Main Discussion Area > Flight Bows
FOC, center of pressure and performance
Del the cat:
--- Quote from: Badger on October 04, 2017, 06:19:53 pm --- I am starting to think a key design feature on a flight arrow might be in it's ability to recover as fast as possible from release. I think Allen had some discussion on this a few years back. A 150 grain arrow can easily leave a 50# wood bow at 250 fps but will not tolerate any sideways motion without loosing most of its velocity. What qualities enhance rapid recovery from slight inconsistencies in release.
--- End quote ---
Yeah, it must be springy enough to recover quickly but not to resonate and keep oscillating, so it needs damping... maybe bamboo stuffed with Christmas pudding? ;)
Del
willie:
--- Quote ---maybe bamboo stuffed with Christmas pudding?
--- End quote ---
Have not tried the pudding yet Del, but I agree about the oscillations and dampening. A thread in the arrow section has a few links to interesting footage of arrows and darts in flight, focusing on those ocillations.
(the recent discussion and links start with Reply #26) http://www.primitivearcher.com/smf/index.php/topic,61394.0.html
I have been experimenting with primitive tapers on Atlatl darts. . The tapers I have tried are copied from darts found in melting ice fields in Yukon Territory that are between 3200 and 4500 years old. A good dart release is not easy, on account of the pronounced lateral displacement of the nock that an atlatl spur creates. Soft spines are required, stiff darts do not fly well at all, and tapering can change the location and timing of the oscillations quite a bit.
Badger:
I have thought about this same thing with the darts, I am not that good with darts but played around with them some and was amazed at how much difference the proper spine makes. I was able to throw a little over 100 yards with a not so hard throw once I got my spine figured out. You could visibly see it oscillate. Intuitively I would think that once they are on the right path the oscillations don't really help but there was no question that my softer spines took off and flew better. I think it was easier for a beginner to get a clean throw.
avcase:
Arrow flex is always a necessary evil with finger release and degree of non-center shot. A wiggling arrow experiencing a lot of excess drag in the early part of its flight, so it’s best to find ways to avoid as much as possible. When it comes to damping our vibrations, I don’t know what may work best. Big fletching helps, but adds lots of drag.
Once the vibration damps out, the air flow boundary layer should start to reattach and become laminar toward the front couple of inches of a polished arrow.
My best arrows are higher density at the point and nock, and light and stiff in the center. It seems like this should be worse for a shot that leaves the bow misaligned, because the arrow has high inertia for the fletching to overcome. However, this higher inertia should be better if we are talking about a “floater”. ;)
Alan
willie:
Alan, are you still describing your bamboo hex shaft arrows, where the outer skin on the bamboo is presumably denser than the interior?
--- Quote --- It seems like this should be worse for a shot that leaves the bow misaligned, because the arrow has high inertia for the fletching to overcome.
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The inertial force causing yaw?
I have been giving some thought to similar mass distributions, ie, heavier footings, both front and rear, or both, on some designs I hope to make soon.
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