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Author Topic: Spine/paradox etc.  (Read 3981 times)

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Offline DC

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Spine/paradox etc.
« on: January 20, 2019, 11:53:53 am »
We all know that the arrow bends around the bow as it's shot. Assuming a properly spined arrow, what starts it bending? Is it just acceleration or is it hitting the bow that starts it?
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Offline Pat B

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Re: Spine/paradox etc.
« Reply #1 on: January 20, 2019, 02:25:18 pm »
The push of the string then the inertia against the weight of the arrow causes the arrow to bend. I'm sure some drag is caused by the arrow touching the bow. The initial direction of the inertia is the direction the arrow will go.
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Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline DC

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Re: Spine/paradox etc.
« Reply #2 on: January 20, 2019, 04:38:36 pm »
Has anyone got a link to a slow mo video that clearly shows the arrow lifting off the bow and going cleanly around it. I've looked at a bunch and the camera angle is wrong on most of them. I'm not disputing this, I just noticed that the arrow pass on my bows is always scuffed up and it just got me thinking. It could be getting scuffed from drawing the bow though.
I'm thinking of making a jig that would compress an arrow lengthwise to see how much force it would take to start bending the arrow. I think it was you PatB that recently said about how much force it would take to start an arrow bending and how easily it would bend after that. If that's the case and the bow has enough power to start it bending might it not continue bending(cause it's easier now). Maybe the string rolling off your fingers causes a little sideways flick that help start it bending.
I'm waiting for some tung oil to dry so I'm at loose ends here ;D ;D ;D
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Offline aaron

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Re: Spine/paradox etc.
« Reply #3 on: January 20, 2019, 07:43:12 pm »
videos in slomo seem (to me) to show that the initial sideways bend has alot to do with the string comming off the fingers. As the string moves from the knuckle crease and off the end of the finger, it moves laterally and the knock goes with it.
Heres a guy in scandanavia with a phantom camera. https://www.youtube.com/watch?v=cP8XVW4H90g
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Offline Pat B

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Re: Spine/paradox etc.
« Reply #4 on: January 20, 2019, 07:52:33 pm »
DC, I was going to suggest Googling "Archers Paradox". I'm sure you'd find lots of examples there.  The video Aaron posted shows it well.
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Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline TSA

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Re: Spine/paradox etc.
« Reply #5 on: January 20, 2019, 08:36:34 pm »
this is a video i have posted a few times.
IMHO the best one out there.
what i really like, is how easy it is to see in the well tuned setup, that the arrow does not touch the bow at all- bar the first inch or two upon release.
That naturally leads to questioning the theories about how a tapered shaft " clears the riser better"

https://www.youtube.com/watch?v=96KGWC0PB6s
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Offline joachimM

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Re: Spine/paradox etc.
« Reply #6 on: January 21, 2019, 10:02:05 am »
TSA, good video. Still, that seems to be a centershot bow, no?
J
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Offline Del the cat

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Re: Spine/paradox etc.
« Reply #7 on: January 21, 2019, 10:49:07 am »
I believe the string slipping sideways off the fingers starts the sideways motion at the nock and the acceleration then causes the arrow to bend.
There is some slo-mo vid on my Youtube chanel... mostly flight arrows which are a underspined because of the low weight and very low point weight.
"shot 2" shows the start of the flexing nicely :)
https://www.youtube.com/watch?v=ZAHRLIekjVU
https://www.youtube.com/watch?v=8iTWSITIHR8
There is also some footage from the shooting machine...
https://www.youtube.com/watch?v=SOcrM7FMQSI
Del
« Last Edit: January 21, 2019, 10:56:41 am by Del the cat »
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Offline DC

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Re: Spine/paradox etc.
« Reply #8 on: January 21, 2019, 11:09:13 am »
I'm still going through the videos trying to see what is happening. I'm changing my mind on a few things. One is when the arrow is too bendy. I previously thought that with the arrow bending too much it just gets launched sideways. What it's looking like to me now is that it bends too much and recovers soon enough for the rear of the arrow to smack the handle. This kicks the back of the arrow off to the left. Del's second video, second arrow shows what I think I'm seeing. I noticed the same thing on Puujousi's (Tuomo) videos. I thought this is what happened when the arrow was too stiff. Some of it is very puzzling as two things can cause the same results. Like poor release can seem to mimic low spine. This will keep my brain ticking over :D
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Offline willie

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Re: Spine/paradox etc.
« Reply #9 on: January 21, 2019, 07:33:10 pm »
always an interesting study of a number of factors that make for a well tuned set up.

 Joachim, Tuomo has quite a bit of footage uploaded to his channel








« Last Edit: January 22, 2019, 05:40:54 pm by willie »
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Offline Tuomo

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Re: Spine/paradox etc.
« Reply #10 on: January 21, 2019, 11:17:25 pm »
It is great that my slow motion videos have still some use! I tried to film every kind of different situations – and I think that regarding DC's question, you can find the answer there.

You can find all the videos from here:
https ://www.youtube.com/channel/UCmVczwYUfq6sQQjCmKd2q5Q

If I could borrow the camera again, I would make some flight archery research. For example, release has a very big impact for arrow flight – see these very light flight arrow videos, with good and bad release:
https ://www.youtube.com/watch?v=PuhFI55NT3Q
https ://www.youtube.com/watch?v=GPHJKqwvNVc
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