Arrow rotation on leaving the bow

[Shirt]

OK, because I'm bored and shooting related stuff beats work...

At two metres from the bow, my arrows appear to have rotated approx 60 degrees from when they started. What I quite like is that this is consistent amongst them.

a) does this imply that the shot is relatively consistent, or would fluctuations be too small at this distance to tell anything?
b) given that these particular arrows have been fletched as near as dammit to perfectly straight as I can get (EP16s) why are they rotating?

[Orinoco]

Not having an answer I did a quick search. Not sure who owns this page but there is more physics here than you can shake a stick at! Don't know if it addresses your question though....

http://homepage.ntlworld.com/joetapley/

Actually, just notice there is a whole section on arrow spin, which does seem to hint that some arrows will not spin. I guess that with the arrow bending during flight (archer's paradox), no matter how straight you fletch your arrows they will at some point present a surface to the air they are passing through and so generate spin. I suppose while you have an odd number of vanes, spin will always be induced because the surfaces presented can be uneven. So would an arrow with an even number of vanes be less likely to spin?

Also, surely some spin is good to help even out imbalances in the arrow's mass?

Anyway I shall stop waffling now.

[pHz]

which way have they rotated and are you RH or LH ?

slainte : rob

[Shirt]

I'm right handed, they've rotated counterclockwise. Sorry, should have put that!

[Ffish]

Originally Posted by Orinoco

Not having an answer I did a quick search. Not sure who owns this page but there is more physics here than you can shake a stick at! Don't know if it addresses your question though....

http://homepage.ntlworld.com/joetapley/

umm, the clue is in the title - it's a fair guess to assume that the owner of that page is one Joe Tapley

I'm sure he'll be along shortly to explain why the arrows rotate, his knowledge of the physics of archery is far greater than mine.

[joetapley]

Originally Posted by Shirt

OK, because I'm bored and shooting related stuff beats work...

At two metres from the bow, my arrows appear to have rotated approx 60 degrees from when they started. What I quite like is that this is consistent amongst them.

a) does this imply that the shot is relatively consistent, or would fluctuations be too small at this distance to tell anything?

Unless a shot was exeptionally poor I think I would go for the doesn't mean anything option.

b) given that these particular arrows have been fletched as near as dammit to perfectly straight as I can get (EP16s) why are they rotating?

All arrows will rotate to some degree (ha de ha). Asymmetry in the flexing of the shaft and the geometry of the fletchings and nock will generate some drag torque rotating the arrow.

[Orinoco]

OK didn't look at the address bar until after I wrote my reply ... but still, interesting site!!

"All arrows will rotate to some degree (ha de ha). Asymmetry in the flexing of the shaft and the geometry of the fletchings and nock will generate some drag torque rotating the arrow."

That's what I meant

See, being a science teacher does finally have a use!!!