Main Discussion Area > Flight Bows
FOC, center of pressure and performance
JNystrom:
I think the arrowhead discussion answered the questions, so let's make another topic.
Cp - center of pressure.
https://www.grc.nasa.gov/WWW/K-12/rocket/rktstab.html
Turkish arrows.
http://www.turkishculture.org/lifestyles/turkish-culture-portal/turkish-flight-arrows-554.htm?type=1
--- Quote from: avcase on September 07, 2017, 01:03:42 pm ---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
--- End quote ---
--- Quote from: willie on September 08, 2017, 02:24:55 am ---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?
--- End quote ---
JNystrom:
Avcase,
I personally have just started to keep a log of all flight shooting. I mark the arrow serial number, weight, spine (deflection in 22" test, exact millimeters), length, balance point, thickness, fletching height and finally the distance arrow has travelled (every shot, not only the longest), the bow from which the arrow is shot.
Lots of info, so lets see how long do i have the patience to continue.
willie:
1) I may have just repeated others words, but i feel there is truth behind the speculation that back balanced arrow keeps itself in flying longer, than tip "heavy" arrow.
2) I haven't tested those 2" -FOC arrows of the Turks, but 1,5" -FOC arrows seemed to fly still ok. To the earlier question have i inspected any Turkish arrow, no way, i haven't seen any even reproduction of Turkish arrows. I live in Finland and well, for many reasons haven't been in any museum to check any. I have seen some of that style arrows made by a Finnish bowyer, with horn nock and pile, fletched with parchment.
3) Good guestion. Just because of gravity?
I don't know if you have visited this page, but it's full of nice information in terms of flight and it's aspects. http://www.tap46home.plus.com/mechanics/
For example the optimum calculated weight of the arrow, 60 grains???
Marc St Louis:
--- Quote from: JNystrom on September 08, 2017, 04:14:57 am ---I think the arrowhead discussion answered the questions, so let's make another topic.
Cp - center of pressure.
https://www.grc.nasa.gov/WWW/K-12/rocket/rktstab.html
Turkish arrows.
http://www.turkishculture.org/lifestyles/turkish-culture-portal/turkish-flight-arrows-554.htm?type=1
--- Quote from: avcase on September 07, 2017, 01:03:42 pm ---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
--- End quote ---
--- Quote from: willie on September 08, 2017, 02:24:55 am ---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?
--- End quote ---
--- End quote ---
Not sure how a rocket can be compared to an arrow since a rocket is under rear end propulsion while an arrow is in free flight
willie:
Thanks for opening a new thread, JN. Lots of good reading for the weekend in that last link.
Once in a while I have an arrow or dart shot that seems to just float exceptionally before it falls, catches air as some say. A statistical outlier to the normal expected range variation. I thought perhaps there is another factor to the equation I am missing......... Lift that keeps the nose up? Allowing the trajectory to stay horizontal longer, in spite of the additional drag caused by the nose up attitude?
Alan, the arrows that fall short and dig in harder must land more vertical that the winning shots. What observations can you offer about the winners? Do they land on their sides or stick in the ground?
Badger:
Willie, very close to 100% of the arrows are stuck in the ground regardless of being a bad or good shot. Most of them are stuck at a higher degree than 45, some of the real bad shots are facing the wrong way.
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