In my case a properly spined arrow helps to compensate for my poor release - which I'm working to correct.

[Dennis La Varenne]

Alan,

Quite off topic, but could I suggest Howard Hill's instruction for what constitutes a good loose?

Pick up a suitcase by the handle using your drawing fingers - and just let it drop. Nothing else! That is what a good loose should feel like.

The wrist should be limp - quite literally.

Also, try drawing through the elbow of your drawing arm. Draw your elbow back until your drawing hand reaches your anchor rather than your drawing hand to your face, and keep a very light but consistent anchor contact - no heavy contact against the face.

With the elbow back, the drawing load falls back on your back muscles which will hold the bow at draw well enough.

Then, keeping the elbow back, just relax your fingers just like you dropped the suitcase. Keeping the elbow back will help prevent the drawing hand creeping forward and shortening the draw. The 'suitcase' loose will help stop any tendency to 'rip' the drawing hand away from the face anchor.

It is so simple that it is difficult!