About arrow points - necessity or useless?

[avcase]

I feel the point shape is less critical than other factors for a high performance flight arrow. However, the ideal shape should resemble the rounded nose shape of a 747 jet airplane, but this may be a relatively small factor as long as it is nicely rounded over.  Sharply pointed shapes work best for supersonic projectiles, which is far beyond the speeds of the fastest flight bows.  One of the worst performing flight arrow shapes that I have experience with are arrows that have a very long needle-like sharp point.

I don't have a very good method to analyze the center of pressure with my Primitive flight arrows. I do a little better job of this with my non-Primitive footbow arrows, by observing how they sink and shoot underwater. I can do this with arrows made of carbon and stainless steel components, but not with an arrow made of Primitive materials.

Probably the best advice I can recommend is to mark all your flight arrows with a permanent serial number and keep a log of how the arrows perform with different bows and shooting conditions. I observed some interesting things when I started doing this. First, I found that I had two or three arrows that were consistently the longest flyers, even if shot from radically different bows using radically different shooting styles.  For example, I have one or two arrows that I found were used to set records for Modern Longbows 35 & 50lb), English Longbows(35 & 50 lb), and Primitive bows (35 & 50lb). Second, the arrows that matched the classic Turkish flight arrow geometry with the maximum thickness in the rear 1/3rd of the arrow were never my best performers. I have better luck with this shape if shot backward with the point where the nock should be, and nock where the point should be. Third, my high FOC arrows fly very consistent, but have not been the farthest flyers for whatever reason. They do seem to drill a deeper hole in the ground, but that is about it.  Fourth, it is very important to pay a lot of attention to the fletching. Thick turkey feathers are the equivalent air-brakes.

Alan

[JNystrom]

Great, thanks! I will try that.

[willie]

Hope I am not going too far off topic, as this  is not much about points anymore, but there are some good observations being shared in this thread about aerodynamics that I would like to follow up on. There might even be some erroneous statements also.  I have to question my own assertation that the Cp moves in relation to the CG as the arrow slows down. The lift and drag forces that act at the Cp on the lever arm are reduced as velocity diminishes, thus lessening the ability of the arrow to restore itself to efficient flight, if disrupted,  but I cannot see why the length of the lever arm would have reason to change.
 
A few different questions have been on my mind.....

1.  what is the gliding effect that JNystrom mentions?

2. why did the reproduction turkish arrows that Alan made, fly better backwards?

3. why do high FOC arrows nose dive more at the end of the flight?

[Selfbowman]

Well I would say do to  gravity and the heaviest part of arrow will have tendency to fall faster, the fletchings will create drag against the heavy end . What goes up must come down. I don't know about the rest. Arvin

[Jan de Bogenman]

I was wondering if this could be a reason to use a minimum of concentrated mass in the point. Its my experience that if shooting over the chrono, same weight arrows tend to be faster if having no steel arrow head. So it might influence acceleration?

[Del the cat]

Well I would say do to  gravity and the heaviest part of arrow will have tendency to fall faster, the fletchings will create drag against the heavy end . What goes up must come down. I don't know about the rest. Arvin

The mass of an object doesn't effect the speed at which it falls (in a vacuum), so it's only drag and position of the balance point that makes it fall point first. If the centre of mass is only just front of centre and you put the fletchings just behind the point it would fall nock first  
I say one arrow shot a few times that flew completely wild, veering sideways, nosediving the suddenly climbing again before eventually settling to a more normal flight on a path about 46 degrees right of the line of aim.
My guess was it's centre of mass was too close to the geometric centre (about 1/8").
It wasn't an arrow that I'd made.
Del