Main Discussion Area > Flight Bows
FOC, center of pressure and performance
Badger:
This is a good conversation, I am going to pour my heart out archery fashion.
One of the reasons I am thinking of going toward longer bows, longer arrows and more energy storage is basically to compensate for inadequacies in my arrows and release techniques for clean arrow flight. I am not so sure about the longer arrow but I know heavier arrows carry much better and are more forgiving. The greater potential I believe is still in the shorter arrows.
One thing that I have only recently appreciated the importance of in recent years is our ability to lower hysteresis in wood bows. The lighter you arrow gets the more significant this becomes. Normally a very well built self bow with a little reflex would usually hit around 172 fps at 10 grains per pound, by controlling set and lowering the hysteresis that number can suddenly jump into the 180's with a bow of identical unstrung profiles. This won't happen every time but if you get everything right you will get some of these super shooters. When it comes to light arrow shooting the lower hysteresis is even more significant and can add over 30 fps to a 200 grain arrow, that might give you 100 yards. I am pretty sure 50# wood bows will eventually hit 450 yards. With the longer arrows and bows I am hoping for shots in the 375 to 380 yard range. Finding a place to practice often, at least a dozen times a year I think would help immensely.
willie:
THE ONES YOU CAN SEE LEAVE vs. THE ONES YOU CAN'T
Badgers observation and comment seems sensible. The short reason is of course, "aerodynamics". The links posted earlier seem to categorize drag values as being highly dependent on whether the airflow past an arrow is considered "laminar" or "turbulent". For a look at the desirable low drag laminar flow around a point, see the pics in
http://sci-hub.bz/10.1177/1754337111430569
Also of note is the assertion that a typical arrow shaft has air flow that is neither laminar nor turbulent, but transitional, (primarily because of its diameter to length ratio). Although airflow may start out as laminar, there appears to be an increasing amount of drag caused by growing turbulence, the further down the arrow shaft you look. The distance from the point that this turbulence begins, and when it occurs during the arrow's flight could be enough to separate the winners from the losers.
The tradeoff/strategy Badger mentions, heavier arrows vs lighter arrow, certainly could be viable on account of the ability to launch a heavier stiffer arrow more consistently. Yaw or angle of attack is a large predictor of point drag when the flow is considered laminar. In this study, after about 3 degrees, it is essentially the same as if the flow was turbulent. See graph 7
https://www.researchgate.net/publication/241124001_Aerodynamic_properties_of_an_arrow_Influence_of_point_shape_on_the_boundary_layer_transition
For whatever reasons turbulence forms (and there are a few more like surface smoothness, wind gusts, etc.), It is unclear (to me) how easy or hard it is for turbulence to subside, once the smoother flow has been disrupted.
avcase:
WIllie,
I haven’t run across that article before. That’s a good one that I will have to read through carefully. I thought the comment about the observation of arrow vibration induced by aerodynamic turbulence was interesting.
I have found a trend that shorter arrows do better than longer arrows with my footbow. These also have a very smooth and polished outer surface. In this case, the arrows are released with a mechanical release, which eliminates a lot of the tuning issues that come with a finger release.
On the other hand, the split cane arrows I posted about earlier are far from being smooth or polished.
Thanks!
Badger:
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.
Del the cat:
--- Quote from: DC on September 25, 2017, 03:27:49 pm ---I think that it's the speed of the arrow rather than the poundage of the bow that determines the spine. In order to get to say, 180 fps the arrow has to accelerate at a certain rate. There is more involved than just bow draw weight. I believe that if you have a 70# bow that has a dry fire speed that is the same as a 30# bow the same spine arrow will work in both.
--- End quote ---
Exactly... it's acceleration that flexes the arrow. I've had 50# spine arrows shot from 120# warbow no prob'...
Mind when I mentioned it on a FB warbow thread I had some bloke who couldn't understand it calling me an idiot ::) . It's sad 'cos the guy didn't even realize how little he knew !
Del
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